"

"

ALPHA-SCATTERING EXPERIMENT ONSURVEYOR 7: COMPARISON WITH

SURVEYORS 5 AND 6

JAMES H. PATTERSONERNEST J. FRANZGROTE\NTHONY L. TURKEVICH

WAYNE A. ANDERSONTHANASIS E. ECONOMOU

HARRY E. GRIFFIN

KENNETH P. SOWINSKI

Reprint fromA

STANLEY L. GROTCHAND

6120

Journal of Geophysical Research Vol.

74,

No.

25,

November

15,

1969

" Alpha-Scattering Experiment on Surveyor 7 : Comparison withSurveyors 5 and 6

James H. Patterson, 1 Ernest J. Franzgrote,2 Anthony L. Turkevich,3Wayne A. Anderson,4 Thanasis E. Economou,5 Harry E. Griffin,1

Stanley L. Grotch,2 and Kenneth P. Sowinski5

The last three Surveyor missions (5, 6, and 7) included an a-scattering experiment thatobtained elemental analyses of surface material at three widely separated locations on themoon. On Surveyor 7, three different samples were analyzed at a terra site near the craterTycho. These samples are much alike in composition but differ from the mare samples ofSurveyors 5 and 6 in their lower content of 'iron' (elements approximately of mass 56). Theanalyses at all three sites are similar to the compositions of some of the most common rocksfound on the earth's

surface,

such as basalts, but are quite different from the compositionsof ultrabasic rocks and chondritic meteorites. The analyses at the three sites make possiblethe prediction of the chemical and physical properties of lunar surface material. The differ-ence between the analyses of the mare and terra samples may contribute to the differencein albedo of these two types of material and may also indicate geological separation oflunar materialsof varying density, as has happened on earth.

The first direct chemical analysis of materialon the lunar surface was obtained on Surveyor5 in Mare Tranquillitatis by the a-scatteringexperiment [Turkevich et al., 19676, d]. Theexperiment on Surveyor 6 was performed inSinus Mcdii [Turkevich et al., 1968a, &]. Theresults obtained at these two equatorial maresites agree closely. Surveyor 7 was, however,sent to a different type of location, a highlandsite near the north rim of the crater Tycho.

Surveyor 7 was the only mission to includeboth the surface sampler and the a-scatteringinstrument on the same spacecraft. Missionplans included the use of the surface samplerto move the a-scattering instrument from onesample position to another, in contrast to thetwo previous missions, on which there waslittle control over the positioning of the instru-

1 Chemistry Division, Argonne National Labora-tory, Argonne, Illinois 60439.

2 Jet PropulsionLaboratory, California Instituteof Technology, Pasadena, California 91103.

3 Enrico Fermi Institute and Department ofChemistry, University of Chicago, Chicago, Illi-nois 60637.

4Laboratory for Astrophysics and Space Re-search of Enrico Fermi Institute, University ofChicago, Chicago, Illinois 60637.

5 Enrico Fermi Institute, University of Chicago,Chicago, Illinois60637.

Copyright © 1969 by the American Geophysical Union.

ment. With the Surveyor 7 it was thus possibleto obtain analytical data on undisturbed sur-face material, a small rock, and subsurface ma-terial from a trench prepared by the surfacesampler [Franzgrote et al., 1968; Turkevichet al., 1968c]. Furthermore, there would prob-ably have been no analyses at all on this mis-sion without the surface sampler, which wasused to rescue the experimentwhen the normaldeployment procedure failed to place the a-scattering instrument on the lunar surface[Scott and Roberson, 1968]. The sampler wasused also to shade the sensor head during the ex-treme heat of the lunar midday, and thus pre-vented possible damage to the instrument.

The Surveyor analytical results reported hereare 'preliminary;"1 i.e., they were obtained fromdata received on teletype, by computers pro-grammed for real-time mission support. Thedata, moreover, have not been corrected ade-quately for small instrumental effects and havebeen analyzed in terms of only eight elements.The analysis of the prime data recorded onmagnetic tapes is not yet completed. The largeerrors reported now are not primarily a meas-

6 Since preparation of this manuscript (March1969) the data from Surveyor 5 have been ana-lyzed more completely. These results have beenreported by Turkevich et al. [1969], and are alsoincluded in Tables 3 and 4 of this report.

< "

SURVEYOR 7— ALPHA SCATTERING EXPERIMENT 6121

"

<"

ure of the statistical reliability of the data,but they do reflect estimates of systematiceffects not taken into account in the presentdata treatment.

These preliminary analyticalresults have beenreported previously in short communications[Turkevich et al., 1967d, 19686, c], A generaldescription of the a-scattering experiment onthe Surveyor missions has been given byTurkevich et al. [1968c.]. The present reportprovides a more complete technical description,particularly of the Surveyor 7 mission. (See alsoFranzgrote et al. [1968], and Turkevich et al.[1968e].) Much of this material applies to theearlier missions. (Details of the Surveyor 5 and6 missions are to be found in the Jet PropulsionLaboratorySurveyor mission reports [Turkevichet al., 19676, 1968a].) This description shouldprovide a more complete basis for evaluationof the reliability and significance of these firstin situ analyses of an extraterrestrial body.

Method of Analysis

The Surveyor lunar surface analysis is thefirst application for chemical analysis of themeasurement of spectra of a particles andprotons that wereproduced by a particles fromisotopic sources interacting with atomic nuclei.The development of this method has been re-ported in previous papers [Turkevich, 1961

;

Franzgrote, 1963; Patterson et al., 1965, 1966;Turkevich et al., 1967a] and will be treatedonly briefly here.

The fraction of its initial energy that is re-tained by an a particle on elastic collision witha heavier atomic nucleus is a function of themass of the nucleus and the angle of scattering[Darwin, 1914]. A typical energy spectrum ofinitially mono-energetic a particles scatteredfrom a thick sample through a given angleconsists of a series of plateaus, each one drop-ping off to the nextone in a sharp break, whoseenergy is characteristic of one of the majorconstituents of the scattering material. Theseparation between these breaks is greatest ata scattering angle of 180°. The resolution de-creases with increasing atomic mass of the scat-tering elements. In the Surveyor instrumentsthe average scattering angle is 172°. Thepractical upper limit for resolving adjacent ele-ments is at approximately mass number 40.For heavier elements quantitative information

is obtained, but there is an uncertainty of oneor more atomic numbers in their identification.The height of a plateau in the scattered spec-trum is a measure of the concentration of thecorresponding element. In the Surveyor instru-ment the spectrum of scattered a particlescontains quantitative information for all ele-ments heavier than lithium.

A minimum in the sensitivity for detectingelements with 6-Mev a particles occurs atabout the element sodium. Since this part ofthe periodic table is of interest in geologicalinterpretation, the method has been enhancedby analysis of the spectra of the protons pro-duced by nuclear reactions of a particles withelements in this region. The proton spectra withthese instruments consist of broad peaks thatare characteristic of the elements in which thenuclear reactions occur.

The theory of the a-scattering method ofanalysis was described by Patterson et al.[1965]. A library of spectral responses of ele-mental samples exposed to a particles is firstdetermined. A weighted least-squares programis then used to find the combination of theelemental spectra of this library that yields the'best fit' to the spectra of an unknown sample.The weighting factor used in this comparisonis the reciprocal of the estimated variance ineach energy channel. This data treatment isdescribed more fully by Patterson et al. [1966]and Turkevich et al. [1968e].

The results of the analysis of eight rocksamples by this method and a comparison withconventional analyses were reported previously[Turkevich et al., 1967a]. The rock samplesincluded a basalt, a granite, a dunite, a chon-dritic meteorite, a tektite, a limestone, a sulfideore, and a syenite. The standard deviations ofthe a-scattering analysis from the conventionalanalysis, in terms of atomic per cent of thesample, were found to be approximately 2 foroxygen and magnesium, about 1 for silicon,'calcium,' and 'iron,' and less than 0.5% forsodium and aluminum. The terms 'calcium' and'iron' indicate the total for elements whosemass numbers are near those of calcium andiron, respectively.

Surveyor «-Scattering InstrumentThe two main parts of the instrument used

in the Surveyor program were the sensor head,

PATTERSON ET AL.6122 SURVEYOR 7-ALPHA SCATTERING EXPERIMENT 6123the sample by (a, p) reactions. This informa-tion was then transmitted by the spacecraft toearth for further analysis.

The sensor head was an approximately cubi- stabilize deployment onto a soft or irregularcal box, 3600 cm3 in volume, with a 10.8-cm surface. A segment of this plate was cut out oncircular opening in the bottom. This opening the inboard side so that the sensor head wouldwas the port through which the samples were be closer to the spacecraft in the stowed posi-analyzed. Six curium 242 a-particle sources tion. The structure and external surfaces wereand two small silicon detectors for registering redesigned for passive thermal control [Walkerthe number and energy of the scattered a par- et al., 1965]. The sensor head was designed totides were located 7 cm above the sample survive temperatures as high as 75°Cand toport. Also in the sensor head were four proton- operate at temperatures between -40° anddetector assemblies, each of which consisted of 50°C. The upper operating temperature limita silicon proton detector backed by a similar was determined by the detectors, whose be-guard detector in anticoincidence, to reduce the havior rapidly degraded above this po;nt Thecosmic-ray background. Alpha particles were necessary thermal controlwas achieved by pro-screened out by an approximately 21-mg/cm2 viding a reflecting gold-plated surface for thegold foil over each proton detector. Drawings sides and bottom of the sensor head in orderof the a sources, a detectors, and proton de- to reduce the absorption of infrared radiationtector assemblies are shown in Figure 2. from the hot lunar surface. These outside partsThe total intensity of the a sources for Sur- were thermally isolated as much as practicalveyor 7at the time of landing on the moon from the top and interior parts that containwas 4.7 X 10" dpm of curium 242, (tv, = 162 the detectors, sources, and electronics. Rigiddays Ta = 6.11 Mcv). The intensity of the mechanical attachment (with minimum thermalSurveyor 7 source was about 70% higher than coupling) between the two sections was achievedthe intensities of the Surveyor 5 and 6at by means of titanium struts of small cross sec-equivalent times, which compensated for the tion. The top surface, a second-surface Vycorshorter average operating time per sample than mirror, was thermally coupled to the interioron previous missions. The full width at half- 0f the sensor head. It was designed to reflectmaximum of the energy distribution of the radiation in the visible region from the sunindividual sources ranged from 1.3 to 2.2%. but to radiate infrared from the instrument toAlso located in the sensor head were the cold space. Isothermal conditions for the in-electronics that amplified the electrical pulse terior of the instrument, including the detectors,from the semiconductor detectors and converted sol.rces, and electronics, were promoted by useit to a time-analog pulse. This signal was then of indium gasketg Heaters had alread beentransferred over a cable to the digital elec- mstaUed in the sensor head and thermal com.tromcs package on the spacecraft. There the partment for control &t bw temperatures.signal was digitized and encoded for transmis- q-, , , , . . , ,sion to earth. The a and proton modes of the , T,h° *f"T, * . T 7"instrument had separate electronic systems and depl°yf? , t0 the "nar SUrfaCe

WaS

fastened t0

128-channel pulse height analyzers. There was " eyebolt on the center of the toP of theessentially no data storage in the instrument,

Sensor

head- 0n Survey°r 7. the eyebolt wassince the event rates (typically 2 sec"1 and 30 as a knob that could be grasped bymiir1 in the « and proton modes, respectively) the Jaws of the surface sampler,are low enough to make possible direct trans- A snort tulje on the outboard side of themission to earth. Also in the electronics package sensor head was used for the introduction ofwere the power supplies and control logic for dry nitrogen to prevent deterioration of the

The total weight of the instrument and as-sociated equipment on the spacecraft was 13kg. The operatingpower was less than 2 watts.An additional 15 watts were used if heatersin both the sensor head and the electronicscompartment were operating. The power forthe electronics was supplied at 29 volts by thespacecraft; power for the heaters was suppliedat 22 volts.

