Professor

Reader:

Senior Fellow

Fellows

13'1966 THE ,.USTRnLL .. N N, .TION._L UNIVERSITY

RESE, ..RCH SCHCOL GF PHYS I C. L SCIENCES

DEP. TMENT OF NUCLE: PHYSICS

1: nnual Repor t t o Council f or 1966

E . W. Titter t on , C. 11.G ., M. S c ., Pl;l .D., Dip . ~d ., F . P. . S .A . , F .A.A.

P. B. Trc~acy , M-.• sc., Ph .D.

D. F. Hebbard , B . Li. . , M. Sc ., Ph .D.

T. R. Op el , B. Sc ., Ph . D.,

H. J . Hc.y , H. Sc ., Ph . D.

G. G. Ohlsen , B ••• • ' t! . s . ' Ph . D.

R. H. Spear , M Sic., Ph .D.

Vi siting Saaior Research Fellows : Profes sor J . • Risser

( ur rived March 1965 - left J an. 1966)

G. J . 1 cCa l l um ( rrived Fcbru::ry 1965 - left Feb. 1966)

Res earch Fellows Nurzynski, D. Sc .

P. G. Young , B.,Sc . M . .. ... •' Ph . D.

G. u. Din , B. Sc . . Ph. D.

Students K. H. Br c.. y , . Sc .

l.\. . v. Elliott , B. E., -• Sc .

F .C. P. HUdng , B. c .

M. I vanovich , B. Sc.

J . 1'1 . Norris , B. Sc ., M. Sc.

J . R. Pa tterson, B. Sc .

J . M. Pod. t e , B. Sc . , ~11 • , C •

B. D. Sowerby , B. Sc .

D. J . Sullivan , • Sc .

G. J . Cl a r k , B. Sc .

w. P. Bourke , • Sc ., ~- . Sc •

c . H. Osman , E. Sc , fv' • Sc .

D. Kean , B. Sc .

G. I' err , B. Sc .

Departmentdl n ssistant

Technica l Officers

Workshop Staff

Apprentice

Microscope Observers

Secretary

2.

E. F. Scarr (Mrs.), B. Sc .

TECHNICnL ST.~FF

N. F. Bowkett

T . i'~ . Brinkley

:.~i. . ull

G. P. Clar kson

W. T. Daniel

• D. Gower

J . S . Harrison

t • • • Marsh

C. J. Hill

W. H. Owen

W. Pfluger

R. McLeod

13/1966

~ . Brinkley (Nrs. ) ( 23.z days out of 5 p. w. )

W. Pfluger (Mrs.) (2~ days out of 5 p.w.)

M. Strautmanis (Mrs.) (4 days out of 5 p.w.)

P. Ual sh (Miss.)

T. F. Sampson (Miss.)

3. 13/ 1966 ST.SF MOVEMENTS L-.ND VISITOF.S

Professor E. U. Titterton spent four weeks overseas in November­

December this year on behalf of the Feder~l Government in the U.S. __ .,

U.K. and Fr ance. uring the peri d he wa s able to visit the Headquarters

of the U.S. , tomic Energy Commission a nd Labora tories of the U.K. t. tomic

Energy .uthority in _ _,ngla nd. Whilst in Fr2nce he visited the French

. ~tomic Energy Commission's Laboratory ~ t Fontenay- a ux-Roses.

Two sta ff members w2nt oversea s on study leav e - Dr. G. G. Ohlsen

to the Los d l amos Laboratories in the U. S • . • in May for a year and

Dr. T. R. Ophel to M.I.T. in the U. S • •• in November for eleven months.

Two distinguished physicists joined th~ group for short term

a ppointments - Profe ssor J . R. Risser of the Rice Institute, Houston,

Texas and Mr . G. J. McCallum Head of the Nuclea r Physics Division of the

New Zealand .~ tomic Energy Huthority. The former spent eight months in

the l aboratory a nd the l a tter, a year .

Dr. G. U. Din, who obt&ined his Ph. ~ from the Rice Institute and

ha s since been ca rrying out r e sea rch work a t the University of Kans s

has been appointed to ~ Re se2rch Fellowship a nd will come to Canberrc in

March, 1966 .

New students to j oin the Depa rtment during the year were Messrs •

. P . Bourke (University of Mel bourne) , G • ..J. Cl drk (University of

Tasmani ~ ) , D. C. !lean (Univ~rsity of Gl ... sgow ) '- ·• ·· C. H. Csman (University

of Melbourne ), and G. W. Kerr (University of Glasgow).

Students who h~ve been offer ed schola rshi ps and who will a rrive

during 1966 a re P. , •• t. ssima.kopoulos (Greek l uclear Research Centre,

n thens), H. Cords (Institute for Experiment~l Physics, University of

Hamburg ) and J . McKeown (Senior Lecturer in Charge of Nuclear Physics

Pl ymouth College of Technology, U.K.). During the Year, Mr. P.G. Young

successfully presented his Ph . D. Thesis and after the award of the

degr~e wa s appointed to a Re sea rch Fellowship in the epartment .

Mr. D. R. Osgood completed his M~ ster's course and wa s awa rded the

M.S c. degree. He wa s appointed ~ s an Experimenta l Officer a t .• . E.R. E.

Harwell o.nd l ef t for Zngl.c.nd in Febr uc-ry .

L~mong the numerous oversa~ s visitors were the following:

Professor W. c • Fowler of t he Californin Institute of Technology who,

during his two month stay ga ve d course of lectures en Nuclea r •• stro-

4. 13/1966

physics, Dr. H. G. B. Ca simir, Director of t he Philips Resea rch Labor­

a tories Holland, Professor R.Uyeda o f Na goya University, J apan, Drs.

J. V. Jelley and Joan Freema n of .t·:.. . E . R . E . Harwell, England, Dr. W.LoW.

Sargent of U.C. , San Diego, Dr. R. W. King of Pur due University,

U. S . i •• , Professor R. s . Krishna n of the Indi a n Institute for Science,

Banga lore, Dr. J. M. Eisenber g of the University of Virginia ,Professor

Hans Rae t her of the University of Hamburg , Germa ny and Professor Fred.

