Cosmic Rays and Humans in Space Cary Zeitlin Southwest Research Institute Boulder, CO.

Cosmic Rays and Cosmic Rays and Humans in SpaceHumans in Space

Cary ZeitlinCary Zeitlin

Southwest Research InstituteSouthwest Research Institute

Boulder, COBoulder, CO

100 Years of Cosmic Ray 100 Years of Cosmic Ray Physics Physics

• Earliest experiments by Wulf, Hess Earliest experiments by Wulf, Hess circa 1912.circa 1912.

• High-energy physics originated in High-energy physics originated in studies of cosmic rays.studies of cosmic rays.

• Still a unique window for observing Still a unique window for observing the universe at the highest energy the universe at the highest energy scales.scales.

Applications of Cosmic RaysApplications of Cosmic Rays

• An important application of cosmic rays is An important application of cosmic rays is in biophysics: Prediction and monitoring in biophysics: Prediction and monitoring radiation doses received by astronauts in radiation doses received by astronauts in space from GCR, SPE, SAA passes for space from GCR, SPE, SAA passes for Low-Earth Orbit (LEO).Low-Earth Orbit (LEO).

• Related subject: Radiation therapy for Related subject: Radiation therapy for cancer using similar beams of protons cancer using similar beams of protons and heavy ions at ~ few hundred and heavy ions at ~ few hundred MeV/amu.MeV/amu.

Radiotherapy and Space Radiotherapy and Space RadiationRadiation

• Cancer therapy with heavy ions and Cancer therapy with heavy ions and space radiation have much in common.space radiation have much in common.– Ions and energies of interest are similar.Ions and energies of interest are similar.– Intersection of nuclear physics and biology.Intersection of nuclear physics and biology.

• A few places - GSI in Germany, NIRS in A few places - GSI in Germany, NIRS in Japan – have active research programs Japan – have active research programs in both areas.in both areas.

Cancer Therapy with Charged Cancer Therapy with Charged ParticlesParticles

• Charged particles Charged particles give better dose give better dose localization than localization than or or X-rays due to Bragg X-rays due to Bragg curve.curve.

• Proton synchrotrons Proton synchrotrons with maximum with maximum energies ~ 200-300 energies ~ 200-300 MeV are used in MeV are used in recent designs.recent designs.

Proton and Heavy Ion Proton and Heavy Ion TherapyTherapy• Proton therapy gaining acceptance: Loma Proton therapy gaining acceptance: Loma

Linda University, Mass. General, MD Linda University, Mass. General, MD Anderson, etc. Anderson, etc. – More coming online in the next few years. More coming online in the next few years.

• Heavy ion therapy initially done at LBL in Heavy ion therapy initially done at LBL in 1980’s & 1990’s, dropped (no funding) , 1980’s & 1990’s, dropped (no funding) , picked up in Japan, Germany, and elsewhere picked up in Japan, Germany, and elsewhere in Europe.in Europe.– No facilities presently in US, nor are any planned.No facilities presently in US, nor are any planned.

• Efficacy of charged particle therapy vs. Efficacy of charged particle therapy vs. conventional still has doubters but the conventional still has doubters but the physics makes sense.physics makes sense.

Heavy Ion Therapy Heavy Ion Therapy AdvantagesAdvantages

• Even better dose localization – ions have Even better dose localization – ions have higher peak-to-entrance plateau ionization higher peak-to-entrance plateau ionization ratio.ratio.

• LBL did only salvage cases LBL did only salvage cases low success low success rate, but GSI & HIMAC have shown clinical rate, but GSI & HIMAC have shown clinical success.success.

• US lagging – regulatory hurdles.US lagging – regulatory hurdles.

From Schardt et al.

Heavy Ion Therapy Heavy Ion Therapy DisadvantagesDisadvantages

• Distal edge due to fragmentation Distal edge due to fragmentation slightly reduces dose localization slightly reduces dose localization benefits.benefits.

