Calhoun: The NPS Institutional Archive

Theses and Dissertations Thesis Collection

1952-05

A photographic technique for the determination of

the angular distribution of neutrons from

deuteron-induced reactions

Barnes, Willis Clifford

Massachusetts Institute of Technology

http://hdl.handle.net/10945/24806

A l'1ii:C>T0ei^lA^'5r'IK: TlrCI'lHlOU!:; f'OR THE

D]S7IUi:;UT10K OF NEJTR.ONS FROMDlrUllillOri !NDUC!iD REACTIONS

WiUJS CIJB'OifiDiAi^MBli'DSON SAIIDNIHR CASi, II'

library ,

U. S. Naval Postgraduate School

Monterey, California

y/Utn^

A FHOTOGRAPHIC TECHWIQtJE FOR THE IXTERillBITIOV

OP rm ahquur DxsnuBUTicm (f mxmsam vsok

DEUTERON-IMDaSSD REACTIOW

Wlllia Clifford BamMIi«tit«nvit, n* s'« Mtj

B.S.y U. S. Ibiral AeadciiQr (1^)

EdsoD QardxMr Case^ II

B.S., U. S. Maval AoadM^ (1^6)

SUBmmD IH nSTIAL FUIFIUieiir of THS RSQUIRSieSTS

FOR TBE I£(ffiEE OP

NIVAL Emwsm

at tte

MISSACHUBETTS IHSTlTIffE OF TECHITOLOGT

(1952)

A PHOTOGRAPHIC TECHHIQTJE FOR THE EETSMIINATIOll OF THE ANGULAR

D13TRIByri(» <F KEDTRORS FROM IKDTEROU-IHDDCED REACTIOSB

LT V. C* Bams, USW and I7J0 £• 0. Ca«« 11, U8V

S«i>altted to the Departsent of Itafval Architecture and SArlae Engineering

m mj 26, 19^ in Partial Folfillwnt of the Bequireaents

for the Decree of NHfel Engineer

ABSTRACT

The object of otor imreetigation vas teofeld. Our prlnarj in-

tereat naa to deeigpi a photographic device for oee Inside th» H.I.T*

eyelotron f<Hr recording neutron dietribiztions frooi dettteroQ-indtsoed

reactions and to ^Tise laboratory techniques for use vith our appar-

atus. Our second probles nas to analyse the data recorded by this

photographic asthod of detection and to detencine the characteristics

of the neutrtm distribixtions , eonparing these characteristics vith

these found ty other isTeetigators vbo used other asl^iods of detee*

ti<m*

Our photographic apparatiiB C(»sii8ted of a cylindrical chaad^er

of over-All dinensions of 2>3^ inch dlaaeter and 2-1/U ineh height

^

se sised that it could be inserted In the |»robe tarfst p«rt of the

cyclotron* Sxperisents could then be o<»%dueted without interfereoM

vith the laboratozy setups wed for itork with the etiteide beam. Ifiu»

trea distributioiM «ere recorded on Eastntn ITTA Buelear-^rack plains

set in a radial array at l5-<iegree intervals around a thick beryl-

liuB target* File developoent ims gSBerally in accord with reco»->

MMlsd procedures^ and tracks nere observed using a binocular Micro-

scope with dark-field illualnation*

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lo itoiftNB twtit taw •*» wi#«4tl#wft dttii ^ awpot Mni^

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9r rsdueing exposure tine^ it ms TormA possible to Halt