"DETECTOR

PLUG

HHOUSING

EALPHA

DETECTOR MASKSPRING GOLD-VYNS FILM

ALPHA DETECTOR

HOUSING \CONNECTOR

CLAMP\SPRING

"Fig. 1. Model of the Surveyor 7 spacecraft.

\

J-—J—The surface sampler is shown moving the a-scat-

proton

detectortering sensor head over a simulated lunar surface.

GUARDDETECTOR

GOLD FOIL

PROTON AND GUARD DETECTORS

which was deployed to the lunar surface, anda digital electronics unit located in a thermally ,— retainer screwinsulated compartment on the spacecraft. Other ——£equipment associated with the instrument were HOUS|NG— *^^^^^^^^§- source plateequipment associated with the instrument werethe electronic auxiliary, which provided the fcss^^c^^^^ (curium 2121.111-

CIC.

1111-111.

(ItlAllld

1> , UIIIUII JJIUVIU-U 111^ k\\\\TPIWtfWWXXNXelectronic interface with the spacecraft, and the '. Ml jmechanism for stowage and deployment of the source holder—^Rn IP _sensor head. Figure 1, part of a full-scale model ♦" w

OV.IIOUI

111 "Ml.

J,'J^UIC 1,

jjtll I.

«J_l

tl

JUII OUUt UIUUCI

s' I

of the Surveyor 7 spacecraft, illustrates how the collimator —

\

—thin film the instrument. sources by atmospheric moisture during theThe sensor head and electronics package were prelaunch period at Cape Kennedy,

described in some detail by Turkevich et al. The aluminum oxide films on the faces of[1966], although the actual Surveyor instru- the radioactive-source collimators were rein-ments differed slightly from these descriptions. forced by VYNS (polyvinylstyrene) on theThe external packaging of the sensor head was Surveyor missions. These films had an over-alldifferent. A 30.5-cm-diameter circular plate was thickness of about 1000 A. A secondary film,attached to the bottom of the sensor head to mounted on a plate perforated with six holes,

sensor head is moved over a simulated lunar ALPHa SOURCesurface by the surface sampler. On the Sur-veyor missions, the sensor head delivered to thespacecraft, via the electronics compartment, in-spacecraft, via the electronics compartment, in- ?,',?,?formation on the number and energy of a par- centimeters

tides scattered back from a sample, and onticies scattered DacK irom a sample, ana on Fig 2 Details of the

MUTOe

and detectorthe number and energy of protons produced in sembles used in the a-scattering sensor head.

,—

CONNECTOR

CLAMP"Jtlr. ;^

PATTERSON ET AL. SURVEYOR 7—ALPHA SCATTERING EXPERIMENT

6125

6124of 15 volts. The sensitive depth was approxi-mately 350 ju, which was sufficient to registerthe full energyof a 6.4-Mev proton. The guarddetectors were operated at a bias of 10 volts;their sensitive depth was 400 jtt.

thus about 600 key. The Surveyor 7 systemwas stable to better than 1.1% over the tenmonths between construction and flight. Theover-all gain of the instrument shifted less than3.4% between -40° and +50°C.

LINEAR _ THRESHOLD _ "q?"^GATE GATE CONVERTER |

TT L—JL-r-'lMIXING POST-CIRCUIT

_AMPLIFIER

| %ANALOG

'

SIGNAL 4LPHAPROCESSOR MODE

BUSY SIGNAL Thin gold-covered VYNS films, which de-creased the energy of 6.1-Mev a particles byonly 0.029 Mcv, were mounted on the collima-tor masks in front of the a detectors to protectthem from radioactive contamination, dust, andexcessive light. On these films, and on the in-side of the gold foil over the proton detectors,were placed very small amounts (less than 1dpm) of einsteinium 254 (£.,_ = 276 days, a-particle energy _= 6.44 Mcv). The high-energya particles from this nuclide were used as aninternal standard for the energy calibration ofboth the a and the proton systems of the in-strument. They appeared in the spectra aspeaks at approximatelychannel 110. The eventrate of these a particles served also as a crudelive-time monitor for the instrument.

The required electrical interfaces among thesensor head, digital electronics, and spacecraftcircuits were provided by an electronic auxil-iary that included command decoding, signalprocessing, and powermanagement. Basic space-craft circuits that interfaced directly with thesensor head and digital electronics were: (1) thecentral signal processor, which provided signalsat 2200 and 550 bits/sec for synchronizationof instrument clocks; and (2) the engineeringsignal processor, which provided temperature-sensor excitation current and commutation ofengineering data outputs. The electronic auxil-iary converted a and proton data streams fromthe instrument into a form suitable for radiotransmission to earth by means of the separatesubcarrier oscillators. Center frequencies of70,000 and 5400 Hz were used for a and protondata, respectively.

LINEAR _ THRESHOLD_ "qI^E

-,

GATE GATE CONVERTER

TTLMIXING POST- _CIRCUIT AMPLIFIER

DELAYLINE

ANALOGSIGNAL I PROTON

PROCESSOR ( MOOEr?v PULSEviv GENERATOR

MODEBUSY SIGNAL

MIXING POST- DISCRIMINCIRCUIT " AMPLIFIER ATOR

GUARDRATESIGNAL

B BIAS VOLTAGE a = ALPHA DETECTORSWITCH P ' PROTON DETECTORPREAMPLIFIER G = GUARD DETECTOR

SPRE

SENSOR HEAD ELECTRONICS

ANALOG SIGNAL DELAYFROM SENSOR —*" LINE

D4TA HEAD CLOCK The electronic circuitry in the sensor headof the Surveyor instruments (shown in Figure3) differed from that described by Turkevichet al. [1966] in that it included an internalpulsegenerator,which could be turned on and off byearth command, a guard rate meter with anoutput reading in volts, and an indicator thattold whether any of the a detectors, or protondetectors, were on. The pulse generator intro-duced electrical pulses of two known mag-nitudes (corresponding to approximately 2.5and 3.5 Mcv) at the detector stages of the aand proton systems. The pulses were producedby an electromechanical relay at a rate ofapproximately20 per second. Further details onthe design, construction, and performance ofthis pulse generator have been described byAnderson et al. [1968].

PROCESSOR(21

PROCESSOR A deployment mechanism designed and builtby the Jet PropulsionLaboratory and HughesAircraft Company provided stowage of thesensor head and deployment to the backgroundposition and the lunar surface. The sensor headwas mounted to the deployment mechanism by

BUSY SIGNAL

SCIENCE DATA OUTPUTTO SPACECRAFT

SYNCHRONIZATIONSIGNAL

IQO

V ,VOLTAGES TO "! Z» POWER

SENSOR HEAD 7 y SUPPLYSPACECRAFT VOLTAGE^ 29 V

DETECTOR I». TVERIFY \i SPACECRAFT

"GENERATOR

DIGITAL ELECTRONICS BACKGROUNDPOSITION^

Fig. 3. Block diagram of the electronic circuitry contained in the a-scattering instrument.

was placed in front of the six sources as further Surveyor 7 mission by coating the sources withprotection against radioactive contamination. a thin layer of carbon by evaporation from a

It was found after the Surveyor 5 mission carbon arc in a vacuum,

that curium 242 deposited by aggregate recoil The detector systems have been changedon the collimator films acted as an uncollimated little since the description by Turkevich et al.secondary source. This produced an instrument [1966]. The a detectors were of the surface-background due to a particles that were scat- barrier type, with a nominal sensitive depth oftered from the inside bottomof the sensor head 50 nat an applied voltage of 4-7 volts. The(which was mostly plated with gold). For the proton and guard detectors used in the flightsources used for Surveyor 6 this background instruments were of the lithium-drifted siliconcontribution was about three times that of type [Tuzzolino et al., 1968], The proton de-Surveyor 5. The condition was improved in the tectors were operated with a collection voltage

The over-all characteristics of the electronicsystem of the Surveyor 7 instrument at roomtemperature can be expressed by the analyzerequations

Ny = 19.16^ - 11.9 (2)

where Eis the energy depositedby the particle _^ty.~-~.,~,

"

7~ 7J^__-.>. .-... - -■ ,

.....I,

i—in the detector (in million electron volts), and lunarsurface

N is the corresponding channel number. TheNis the corresponding channel numoer. tne Fig 4 Operation of the a-scattering deploymentthresholds of the a and proton systems were mechanism.

" P-]

'

■*""

r.OMMANn SIGNALS P-2 COMMAND -^ ASr T

TO SENSOR HEAD P-3 MEMORY

«,_

FROM SPACECRAFTP-4 ■*—

TO PULSE l J

N

a

= 18.08£„ - 10.9 (1) j- "- 1

NYLONCORD

N PULLER

■SPOOL

OUND

I j

_■ATTACHED TO

SPACEFRAME

STOWEDSENSOR HEAD

CABLE FEED

! ELECTRICAL

CONNECTOR

\. V i 'O !Xj. _"s>V_. V ! i1 IMOUNTING

PLATFORMANO

STANDARDSAMPLE1| I >I I

-PIN PULLER

6126 PATTERSON ET AL.

means of three support lugs on the bottomplate. Clamps that engaged these lugs werereleased in the first stage of the deploymentoperation.Figure 4 shows the two stages of thisoperation. The sensor head was first releasedfrom the stowed position to a suspended posi-tion 56 cm above the nominal lunar surfacewhen the mounting platform fell aside on theactivation of an explosive pin puller by com-mand from earth. From this background-mcasurng position, the

s?nsor

head was loweredto the lunar surface on command, by activationof another explosive pin puller. The speed ofdescent was controlled by an escapement de-vice.