• Machines are expensive. Machines are expensive. – Costs coming down, may soon be Costs coming down, may soon be

competitive with proton accelerators.competitive with proton accelerators.

• Lack of FDA approval.Lack of FDA approval.

Heavy Ions in SpaceHeavy Ions in Space

• Same types of particles used to treat Same types of particles used to treat cancer may also induce it, even at low cancer may also induce it, even at low doses.doses.

• Long-duration spaceflight increases Long-duration spaceflight increases risk of cancer, cataracts, maybe CNS risk of cancer, cataracts, maybe CNS damage.damage.– Earlier onset of cataracts seen in Earlier onset of cataracts seen in

astronaut cohort.astronaut cohort.– No experience with long-duration flight No experience with long-duration flight

outside LEO.outside LEO.

Radiation Exposures in Radiation Exposures in SpaceSpace• Complicated exposures – GCR gives a mix Complicated exposures – GCR gives a mix

of particles & energies.of particles & energies.– Huge unknowns in the biology. Huge unknowns in the biology. – Some unknowns in the physics.Some unknowns in the physics.

• Some of the exposure can be due to Solar Some of the exposure can be due to Solar Particle Events (mostly protons).Particle Events (mostly protons).– Modest shielding prevents acute effects, even Modest shielding prevents acute effects, even

in intense events.in intense events.

• In LEO, also get dose from passes through In LEO, also get dose from passes through SAA (trapped protons).SAA (trapped protons).

Exposure to GCRExposure to GCR

• Dose mostly from protons and heavier ions, Dose mostly from protons and heavier ions, with energy in the 10’s of MeV/nuc to ~ 10 with energy in the 10’s of MeV/nuc to ~ 10 GeV/nuc.GeV/nuc.

• Health physics: Dose equivalent is the Health physics: Dose equivalent is the measure of risk for cancer induction. measure of risk for cancer induction.

• Conventional wisdom: 1 Sv Conventional wisdom: 1 Sv 3% increase in 3% increase in fatal cancer risk.fatal cancer risk.– Based largely on Japanese A-bomb survivors.Based largely on Japanese A-bomb survivors.

• Hard to estimate doses retrospectively.Hard to estimate doses retrospectively.

– 3% is also the US legal maximum for job-related 3% is also the US legal maximum for job-related health hazards.health hazards.

1%

0.1%

.01%

Maximum Acceptable Risk = 3%

Shuttle Mission

ISS Mission

Mars Mission

Increase in Individual’s Risk of Fatal Cancer

▲

▲

▲

10%

Lunar▲

Uncertainties in Risk Uncertainties in Risk ProjectionsProjections

1%

0.1%

.01%

Maximum Acceptable Risk = 3%

Shuttle Mission

ISS Mission

Mars Mission

Increase in Individual’s Risk of Fatal Cancer

▲

▲

▲

“95% Confidence Interval”

10%

Lunar▲

SPE??

Uncertainties in Risk Uncertainties in Risk ProjectionsProjections

Cosmic Ray SpectraCosmic Ray Spectra

• GCR ~ 90% protonsGCR ~ 90% protons

• Most of the rest is Most of the rest is He.He.

• Electrons and heavy Electrons and heavy ions (Z > 2) are 1-ions (Z > 2) are 1-2% of the total flux.2% of the total flux.

• But contributions to But contributions to dose go as Zdose go as Z22……

Abundance of Galactic Cosmic Abundance of Galactic Cosmic Rays by Species in Unshielded Rays by Species in Unshielded Deep SpaceDeep Space

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1 3 5 7 9 11 13 15 17 19 21 23 25 27

Nuclear Charge

Re

lati

ve

Co

ntr

ibu

tio

n

FluxBadhwar- O’Neill Model

Abundance weighted by Abundance weighted by <LET><LET>

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1 3 5 7 9 11 13 15 17 19 21 23 25 27

Nuclear Charge

Re

lati

ve

Co

ntr

ibu

tio

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FluxDose

Abundance weighted by Abundance weighted by average dose equivalentaverage dose equivalent

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1 3 5 7 9 11 13 15 17 19 21 23 25 27

Nuclear Charge

Re

lati

ve

Co

ntr

ibu

tio

n

FluxDoseDose equivalent

Fe is the tallest pole!