baekgrouzid radiation to an acceptable nlaismra vlthout resorting to

bullcgr shielding^ and yet retain a significant nisiiber of neutron-

eatuMd traeks In the developed plates. Throvgli saleeti-ve cooiting,

cnfKlar dlstributioos of a gi-ven neutron energy band, or those dus

to all energies abote or belos a given neutron enssrgy^, could be deter-

aiaed* Because of the statistical nature of the processes involved,

however, a large nndaer of eoimts bad to be aade to reduce the sta-

tistical error to acceptable lijslts* ^^teaatio errors in energy

could be kept to 8 pen^nt, but angular defiaitiosi vas Ujdted to 7

dftgrees because of the snail arfer-«ll sise of ottr unit* In ecnpartng

ow distributions vith published results, good correlation at los

mn^ttcaa energies was found ni^ the eurws of Schecter, but the

dovble peak reported by Palk at hi^ier energy «as not c<»cluslTsly

proved by our distributloiui, although there were indicatioiw that

furUier experiaentation would lead to a oanfimation of this doifclB

peak*

It can be ooncluded that the apparatus and technKius ners

found adequate for use Inside 1^ lf*I*T« eyolotron in the detendna-

tion of the gross character of the distributions involved* Finer

ezperlaental i«ork eaid sore involved eowiting sight lead to a deter-

ination of spin and parity values of the nuelsar states involvsd

throu^ eorrelatiott with Butler's hypothesis of the stri^sping proe-

•saes involved in deuteron-induoed nuolear reactions*

Thesis ST5)ervisort M. Stanley Livingston

Title t Associate Professor of Physics

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16 Ifcy, 1952

Professor L« ?• HisiltaaAssistant Sccrstary of ths Facultylluisaehiisetta Ifistitttte of TechnologyCsirinrldgs, Massachusetts

Osar Slrt

In aooordanee vltb the reqtdrensnts for ths Osgrss of

It'ral Engineer, a thesis entitled t "A Fhotograplilo TechniqtM

for the DeteraiBation of the Angular Distribution of lieutrons

from Deiiteroii->Induoed BeactioxM" is herewith snbaitted*

RespectfuUy,

kCKsofummms

The authors are indebted to Professor M* Stanley Hrliigston

for his invaluable guidance and siq^ervision throoghoDct this iznres-

tigstlon* We also nish to thank %*• Earls F* White, chief cyclotron

operator, for his cooperation, and Mr. Anthoiqr Sperdnto of the High

Voltage laboratory and iMr. H. A* Lmdqiiist of the Experimental

Ffcgrsics Laboratory for their assistance and technical advice.

TABi£ GF ccmsms

ABSTRACT

I. mrRODiKJTioir

T!» (d^) B«actlesi X

Tbs Fhotf^mpbic Taefaniqtit %

Th* Scattering Caaerft §

Tfaft Photographic PIttaa 22

S^peaam 26

Frocaaaiag 19

Comting 29

Accuracy 21

rn. RESUETS 27

n. DisciBsicffl or REsuiafs 29

Baaulta 29

ConeluBiosui 3^

Racuiiiaimilritiflna 36

T. caszuBicm ard rscoiiibiidatic»c 39

Concluaiooa 39

RaeanoBfidatieBa 39

TI. APPEMDH Ul

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I. IHTRODUCYIOir

1. Tto (d.n) Reaction

Recent llterattire gives a rather clear ii»i^t into the

physical processes involTsd In ctouteron->induced reactions. These

reactions differ from ordinary nuclear reactions in that a cooipound

nucleus y in the tuml sense of the word, is not alvays foraed* The

deuteron as a xmit nay not coalesce wi^ the target nucleus , but

either one of its proton or neutron constituents wbj enter the target

nucletis, while the cUier is sheared off and escapes* Such a conten-

ti(m oay be prored by the fact that the reaction "goes" when the

energy of the incident deuteron is beloe the Couloob barrier and

irtien a eomrenticHaal nuclear reaction is energetically unlikely. This

nuclear process, pecullAr to deuteron- and perhaps tritims-induced

reactions f is called the Oppenheiner-Fhilipe reaction^ or acre sinplj,

the stripping reaction. Both nsutr«M and protons are produced by

this process, but our interest nas liaited to ihs neutrons released

in the stripping r^ietion.

The «i<ki sepamtion of the deuteron nuelear constituents and

the deutercm's relatively low binding energy are its d(nBinant fea-

tures and account for the isportance of the stripping process. The

binding energy has a eoaraemly accepted value of 2.23 S»v^, and the

radiitt of the deuteron is 2.1 x lOT^ en. Because of this vide sepa-

ration of constituents, the deuteron is a very loosely bound system,

the proton and neutrcm actually spending BK>st of their tine outside

the ran^ of their »xtual forces. Usually one or the other of the

-fl»#ii»o « daws .MqAOM fiaB tl« brsMd* •! iwju© mis- :!X 1 , n

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t»o particles , upon arriving at the surface of the target nacleus.