A sample of known composition was attachedto the platform on which the sensor head wasmounted in the stowed position. This standardsample covered the circular opening in thebottom of the sensor head during spacecraftflight and landing to minimize the entranceof dust and light. It provided a means of as-sessing instrument performance by presentinga relatively complex mixture for analysis underlunar conditions. The standard sample was apiece of glass (specially prepared by the Gen-eral Electric Company), whose principal con-stituents were oxygen, silicon, magnesium, so-dium, and iron. It was partly (20-25%)covered by a polypropylene grid to provide aresponse from carbon. Measurements of theactual sample carried on the mission were madeby the instrument at the time that the ele-mental library for the instruments was firstobtained (the science-calibration stage) . Duringthe final calibration at Cape Kennedy, themeasurements were repeated on another similarsample.

Experiment ControlThe a-scattering experiments on the Surveyor

missions were controlled from the Space FlightOperations Facility (SFOF) at the Jet Propul-sionLaboratory, Pasadena, California, by meansof commands transmitted to the spacecraftfrom tracking stations at Goldstone, California;Canberra, Australia; and Robledo, Spain. Thecontrol decisions were based on the analysis ofdata received from the spacecraft and relayedto the SFOF during the mission. Commandswere provided for on-off switching of powerto the instrument, the electronic calibration

pulser, and the thermostated heaters in thesensor head and the electronics compartment.The output of individual detectors could beblocked by command. In addition, there wereirreversible commands to deploy the sensorhead to the background position and to thesurface.

Seven engineering measurements were moni-

tored. Sensor head and digital electronics tem-peratures were measured to determine whetherthey were within operating limits, to plan mis-sion operations, and to provide an approximatecorrection to the energy spectra in the real-time data analysis. The 7- and 24-volt powersupply voltages were monitored to determinewhether theywere within limits and to diagnosepossible problems. Digital signals, indicatingthat at least one a detector, or at least oneproton detector, was on, were a check on theproper receipt of commands. The guard-ratemonitor provided information on the radiationbackground as well as on the properfunctioningof the anticoincidencedetectors.

The science data cons-'sted of a 9-bit digitalword (a synchronization bit, a parity bit, and7 bits to define the energy channel) for eacha-particle or proton event recorded. These datawere generated as separate a and proton bitstreams and were combined with the engineer-ing data for transmission by the spacecraft toearth. Science and engineering data were re-ceived independently, so that instrument tem-peratures could be monitored when the powerto the instrument was shut off. The compositesignal from the spacecraft, which included otherthan the a-scattering data, was recorded onmagnetic tape at the tracking stations. Thesetapes contained the primary a-scattering datafor use in post-mission analysis.

In addition to being recorded for later use,the data were monitored and subjected to com-puter processing during the mission, so thatproper control over the experiment could beexercised. This real-time data-handling capa-bility permitted assessment of the quality ofthe standard sample and background data be-fore irreversible deployment steps were taken.It allowed the continued monitoring of theperformance of the instrument, so that de-cisions could be made, e.g., the decision to blockthe output of a noisy detector to prevent de-gradation of the data stream. It also made

missions until the analysis of the primary dataC has been completed. (See footnote 6.)

For this real-time data processing, the a and

I 1!M17 |.V The prime data tapes recorded at the track-

ing stations have been processed with aUNIVAC 1219 computer at the Jet PropulsionLaboratory. In this processing, data of interestto the a-scattering experimenthave been trans-ferred to separate digital magnetic tapes. Thesedata are now under analysis at the Universityof Chicago.

SURVEYOR 7—ALPHA SCATTERING EXPERIMENTpossible the preliminary analyses, which are theonly analytical information available from the

proton data streams, after demodulation anddiscrimination, entered an SDS-920 computerat the deep-space tracking station, whereperiodic accumulations of the spectral datawere made on command. These accumulatedspectra were transferred to the Jet PropulsionLaboratory by teletype.

There the data were processed by IBM 7044and 7094 computers. The data were correctedfor errors in transmission, both between themoon and the earth, and between stations onearth, by means of the parity information trans-mitted. Also, the energy scales of the datawere corrected approximately for temperature,on the basis of pre-mission calibrations. Thesecorrected spectra were further analyzed, bothindividually, and cumulatively in larger batches,by subtraction of background spectra, followedby a least-squares spectral fitting with an B-element library. Pulser calibration spectra werealso processed by the 7094 computer. Positionsand widths of the peaks and the resultingenergy scale parameters were determined. De-tails of the methods used in real-time science-data processing have been reported by Grotch

Mission Operations

Prelaunch operations. The a-scattering in-struments on Surveyors 5, 6, and 7 were de-signed and built by the Laboratory for Astro-physics and Space Research of the EnricoFermi Institute at the University of Chicago.The instrument used on Surveyor 7 was com-pleted in March 1967 and was given thedesignation F-2. (The instruments on Surveyors5 and 6 were P-4 and F-l, respectively; theinstrument used as a backup for all three mis-sions is designated F-3).

6127The Surveyor 7 instrument was tested shortly

after construction in a vacuum at temperaturesof -40°, +25°, and +50°C, to establish thetemperature coefficients of the system. Thesecoefficients were later used for the approximatetemperature correction of the energy scale inthe near-real-time data treatment during themission. The instrument then went into ascience-calibration stage, in which, with the useof flight-intensity sources, its response to aboutfifteen samples of pure elements and simplecompounds was determined. This procedureprovided a library of elemental spectra thatcould be used for the interpretation of the lunardata.

After the sources were removed, the instru-ment was carried through another thermal-vacuum sequence for the flight acceptance testat the Jet Propulsion Laboratory (JPL). Thenthe performance of the guard detector systemwas tested with 50- to 450-Mev protons fromthe University of Chicago synchrocyclotron.After the shock and vibration portion of theflight acceptance test at the JPL, the instru-ment was delivered to Hughes Aircraft Com-pany in May 1967 for further testing, matingto the spacecraft, and operation on the space-craft under simulated mission conditions.

After arrival at Cape Kennedy in December1967, the sensor head went through an addi-tional check of its characteristics over a tem-perature range of 0° to 40°C. The flight sourceswere then installed, and spectra from back-ground and a selected set of samples were meas-ured before the sensor head was again installedon the spacecraft for final prelaunch tests. Toprevent deterioration of the sources by atmos-pheric moisture, dry nitrogen was flushedthrough the instrument containing the sourceswhen it was not in a vacuum. Surveyor 7 waslaunched from Cape Kennedy at 06h 30m UTon January 7, 1968.

Operations on the lunar surface. The Sur-veyor 7 spacecraft landed 30 km north of therimcrest of the crater Tycho on January 10,1968, after normal transit and approach to themoon. The spacecraft came to rest on a nearlyhorizontal surface (slope approximately 3°)with the outboard side of the sensor head facingabout 20° west of north. Local surface char-acteristics differed visibly from those of themare sites observed on all previous Surveyor

6128 PATTERSON ET AL. SURVEYOR 7—ALPHA SCATTERING EXPERIMENT 6129SURVEYOR _2T

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>*^ — LUNMSAMPLE I NIOH TEMPI"ATUMI £?(IiTI IJINU.m

IMA,

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—I—l1—I

v* elevation

mwnoN

«LPH_-K_TTf«Mg

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CA. IM-TIOM

Fig. 5. Mission-operations summary of the a-scattering experiment for the first lunar daysof Surveyors 5, 6, and 7.

missions; the surface reflectivity, in agreement from the tracking stations. These data, alongwith earth-based observation, was significantly with calibration spectra obtained with thehigher than had been found in the lunar maria. pulser, showed that the instrumenthad survivedLikewise, the abundance of rocks and fragments the launch and landing and was capable ofwas appreciably greater than hadbeen observed providing analyses in the lunar environment,at earlier Surveyor sites. The command was therefore given for the plat-

The experiment was designed to operate in form containing the standard sample to fallthree successive stages after spacecraft landing. aside, which allowed the sensor head to hangIn the first stage the standard sample was by a nylon cord about 0.5 meter above theanalyzed; next the standard sample was re- surface. After accumulation of data in thismoved by earth command and the background position for 4.8 hours, it was decided that suf-for the experiment was measured with the ficient good background datahad been obtainedsensor head suspended over the lunar surface. to be used in the analysis. Therefore, the finalFinally, on earth command, the sensor head deployment step, to the lunar surface, waswas lowered to the lunar surface and the ordered. This step consists of the firing of ananalysis was begun. Figure 5 shows the details explosivesquib, which, under normal operations,of these mission operations of the a-scattering releases the lock on the spool of nylon cordexperiment on the Surveyor 7 mission during allowing the sensor head to be lowered to thethe first lunar day. Indicated are the periods surface. The same operation also releases theduring which power was applied to the instru- door holding back the folded-up electrical cablement (during this time the rate of events in connecting the sensor head to the spacecraft,the anticoincidence counters could be moni- On previous missions when the sensor headtored), the periods of data accumulation, and was lowered to the surface from the backgroundthe times of pulser calibrations. Corresponding position, a sudden rise in the rates of both aoperations for Surveyors 5 and 6 are also and proton events was observed. On the Sur-shown for comparison. veyor 7 mission, no increase in the event rates

Accumulations of standard-sample spectrafor was observed when the command was given,a total of 5.2 hours were received by teletype This indicated that there was no measurable

movement of the sensor head from the back- sampler brought the sensor head to the sur-ground position. A second command for the face. In the meantime background data haddeployment brought no increase in the event been accumulated for an additional 7.2 hours,rate. Later television pictures confirmed that In this first location on the lunar surfacethe sensor head was still in the background (sample 1) data were collected for a total ofposition, even though the cable-retaining door 28 hours. Data collection was interrupted for

j had opened. The squib-activated pin puller had a 6-day period during which the sensor head% operated ; thus, the problem was isolated to the was too hot for operations, even when shaded

nylon cord, the storage spool, or its escape- by the surface sampler. During 6 hours of thement mechanism. data accumulation the temperature of the

Attempts to jar loose the obstruction by sensor head was between 58° and 62°, wellvibrations set up by moving the solar panel above the designed operating maximum of 50°C.and planar array were unsuccessful. The sur- The noise level of the proton system underface sampler present on Surveyor 7 could not these conditions seemed to be higher than usual,be lifted high enough to be placed on top of the The rest of the data was collected over asensor head in this position. An attempt was temperaturerange of 35° to 50°C.made to release it by pushing down on the In the late lunar afternoon the surface sam-circular plate with the surface sampler, but pier was used to move the a-scattering sensorthe suspended sensor head swung away before head to a new position, overa small lunar rockenough force could be exerted to bring it down. (sample 2). Data were collected in this posi-The surface sampler was eventually used to tion for 11.2 hours. Finally, shortly before sun-accomplish the deployment [Scott and Rober- set, the surface sampler placed the sensor headson, 1968, 1969] by wedging the sensor head over a 5-cm-wide trench in the nearby lunaragainst nearby parts of the spacecraft and surface that had been previously prepared byexerting a downward force. This caused the the surface sampler (sample3). There was timesensor head to drop far enough that the sur- for data accumulation for only 7.5 hours on'ace sampler could be placed on its top. From this sample before the sun set on the first lunarthis position, downward thrusts by the surface day. However, the a-mode data were accumu-