What is Dose Equivalent?What is Dose Equivalent?• Unit of dose is Gy = 1 J/kg. Purely physics.Unit of dose is Gy = 1 J/kg. Purely physics.• Unit of dose equivalent is Sv, same units, but Unit of dose equivalent is Sv, same units, but

with a weighting factor that varies by radiation with a weighting factor that varies by radiation type to approximate biological effectiveness.type to approximate biological effectiveness.

• For exposure to a single radiation type, the For exposure to a single radiation type, the specific radiation weighting factor is used, wspecific radiation weighting factor is used, wRR..– wwRR = 1 for = 1 for , , ee--, , ; 5 for protons; 20 for ; 5 for protons; 20 for and heavier and heavier

nuclei.nuclei.

• For a mixed field, one integrates the “LET” For a mixed field, one integrates the “LET” spectrum (LET = dE/dx in water) vs. a “quality spectrum (LET = dE/dx in water) vs. a “quality factor” which depends only on LET, Q(L).factor” which depends only on LET, Q(L).

Mixed-field Quality Factor Mixed-field Quality Factor Q(L)Q(L)

• Traditional view: effects Traditional view: effects increase to ~ 100 keV/increase to ~ 100 keV/m, m, and then decline due to and then decline due to “overkill.”“overkill.”– Can’t kill a cell more than Can’t kill a cell more than

once. (Dead cells aren’t once. (Dead cells aren’t really the problem anyway.)really the problem anyway.)

• Huge scatter in the RBE Huge scatter in the RBE data.data.– Lots of questions: what is Lots of questions: what is

(are) the right endpoint(s)?(are) the right endpoint(s)?– Can we extrapolate cells or Can we extrapolate cells or

small animals to humans?small animals to humans?Figure courtesy of F. Cucinotta, JSC

Nuclear FragmentationNuclear Fragmentation• N-N collisions N-N collisions fragmentation of heavy ions fragmentation of heavy ions

into lighter ions.into lighter ions.• ““Projectile fragments” ~ preserve Projectile fragments” ~ preserve and and

direction of incoming ion.direction of incoming ion.• ““Target fragments” are MeV’ish Target fragments” are MeV’ish

– Charged particles are short-ranged.Charged particles are short-ranged.– Neutrons with high wNeutrons with high wRR are produced. are produced.

• For total dose, fragmentation helps:For total dose, fragmentation helps:– dE/dx ~ dE/dx ~ ii Z Zii

22 and sum of squares < the square of and sum of squares < the square of the sum.the sum.

– Effect on dose equivalent not so easy to Effect on dose equivalent not so easy to characterize.characterize.

Transport CalculationsTransport Calculations

• Analytic and Monte Carlo approaches.Analytic and Monte Carlo approaches.

• NASA codes date to 1960’s, when MC NASA codes date to 1960’s, when MC was impractical due to CPU limitations.was impractical due to CPU limitations.

• Analytic solves the Boltzmann equation Analytic solves the Boltzmann equation with many approximations and less with many approximations and less realism, e.g., problem is reduced to 1-d.realism, e.g., problem is reduced to 1-d.

• Either way, need knowledge of many Either way, need knowledge of many nuclear fragmentation cross sections.nuclear fragmentation cross sections.

Cross Sections and Cross Sections and TransportTransport

Fragment production cross sectionsCharge-changing cross sections

Z. Lin, Phys Rev C 75, 2007

J. Wilson et al., NASA TP, 1995

Nuclear Cross Section Nuclear Cross Section DatabaseDatabase

• Or, “What can a 3-person group do with a Or, “What can a 3-person group do with a tabletop experiment using 80’s technology?”tabletop experiment using 80’s technology?”