Reines of the Case Institute, Cl ev el and , U. S •. -\. .

RES&~~RCH EQUI PMENT

The Tandem Li..Cce l er a tor - 1965

Tandem opera tion was particula rly reliable during the year. Only

one unscheduled t a nk opening, in order to repla ce a broken column-to­

tube connecting spring, was necessary. No f a ilure of column resistors

ha s occurred since ,.~pril 1964 when a r esistor, ma de up of Welwyn Type

44F high volta ge r e sistors , wa s placed in the critica l position a t the

termina l end of the low energy column. a ctual oper a tion amounted to

a bout 6 ,000 hours of which t he ma jor portion (80 %) was devoted to the

a ccel er a t1.on of He3 and He4 beams using t he 2 MeV helium injector.

Ma jor modi f ica tions wer e effected during two shutdowns in February

a nd J uly. During t he former period , inclined f i e l d tubes were insta lled

in the high energy s ecti ons. £.S compa r ed to oper a tion during the pre­

vious twelve months with inclined f ield tubes in only the low energy

sections, some improvementsof hi gh volta ge perform2nce wa s obta ined.

Opera tion ha s been a ttempted successfully for t ermina l voltages up to

7 MV. On the other hand , a t low t ermina l volta ge s (below 2 MeV) beam

transmission, for protons and deuterons especia lly, has deteriora ted.

Typica l proton beams, measured immedia t ely before t he 90° ana lysing

magnet, a r e a s follows:

TERMIN1-_L VOLT~ :.GE

1.5 MV 2 . O 11.V

2.5 MV 3.G MV

BEL J~1 CURRENT

1.5 µa

2. 0 µa

3 . 6 J.La

7 . O µa

3 .5 MV 6 . 0 µ a

4. 0 I'1V 5 . 0 µ a

L: ... bout 90% of the se beam intensities can be ob t .::-.. ined a s ana lyzed beam current. The f a ll-of f &t low term~nal voltages i s more pronounced

5. 13/1966

than wa s previously the case. Beam transport into the t a rget area

ha s been more difficult since optimum transmission is sensitive to

both the input and output beam directions and t he se directions depend

critically on t he t ermina l voltdge. The helium beam intensitiee ar e

found to be much l e ss energy-sensitive but decrease slowly for termina l

voltages below 2 MV .

During July, a s~cond 90° analyzing magnet wa s installed. The

origina l magnet (product 36 ) wa s moved back to defl ect beams into a

second t a rget area and the new magne t (produce 52) loca t d in its

place to serve as ana lyzer for the origina l t a r get a r ea . The product

52 system ha s performed well; in pa~ticular demonstra ting no detectable

differentia l hyster esis 1vith r e spect to the NJ.V1R method of fi eld meas­

urement. c na lyzed beam observed on a beam stop beyond the r ear magnet

is identica l with t hat obta ined on the beam stop after deflection with

the front magnet. Deta ils of the magne t systems and the necessary con­

sole r earrangement are available a s a l abora tory report.

Since helium beams were required for a lmost the entire experi­

menta l programme , r eliabl e performance of t he 2 MeV injector wa s

manda tory and , fortuna t ely, posattle . Early in the year, the va cuum 0 chamber of the 20 magnet wa s r epla ced with c chamber which enabled

deflection of the r e sidua l charged b8am (after pa ssage through the

exchange canal) through an angle of 25° onto slits. Signals from the

slits controlled the corona load so a s to st2bilize the injector. This

method, using the defl ected doubly-charged beam component, ha s worked

well and the consequent stabl e injector oper a tion ha s proa'Jced .. ~~y

steady t arget currents. 9" oil di f fus ion pump and refriger a t ed

baffl e were insta lled in pl ce of the smaller mercur~r pump which had

never performed satisfactorily. Improved ultimate vacuum and a much

f a ster pumping speed have r esulted. The va cuum con t rols have been

modified and reloca ted and the ion source control switched-selsyn wa s

repla ced by three individual selsyn controls. ..pc:..rt from routine r e ­

newals of ion source units (a t intervals of 500-1,000 hour s) and corona

points and the replenishment of helium gas , t ank opening s have been

necessary only to repla ce the a lterna tor bearings (once) and for occa s­

iona l r epla cements of components in the osci l l c tor and focus power

supplies.

6. 13/1966

The new t arget ure became av ilable late in the year. Three

beam lines~ each pumped with a 500 litre/sec. vacion pump, a re planned.

i second 20 11 diamet r sca ttering ch:..mber is in use on one line and

gamma r ay equipment is being as sembled on anoth r line.

With the increa sing number of data output devic--.s in use, per

medium of th Output Selector unit and the need to coordina te effect­

ively th ~ activities of two t arget ar eas, considerabl2 effort ha s gone

into reorganiza tion of the control room. ~ centra l control station has

be n established for al l control, a na lysis and data output units. In

this way and with only d r l a tively modest amount of electronic equip­

ment, t nndem opera tion by one group is possible simultaneously with

other groups setting up und testing equipment .

utomatic Plotting System

Since the start of its opera tion early in the second half of the

year, there has been a substanti 1 dem nd for the facilities provided .

Currently , these f cilitie s . r2:

1) Punched t ape to punched card conversion.

2) Punched t ape or c.:-.-rds to c...n X-Y plot, with a wide choice of

X and Y scales , symbols, dat~ format and X or Y sca l e offsets.

The design a ims for the system accur~cy, r eliability and speed have

been achieved. 1. s more h~rdware becomes available, additional facil­

ities are being added .

Output Selector

i~ second (mobile) output selector has be n constructed . This

will a llow the RI DL pulse height analysers to control a paper t ape

punch or a card punch when working in th2 HTl control a reu. It will

&lso act ~ s a back-up system in ca se of breakdown in the output selector

mounted in the t andem electronics r a cks.