SIIIIIISIIIaIIIT. 1 1 1 S 1 1 1 5 1 1 1 s 1 11 1 " 1"

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SURVEYOR 7—ALPHA SCATTERING EXPERIMENT

6131

6130 PATTERSON ET ALFigure 7 shows the sensor head on the lunar surface, is visbile as an exposed object on pic-

surface on top of sample 1. Figure Bis a view tures of the lunar surface taken before the sur-of sample 1 after the sensor head had been face sampler operations. The measured a-eventmoved to sample 2. Sample 1, which is ap- rate on this sample was about twice the rateparently undisturbed lunar material, lies in the for a sample at a standard distance, indicatingarea outlined by the circle in Figure 8. Al- that therock protruded slightly into the bottomthough several fairly large fragments can be of the sensor head. Models of this rock and itsseen on the surrounding surface, the material surroundings have been made and are beingwithin the central part of the area outlined by studied to determine the effect of this abnormalthe circle can be seen to be relatively smooth; geometry on the analysis. Figure 9is a televi-the largest visible particle is about 1.5 cm sion picture of the rock after the sensor headacross. A rock about 4 cm across was located had been removed.

m

*under the inboard side of the sensor-head plate. Sample 3 is a trenched area of the lunar sur-This rock caused the sensor head to be raised face previouslyprepared by the surface sampler,on this side, and the sample examined is there- Figure 10 shows this sample; the outline offore farther than the standard distance from the sensor head has been drawn to show itsthe sources and detectors. This is confirmed by position during the analysis. The materialthe a-event rate, which was lower than ex- analyzed consisted, at least in part, of sub-pected. surface material. From the intensity of back

Sample 2is a lunar rock about sX7cm on ward-scattereda particles, the average distanceits upper face. This rock, which is somewhat of the sample analyzed in this location was

/

* brighter in appearance than the surrounding greater than standard.Fig. 6. Plan view of Surveyor 7 spacecr

a-scattering instrument on the lunar surfaceoperation of the surface sampler.

ft showing the three sample locations of theThe large sector of a circle shows the area of

lated for an additional 24.5 hours on the second preserved during the prelaunch and launchlunar day. The proton digital electronics had phases of the missions. Similarly, all electronicsevidently been damaged during the cold lunar components behaved well. Of the more thannight;

therefore,

no further proton spectra 1000 commands transmitted to the instrumentswere obtained. during the three Surveyor missions, all but two <»The performance of the a-scattering instru- appeared to give the proper response. Thement and support equipment during all three principal instrument design inadequacy thatnSurveyor missions (5, 6, and 7) was excellent, showed up was the higher-than-predicted ter-The semi-conductor radiation detectors had peratures of the sensor head on the lunar sur-been expected to be the least reliable compo- face on all three missions. This limited some-nents in the instruments. Of the thirty dctcc- what the amount of data obtained.tors operated on the moon, only one detector The relative positions of the three samples(on Surveyor 6) became noisy for any appre- analyzed on the Surveyor 7 mission may beciable time when operating within the design seen in Figure 6. A mosaic of television photo-temperature limits of -40°Cto +50°C. When graphs of this area taken on January 21, 1968,communications with Surveyor 5 and 7 were is shown in the accompanying paper by Scottre-established on the second lunar day, it was and Roberson [1969], In their Figure 24 thefound that the detectors had survived the lunar sensor head is in the sample 2 position, overnight, and they operated normally after initial a rock that fills a large part of the sampleperiods of noisybehavior. opening. A ring in the surface material near

Data received during each of the Surveyor the bottom left part of the television mosaicmissions showed that the thin films covering is the impression made by the skirt of the sensorthe radioactive sources and the a detectors had head in the sample 1 position. To the rightsurvived the launch, the midcourse maneuvers, of the sensor head in that figure the surfaceand the lunar landing operations. Likewise, the sampler is seen in a trenching operation pre-quality of the radioactive sources had been paring material for sample 3.

The Surveyor 7 a-scattering sensor head on sample 1, an undisturbed area of thelunar surface.

Fig

ox

6132 PATTERSON ET Al SURVEYOR ALPHA SCATTERING EXPERIMENT

6133

radioactive contamination. The data are similar adequately, and there are small systematicto those observed in previous missions. The deviations that must be investigated,highersource strength (70% higher) led to pro- Table 2 presents the resulting chemicalportionally higher counting rates and better analysis of the standard sample of Surveyor 7,signal-to-background ratio, particularly in the obtained under lunar conditions. Also shown areproton mode. The characteristic a-spectrum the results of a conventional chemical analysisbreak points of carbon, oxygen, silicon, and iron of the glass part of the sample. Although theare plainly seen, as well as some of the proton analysis under lunar conditions deviates some-spectrum features of silicon and sodium. The what more than is desirable from the resultsdata are similar to those obtained before launch by conventional techniques, it gives adequatewith a similar standard sample. They differ assurance that the instrument was in satis-principally in the effects of different back- factory condition to perform chemical analysesgrounds on the earth and on the moon. The of lunar surface material.

%

backgrounds observed on the moon in the Background data. The a and proton spectranext stage of the experiment (see below) are of the certified background data obtained onindicated in Figure 11 by the solid lines. the Surveyor 7 mission are shown in Figure 13.

Figure 12 shows the spectra with background The visible features of those spectra are assubtracted, and the computer fit from the pre- expected from experience on previous missions,liminary treatment with an eight-element li- The high intensity in the first few channels ofbrary. The main features of both a and proton the a spectrum is due to y and neutron emis-spectra are well reproduced from the library. sion from the curium sources and to instrumentThe energy scales have not yet been matched noise. There is some structure in the next 70

Fig. 8. Surveyor 7 sample 1 after the sensor head had been removed. The sample is wilhiithe area outlined by the circle

Results be observed that more standard sample and 1%The prime data from the a-scattering experi- background data have been certified fromments on all three Surveyor missions were re- Surveyor 7, but the periods of accumulationcorded at the Deep Space Network stations. °f certified data on the lunar samples of thisThe a-scattering data have been separated mission were shorter than on the other mis-from the other data too recently for their sions. This shorter accumulation period is some-analysis to have progressed any further than what compensated for by the higher sourcethe qualification of their format and the check- strength on the Surveyor 7 mission. These certi-ing of their completeness. The results discussed fied data were corrected approximately forhere are therefore still based on the preliminary instrument temperature effects. Preliminary re-analyses obtained from the teletyped spectra suits were obtained from these data by meansreceived at JPL during actual missions. (See of an eight-elementlibrary obtained soon afterfootnote 6.) Some of these spectra and their instrument construction, many months beforecomputer analyses were subjected to 'certifica- the mission.tion;' i.e., they were carefully inspected, and Standard sample. Figure 11 shows the adata that were suspect for any reason were re- and proton spectra of the certified data ob-jected for the preliminary analysis. Table 1 tamed from the standard sample on the mooncompares the number of hours of certified data during the Surveyor 7 mission. These dataused for analysis in various phases of this showed that the instrument survived the tripmission with the hours of accumulation of and that the protective films over the sourcescertified data for Surveyor 5 and 6. It will were intact, since there was no evidence of li 0 Surveyor 7 sample 2, a lunar rock, alter the sensor head had been removed. Thf

sample is outlined by an ellipi

TERING EXPERIMENT6134 PATTERSON ET Al SURVEYOR ALPHA SCA

6135

tfij f V BulU

STANDARDSAMPLE

-- '"

STANDARDSAMPLE

WJffr' 'iJ- _-_*rf*^__l I " ALPHA

MODE

- -\""--

PROTONMODE

'Ik'Vi * lo°- + s

\

* * iloo

IV% ! s ~T^^itffn —~---JWlif\ ■■I _k *- j__#3 o- 1 nl/ 1 1 riW fitii -

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■

.SM Ms _^_^_h?& M_k '' _ff ##■" J -MMfin AwLT*^m ii i i i i i i i i i i . llltlli 1 1 i i—i—l—i—i—i—i—i—i—i—Ji■X i__fl\^__l Hr *^V ° 10 20 30 40 50 60 70 80 90 100 110 120 0 10 20 30 40 50 60 70 80 90 100 110 120

Wr'W^ 1

CHANNEL

NUMBER

CHANNEL

NUMBER

7Jm ■_»''jW^ii__fi *^k *! ' '"" *'" The a ilnc' Prolon spectra of the certified data for the standard sample on Sur-jM __V> sfl _^' "^J__L veyor 7. The abscissas in these and subsequent spectra are channel numbers of the 128-

if-tfli Wjtw channel analyzers and are related to energy deposited in the detectors by equations 1 and 2.29W8-_^_sji_Bß_^^^ «<f * ''"' ordinates arc intensities of scattered a particles or protons in units of events per channel

per thousand minutes. The height of the crosses at the experimental points indicates thef\mk statistical error (standard deviation). The solid curves are smoothed versions of the back-

ground spectra observed in the next phase of the lunar operations. The plateaus in the aspectrum ending at approximately channels 14, 27, 52, and 73 are characteristic of carbon,oxygen, silicon, and 'iron,' respectively. Higher concentrations of sodium, magnesium, alumi-num, and 'calcium' would produce similar plateaus ending at channels 36, 38, 49, and 64,respectively. In the proton spectrum magnesium and silicon contribute to the intensity upto approximately channel 30. Beyond this point the intensity above background is duealmost entirely to sodium. Aluminum, if it were present, would have a contribution to theproton spectrum up to approximately channel 103. Characteristic of aluminum is a sharpbreak channel

02,

followed broad peak. Shapes of the contributions of individualFig. 10. Surveyor 7 sample 3, an area of the lunar surface trenched by the surface sampler, elements to a and proton spectra are shown in Figure 16. The peaks at approximately channel

before analysis. The outline shows the subsequentsensor head and sample positions. 110 are from the Es25* located near the detectors as calibration sources.

channels thai is due to the scattering from the and the higher-intensity sources on Surveyor 7. 4lunar surface 0.5 meter away. This effect, al- The plateau with the break at about channelmost undetectable in previous missions, is 90 is caused by the scattering of a particles ____________________________________________

T

-__^_ r

__

r__^_, r

_-

r __^_ r __-,_^

noticeable because of the longer counting time from the curium 242 on the source protector l0'000 :Vi-% '

surveyor

zn

surveyor

znfilms. The plateau ends at an energy character- : standard sample standard sample...,,. - i " , E 1

RESULTSOFCOMPUTERANALYSIS

"

RESULTS

OF

COMPUTERANALYSIS

TABLE 1. Total Time Represented by Certified istic of gold, since most of the internal sur- s ALPHA

MODE

lW

PROTONMOOE

Data faces seen by these a particles are gold-plated. § looo^

W,

\j-i_____J». - -^^^^V "'00°Used in calculations of preliminary results. The carbon coating of the sources before en- £ ""* ' ""S X^/U(V

ufc

capsulation was only moderately successful in . \AI \^jP \Total Time, hours reducing this cause of background (see previous I ioor TW V ilOO

D, 7i T~a Til w section on a-scattering instruments). This com- 5 \Phase Surveyor o Surveyor 6 Surveyor 7 »i_

.__> _.

c

"

. Iponent of the background spectra aftects the y \T

_.