• Turns out there is (or was) a niche: Most Turns out there is (or was) a niche: Most cross sections needed for transport models cross sections needed for transport models not measured (& never will be).not measured (& never will be).– # of exclusive final states is ~ intractable.# of exclusive final states is ~ intractable.– Inclusive reactions to be studied are of the form Inclusive reactions to be studied are of the form

(Z(Zpp, A, App) + (Z) + (Ztt, A, Att) ) (Z (Zff, A, Aff) + X) + X

• Small subset of possible reactions was used Small subset of possible reactions was used to “validate” models (30-50% errors o.k.).to “validate” models (30-50% errors o.k.).

Experimental ProgramExperimental Program

• Measure as many cross sections as possible.Measure as many cross sections as possible.• Silicon detectors upstream & downstream of target. Silicon detectors upstream & downstream of target. • Main issues are dynamic range of readout electronics Main issues are dynamic range of readout electronics

– need 3 orders of magnitude – and availability of – need 3 orders of magnitude – and availability of beams.beams.

• Unlike earlier experiments, use small-acceptance Unlike earlier experiments, use small-acceptance detectors to measure light fragments.detectors to measure light fragments.

target

d3mm1/2

Scint 2

NaI

d3mm3/4

d3mm5/6

Scint 1

TOF path2-4 m

target

d3mm1/2

Scint 2

NaI

d3mm3/4

d3mm5/6

Scint 1

TOF path2-4 m

Large & Small Acceptance Large & Small Acceptance SpectraSpectra

• Upper histogram is typical Upper histogram is typical for this type of experiment – for this type of experiment – resolve fragments down to resolve fragments down to ZZfragfrag ~ Z ~ Zbeambeam/2./2.

• Previously, cross sections Previously, cross sections only reported for these only reported for these “peripheral” interactions.“peripheral” interactions.

• Rough analogy to deep Rough analogy to deep inelastic scattering: if we inelastic scattering: if we only test Zonly test Zfragfrag Z Zbeambeam/2, /2, we’re not going very “deep.”we’re not going very “deep.”

Experimental DatabaseExperimental Database

• Accumulated over 12 Accumulated over 12 years of ~ 1 week/yr years of ~ 1 week/yr of beam time.of beam time.

• For each beam ion/ For each beam ion/ energy, full target set energy, full target set was C, CHwas C, CH22, Al, Cu, Sn, , Al, Cu, Sn, and Pb.and Pb.

• ~ 200 charge-~ 200 charge-changing cross changing cross sections, ~ 2000 sections, ~ 2000 fragment production fragment production cross sections cross sections measured.measured.

5656FeFe 400400 500500 600600 800800 10001000 30003000 50005000 1000100000

4848TiTi 100010004040ArAr 290290 400400 6506503535ClCl 650650 100010002828SiSi 290290 400400 600600 800800 12001200 30003000 50005000 10001000

002424MgMg 4004002020NeNe 290290 400400 6006001616OO 290290 400400 600600 100010001414NN 290290 4004001212CC 290290 400400 30003000 50005000 10001000

001111BB 290290 4004001010BB 290290 40040044HeHe 230230

Ion Energy (MeV/nuc)

Fragmentation Data vs. Fragmentation Data vs. ModelsModels

• Simple model of overlapping Simple model of overlapping spheres describes charge-spheres describes charge-changing changing ’s to ~ 5-10%.’s to ~ 5-10%.

• Older parametric models predict Older parametric models predict monotonically decreasing monotonically decreasing fragment production cross fragment production cross sections as a function of sections as a function of Z.Z.

• Missing physics: Missing physics: – Odd/even effectOdd/even effect– Suppression of Z=9Suppression of Z=9– Increased cross sections for CNO.Increased cross sections for CNO.