Data Control Unit

i fter a detuiled survey of the needs of the department r nd ava il­

able devices, an IB 1800 D t a L~cquisition , nd Control Unit was sel~cted

for purcha se. The proposed configuration, with 8K words of core stor­

~ge , should provide a simple and f l exible means of controlling experi­

ments c:.nd recording dat ·> . The I BN 1800 will work in conjunction with

the automa tic plotting system c. tnd with the ma in University computer in

displaying nd ana lysing dat~ .

f F RTR -N SU~ROUTINE for th~ t>Utomatic Plott ~r

7. 13 / 1966

. , s ubr o t i n e h-:i s b~ :=n wri tt2n to a llow -~a s } pr~para tion of c a r d s

f or thP. lo t t 0 r . One data point is p l otted e r ca rd . The subroutine

mu st bP. i n f ormed o f the X and coC"rdins t e s o f the point the positive

and n epa ti v e ~rrors ( i f a pplica r·l e) i n the _- va l u e and th9 d esired S ' '111-

toL Th~ olo tt~r t h o.n draws th ~ s mbol (on~ 0 f n ) wi t h (if applica ble )

tl. ~ e norooria te "'r ror ba r ,

Th~ ( 5 cm , B ~uchner Sp~ctrcPran~1

Th is ha s ~p erat ~d r~liabl~ t h r c u ahcut t .e vea r . It s p r ecisi n

is su ch that i t s erve s t o s how · p s .o r t comin ps i n t he Tand em ooerati on.

One of t h e s o. ~ ff ec t s a s ~e~n t g o res ence cf r edu c e d en~rgy particl e s

i n t . e b~am d'.l '? t o scatterinP from a p Artur e s etc . aft~r t e 90° a na l y ·-

sin['" marne t. I n a diff ~r~ntial so e c t r um th~ s e particl e s may pive low

~nerp•r tails t o s ha r p o ea. s wi t h i ntensitv 1 - 3 to 10 -S of t h e p~ak .

When t~e tai l is inteprat~d it mi aht ~e £ und t h2 t fro~ . 5 t o a s mu c h

a s 5% of the chaT7e is net of t e correct 2n':!rf~ r . L'.no th~r eff ect ha s

~ corn~ noticed sin c e t h 2 insta lla ticn of inclined f i gld t u bes . This is

a l ar0 e i ncre& s e in the ~ner?y spr~ad of t he a na l 1 s gd beam. Previou sl7,

1i t :. t r.; " s t r A- i ;rh t" t u1: ~ s t h e omo g eneity with c b "ect sli t s wid~ op en

wa s tupica ll,, abrut 1 pa r t in 5 .. 000. Now it is r a r e l y Le t ter t a n 1

oart i n 70C, · ~ow~v=r . th~ t: eo ret ica l ma ryn_ t r~ sol•1tion cen still b e

obtain~d b,, r~ducin~ c ~i~ct s lit s s ttinp s r~ sul tinp i n sli ahtly dimin -

ish ed b =am .

':'.:'h ~ 2411 Doubl = Fo cu ssino Sn : c t r r meter

Ma fo r modificati c n s .av~ ..,_· ~ en ma de t o t h = Spectrome t e r to brine

i t to f ull cepc.bi li t " a s a s t a nda rd i n s t r ument . Th :se i nclu d e :

i nr.,. co il s to smoo U out f i '3l d i n . cmo -, ::!rn~i t' r n~c:..r th~ s ampl -=. /. pilo t

mod ~l wa s cons truc t~d a nd t<: s t ~d and f o-_md to Ls v~rv s t isfa cto r . I t

is prooos ~d tc mo 1.mt t h?! r e' = n :; ·:: r t u'3 '"'ntr anc f:! tc t he magnetic f i e ld

t. ~ ca•1s e i t is C<'nsidgr ed t hat me· nti n o nea r t h e; exit would si pni f icantl

r9d·1c~ t h e a r :a r:'.: fo ca l pl -~n~ ~vailac le fer d !t:ctcr ins t r ument a tion.

2 ) L ;v~llin~ d evice s h~v2 b: =n construc ted and i n s t &ll 8d t o corre c t

f o r irrepu l a r iti e s in t h ; tn~ cL

3 ) .n entranc ~ slit s~ 1 s t r;m t r d~fin8 th~ s c lid anr'l ~ o f t he s p8c t ro-

a. 13/1966

meter is under construction and approa ching completion.

4) •-~ system for rigidly defining the beam a t· the entrance to the

t a rget chamber had been designed and most of the components h~ve been

constructed.

5) i. new v cuum system hr s been designed; h.:irdware ha s been construct­

ed and va cuum pumping equipment purcha sed .

6) The vacuum box ha s been removed nd sections a t the entrance and

exit have been cut off to rectify deficiencie s in the origina l design.

New flanges have been a ttached and an incision made in the box to llow

insertion· of the N.t .R. magnetometer. Considerable difficulty was

experienced in procuring suitable non~magnetic sta inless steel and in

- chieving non-magnetic welds. The modified box will a llow for more

satisfactory entrance slits and det~ctor syst~m, It will bQ remounted

in the magnet early in the new year,

7) ~.nti-scatter baffles for insertion in the va cuum box have been

des~gned.

Mea surements using Target liodula tion

The t urget modula tor described in l a st ye~r's report h::l s been

brought into full oper&tion. Various applic· tions of the device to

nuclea r spectroscopy have been examined . L~part from the simple applic­

a tion of the autom~tic recording of excita tion functions, the method is

well- a dapted to a ccurci t e me surements of resonance widths, t~rget thick·

nesses by means of resononce displa cement and ca libra tion and evalU.'.lt­

ion of acceler~tor beams.

The system used consisted of 100 'CV power supply modula ted to

provide s~wtooth w· veform outputs with peak-to-peak amplitudes of 3,

6, 12, 25, 50 and 100 KV . Most of the mea surements were made with t~~

l ;:2. MW~: =G'~ti~cro.f.t ... t<Jal.t:on ~.a.~c4Le·Ta tor.