. _ „„ analysis for major constituentsonly by increas- £ | ,„Inflight 0.33 ■"■ """ . ... J , T/, , g l0 f = . ll = 10

Standard sample 1.00 4.3 5.0 m" sll§htly the statistical errors. It does de- g |Background 2.33 6.10 10.5 crease seriously the otherwise high sensitivity l|Sample 1 15.0 13.2* 11.2 for elements heavier than the major constitu-Sample 2 34.5 """ 9.7 cnts, however, especially the sensitivity for gold o io 20 30 40 so co 70 co 90 100 no 120 0 10 20 30 40 50 so 70 so 90 100 no 120Sample 3 """ """ 5.9 __,j __i „_, "_, .. , channel number channel numberv and elements near it on the atomic mass scale. uwn"_l iwratn

* Part of the datafrom this period was recorded ."c hlgh event rates ln the lowest channels Fig Surveyor 7 standard sample spectra after background subtraction. The experi-with three of the four proton detector systems m the Proton mode are due to ihe cosmic and mental data are shown as crosses with statistical (10-) error bars. The computer fit is shownoperating. solar protons that are entering the detectors with solid lines.

SURVEYOR 7—ALPHA SCATTERING EXPERIMENT6136 PATTERSON ET AL.

6137

TABLE 2. Analysis of Standard Sample on ground wouldbe at least five times the observedSurveyor 7 (in Atomic %) value without the protection of the guard de-

Elements lighter than beryllium have been tector system, since this allows only the regis-" tration of protons entering from the sides ni /*^^

„ _ ... . the instrument. *Surveyor 7 Mission

__

, . _ . , , , 11n .excluded.

The peaks at approximately channel 110 inboth the a and the proton spectra are from thesmall amount of einsteinium 254 thatwas placedin front of each of the detectors. The peaks arenot as narrow, especially in the a spectum, asthey were for the previous missions. Since thehigh-energy edges are sharp, however, the ein-steinium is still useful for energy calibration.

ConventionalTotal Glass Analysis of

Element Sample Portion* Glass Portion

c(1

20.244.0

lo10

59NaMgAl

8.0 87.6 9II 0 0

Si 13.2 1(1 17'Ca''Fe'

0 (I 07.4 9 7

* Standard sample was covered by a poly-propylene grid. This column gives the analysis ofthe sample excluding the polypropylene.

from the side; such protons, in the 50- to 200-Mcv range, provide the main contribution tothe proton background spectrum in the higherchannels as well. The observed background inthe proton mode agrees adequately with thatcalculated from satellite measurements beforethe Surveyor missions. These protons do notappreciably affect the a spectrum, because theenergy deposited in the sensitive volume is notgreat enough to exceed the 0.6-Mev threshold.Tt has been calculated that the proton back-

T10.000

SURVEYOR

ZUBACKGROUNDALPHAMODE

§ 1000o

"%\1 1'HwV'y

i! ll10 20 30 40 50 60 70 80 90 100 110 120 0 10 20 30 10 50 60 70 80 90 100 110 120

CHANNEL NUMBER CHANNEL NUMBER

Fig. 13. The a and proton spectra of the background data from Surveyor 7. The peaks atapproximately channel 110 are from the Es26* located near the detectors as calibrationsources.

The backgrounds observed in the protonmode on the Surveyor 5, 6, and 7 missions hadqualitatively the same shape (except for smalldifferences in the Es2M region) and were ap-proximately of the same magnitude. For ex-ample, the integratedbackground in the energyregion 6.5-7.1 Mcv was the same in the Sur-veyor 6 and 7 missions (well within the lastatistical errors of 5%). This means that theflux of 50- to 200-Mev protons (the particleswhich, incident on the instrument from thesides, would contribute to this background)was the same on the moon at the Tycho site(40°S) in January 1968 as it was at the equatorin November 1967. This isotropy is consistentwith the lack of an appreciable magnetic fieldnear the moon. On the Surveyor 5 mission, thisbackground was slightly lower, possibly be-cause of shielding by the local topography, sinceSurveyor 5 landed inside a small crater.

10,000

SURVEYOR ZH

BACKGROUND

PROTON MODE \1000

100

0

In analyzingthe data from the standard sam-ple and from the lunar samples, the a andproton spectra observed while the instrumentwas suspended were subtracted from thespectra obtained from the samples. The back-ground in the a mode was adjusted approxi-mately for the growth of the aggregate recoil

il i i I i i i l 1 1 1 U 1

O io 20 30 40 50 60 70 60 90 100 MO 120CHANNEL NUMBER

Fig. 14. The a and proton spectra of the c7. The solid curves in each spectrum are thein the previousphase of lunar operations.

SURVEYOR

ETLUNAR SAMPLE I \\\

SURVEYOR

J__7LUNAR SAMPLE 2 _ >

ALPHA MODE_ _\

_J I

X

certifiedsmoothed

contribution by using the observed changes inthe intensity in channels 73-90.

Changes in the solar and cosmic proton fluxat the moon's surface would have a very strongeffect on theproton background and lessereffecton the a background. For this reason, thechanges in the contribution from this source

"310,000SURVEYOR

mLUNAR

SAMPLE

I IPROTON MODE

1000

Iffli

310.000

SURVEYOR

mLUNAR

SAMPLE

2PROTON MODE

31000

1100

% -

_l ll!10.000

SURVEYOR

J__7

LUNAR SAMPLE 3PROTON MODE

jiooo

VM*^ 100

ll20 30 40 50 60 70 80 90 100 110 120

CHANNEL NUMBER

data for the three samples on Surveyorled version of the background observed

the instrument.

0-UJo._l

I 1002o___:UJQ. LV)t; ioUJ>UJ

\ '"""■~\s*^\ Wwf^S .100

6138 PATTERSON ET ALSURVEYOR 7—ALPHA SCATTERING EXPERIMENT 6139

10,000

K. curves represent the background spectra ob-served when the instrument was suspended overthe lunar surface. (In the figure thebackgroundshave not been corrected for the growth of theaggregate recoil contribution.) In comparingabsolute rates from the different samples, itshould be remembered that the average dis-tances of the three samples from the a detec-tors were different, with a ratio of 1 to 0.7 to0.9. The 70% higher intensity of the sourcesin the Surveyor 7 mission gave better statisticsin a shorter period of time and a better signal-to-background ratio than had been obtainedon previous missions. On the other hand, thenonstandard geometry, particularly in the caseof the rock sample on Surveyor 7, producesnoticeable effects on the proton spectra.

Whether these deviations are the result of thecrude treatment of the primary data or are theeffect of a larger than nominal distance will haveto be established.

LUNAR

SAMPLE

I

RESULTSOECOMPUTERANALYSIS

ALPHA MODEE

o 1000 (%LU

a.

The preliminary analytical results obtainedfrom this treatment of the data are presentedin Table 3 [Turkevich et al., 1968c.]. Alsoshown are the results of the treatment of thedata obtained from Surveyor 5 and 6 [Turke-vich et al., 1969, 19680]. In all cases theanalytical results are expressed in terms of percent of atoms heavier than lithium. The indi-cated errors are larger than statistical; theyinclude an allowance for systematic errorsarising from the type of data available, thetemperature and energy scale corrections made

_!UJ§ 100<xva:UJXt; 10UJ>LU

ll( 40 50 60 90 100 110 120

CHANNEL NUMBER CHANNEL NUMBER

Fig. 15. The a and proton spectra of Surveyor 7 lunar sample 1 after background sub-traction. The experimental data are shown as crosses with statistical (la) error bars. Thecomputer fit is shown with solid lines.

The qualitative features visible in the rela-tively raw data of Figure 14 are the same forall three samples examined on the Surveyor 7mission. These features are similar to the onesobserved in the data from the samplesexaminedon the Surveyor 5 and 6 missions, and in dataobtained from many terrestrial rocks with Sur-veyor-type instruments. In the a mode, themost prominent characteristic of the spectra isthe sharp decrease in intensity at approximatelychannel 27 (always present when there is Ole inthe sample), a drop often preceded by a slight'bump' at approximately channel 52 (charac-teristic of the presence of silicon), and the finaldecrease in intensity to close to backgroundlevels at approximately channel 73, which indi-cates the presence of elements in the region ofiron in the samples. In the proton mode, thegross data from all the samples show a sharpdecrease in intensity at approximately channel62 and a very broad peak between approxi-mately channels 73 and 100. These features inthe proton mode are characteristic of the pres-ence of aluminum in the samples.

were monitored throughout the mission in sev- during this and the preceding missions fromeral ways. The most sensitive internal measure the Imp 4 satellite, which was orbiting theis the event rate of the guard system. Other earth. None of these monitors gave indicationindicators followed were the event rates in the that there was any significant change in then and proton spectra above the einsteinium solar and cosmic proton flux during the Sur-peaks. In addition to these internal measure- veyor 5, 6, and 7 missions.ments, the general radiation level in space dur- Lunar samples. Figure 14 shows the a anding the last three Surveyor missions was moni- proton spectra of the certified data for thetored by means of data received every 4 hours three lunar samples on Surveyor 7. The smooth

TABLE 3. Chemical Composition (in Atomic %) of the Lunar Surface at the Surveyor 5, 6, and 7Landing Sites

<"Mare Sites Terra Site

Element

I . I I I 111 I I10 20 30 40 50 60 70 80 90 100 110

The data of Figure 14 for the first samplehave been treated by subtracting the back-ground and analyzing it in terms of an eight-element library. The resulting fit of the calcu-lated spectrum to the data (after backgroundsubtraction) is shown in Figure 15. It is seenthat the major features of both a and protonspectra arewell reproduced. There are, however,significant deviations in detail, such as near theoxygen end point of the Surveyor 7 a spectrumand near channel 95 of the proton spectrum.