• PHITS & FLUKA use different PHITS & FLUKA use different flavors of QMD and do much flavors of QMD and do much better than older models, but better than older models, but still off.still off.

Shielding Effectiveness: Another Shielding Effectiveness: Another Way to Look at the Same DataWay to Look at the Same Data

• 1 GeV/amu 1 GeV/amu 5656Fe beam with many Fe beam with many materials, including spacecraft materials, including spacecraft shielding candidates.shielding candidates.

• Nobody has a metric of shielding Nobody has a metric of shielding performance, so we made one up performance, so we made one up based on physics (not biology).based on physics (not biology).– DDnn = change in avg. dose per = change in avg. dose per

particle behind the target.particle behind the target.

• Take out depth effects, get Take out depth effects, get unsurprising result: hydrogen best.unsurprising result: hydrogen best.– Fragmentation drives dose Fragmentation drives dose

reduction.reduction.– Mass ~ A, Mass ~ A, ~ A ~ A2/32/3, so as A increases , so as A increases

the # of interactions per unit target the # of interactions per unit target mass goes down.mass goes down.

• Predicted by Wilson et al. for GCR, Predicted by Wilson et al. for GCR, nice to validate in lab.nice to validate in lab.

Beam Dependence of Shielding Beam Dependence of Shielding ResultsResults

• Wilson calculated for GCR.Wilson calculated for GCR.• Are the experimental results Are the experimental results

beam-dependent?beam-dependent?– Can a single beam/energy Can a single beam/energy

serve as proxy for the GCR?serve as proxy for the GCR?• Looked at dose reduction Looked at dose reduction

with the same CHwith the same CH22 target in target in several different beams.several different beams.

• It seems any energetic heavy It seems any energetic heavy ion beam of Z ion beam of Z 14 and E 14 and E 600 MeV/amu or greater 600 MeV/amu or greater yields ~ similar results.yields ~ similar results.

TEPC CharacterizationTEPC Characterization• Experiments with T. Borak (CSU) Experiments with T. Borak (CSU)

to characterize response of to characterize response of tissue-equivalent proportional tissue-equivalent proportional counters to heavy ions.counters to heavy ions.

• Simple device with complicated Simple device with complicated response function.response function.– Widely used in health physics.Widely used in health physics.– Used by NASA on ISS, Shuttle.Used by NASA on ISS, Shuttle.– Response not systematically studied.Response not systematically studied.

• TEPCs measure “lineal” energy TEPCs measure “lineal” energy transfer, typically equated to LET transfer, typically equated to LET (but not rigorously correct).(but not rigorously correct).

• Avg. energy deposited vs. impact Avg. energy deposited vs. impact parameter looks strange…parameter looks strange…

Tissue Equivalent Proportional Tissue Equivalent Proportional Counters Counters • For these experiments, used spherical TEPC For these experiments, used spherical TEPC

with field-shaping helical wire surrounding with field-shaping helical wire surrounding anode.anode.

• Tissue equivalent wall - Tissue equivalent wall - wall effects crucial.wall effects crucial.

• Fill with TE gas @ ~ 100 millitorr to simulate Fill with TE gas @ ~ 100 millitorr to simulate a 1 a 1 m diameter tissue volume.m diameter tissue volume.

• Helical wire causes artifacts, tooHelical wire causes artifacts, too– Flight TEPCs are cylindrical, no wire.Flight TEPCs are cylindrical, no wire.

• Result shown on previous slide (Result shown on previous slide ( vs. b) vs. b) greeted with scorn by “experts” at first.greeted with scorn by “experts” at first.

Modeling Explains Modeling Explains MeasurementMeasurement

• Proposed mechanism for Proposed mechanism for “boomers” – ionization “boomers” – ionization cloud formed in wall near cloud formed in wall near cavity boundary leaks in.cavity boundary leaks in.