Self-supporting t a rgets of thicknesses a s small a s 5µgm/cm2 have

been mea sured with good accurucy <lnd it is hoped to be abl e to adopt

the method to me~sure dE/dx f or various foils over & wide energy r ange.

Probably the mos~ significdnt results obt ined thus far concern

the energy distributions of particles af ter pa ssage through thin:foils.

By interposing Ll foil be tween t he b2nm und the t a rge t end modula ting the

t orget potentiul, ~ na rrow nucl e r resonance c~n be used Q S a good resol-

9. 13/1966

ution detector to scan the energy distribution of the particles.

Asynunetries of the distribution, corresponding to a difference between

the most probable energy loss and the average energy loss, were obser-·

ved. It was found that the theory of Symon, which is applicable at

higher energies (.vlo MeV), provided a reasonable fit to observed dis­

tributions at 1 MeV exc~pt that more low energy particles than predic­

ted were present.

The Deuteron Polarimeter

The device described in last year's report, which utilizes the

He3(d,p)He4 . .-reaction to determine deuteron tensor polarization, has

been developed to the stage of routine use. Improvements made during

the year include insulation of the chamber to permit measurements at a

laboratory angle of o 0 for (a,d), (He3 ,d) and (p,d) processes. Experi­

mental work with the equipment will be described later in this report.

RESEARCH PROGRAMME

During the year thirty-three papers were published while three

were in press and seven in preparation at the end of the year. Two

theses were presented by students finishing - one for the Ph. D. degree

and the other for the M. S~.

Research work was concentrated entir~ly~tn the region of the

light elements, AS. 27, in studies involving proton, deuteron, He3 and

He4 bombardments.

The summaries which follow are arranged ·.in ascending order of ·::: :.;::.-1

target mass.

Tensor Polarization of Deuterons from p-d Elastic Scattering.

The tensor polarization of the recoil deuterons from p-d elastic

scattering was measured at six ~nergy-angle pairs between 4 and 9 MeV

and between 30° and 45°. The small but non-zero values of some of the

polarization tensors indicate that spin orbit or tensor forces are

necessary to describe low energy nuclear-deuteron scattering, although

the effects of such forces are relatively small.

He3-T Elastic Scattering

The elastic scattering of He3 by tritium has been studied at

He3 energies between 5 and 11 MeV. Three excitation functions and

four angular distributions were obtained to an absolute accuracy of 7%.

1 •

{Alpha Triton Elastic Scattering

13/1966

Five angular distributions and six excitation functions for

He4 -T elastic scattering have been obtained at He4 energies between

5 and 11 MeV. A phase shift analysis of the data is in progress, and

level parameters for states in Li7 will be extracted.

Tensor Polarization in d-a Scattering at Large Centre-of-Mass Angles

A :totiJ.i;<-:of thirteen measurements of the deuteron tensor polariz­

ation in d-a scattering has been made at centre-of-mass angles of 120°,

135° and lao0 between the He4 energies of 4 and 11 MeV. These results

are being used to check the nuclear phase shifts obtained in work

performed in other laboratories.

He4 (a a) Scattering near 4 MeV.

Analysis of data from other laboratories has suggested that

information on phase shifts near the d-wave "threshold" is unreliable,

and several accurate angular distributions have been measured be~ween

l and 6 MeV Bea energies. Results confirm that earlier data were in-

accurate in this region.

Li6 (d,a)He4

This reaction, which is highly exothermic, is being used to

look for a 6+ state in Be8 near 30 MeV. rtngular distributions have

been measured with beam energies up to 12 MeV and seem to show that such

a state is contributing. Detailed measurements over a wide energy range

are being carried out.

t.i7(p,y)Be8(a)He4

A study is continuing of the 16.63 and 16.92 MeV states of Bea.

&n earlier experiment on Be9:·(He3 ,a )ne8(a )He4 confirmed that these

states are of spin-parity z+. The present study is being undertaken

on the Cockcroft-Walton H. T. set to attempt to measure accurately the

intensity of magnetic dipole to electric quadrupole transitions to

these states from the 17.6 MeV state in Be8 •

Be9 (p d)Bea

Deuteron spectra have been taken for proton energies of 1.7, 2.5

4.0 and 5.2 MeV, at angles from 10° to 60°, in order to obtain details

of the shape of the ground state of Be8 at excitation energies a long

way from the sharp peak. The ground state has a second broad maximum

between 0.5 and 1 MeV, with a height less than 6%/J.!ieV relative to the

• ,. 11. 13/1966 I

integrated sharp peak at 0 MeV excitation. Attempts to reconcile this

"ghost" with various theories have not succeeded. The shape is much

as expected, but, in comparison with the level parameters deduced

from a-a scatte~ing, the observed height is too small. The nearest

prediction is aboutlD%/MeV from single level R-matrix theory.

Be9 (He~a)Be8 , B10 (d,a)Be8 , and B11 (p,a)Be8

These reactions are being investigated at incident energies up

to 13 MeV, observing transitions to levels in Be8 between 16 and 19 MeV,

in particular to the 2+, T = 0 and 1 levels at 16.6 and 16.9 MeV. The

reaction mechanisms are obviously very different. The (da) reaction

can only lead to T = 0 states, and the spectra show interference be­

tween the two levels.

BlO(He3p)Cl2

The B10 (He3 ,p) reactions tc the ground state, 4.43 MeV, 7.66 MeV

and 9.64 MeV excited states of 12c have been investigated from 1.2 -

12 MeV bombarding energy. In order to stop the energetic protons a

3 mm lithium drifted counter plus absorbing foils were used. fin excit­

ation function at 150° has been measured for each group and a total

cross section obtained as a function of energy for p0

and p1 from

sets of twelve angular distributions measured throughout the energy

range. In addition distributions have been obtained for the p2 and p3 groups at 5.4 MeV. The excitation functions show considerable correl­

ated structure, confirm the 26 MeV state in 12N observed in earlier 10 3 10 3 . B( He,a

0) and B( He,d

0) studies (reported below) at 5.8 MeV bombard-

ing energy and suggest further states of a similar nature at approxim­

ately 22 MeV, 24.5 MeV and 27.9 MeV excitation. The angular distrib­

utions show a behaviour too complex for level parameters to be extract­

ed from a simple Legendre polynomial analysis.