Hill be ianediately absorbed and iffill aband<m the other particle

vhich will escape -nithottt encoimtering the nucleus* At otor range of

energies (15 ^Mbt), single neutron enission is due alsost entirelj to

the stripping reaction* Only in this loanoer vould it be possible for

a target nucleus to absorb a proton in a low enough energy state to

arrold the enission of another particle by the c(»ipouDd nucleus*

Theories of nuclear level densities suggest that two-particle ccaq>e~

tition In a conrentional nuclear reacti<» usually becones important

in the region where the incident energy appreciably exceeds 10 Mer*

HoneTer^ in this energy region, the stripnlng process still allows an

appreciable probability that the neutron, in escaping, will carry

away all or nearly all of the incident energy^ leaving the costpouad

nucleus In a bound state*

All this is not to iapute that all neutrons released by a

deuteron bondaardaent are due to the stripping process* This reaction

is always in conpetition with the eonventional nuclear process of

complete deuteron absorption* At low energies, the principal eon-

petition is between the stripping iinrocess and the (d^n) coaqpound

Boeleus reaction, while at higher energies the (d,pn) and/or (d,2n)

is the cooqietlng pixKsess* It has been estinated by authorities,

hcwerer^ that at incident Clergies up to 200 Mev, the stripping proe-

•M accounts for approxiBately one^ialf of the released neutrons*

It is these stripped neutrons that give particular character

to the coaposite neutron distribution curves* Neutrcns released by

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the conrentional reaction have an isotropic, or nearly isotropic,

angolBr diatribation. Since the released neutron is not necessarily

the OBS that nas added by tl» deuteron to the target ntasleuts, there

is no T>articular reason for it to hare &ny preferred directtcm in

escaping froa the c{»spotBid ntcleus* Because of the preriouBly sao-

tioned nature of the stripping pn'ooess, however, there is a strong

tendency for stripped neutrons to be concentrated in the forsard

direction; that is, the direction of the incident deuteron beam*

The etmpoaite cvrret is thus peaked in the forward direction, nith

tailing off at 90 and 270 degrees and beyond to an isotropic

distribution*

9Experiaental observations hj Schecter and others hare coof

firasd this expected shape, and both he and Falk^ have fomd that,

at higiier energies, there is a double peak with particular target

nuclei. With berylliuB as a target, Falk finds the doidt^le peak

with anziaaai dispHaoed 1$ degrees froa the incident beaa at energies

above 9 Mer* Schecter reports a broader distribution at this energy

as compared to 2 Mnr, and the do^le peak at energies aboTe 20 Ifey.

llMse results are in quantitatiire agreeaent with the recent theoreti-

cal porediction of dlstributicms by Butler^. His paraasters are

(a) the radius of the target nucleus; (b) the incident deuteron

energy; (c) the outgoing neutron energy; (d) the angular aoaentiai

df \im proton that "sticks." Depending on the particular coabinao

tlon of the above factors, he pr<^ict8 the angular distribution to

be expected* All curves show a pronounced aaxiaua near or in the

inxuendt 'sdt tii :.. -.^.'j «:» © tot itpmi^»»&

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1!-.;,;--'-^'.;-. '.i-j-i.., .-... ^b> p' -• •-•- ; :- •-•n -.J ;c^ t" " -: •>

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forward direction. According to Btztler, the position of tbf»«e

is d«temined by the spin and parity values of the nioclear states

involved y as the requiroiaents of the conservation of angular BMSBn-

tai and parity allanv the nucleus to accept the proton vith ctHj very

liBdted differences of angular moaenta Ai • For deutercn energies

above the Coulorib barrLer, Butler distribtttions for a/ » show a

axjami at zero degrees and a ninor peak at * IS degrees; for

A X » 1, the BBZisuB at *^ 20 degrees, and a minor peak at * 70

degrees; and aX « 2, a aziaim at j^ ItO degrees, and idnor peaks

at sero and ^ 80 degrees.

If oorrelaticn could be ocnclusively proved between experi*-

ental distributions and Butler's theoretical predictions, a aethod

of assigning spin and parity values to nuclear levels could be de-

vi^d* If the spin and parity of the ground state of the target

Bttcleus were knomiy and assuming that the angular distribution of a

narroa energy band of released neutrons could be photographically

recorded, the spin and parity values of excited states of the con-

pound nucleus could be detendned by comparison with Butler's curves*

Such knowledge would be of great aid in understanding the ccnplez

internal structurs of nuclei.

2. The Photographic Technique

Meet Investigators of angular distrlbutiMis of neutrons have

•ployed threshold detectors or proportional comters for detectioj^*^.