• First good model First good model calculation by Nikjoo calculation by Nikjoo agreed with the data.agreed with the data.

• Later modeling by Taddei Later modeling by Taddei et al. using GEANT4 et al. using GEANT4 supports conclusion.supports conclusion.

GEANT4 simulations by Taddei, Zhang, and Borak

Flight MeasurementsFlight Measurements• Impossible to measure all particles of interest – Impossible to measure all particles of interest –

many trades to make a flight instrument. many trades to make a flight instrument. • Typical allocation for a NASA ESMD instrument: Typical allocation for a NASA ESMD instrument:

few kg of mass, a few W of power, a few $M. few kg of mass, a few W of power, a few $M. – Hitch a ride on an interplanetary mission (MARIE on Hitch a ride on an interplanetary mission (MARIE on

Mars Odyssey, RAD for MSL, CRaTER on LRO), or to Mars Odyssey, RAD for MSL, CRaTER on LRO), or to ISS.ISS.

• NASA JSC has operational responsibility for NASA JSC has operational responsibility for crew dose monitoring – they rely on TEPC, crew dose monitoring – they rely on TEPC, passive dosimeters, and some data from passive dosimeters, and some data from international partners.international partners.– JSC particle spectrometers flown to date on ISS, JSC particle spectrometers flown to date on ISS,

Shuttle had lots of problems.Shuttle had lots of problems.

MARIEMARIE

• Martian Radiation Environment Experiment Martian Radiation Environment Experiment flew on 2001 Mars Odyssey spacecraft.flew on 2001 Mars Odyssey spacecraft.– Original plan: Odyssey was orbiter + lander. Idea Original plan: Odyssey was orbiter + lander. Idea

was to have an instrument on both.was to have an instrument on both.– After MPL crashed, NASA got cold feet & Odyssey After MPL crashed, NASA got cold feet & Odyssey

became an orbiter only. (Lander became Phoenix.)became an orbiter only. (Lander became Phoenix.)

• Straightforward silicon telescope built by Straightforward silicon telescope built by NASA-JSC, similar to ISS instruments.NASA-JSC, similar to ISS instruments.– Worked for 20 months, failed in Halloween ’03 SPE.Worked for 20 months, failed in Halloween ’03 SPE.– Many hardware & firmware problems.Many hardware & firmware problems.

CRaTER (Cosmic Ray CRaTER (Cosmic Ray Telescope for the Effects of Telescope for the Effects of Radiation)Radiation)

• Built by Spence et al., Built by Spence et al., Boston University.Boston University.

• Si telescope with Si telescope with alternating pairs of alternating pairs of detectors and pieces detectors and pieces of tissue-equivalent of tissue-equivalent plastic.plastic.

• Will fly on Lunar Will fly on Lunar Reconnaissance Reconnaissance Orbiter (LRO), launch Orbiter (LRO), launch scheduled for May.scheduled for May.

Mars Science Laboratory (MSL)Mars Science Laboratory (MSL)

• MSL is the largest Mars MSL is the largest Mars rover to daterover to date– 850 kg, 10 instruments850 kg, 10 instruments

• Launch date – Fall 2011 Launch date – Fall 2011 (was to be Fall ’09).(was to be Fall ’09).

• Arrives at Mars between Arrives at Mars between July & September 2012.July & September 2012.

• Prime mission duration Prime mission duration 1 Mars year (687 days)1 Mars year (687 days)

n

RAD for RAD for MSLMSL

• Kiel University built sensor head, SwRI built Kiel University built sensor head, SwRI built electronics. electronics.