[20CHANNEL NUMBER

1.9 ± 0.8 2.3 ___ 0.8Fig. 16. Contributions of the individual ele-

ments to the least-squares computer fit for sam-ple 1 of Surveyor 7. The library data for theseparate elements are shown in the relativeamounts needed to explain the observed lunardata. The solid-line sum of the spectra is thecomputer fit shown in Figure 15. The portions ofthe 'calcium' and sodium a spectra below channel30 are theresult of small differences between largenumbers, and they are therefore subject to largeerrors.

3.7 ± 0.6 3.7 ±0.6 5 ± 2 2 ± 1

% The values from the Surveyor 5 Mission are the results of the more complete dataanalysis reported byTurkevich et al. [19691; those for Surveyors 6 and 7 are still preliminary.

* The value for aluminum for sample 1 on Surveyor 7 has previously been reported as 8 ± 3%[Franzgrote et ah, 1968]. Additionaldata analysis indicates the present reported value as being more nearlycorrect.

f 'Ca' here denotes elements with mass numbers between approximately 39 and 44 in the Surveyor 5results. For Surveyors 6 and 7 this range is 30-47. The mass range included in 'Ti' is 45-51. The massranges for 'Fe' are 52-61 for Surveyor 5; 47-65 for Surveyors 6 and 7.

SURVEYOR

ETI lINAR

SAUPI

F I

Surveyor 5J Surveyor 5JSample 1 Sample 2

Surveyor 7Sample 1Surveyor 6

C<>

0.2 ± 0.8 0.9 ± 0.8 <262 ± 2 61 ± 2 57 ± 50.3 ± 0.4 0.5 ± 0.4 <22.8 ± 1.5 2.4 ± 1.5 3 ±36.2 ± 0.9 6.2 ± 0.9 6.5 ± 2

16.3 ± 1.7 17.4 ± 1.7 22 ± 46.3 ± 0.9 5.4 ±0.9 6 ± 2

<258 ± 5

<3NaMgAlSi'CatTi'f'Fe't

4 ± 39 ± 3:

18 ± 46 ± 2

SURVEYOR 7—ALPHA SCATTERING EXPERIMENT 61416140 PATTERSON ET AL.

cium,' and 'iron,' which are responsible for most earth. The data appeared more consistent with

10,000

i 310.000

of the intensity in the a spectra. Figure 17 the amounts of radioactive elements in terres-SURVEYOR 2

SURVEYOR

ZHLUNAR SAMPLES I AND 2

ALPHA MODELUNAR SAMPLES I AND 2 shows a comparison among the a spectra ob- trial basalts, with the terrae perhaps having

|[IA tamed on the Surveyor 5, 6, and 7 missions. less radioactivity and so possibly being chon-The background has been subtracted in each dritic in composition.

T. ALPHA

MODESAMPLE

I+ SAMPLE 2

less radioactivity and so possibly being chon-1000 dIOOO> dritic in composition.

case, and the data have been normalized so The results obtained as a result of the Sur-that they match in the 'oxygen' region (chan- veyor missions and presented in Table 3 are100

nels 8-25). Theright side of Figure 17 compares more direct and comprehensive. It is true thatthe data from the second and third samples they have been obtained at only three lunar

IooocrLU0

with the data for the first sample of Surveyor sites. Also, at the present stage of data avail-7. The upper left portion of Figure 17 com- ability and analysis, the limits of error on somepares the a spectra of the two samples at the of the analytical results are rather large. How-Surveyor 5 site, and the lower left part is a ever, they would appear to account for at leasti ,1

§ 10,000Io

comparison of data from the first samples on 90% of the atomspresent (excluding hydrogen)

310,000SURVEYOR

Z, J_7 AND ZULUNAR

SAMPLE

IALPHA MODE

each of the three missions. and so are the most complete analyses of lunarsurveyor En-crUJQ.

z 1000UJ>UJ

LUNAR

SAMPLES

I AND 3ALPHA MODE Figure 17 shows very good agreement among material that are available. They indicate that

* 1 the a spectra from all the mare samples. Like- the most abundant element on the moon, as on

SURVEYOR

V

SURVEYOR

ZISURVEYOR zn "^-—

■

i.

JlOOOW wise, there is adequate agreement among the the earth's surface, is oxygen. More than halfspectra of the three samples examined at the of the atoms (not including the undetectable

iTycho terra site. All data from the terra site hydrogen) are of this element. Second in abun-

100 :100 differ from the data from the mare samples in dance, again as in the rocks making up the*\ that they have about a factor of 2 fewer scat- crust of the earth, is silicon. Aluminum is very

Vk tered a particles in the energy region repre- prominent (6 to 9 atomic %); it is the thirdsented by channels 63-73, relative to the num- most abundant element in the crust of the earth.:'

. ber scattered in the oxygen region. At present, only upper limits can be placed on

SAMPLE

ISAMPLE 3 Although no quantitative information is de- the amounts (2 to 3 atomic %) of carbon and

duced at present from the proton spectra from sodium in the samples analyzed by Surveyors

_J

I I I I I J I I_______

I20 30 40 50 60 70 90 90 100 110 12020 30 40 50 60 70 80 90 100 110 120

samples 2 and 3on the Surveyor 7 mission, the 6 and 7. Thus, inspection of the values givenCHANNEL NUMBER CHANNEL NUMBER

Fig. 17. Comparisons of the a spectra of the i

7. These include comparisons of sample 1 of eaof that mission, as well as a comparison of thmissions. The background-subtracted data wereoxygen plateau (approximately channels 8-25).

c six samples analyzed on Surveyors 5, 6, andeach mission with each of the other samplesthe spectra of the first samples of all three;re normalized so that they coincide in the

data (Figure 14) show clearly the presence of in Table3 indicates a gross similarity in chemi-aluminum in these samples in comparable cal composition to thatof many rocks found onamounts to that found in the other lunar sam- earth.

( Pies analyzed. Reliable quantitative results on Bef<Before proceeding to a more detailed consid-these two samples will require evaluation of eration of the results, it is worth recalling somelaboratory simulation studies reproducing the characteristics of the a-scattering technique ofso far, and possible geometrical effects arising butions. It is clear from Figure 16 that the

from the nonstandard relation of sample 1 relatively small contributions of C, Na, and(Surveyor 7) to the instrument. These geomet- Mg to the a spectrum cause their abundancesrical effects may be larger for the second and to be much less well established than thosethird samples of Surveyor 7. For this reason, of other elements. For this reason, at present,no quantitative analysis of the data from the only upper limits are placed on the carbon andsamples is presented, pending the results of sodium contents of the sample, and a ratherlaboratory investigations of these geometrical large error is assigned to the magnesium con-effects, particularly on the proton mode. The tribution.Similar considerations were applicableerrors of Table 3 have been assigned conserva- to the early analyses of the Surveyor 5 and 6tively enough so that the true values should lie samples.

geometrical relationships of the samples and chemical analysis and some of the aspects ofinstruments. the Surveyor missions that might affect the

interpretation of the analyses.Discussion First, the technique provides information on

The analytical results deduced from a-scat- the composition of only the topmost micronstering experiments on the Surveyor missions of the sample being examined. The possibilityrepresent the first on-site chemical analyses of that this topmost layer is not representative ofan extraterrestrial body. Before these results the composition of the bulk of the material,became available, the observation most directly especially under the conditions existing on therelated to thechemical constitution of the lunar lunar

surface,

must always be kept in mind,surface was the y-ray experiment on the Rus- Second, there is the question whether theoutside the indicated limits in not more than The a mode of the instrument is rather in-

-10% of the cases. sensitive to the geometrical effects of sample sian orbiter Lunar 10 [Vinogradov et al., 1966]. 'undisturbed lunar surafce,' as exemplified byThe intensities and spectral distributions of y the first samples examined on the Surveyor 6Figure 16 shows, for sample lof Surveyor 7, shape and distance. Therefore, even though the

the separate contributions of the eight-element uncorrected geometrical effects on the protonlibrary to the calculated spectra of Figure 15. spectra prevent the presentation of analysesIt illustrates the relative contributions of the for samples 2 and 3on Surveyor 7, the a spectravarious elements to the gross spectra as well may be compared to obtain information on theas the energy regions sensitive to their contri- relative concentration of oxygen, silicon, 'cal-

rays observed on this satellite were used to set and 7 missions (the sample examined by Sur-limits on the content of radioactive elements in veyor 5 clearly had been mechanically dis-lunar surface material. The conclusion was turbed), were really 'undisturbed.' One possi-drawn that these limits were inconsistent with bility is that, during the landing operation, thethe granitic type of rocks as they exist on spacecraft chemically contaminated the surface,

SURVEYOR 7—ALPHA SCATTERING EXPERIMENT6142 PATTERSON ET AL. 6143either by reaction with or by deposition of theretro-rocket or vernier rocket exhausts. Surfacecontamination by the Al.O. from the mainrocket exhaust is considered to be negligibleboth from the theoretical calculations as to theamount and nature of its deposition [Turkevichet al., 1967c] and from the observations of nodifference (within now quoted errors) in thealuminum content of samples on Surveyors 5and 6, which had different exposure to theexhaust.

The possibility of reaction of the topmostlayer with the products of the vernier engines(which operated much closer to the surfacethan the main retro-rocket) seems unlikely be-cause of the lack of any visible changes inappearance of the surface closest to the pointsat which their products impinged. Also, pre-liminary investigation of the presence of nitro-gen in the first sample examined by Surveyor5 gave amounts below the detection limits.(The vernier engines operate on dimethyl hydra-zine and nitrogen tetroxide.) Moreover, thepresence of significant amounts of carbon inany of the Surveyor samples has not been estab-lished. These results are consistent with thepre-mission tests on powdered terrestrial mate-rials (basalt, granite, and iron), which wereexposed for long periods separately to the room-temperature vapor pressure of dimethyl hydra-zine and nitrogen tetroxide and which showedno detectable effects as measured by a Sur-veyor-type instrument.

The possibility of some physical removal ofthe topmost layer of the lunar surface by thevernier engine blast on landing is harder toexclude. Again, there appears to be no obviouschange in physical appearance of the surfacenear the points at which the vernier enginesoperated. Moreover, the topmost (<1 mm),fragile, higher-albedo, surface layer seems to bestill present at the Surveyor 6 and 7 sites wherethe analyses were made and at the Surveyor 5site where the throwout material from the foot-pads did not disturb it. Finally, theoreticalesti-mates of the force exerted on the surface by thevernier blast at the time of cutoff indicatevalues that aresmaller than the values observedto be necessary to produce visible changes inthe material, such as tracks made by rollingstones. These are all arguments against thelikelihood of physical removal of the topmost

layer by the vernier engine blast upon landing.Thus, certainly within the now quoted errors

of analysis, several of the samples examined by Jj^^the Surveyors may reasonably be considered to | Hbe characteristic of undisturbed lunar surfacematerial. These considerations will bear furtherexamination as the more complete data are usedto provide more detailed and accurate analyses.