BlO(He3d)Cll

This reaction w s investigated over the energy range 3.5 to

10 MeV. Excitation functions for th~ ground state transitions were

obtained a t laboratory angles of 45°, 90° and 150° and detailed angul~r

distributions were measured at bombarding energies of 3.7, 5.8, 7.5

and 9.8 11eV. The 150° excitation function showed a resonance at

approximately 5.8 MeV, corresponding to an excitation of 26 MeV in the

12 • 13/1966 . 1 'l__

-N system. This r €9onance , a lso observed in an earlier study of the

l OB( He3 , a )B9 reaction reported below may be identified with giant

resonance structure in 13N. A measurement of the tota l deuteron

cross section by an activa tion method shows no evidence f or t he r e s­

onance. The ( 3He ,d0

) angular distributions indicate the reaction

to be predominantly a direct process and they have been f itted

successfully using a Jl.JBA analysis. Only a stripping mechanism is

necessary to explain the forward and backward peaking.

Lngular distributions and excitation functions for the

tPB( 3He,a0

)9B and lOB( 3He, a 1 )9B (2.34 MeV) reactions were measured

f or 3He bombarding energies between 2.0 and 10.0 MeV. Differentia l

cross sections were determined. The angular distributions varied

smoothly with energy and showed a tendency for both forward and back­

ward · ~ea~ing .':.· - . . . The a0

angular distributions and the excitation func­

tion measured a t 150°(lab.) indicated a strong resonance, with ~-lMeV,

at 5.8 MeV bombarding energy, corresponding to an excitation of 26.l

MeV in the 13N system; but the a 1 data do not show a similar resonance.

The occurrence of minor structure in the excitation functions with

period of approximately 2 MeV may be evidence for compound nucleus

f luctuations. The results suggest that the reaction proceeds mainly

by direct proce sses with a competing resonance process at 5.8 MeV.

Bll(He3, a )Bl 0

Particle spec tra f rom t his r eaction initiated by 10 .5 MeV He3

particle s have been r ecorded a t 13 angles from 10° to 150°. 16 narrow

levels below 9 MeV in B10 have been identified and their positions

mea sured to within 5 keV. The angular distributions are genera lly like

ones which have been found for He3 energie s between 2;..and 5 MeV .

While they suggest tha t direct<reaction processes are dominant, they

cannot be fitted with simple stripping distributions, and it does not

seem that better fits will result f rom a DWBA analysis.

c12 (aa ) Sca ttering f rom 3 to 7 MeV

Detailed angular distributions have been measured a t points

between well-known sharp r esonances in this process. It has been

found that inconsistencies reported be tween work a t Rice and Wisconsin

r • r-- _,, .. -- ~;· ·.: - , ..

' 13. 13/1966

Universities can be r e solved by re-defining pa r ameters for the very

broad sta tes a t about 11 .26 MeV(O+) and 11.63 MeV(3-). Results of

this work have been ana lysed using a modified search progra mme for

pha se shift a na lysis on the C. S.I.R.0 . 1 s CDC 3600 computer.

c13(a,a)c13 and c13(a,n)o16

The c13(a,a)c13 ela stic sca ttering using 25.30 keV self support­

ing t argets with 60% c13 were mea sured from 3.5 to 5 MeV a t four centre-0 0 0 0 of-ma ss angles: 169.6 , 149.4 , 90 a nd 54.7 •

and distinct in this energy r ange and have l arge

va lues can be a ssigned.

Resonances a re narrow

T1 IT\ so th t J11

a

In the ca se of c13(a,n)o16 , angular distributions were t aken

a t : 4.593, 4.985, 5.0 37, 5.18, 5.40 5, 5.525, 5.63, 5.78 and 5.96 MeV.

A ground-sta te neutron excita tion curve ut o0 and 90° (lab.) wa s mea s-

ured from 4.94 to 6.48 MeV. Most of the angula r distributions were

t aken on strong resonances. Most have high forward peaks.

The ela stic da t ·- wa s t aken only up to 5 ~eV because a new 13 16 reaction channel - C (a,'1_)0 ,neutron decJ y to the first excited

sta te of 016 - opens a t 5.1 MeV. Comple t e ana lyse s of sca ttering and rea•

etion data is probably only sa tisfactory below 5 MeV. It will certa inly

be difficult 8bove 5 MeV. ~ t the same time the 3.5 to 5 MeV region is

very interesting, with v ery n~rrow (some 5 keV or less) resonances,

The neutron experiments above 5 MeV show pronounced r e sonance

structure and probably will ullow r easoneble estimates of J va lues.

They a re certainly worth while in showing the continuation of reson· n­

ee structure to quite high energtes.

The excita tion function for the reaction is be ing studied, to

extend the mea surements made on the same reaction over the l a st few

years on HTl. Some of t he e rlier da t a showed the need for mea sure­

ments a t higher energie s in order to obta in a reliable extrapola tion

of the cross sections to stella r energies. The t andem perform~nce, of

up to 1 µa a t energies well below 2 MeV, ha s been sa tisfa ctory.