For good geosBtry and hig^ angular resolution, the detecting device

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otost subtend a snail azigle at the target, tilth the consequence that

the cun^nts or coimts are low* The liadts of the mthod are z*eached

when the background counting rate caused by stray neutrons becomes

an tDoacceptably lai^ part of the total counting rate* Satisfactory

definltlcm of the energy requires either thin targets, or the use of

soae sort of threshold detector nhich will elloinate the counting of

neutrons belos a certain InliBiw energy* In using threshold detec-

tors » therefore, energy detersdnatlons cannot be ccsitlnuoiss, but

must be ccmflned to fairly broad bands bounded by the tlireshold

•nsrgles of a relatlY»ly anil nusber of sxiltable detectors* fhm

hlg^ stray neutron background frwa the cyclotron, especially when

deuterons are being accelerated, makes these energy detemlnatlatMl

still More difficult.

It has long baen realized that ohotogrephie detection offer*

oasiy advantages in the soltibion of these problens^* The asthod has

been proved reliable for deterainatlons of both the energy and tbt

intensity of scattered p^rticles^' * In addition, it has the par-

ticular advantage that all the desired data can be recorded siaml-

tansoQsly, thus greatly redmlng ti» operating tiae of the cyclotron

or other accelerating apparatus, coapared to that require»d for t^

aaai inrestigatlon using other oethods of deteotion* Furthermore,

since ths relationship between the energy of a particle and its range

in the photographic ennlsion is veil defined, the photographic plata

can be used to deteradne the number of particles per unit energy

l^*^f or as a threshold detector for partiolis above any desired

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onergy eorrospoiidliig to a mInljBiSB track length* Cons«qiientlyy the

photographic techniqas at presant is the aost conranldnt and precise

nethod of analysing neutron spectra. The dteTSlopnent of a photo-

graphic device that could be used inside the cyclotron vould there-

fore take adrantage of these desirable features of pfaotograiiAiie

detection, and yet require no interfierence with aore e!U1:K>rate ex-

periaental arrangeaients used in nork vith the outside beam*

Da spite of the fact that a wealth of experiaental data <m all

nuclear particles can be obtained fairly easily t»ing a photographic

technique, aost investigaticHis of angular distributions by this aethod

hsTS been confined to charged particles^* xO-Jj^ Gibson and Livesey^,

in an investigation priaarily concerned vith neutrcm energy determina-

tion, obtained sufficient data to indicate that angular distributions

eould be Accurately determined by this metluxl, but little work has

been done in this field* In general, work iiith ]^otographic emol-

sions has required the use of considerable shielding to reduce foggiag

and background, particularly i^en deuterons are used in the primary

beam* llsually lead shielding has been used against gamma- and x-rays,

and paraffin against stray neutrons* Ho«e-ver, the else limitation

imposed by the requirement that the derlce be imed inside the oyelo-

tron precludes the T»e of az^ effective thickness of lead shielding,

and the vacuim requirements prohibit the use of paraffin* Since the

cyclotron in operation is a copious source of sum**> and x-rays, as

veil as charged particles and neutrons resulting from partial scatter-

ing of the deuteron beam in its passage through the dees, deflector

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ohaxinely and septua^ it appeared that a techniquB voiild ha-re to ba

deTeloped to reduce these eztraneotie radlationa to a nlnlwni vlthotct

resorting to btillcy shieldizig* Alao^ It vas anticipated that the

external parts of the apparatus would beeeae radioactive because of

straj deuteroQ Isipaet} the resulting radiation fro« the apparatus

itself not onlf votOd increase the backgrowid difficulties, but also

would eooplicate the handling of ti» dsTiee after exposure*

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1* The Sotterlng C—era

The design of the photographic apparatus for recording the

angular distrlbutiona of neutrons vas based upon the designs of

slsdlar dSYioes, usually called scattering eaneras, successfully used

hy other investigators^' 10-13^ ^ analysing charged-particls scat-

terlngt The controlling factor in the design vas the sise of the

opening throu^ vhloh the cansra could be inserted into the cyclo-

tron* The easiest access was the existing probe-target port, which

had the additional advantage that it nas equipped nith a facmus

lock through which the eaaera could be inserted without breaking the

cyclotron -vaeuua* Also, the cooling-«ater tubes and the Wilsen

vacuun seal used with ordinary probe targets would provide osans of

support and orientation of the oanera inside the cyelotrcm* In this

wummr, the caaera could be adjusted so as to Intercept the deuteron

beaa after its passage through the deflector channel. A scheaatle

diagran of the arrangeaent of the oaaera inside the cyclotron is

shown in Figure I*

Since the beam at the r>oint of interception is ribbon-shaped,

with a horiscmtal dinension of about 1 inch and a height of about

1/8 Inch, the best angular resolution could be obtained by designing

the casera in the form of a cylinder which, when in positicm, would

have its axis parallel to the long dinension of the bean and per-

pendicular to the direction of the bean* The sise of the probe port

•'C"*

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-fc 3«0lL add C4- i:%IXw^A sixiJ 3.f2 inrnd