Intercomparison of results on different sam-pies examined on the Surveyor missions. Thelimits of error quoted in Table 3 are large andcould accommodatesignificantly different chemi-cal compositions for the different samples. Fig-ure 17 shows, however, that the scattered aspectra of the two samples at the Surveyor 5site agree and are very close to the spectrumobserved at the Surveyor 6 site except in theregion beyond channel 60. The proton spectraof these three samples likewise agree through-out the energy range. It must be concludedthat, relative to oxygen, the amounts of theelements contributing in a major way to thea and proton spectra (Si, Al, 'Ca,' and 'Fe')in all three mare samples are the same, prob-ably to within better than 20%. Smaller differ-ences, such as in the apparently greaterTi con-tent in Surveyor 5 [Turkevich et al., 1969],may become established after a more detailedanalysis of the data.

There is an additional fact pertinent to thegenerality of these analytical results on mare A^^samples (Surveyor 5 and 6). Surveyor 5 landed Iinside a small crater in Mare Tranquillitatis,and the two samples examined were, at leastin part, material ejected by the footpads duringthe landing. Surveyor 6 landed in Sinus Mcdiion a relativelyflat region, and the sample exam-ined was, as far as can be determined, undis-turbed surface material. The close similarityof the a and proton spectra obtained at thesetwo mare sites, 700 km apart, one representingundisturbed and the other two slightly disturbedmaterial, makes it unlikely that the chemicalcomposition derived is applicable only to thespecific landing sites of Surveyor 5 and 6. Itappears much more probable that the grosschemical composition is representative of largeportions of the surface material of lunar maria.

The scattered a spectra from the terra sam-ples examined by Surveyor 7 are distinctlydifferent from those of the mare samples (Fig-ure 17). The difference is largest for the highest

energies (channels 63-73) that record the aparticles scattered from the elements withatomic weights between those of calcium andnickel ('iron'). The differences at lower ener-gies are primarily a reflection of the lower con-tribution by this group of elements. The dataon all three terra samples imply that the 'iron'content is lower by about factor of 2 than thevalues determined for mare samples. This isconsistent with the calculated results of Table 3.

The other differences between terra and maresamples implied by the mean values of Table 3depend strongly on the proton mode of the in-strument. Since this mode is more sensitive togeometrical

effects,

these differences cannot betaken as established at present.

Chemical state of lunar surface material. Thea-scattering experiment provieles no direct in-formation about the chemical state of the ele-ments measured. However, chemical experiencemakes possible an extrapolationfrom the dataof Table 3 to the probable chemical state ofthe bulk of Surveyor-type lunar surface mate-rial. Specifically, the large atomic fraction ofoxygen, larger than 0.5, suggests that the metalspresent are mostly in oxide states. The meanvalues, if taken literally, indicatea slight oxygendeficiency. Well within the present limits oferrors, however, there is enough oxygen tocombine with all elements considered. For ex-ample, Table 4 presents the weight percentagesof oxides that would be consistent with theanalytical results from the Surveyor missions.Different compositions are presented for theterra and mare samples, reflecting the meancomposition of the mare samples as presentedin Table 3.It must be emphasized that the assigned

percentages in Table 4 are far from unique inrepresenting (within the given error) the ana-lytical results of Table 3. The limits of varia-tion are hard to estimate at present. However,the table is an example, consistent with theresults of the a-scattering experiment, of thechemical state of the major elements and theirrelative proportions in the lunar mare andterra surface material examined thus far.

It should be noted that Table 4 is meantto illustrate the oxide composition of the bulkof the lunar materialexamined. Minor constitu-ents, adding up to maybe as much as 10% byweight, may be present. In addition, the ana-

lyrical errors do not exclude some unoxidizedmetal, or radiation-decomposed oxides. A limitto the amount of metallic iron at the Surveyor6 site has been set by the magnet test at about%% by volume [deWys, 1968].

It is possible to speculate even further aboutthe chemical state of the lunar material. It isimprobable that the lunar material exists as asimple mixture of oxides. Rather, these oxidesare likely to be combined into more complexminerals. Material of similar chemical composi-tion in most other natural samples, such asterrestrial rocks and meteorites, occurs in thisstate. (In making this additional extrapolationfrom the basic analytical results, it must beremembered that, on the lunar surface, thematerial may be in a noncrystalline form, eitheras a glass or as particles too damagedby radia-tion to be identified crystallographically.) Evenwith the present large analytical errors, thetypes of possible minerals are strongly restricted,although not defined uniquely. For example,the chemical composition of mare materialgiven in Tables 3 and 4 is consistent with thepossibility that most of the material is a mix-ture of minerals of the feldspar and pyroxeneclasses. A more extensive consideration of themineral composition of lunar materialconsistentwith the present analytical results has beenmade by Gault et al. [1968]. As the analyticalerrors are reduced and as the amounts of theminor constituents are established, it will bepossible to refine such considerations further.

TABLE 4. Oxide Compositions (in Weight %)of Lunar Surface Material Consistent with the

Surveyor Analytical Results

Surveyor 5 Surveyor 7(Mare) (Terra)Oxide

Na20*MgO

0.64.4 7

Al.0SSiO.

14.4 2146.4 50

CaOTiO.FeO

1514.57.6

12.1 7

* The presence of sodium in Surveyor 7 sampleshas not yet been establishedwith certainty. Si)diumoxide could be present in amounts up to 4% byweight in the terra samples of Surveyor 7.

SURVEYOR 7-ALPHA SCATTERING EXPERIMENT 6145PATTERSON ET AL6144

it.

it is of interest to compare the present results face, at the landing sites of Surveyors 5, 6, and

V//////ASOLARATMOSPHERE

p_ I I

AVERAGE

MARE

SITE

0"l 1 TERRA

SITE

1

"

R!_

"

°-81i - - 0.6

'- n n 04

> - '■■;■ ?_ _ - 0.2

_rPi ■ n-,m_l [\H fjjj NU rjjj NHoNa Mo Al SI "Co" "F«"

void-free densities of 3.2 and 3.0 g/cm3 forlunar mare and terra material, respectively,from the preliminary analyses.

with the chemical composition of some materials 7, cannot consist entirely of material similar tothat have been considered as constituents of the terrestrial ultrabasic rocks such as dunite orlunar surface. In Figure 19, the present results to chondritic meteorites. Just as in the com-pare and terra) are compared with the anal- parison with the condensed solar atmosphere,

Finally, since the first lunar samples returnedby the Apollo program are coming from mareregions, the present analytical results shouldmake possible more definite and economicalplans for their investigation.The agreement ofthe results from Surveyors 5 and 6 also im-plies that the results of the investigations ofeven the first returned lunar samples will havemore generalapplicability than could have beenexpected before the Surveyor results were avail-able.

yses of average dunites, basalts, granites, tek- the lunar samples have too much aluminum,tites, chondritic meteorites, and basaltic achon- 'calcium,' and silicon, and not enough mag-drites [Palm and Strom, 1962; Turekian and nesium.Wedepohl, 1961; Condie, 1967; Urey and Craig, At another extreme of the rock spectrum,29531 Figure 19 also compares the present results withIt is seen from Figure 19 that the lunar sur- the chemical composition of terrestrial granites

02

Comparisons with the chemical compositionof various material. Although at present theassigned errors to the analytical results ofTable 3 are large, they still allow some signifi-cant comparisons to be made with the chemicalcompositions of various samples of the solarsystem.

Fig. 18. Comparison of the analyses of lunarmaria (average ofpreliminary results of Surveyors5 and 6) and the lunar terra analysis (Surveyor7 sample 1) with the composition of the nonvola-tile elements of the solar atmosphere from thereport by Urey [1967]. The comparisons havebeen normalized to unity for silicon.

z.UJoIX.UJQy

5

The first such comparison is of the presentresults on samples of the lunar surface withthe chemical composition expected if the moonwere an accumulation of condensed solar-atmosphere material. In this case, it may beexpected that the volatile elements (e.g., hydro-gen, noble gases) would have escaped as wouldhave the gases forming volatile hydrides (suchas oxygen, sulfur). For this reason, the com-parison is made only with the metals determinedin this work, and silicon is taken as the refer-ence point. This comparison, shown in Figure18, was made by using the values found in thisworkfor Na, Mg, Al, (Si), 'Ca,' and 'Fe' in themaria and terrae. The values for solar atmos-phere are taken from Urey [1967].

Although these interpretations of the ana-lytical results represent an extrapolation fromthe actual results of the a-scattering experi-ment, they should provide a more secure basefrom which to predict various other propertiesof the lunar mare surface material than hasbeen available until now. For example, lunarmaterials in the chemical states postulatedshould be chemically inert. They should notreact with the usual materials of instrumentsor of structures brought in contact with them.This statement is consistent with the lack ofobvious chemical action of lunar surface ma-terials with the aluminum-clad footpads of theSurveyor spacecraft. Similarly, since the pres-ent analytical results provide information notonly on the principal chemical elements, butalso on their probable chemical state, it is pos-sible to evaluate more confidently the practi-cality of utilizing the raw materials on themoon.

8

Im

It is clear from Figure 18 that the surface ofthe moon, at the places sampled by the lastthree Surveyors, does not have the chemicalcomposition of condensed solar material. Inboth mare and terra samples the magnesiumcontent is too low and the aluminum and 'cal-cium' values are too high.

1-z

O

£If

8Another example of the use of these prelimi-nary results is the improvement of the predic-tions of detailed physical properties (such asmeltingpoint, density,hardness, compressibility,etc.) of the particles making up lunar surfacematerial, by comparison with terrestrially avail-able substances of similar chemical composition.For example, Gault et al. [1968] have deduced

The elemental analyses of Table 3, as well asthe representative oxide compositions of Table4, suggest silicate rocks such as are commonboth on the surface of the earth and in manymeteorites. Although an elemental analysis(even one more precise than the present anal-ysis) can be only a rough indicatorof rock type,

.»1.0

i 0.6fef 0.6<trQ.

<2 04

r-

<

70 " "■—-1 DUNITE H-i [=3 CHONDRITE

6° CD __Z__

AVERAGE

MARE

SITE

60 60 _, [==]

AVERAGE

MARE

SITE

f" I=l TERRA SITE T_- _=_Z1 TERRA

SITE

50 50 50UJ

„ -40 E 40--40 £O

30 *> | 3°20 n j-b -20 2°- :-

"LJlll r- llffl jl§ Jj, t L [111 llg j] [111 rffl [H;""iT "o" "no" "m 7"aT "si" "w c ° No Mg Al

SI

"Co" "F."