Energy Levels of 0 16

Subsequent to t he identifica tion of l ev els a t 13.10(1-), 13.1

(2+) und 13.15(3-) MeV , further mea surements hav e been made which a re

14.

p'ertinent to thii..S :-:region of excitc.. tion: --

12 (a) C (a,a0

)

13/1966

It is considered t. u. t ::.11 of the c12+a and N15+p datu. are

consistent with the three levels given above with the possible except­

ion of the c12 (a,a0

) re · ction. Consequently, ~he elastic scattering

data h ve been remea sured for a lpha pa rticle energies between 6.6 and

8.5 MeV. Excit£tion functions were me~sured ~t 7 ang~es and angula r

distributions a t interv~ls of 50 keV. In addition, the relative cross­

sections of the two other rea ction channels, viz. the c12 (a,p) and

c12 (a ,a 1 ) reactions, h.::ive been established. 1'4ethods of analysis are

being considered.

( b ) C 12 (a , yy )

h . previous mea sur_ment of the (coincidence); excita tion function

of this reaction found a well-defined resona nce - t Ea= 8.15 MeV, corres­

ponding to the well-known 3 level a t 13.25 ~eV, ~nd the suggestion of

a weak resonance a t a bout 7.95 MeV which could be a ttributed to either

the 2+ or the 3 level o t 13.15 MeV.

The mea surement ha s been repeated, using a differant configur-

a tion of the two counters mployed to derive the ca scude yield, and

with .:::.dded precnutions to nvoid contributions from the contaminant ·.

c13(a,ny) rea ction. Two well-defined resonances were observed at 7.95

MeV and a t 8 . -~5 MeV. The former reson~nce Wc..s consider .... bly n-..rrower

than would be expected for the 2+ level from the c12 (a,yo) dat.:::. ; thus

the reson~nce is believed to provide strong confirmation of the 3

level e. t 13.15 Nev.

Elnstic Scu ttering of 3He purticles on 160 nucle i.

Energy ~nd angulJ r dependJ nce of 3He ela stic scattering on 160 nuclei ha s been studied for energies between 9.8 a nd 11.8 UeV and

for sc<l ttering angles between 15° a nd 165°. .Analy.sis ... in:-.in~,progr ~$s.

. . . .. ' . : .· . .... · ... ·.. ... .. .; ~

~ ga s t 2rget h~ s been used in the se meusurements. The mea sure-

ments were carried out for L number of energies between 9.8 nd 11.8

MeV and in a wide r~nge of ·ngles between 15° - nd 165°. Excita tion

functions were measured ._.. t .!~0°, 70°, 11C0 .::md 165° for 8 - 12 MeV.

15. 13/1966

Some interesting ~nomalies so f a r reported only for elastic scattering

but not for reactions were observed. • .. short report will be soon pre-

pared a nd n extended pc.per will rppec::.. r l a ter.

Excita tion of collective mod~s of motion.

c new progra mme to study collective modes of excit&tion has

been initi ~ted. One- and two-phonon trr nsitions · re investiga ted.

· ttention is - lso p · id to the excit~tion of o+ sta tes to expla in their

n ture c'.lnd to unnrttura l p2rity states to explore the mecha.nism of their

excit2tion. In the first set of experiments nucl i of 2~e , 2411g and 28si are to be investiga ted.

20N ( r )2CN e a,a e

Some me · surements have been perform d for inela stic sca ttering

of a p rticles on ~Ne nuclei. .. .lph~ groups corresponding to the

+ + ~ - -ground sta te, 1.63(2 ) , 4.25(4 ), 4.97(2 ), 5.63(3 ), 5.80(1 ), 7.03

(4-) ~ nd 7.17/7.20 MeV excited st~tes in 20 e have been identified •

. ngula r distributions corresponding to the ground stute, z+, 4+ and

unnatural parity 2 sta tes h .... ve b~en ii.lre .... dy c ..... lcul· .. ted from recorded

spectr~ •

.. -. test run with ..... source of neg i tive 4He ions h;1s been a lso

a ccomplished to study fec sibility of using neg ..... tiv2 be~m in the first

st<lge of J cc ler.::.. tion in c .. rrying out proposed experiments. Sa tisfactory

results have been obt&ined.

Energy Levels of Mg25

• det<:. iled study of the levels of I-1g25 up to nn excit-. .. tion

energy of 3.408 MeV h ... s been - initL .. ,t cd. Work hn s been principa lly

concentra ted on double ~nd triple g~mm2 r~y angul~r correl~.tion measure­

ments t reson .... ,nces in the Fg25 (p , p 'y ) reu.ctions. The following prelim­

in...lry results h.lve been obt·' ined for the 32/ ~1 emplitude mixing r a tio

( ) of the 1.962 g . s . [·md the 1.962 0 . 976 tr~nsitions; ·.\.1. 96=-3 or

C. 2 and 8 .9.q 6·=-0. 6 or -0 . 16. ~ .rn.lysis of the dc.. t d concerning ~he

high2r levels is in progress. Currently Ge (Li) detectors ure being em-

ployed to obt~in further det~ils of the y-r~y spectr~ ~nd the Doppler

shift a ttenU:.: tion method is being employed to d termine the lifetimes

of the second nd third excited st~tes.

16. 13/1966

Eif etime Effects in Ga s Targets

In the course of preliminary studies on the Ne22 (a,ny)Mg25 reaction

using a Ne22 gas target the 584 keV radia tion showed a mark0d anis­

otropy instead of the expected isotropic distribution. It was real­

ized that this effect was caused by the finite lifetime (~5ns) of the

first excited st~ te. Further theoreticc l and experimental studies on

this effect in ga s t a rgets were undertaken; a paper on this subject is

being prepared for publication.