• 1.5 kg, 4 W 1.5 kg, 4 W • ~ 10~ 1044 dynamic range in dynamic range in E for charged particles: Si E for charged particles: Si

telescope (A+B+C) & CsI(Tl) (D). telescope (A+B+C) & CsI(Tl) (D). • CsI stops protons up to ~ 100 MeV (good for SEPs).CsI stops protons up to ~ 100 MeV (good for SEPs).• Plastic scintillator (E) for neutrons with energy > 10 Plastic scintillator (E) for neutrons with energy > 10

MeV.MeV.– Large neutron flux from RTG at lower energy.Large neutron flux from RTG at lower energy.

• Plastic scintillator anticoincidence shield (F).Plastic scintillator anticoincidence shield (F).

A Solid State Detector (SSD) A

B SSD B

C SSD C

D Cesium Iodide (CsI)

E Neutron Channel (Bicron 430M scintillating plastic)

F Anti-coincidence Shield

A Solid State Detector (SSD) A

B SSD B

C SSD C

D Cesium Iodide (CsI)

E Neutron Channel (Bicron 430M scintillating plastic)

F Anti-coincidence Shield

MSL RAD ScintillatorsMSL RAD Scintillators

• Scintillators read Scintillators read out by out by photodiodes.photodiodes.– Keeps mass down.Keeps mass down.– Only one bias Only one bias

voltage (-70V) voltage (-70V) needed, no risk of needed, no risk of coronal discharge.coronal discharge.

– Anticoincidence Anticoincidence also read out by also read out by photo-diodes.photo-diodes.

CsI (D)

D Readout Diode

CSA

Retainer

E Readout Diode

Neutron Channel (E)

RAD ElectronicsRAD Electronics

• Preamplifiers & 1Preamplifiers & 1stst-stage shaping amps -stage shaping amps built into sensor head.built into sensor head.

• Analog outputs Analog outputs electronics box, into electronics box, into VIRENA (36-channel custom ASIC).VIRENA (36-channel custom ASIC).

• VIRENA multiplexes outputs for the 14-bit VIRENA multiplexes outputs for the 14-bit ADC.ADC.

• Digitized data processed in Level 3 by a Digitized data processed in Level 3 by a virtual 8051 instantiated in the RDE FPGA.virtual 8051 instantiated in the RDE FPGA.– Most events histogrammed, a few high-priority Most events histogrammed, a few high-priority

(high LET) events will be telemetered down.(high LET) events will be telemetered down.– Only sending down ~ 400 kB/day.Only sending down ~ 400 kB/day.

VIRENA ASICVIRENA ASIC

• Built by NOVA R&D.Built by NOVA R&D.• Fast & slow discriminators, additional shaping stage, sample & Fast & slow discriminators, additional shaping stage, sample &

hold, output multiplexer.hold, output multiplexer.• Highly configurable.Highly configurable.• Controlled by the “RAE” FPGA which runs Level 1 software for Controlled by the “RAE” FPGA which runs Level 1 software for

trigger & readout control.trigger & readout control.• Same FPGA runs Level 2 software (uses digitzed data) for low-Same FPGA runs Level 2 software (uses digitzed data) for low-

level data processing – applies calibration constants, chooses level data processing – applies calibration constants, chooses best gain readout, etc.best gain readout, etc.

Beamline Setup for Beamline Setup for CalibrationCalibration

Beam incident from left.

target

Some beam ions survive the target, others fragment into lighter ions. (Just like fragmentation experiments.)

Need to calibrate quenching, esp. in E, for heavy charged particles.

Species Resolution in Si Species Resolution in Si DetectorsDetectors

Scale PH to ion charge

RAD for ISSRAD for ISS

• Charged particle capability ~ same as MSL Charged particle capability ~ same as MSL RAD.RAD.– Slightly enhanced – CsI replaced by larger BGO for Slightly enhanced – CsI replaced by larger BGO for

more stopping & to eliminate possible issue with more stopping & to eliminate possible issue with moisture. (ISS can get humid.)moisture. (ISS can get humid.)

• Greatly enhanced neutron capability.Greatly enhanced neutron capability.• Neutrons are created by nuclear interactions.Neutrons are created by nuclear interactions.