70 "I" T! ! basalt

H-,

I 1

BASALTICACHONDRITE

60 [TD I 1

AVERAGE

MARE SITE *> «°

"

rf - l=_l AVERAGE MARE

SITE

C=l TERRA

SITE

|_- !______ TERRA

SITE

50- "" =° X =°z40 I 4°-

-*>§*>-_"1 -20 20 -20 p-6 r~-n -io io- - !_.'LJlLj^lri^ oL ml rg ffn ml Fffl rfk

vv^^^r^^^ ° ° n° m" ai si "c°" " f<i"_170 70170[~

«

GRANITE

n-n " TEKTITE60- [TfJ =_]

AVERAGE

MARE

SITE

"«> «" „ - ______)

AVERAGE

MARE

SITE

___=. TERRA

SITE

--

CZ3

TERRA

SITE/,--

50 50--5- § *■

_J

40 fee 40 -40 UJ

O30 _| 30

50 8 _,

r<-__

5 t>l[-] zo z°- (:■n - io io - _

* "_^oLiJJLni^ajfMl^ oLim^^fflHjcfflaT T X'^ "c°" "F°" c o no m, ai si "Co" "re-

Fit. 19 Comparison of the average mare analysis and the lunar analysis with six rockcompositions The top of the lunar bars represents the upper limit establishedby the prelimi-naryAnalyses, the Zvy line is the mean value, and the third line is the lower limit.

6146 PATTERSON ET AL. SURVEYOR 7—ALPHA SCATTERING EXPERIMENT 6147

content of the elements heavier than calciumat the terra site, this difference could be sig-nificant if it applies generally to the terrae. Itshould be remembered that these elements, atthe present stage of data analysis from thea-scattering experiment include the elementstitanium, chromium, manganese, iron, cobalt,and nickel. In general, these elements impartcolor to rocks. Terrestrial rocks that have moreof these elements are usually darker, and theytherefore have a lower albedo than rocks withsmalleramounts of these elements. This relationis illustrated in Figure 20, which is a photo-graph of samples of terrestrial rocks of varying'iron' content. The rock samples have been re-duced to a common particle size. Thus, althoughthere are several possible reasons for the higheralbedo of the terrae of the moon relative to thealbedo of the maria, the lower content of the'iron' group of elements, as found in the Sur-veyor 7 samples, may be a contributing factor.

Similarly, the lower 'iron' content of theSurveyor 7 samples, if it is characteristic ofterrae in general, suggests that the bulk den-sity of the subsurface rocks of the terrae isless than that of comparable material in themaria. In this case, the verygross topographicalrelationships of the lunar surface would besimilar to those on the planet earth, where, ingeneral, the continents are composed of ma-terial less dense than thebasaltic ocean bottoms.In addition, all the samples examined by theSurveyor missions indicate a void-free densityfor surface material (3.2 and 3.0 g/cm* [Gaultet al., 1968]) significantly lower than the valuefor the moon as a whole (3.34 g/cm"). Thus, thechemical results imply a moon that is chemi-cally heterogeneouson a large scale, both hori-zontally and vertically, with heavier materialconcentrated toward the center.

ray A. Perkins, Dr. Julius

Kristoff,

Mr. GeorgeHo, and Mr. William Six were among the par-ticipants. The electronicssystem was adaptedfromthat developed for the cosmic-ray research ofProfessor John A. Simpson, who also arrangedfor delivery of Imp 4 radiation level information." #i

At the Illinois Institute of Technology, Dr. G.Walker and Mr. Lou Wolfe were responsible forthe basic design of the passive temperature con-trol of the sensor head of the instrument.

—.i <§"I

Hughes Aircraft Co. was responsible for theintegration of this experiment to the Surveyorspacecraft. This work was largely done by a teamled by Mr. Robert Dankanyin and including Mr.John N. Buterbaugh, Mr. Heaton Barker, andMr. Eugene Henderson.

■m

0 2 3 4ATOMIC PERCENT OF "IRON" The radioactive sources were prepared and

tested at Argonne National Laboratory. Partici-pants in this work included Miss Carol A. Bloom-quist, Dr. E. Philip Horwitz, Mr. Howard W.Harvey, Mr. Michael A. Essling, and Mr. Dale J.Henderson of the Chemistry Division. Mr. DaleE. Suddeth of the Electronics Division workedwith the group at LASR on the design and test-ing of the instrument electronics.

Fig. 20. A series of powdered rock samples arranged in the order of their 'iron' content.The rock powders are all in the 37- to 50-/J. particle size range. In order of increasing concen-tration of iron-group elements, the rocks are: Mono Crater obsidian,

0.3%;

Argus granite,

0.7%;

Half Dome quartz monzonite,

1.0%;

Black Peak quartz diorite,

1.8%;

Loomis-88diorite, 2.2%; Little Lake basalt,

3.1%;

San Marcos gabbro,

3.3%;

and Pisgah basalt. 3.6%.These rock samples were provided by John B. Adams and Alden Loomis of the Jet Propul-sion Laboratory. Members of Jet Propulsion Laboratory who

contributed to the monitoring of the instrumentdevelopment, construction, and testing of the in-strument and to mission operations include Dr.Dennis

LeCroissette,

Mr. C. E.

Chandler,

Mr.Robert J. Holman, Mr. Henry C.

Giunta,

Mr.Charles C. Fondacaro, Mr. George O. Ladner, Jr.,and Mr. Richard E. Parker.

and oi sonic tektites. Here the lunar results it has been sampled by Surveyors 5, 6, and 7, ifmatch more closely. However, the lunar samples it originallyhad such a primordial composition,appear to have too much 'calcium' and, in must have undergone cosmochemical or geo-general, too little oxygen and silicon. The 'iron' chemical processing to change, for example, thecontents of the granite and tektite agree with relative amounts of Mg, Al, and Si to thethat of the terra, rather than with the higher amounts now found on the lunar surface. It isvalue for the maria. not so clear from such arguments alonewhether

Support by the Television Experiment Teamheaded by Dr. Eugene M. Shoemaker and assist-ance by Dr. RobertF.

Scott,

Mr. Floyd I. Rober-son, and Mr. Maurice C. Clary of the SurveyorSoil Mechanics Surface Sampler Experiment werevital to the success of the experiment in Sur-veyor 7.

Of the comparisons made in Figure 19, the these processes occurred before or after forma-composition of the lunar samples agrees most tion of the moon, or whether they are stillclosely with the chemical composition of ter- occurring.restrial basalts and with the chemical composi- The comparisons of Figure 19 also make ittion of a somewhat rare type of meteorite, the unlikely that the majority of the meteoritesbasaltic achondrite. The basaltic materials agree that fall on the earth (metallic and chondritic)with the lunar samples in all the major elements originated on the surface of the moon. Theexcept 'iron.' The more complete analysis of the lunar maria as sources of the most commonSurveyor 5 data [Turkevich et al., 1969] mdi- types of tektites also appear to be excluded.cates, however, that the high titanium and low To the extent that the other terrae have thesodium contents of Mare Tranquillitatismaterial same composition as that determined by Sur-makes it distinctly different from any common veyor 7, the tektites could not originate thereterrestrialrock or meteorite. either. The carbonaceous chondrites are also

<%The entire Surveyor program was conducted un-

der the auspices of the National Aeronautics andSpace Administration. The support of the Head-quarters Staff of this agency and, in particular, ofMr. Benjamin Milwitzky and Mr. Stephen E.Dwornik to this experiment is acknowledged withappreciation. The work at Argonne National Lab-oratory was done under the auspices of the U. S.Atomic Energy Commission.

Acknowledgments. The a-scattering experimenton chemical analysis for the Surveyor lunar mis-

sions is the culmination of many years' work towhich many people have contributed.

The instrument was designed, built, tested, and

installed at Cape Kennedy by the Laboratory ofAstrophysics & Space Research of the EnricoFermi Institute and the Central DevelopmentShop of the University of Chicago. Mr. Ed Blume

and Mr. Bernd Wendring of the Central Develop-ment shop and Mr. James Lamport, Mr. GeneDrag, Mr. Blame Arneson, Mr. Richard A. Em-mert, Mr. Robert

Saver,

Mr. Robert Takaki Mr.Myron Weber, Dr. Anthony Tuzzolino, Dr. Mur-

ReferencesAlthough it is not possible, at present, to ruled out by the analytical results. Thus, on

choose uniquely terrestrial rocks to match the these assumptions, only a small fraction of theresults of the analyses of the lunar samples, it meteorites falling on the earth can now be con-is quite clear that all the lunar analyses are in sidered as having an origin at the lunar

surface,

strong disagreement with the results expected Differences between terra and mare samples.for primordial solar-system material (whether Although the difference established between thethis be considered condensed solar atmosphere, chemical composition of the samples examinedor terrestrial ultrabasic rocks, or chondritic by Surveyor 7 and the mare samples examinedmeteorites). The lunar surface material, where by earlier Surveyors is confined to the lower

Anderson, W. A., J. E. Lamport, A. L. Turkevich,A. J. Tuzzolino, J. H. Patterson, and D. E.

Suddeth,

Final engineering report: Alpha-scat-tering instrumenthardware

fabrication,

test, andsupport, Lab. for Aslrophys. Space Res. EFIPreprint 6S-J,l, University of Chicago, Chicago,

111.,

1968.Condie, K.

C,

Composition of the ancient NorthAmerican crust, Science, 155, 1013, 1967.

Darwin, C.

G.,

Collision of alpha particles withlight atoms, Phil. Mag., 27, 499, 1914.

PATTERSON ET AL.6148de Wys, J. N., Electromagnetic properties: Mag-

net test, in Surveyor 6 Mission Report, Part 2,Science Results, Jet Propul. Lab. Tech. Rept.

32-1262,

Pasadena,

Calif.,

1968.Franzgrote, E., Compositional analysis by alpha

scattering, Jet Propulsion Lab. Space ProgramsSum. 37-20, Pasadena,

Calif.,

1963.Franzgrote, E. J., J. H. Patterson, and A. L.

Turkevich, Chemical analysis of the moon atthe Surveyor 7 landing site : Preliminary results,in Surveyor 7 Mission Report, Part 2, ScienceResults, Jet Propul. Lab. Tech. Rept. 32-1264,Pasadena,

Calif.,

1968.

Gault,

D. E., J. B. Adams, R. J.

Collins,

G. P.Kuiper, H. Masursky, J. A.

O'Keefe,

R. A.Phinney, and E. M.

Shoemaker,

Lunar theoryand processes, in Surveyor 7 Mission Report,Part

2,

Science Results, Jet Propul. Lab. Tech.Rept. 32-1264, Pasadena,

Calif.,

1968.

Crotch,

Stanley L., Alpha-scattering science dataprocessing, Proc. 13th Annu. ISA AerospaceInstr. Symp., 325, Instrument Society of Amer-ica, Pittsburgh, Pa., 1967.

Palm, A., and R. G.

Strom,

Elemental abundancesof the lunar crust according to recent hypotheses.Space Sci. Lab. Res. Rept. 3-5, University of

California,

Berkeley, 1962.Patterson, J. H., A. L. Turkevich, and E. Franz-

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