Proton Scattering from i 127

The scattering of protons from 271.l ha s been studied for proton

energies from 3.5 to 11.3 MeV with an energy resolution of approximately

10 keV. Excita tion functions have been obta ined a t laboratory angles

of 90° and 140° for groups corresponding to the ground and first six

excited sta tes of 27. 1. The va lidity of a fluctuation theory inter­

pretation of the da t u has been investiga t ed; it is concluded that such

an interpretation is valid for the upper pa rt of the range but is quest­

ionable for the lower energies. The distortion of auto-corr"f~latd.on -..fiun­

ctions due to non-st&tistical va rid tions in the reaction yield ha s been

eliminated by calcul~. ting fluctuations with respect to an avera ge cross

section defin~d by using an ~ v ~raging interva l of 400 keV. 1.n auto­

correlation an~lysis indica tes that the mean width of 28si levels part­

icipating in the reaction is approximcttely 34 keV a t a n excita tion

energy of 21. 5 NeV. Estimates of 1 vel width ba se( on· the d.en.si.ty of

maxima in the excitation functions are in satisf&ctory agreement with

this value. The da t a show some evidence for t e presence of intermediate

structure of width and spa cing of the order of severa l hundred keV. 27 .3 26 l'.l ( He ,a) ._l

· ngular distributions corresponding to the ground stute and 0.229

0.418, 1.059, 1.760 , 2.072 and 2.547 MeV excited sta tes in 26 . • 1

nuclei have been mea sured fer re ction angles between 15° and 165°

in interva ls of s0• The me surements w2re ca rried out by using

solid state silicon detectors and nctura l .• 1 t a rge ts. Cross sections

as low a s of the order of 2 µ /sr have been m2asured. In order to im-

prove the a ccura cy of mea surements two permanent detectors were mounted

in the scattering chamber, one to provide an additiona l control of the

17. 13/1966

Intensity of the incoming beam and another to monitor the target.

The detectors ar e used in other experiments , too. Angula r distribut­

ions were ca lculated from mUlttChann.el«.ania~yEer spectra by using a

progra rrune for unfolding Gaussian distributions (see below). Th2

ca lculations were carried out on the IB~I-1620 computer. The resul~s

were presented a t the nINSE Conference on Nuclear Physics , Melbourne

23-25 .August, 1965 and they a r e being prepared for publica tion.

Si28 (He3 )si27

Alpha groups corresponding to the ground state, 0 .78 , 0 .96, 2.17

2.65 a nd 2.87/2.91 MeV excited sta t e in 27Si nucleus were identified

and the relevant "ngula r distributions are being mea sured. In addi tion

elastic sca ttering is being a lso studied to provide suitable data

for DWBa analysis.

CONFERENCg

The Australian Institute of Nuclear Science and Engineering , in

collabora tion with the Department of Physics , Univ~rsity of Melbourne ,

organized a Nuclear Physics Conf2rence held in Melbourne during august

1965.

Li. t the meeting the following papers were presented by sta ff nd

students of the Dep~rtment; n

Line Shapes of Low Levels in Be0 I: H. J. Hay n

Lineshapes of Low Levels i~ B~ Il_; P. B. Tree.cy •

... .. .... 3 ··1evels in Be7.i Li7 Nucl8i . H. Iv.: novich , P. G. Young and G. Ohlsen.

16 The En ergy Levels 0£ 0 in the Vicinity of 13 MeV . T. R.Ophel ( and

J. Morris). 3 27 The Elastic Sca ttering of 5.5-10 . 0 MeV He pa rticle s by i·:..l Nuclei:

J. Nurzynski.

P. Study of {3HeJ a) reaction l eading to 26f'l.l: J . Nurzynski

Reactions Induced by the HG 3 bombardment of B10 • J . R. Patterson,J. Poate

and E. ~J . Ti tterton.

Scattering of Protons from d~27 : R. V. Elliott s nd R. H. Spear

The Tensor Polarization of Deuterons Sca ttered from He4 : ~. G. Young,

!"I . Ivanovich and G. G. Ohlsen .

Nuclear Life time Eff ects in Ga s Targets:G . J. HcCa llum a nd B.Sowerby.

Data Handling for ,,·, .N. U. Nucl2ar Physics: D. :F. Hc:.bbard.

The Be9(He3 ,a)Be8 Reaction to High States of Be8 ,D.Sullivan, P.Treacy

18. 13/1966

OTHER .:·.CTIVITI ES

Professor Titterton was appointed Dean of the Resea rch School

of Physical Sciences for thr~e yea rs from J anua ry lst, 1966. He

wa s reappointed Vice- resident of the ~~ustralian ,,cademy of Science

and remains on the Council of tha t body.

During the yea r Professor Titterton a ttended a number of meetings

of the Defence Research and Development Policy Committee and the

National Radia tion ctdvisory Committee.

Under the joint auspices of the dustra lia n Institute for Nuclear

Science and Engineering ~ nd the University of N.S .W., Professor

Titterton gave a public lecture on "Nuclea r Physics in ... ustra lia 11

on the occa sion of an n .I.N. S .E. Council meeting a t the University of

NoS.W. in ,.ugust.

During the year, a number of course s were given for va ca tion

schola rs and for Ph . D. students . Notable among the l a tter were the

following courses:

11Hn Introduction to Scattering Theory a nd Direct Reaction"

by Dr. B. Robson.

"Nuclear .. -. strophysicsVI

by Professor W. ~~ · Fowler .

"Recent Researches in Nuclear Physics a t a . Z.R.E. 11

by Dr . J. M. Freeman.

Osgood, D. R.

Young , P. G.

THESES PRESEHTED DURING THE Y&~

11Gamma-ra y Studies of some Light Nuclei11

' 'Some Experiments involving Hydrogen and Helium

Isotopes.

• PUBLI CnTIONS FOR THE Y&Ul 13/1966

including some from 1964 not listed in l a st year's annual report)

Almond, P. R. -t{ and Risser, J .R.

"Differentia l cross-section a t o0 and angula r distributions of

resolved neutrons from B11+d"

Nuclear Physics, 72, 436, 1965

Bray, K. H., Nurzynski, J . and S tchler, G. R.

"The El a stic Sca ttering of 5.5-10 .0 MeV 3He Particles by 27.h.l

Nuclei"

Nuclc...ir Physics, 67, 417-427, 1965

* * * Bryant, F .J,Gibbs, W.J., Moroney, J. R., Stevens, D.J. and Titterton,E.W.

"Strontium-90 in the Australian Environment during 1963"

Australian Journa l of S ci~nce, 27, 222, 1965

Bubb, I. F.*, Poa t e , J. and Spear, R. H.