– Important behind large depths of shielding.Important behind large depths of shielding.– Estimated to contribute 30-50% of dose equivalent Estimated to contribute 30-50% of dose equivalent

in ISS.in ISS.– ISS shielding highly variable, averages 20 g cmISS shielding highly variable, averages 20 g cm-2-2..

Neutron CoverageNeutron Coverage

• MSL RAD not MSL RAD not designed for lower designed for lower energies because of energies because of RTG.RTG.

• ISS RAD will be used ISS RAD will be used for crew dosimetry, for crew dosimetry, must measure 0.5-must measure 0.5-10 MeV neutrons.10 MeV neutrons.


MSL RAD




MSL RAD

ISS RAD



Adding Neutron Spectrometry to Adding Neutron Spectrometry to RADRAD• Plan: Use boron-loaded plastic scintillator (Bicron Plan: Use boron-loaded plastic scintillator (Bicron

BC-454 or Eljen EJ-254) and capture-gating.BC-454 or Eljen EJ-254) and capture-gating.• Unique signature of capture events: first pulse Unique signature of capture events: first pulse

from interaction(s) with protons, neutron is from interaction(s) with protons, neutron is thermalized, captured by thermalized, captured by 1010B.B.

• Amplitude of 1Amplitude of 1stst pulse pulse neutron energy neutron energy no no unfolding. unfolding.

• Second pulse is due to Second pulse is due to 1010B (n,B (n,))77Li* reaction.Li* reaction.– About 2.3 MeV released, but light output is heavily About 2.3 MeV released, but light output is heavily

quenched quenched 60 keVee. 60 keVee.– t distribution is exponential, <t> ~ 2 t distribution is exponential, <t> ~ 2 sec for usual B sec for usual B

concentration.concentration.

B-Loaded Plastics in Flight B-Loaded Plastics in Flight ExperimentsExperiments

• Double-pulse method used by Double-pulse method used by instruments built for planetary science:instruments built for planetary science:– Mars Odyssey Neutron Spectrometer Mars Odyssey Neutron Spectrometer

(LANL).(LANL).– Mercury Messenger Gamma-Ray and Mercury Messenger Gamma-Ray and

Neutron Spectrometer (JHU APL).Neutron Spectrometer (JHU APL).

• Both use PMT’s for readout.Both use PMT’s for readout.• GRNS uses scanning ADC with FPGA GRNS uses scanning ADC with FPGA

doing all the coincidence logic.doing all the coincidence logic.

Capture GatingCapture Gating

• Can’t see 2Can’t see 2ndnd pulse above noise with pin pulse above noise with pin diodes – noise is 1 MeVee FWHM at best.diodes – noise is 1 MeVee FWHM at best.

• Investigating APD’s + optimized preamp Investigating APD’s + optimized preamp design.design.– Present preamp excellent for low-Present preamp excellent for low-

capacitance detectors; APD’s are high-capacitance detectors; APD’s are high-capacitance.capacitance.

– Have to add ~ 400V HVPS.Have to add ~ 400V HVPS.– Fallbacks are SiPM’s and (worst case) PMT Fallbacks are SiPM’s and (worst case) PMT

since constraints are greatly relaxed for ISS.since constraints are greatly relaxed for ISS.

ConclusionsConclusions

• Space radiation health presents Space radiation health presents many challenges – small but many challenges – small but important role for physics.important role for physics.



• Severely resource constrained, but Severely resource constrained, but that’s part of what makes it a that’s part of what makes it a challenge.challenge.



• Severely resource constrained, but Severely resource constrained, but that’s part of the challenge.that’s part of the challenge.

• Thanks for your attention!Thanks for your attention!

Cosmic Rays and Humans in Space Cary Zeitlin Southwest Research Institute Boulder, CO.

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Transcript of Cosmic Rays and Humans in Space Cary Zeitlin Southwest Research Institute Boulder, CO.