" Excita tion function of th.~ reaction 1-:..127 (p,n)Si2711 •

Nuclear Physics, 65, 655, 1965

Gibbs, W. J. *, Moroney ,J . R. * , Stevens, D .J. -t·Ti tterton, E. W. and WilsonG . B.

" Strontium-90 in the Australian Environment 1961-63"

Australian J ourna l of Sci c~nce, 28 , 44, 1965

Groce, D.E. and Lawrence, G. P.

"A study of t he reaction c12 (o16a)Mg24below and nea r the

Coulomb Barrier"

Nuclear Physics, 67, 277, 1965

Groce , D. E. and Shdmu, R. E.

"N-D Scattering and the Dineutron' '

Report of t he Congres Interna tiona l de Physique Nucleaire, Paris

1964. Centre Nationa l de l a Recherche Scientifique Paris,

Vol. II, page 167, 1964.

Groce, D. E. and Sower by, B. D.

"Neutron Groups from Be9(a,n )c1311 •

Nature, Volum8 206 , 484-5.1965.

Groce, D. E., Sowerby, B. D. and Morris, • M.

"Neutron-proton Tota l Cross Sections near 20 , 24, 28 MeV"

Physics Letters, 17, 40 , 1965

Jenkin, J. G. and Sh<mu, R. E.

"High Pressur e Gas Scintilla tion Counters II "

Nuclear I nstruments and Het hods, 251, 44, 1965

•

" omarov, V. V. + and Popova, A.M. ·· 13/1966

"Integral equations f or 3-particle interaction amplitudes in

the non- relativistic case"

Australian Journal of Physics, 17, 440,1964

+ Komarov, V.V.

"A theory of deuteron-induced low-energy reaction"

Proceedings of the Physical Society, 85, 867, 1965

Komarov, V. v: and Popova, A . n. * "Non-relativistic Three-body problem" page 272, 1964.

"Amplitudes of Interaction of Four and Five Nucleons at Low

and Medium Energies, page 274, 1964.

Report of Congres International de Physique Nucleaire, Paris,

1964, Centre National de l a Recherche Scientifique Paris

Vol. II.

* Lawrence, G.P. and Quinton, . R.

"St:ntistical Fluctuations in the rm ction A.l 27 (p,a) Mg24 11 •

Nuclear Physics, 65, 276, 1965

Fowler, W .A. +

"Nuclear Astrophysics", 1-\NU- P/351, 1965 . !"<

Mccallum, G.J. and Ferguson, i .J. ~

"Elastic Scattering of a-particles by 0 between 7.2 and 8.5 MeV"

Canadian Journal of Physics, 43, 111, 1965.

Mitchell, I.V. and Ophel, T.R.

"Energy Levels of c16 in the vicinity of 13 MeV - II"

Nuclear Physics, 66, 553, 1965

Mitchell, I.V. and Ophel, T.R.

"Energy Levels of o16n

Report of Congres International d2 Physique Nucleaire, Paris

1964, Centr~ National de l a Rech8rche Scientifique Paris, Vol.

II, page 37, 196~

Nurzynski, J.

"A conversion function for ca lcula ting El a stic Scattering

Angular Distributions"

ANU-P/349 , 1965.

Nurzynski, J.

"Isotopic-Spin Gff~cts in El astic Scattering" i\NU-P / 359.

•

,.

Nurzynski, J., Niewodniczans ' i, H. .. ... ,,, . ..

and Strc...xc.. l kowski, a . •

13/1966

" Some nucl ear r eactions on Ca I nduced by 12 . 8 MeV Deuterons"

Report of Congre s Interna tiona l de Phys ique Nucleaire , Paris

1964. Cent r e National de la _echerche Sci entifique Paris.

Vol. II, p&ge 96 , 1964.

Ohlsen, G. G. and Young, P. G.

"Protons f rom Deuteron Bombardment of He4 11

Physica l Review, 136, Bl 632, 1964.

Osgood, D. R. and Ophel, T. R.

"The 992 keV resonance of th~ L.127 (p,-y ) r eaction"

Proceedings of t he Physica l Society, 85, 1965

Osgood, D. R., Pa tterson, J. R. and Titterton, E. W.

"The excita tion f unction f or t he r eaction c 12 (He~,n )o15 between . 0

thre shold and 11.45 MeV"

Nuclear Physics, 160 , 50 3, 1965

Patterson, J . R., Poa t e , J . R. and Titterton, E. W.

"1~ s tudy of the Reaction B1G( He3 , a )B911

Proc~eding s of t he Physical Socie ty, 1085 , 196 5

Shamu, R. u . and Jenkin, J . G.

"Neutron, ldpha sc· ttering in t he 20 MeV r o.nge" <J

Report of Congr2s I nterna tiondl de Physique Nucleaire, Paris

1964. Centre Nc..tiona l de le:" Recherche Scientifique Pari s

Vol. II, p~ge 13, 1964.

Titterton, E. W.

"The Nuclea r Power Industry in 1965" .

El ectrica l Engineer, 42, 8, 1965,.

Titterton, E. W.

"Science dnd t he Citizen" ,

Hemispher~ , 8 , 2 , 1965

Titterton, E. w. " Engineering Uses of Nucleur Explosive s"

Financia l Revi ew, 1145 , p ge 2 , 1965 .

'

• Treacy, P. G.

"A Regge Trajectory for energy levels of Be811

Physics Letters, 14, 125, 1965

Treacy, P. B. and Islam, M.r . * "The First Excited State of B911

Nuclear Physics , 1965. 70, 236-240.

Young, P. G., Ivanovich, H. and Ohlsen, G.G.

13/1966

"Tensor Polarization of Deuterons from p-d elastic scattering"

Physic 1 ~eview Letters, 14, 831 , 1965

'" Not a member O.L this University.

+ Visiting Research Worker.

~ Based on work done while a member of the Department.