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FIGURE I

SCHEMATIC DIAGRAM OF CYCLOTRONSHOWING LOCATION OF SCATTERING CAMERA

^COOLING WATER TUBES

^WILSON VACUUM SEAL

.VACUUM LOCK

PROBE TARGET PORT

SCATTERING CAMERA

CYCLOTRON TANK

PATH OF OUTSIDE BEAM

TOSCATTERINGCHAMBER

DEFLECTOR

-9-

llalted the diaaeter of the cjllnder to 3 Inchsa, and the requlre-

int that the grate (ae© Tigto:* T) be able to claar the canera ^th

the latter in its ful3y retracted positlcm within the TactnuB lock,

limited the aicial dimension of the cylinder to 2-1/1: inches. With

these severe dlaensional Itadtaticms, it was obviota that in order

to obtain reasonable angtilar resolution the photographic plates would

hare to be placed as far as possible froa the centrally located tar-

gat and that, coxtseqixsntly, no iisefal amormt of external shielding

could be incorporated into the design*

The scattering oaaera, which was constructed by tl» authors to

set these requlrensnts and other probleoKi which developed as the

work progressed, is shown in the jAiotographs , Flgiarea II, III, and

!?• The orer-all diaensions of the cylinder aret diaaetar 2-3

A

inches J height 2-1^ inches* Brass was used in the construction

because of its good aachinabllity. Ths base is a disc of a naxioEan

thickness of 1 inch and diaaeter of 2-3^ inches, provided with

sockets into which the cooling-water tubes are soldered* Originally,

the base was hollow for water cooling, but the short exposures re-

quired made this feature unnecessary, and the tubes are i»ed for

support only. A 1/16 inch hole drilled through the base prevents

excessive pressure differential froa blowing out the dural-foil

window Trtiile the vacuus lock is being evacuated. The sides of tht

cylinder are 2-3A inch brass pipe of wall thickness 1/8 inch, aade

to fit sm^ly over a shoulder on the base* A 1 inch by l/h inch slot

is cut in the side to provide a window for entrance of the deuteron

-^viluptn 6c.i acts ,8«lani- t ' •"-^:' i-:'T-- '^i+ ":•:> " •,• -r.;

tttno tit t%Ai ', : rfoi;t&tl«iX tr

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FIGURE nASSEMBLED CAMERA AND WILSON SEAL

CAMERA

SECURING SCREW

DUAL FOIL WINDOW

COOLING WATER TUBES

WILSON VACUUM SEAL

-9b-

-9c-

FIGURE IV

FILMHOLDER UNIT MOUNTED ON BASE

ASSEMBLY SCREWS

LEAD CYLINDERS

ENTRANCE SLOT

-10-

I, and the slot is nade light tight bj covering it vrith « l-oil

piece of dural foil attached to the inside nail. The carer is a

disc of thickness of 1/8 inch and diameter of 2-3/1 inches, aachlned

with a shoulder vhich is a sntig fit inside the side nails* This

eonstrueti(Hi, like that of the base, aAkss the Joint light tight

,

stable, and yet easily separable* A ssall screw is set through the

cover near the center* When the sides and cover are properly

aligned with each other and the tese by scribe narks, this screw

can be set into the target holder, which is in turn screwed into

the base* This holds the caaera ti|^tly together against any pres-

sure differentials and Insures lif^t tightness and proper alignaent,

while at the sane tine it provides for quick disasseaibly* Figure IX

shows the assenbled caaera attached to the cooling tubes, and the

Wilson Mwl which in operation is bolted to the outer flange of the

Tecum lock of the cyclotron chaift)er*

The internal arrangeaents can be seen in Figure III* The tar-

get holder, which screws into the center of the base, is aade of

3/8 inch brass rod 1-1/8 inch long and is oachined so that, when a

1/16 inch thick target is attached to it as shown, the plane of the

target f^ce is exactly diaaetral and perpendicular to the enterix^

beaa* The top of the target holder is flush with the undexvide of

the cover and is tapped to receive the securing screw preTiously de-

scribed* nie 1/li indh thick lead cylinder, irtiich surroonda the target,

serves two purposes* First, it stops loe-ensrgy gasm-radiation and

charged particles scattered frosi the target by the impact of the beas

-01-

A «1 1WV09 o'^ «XX«r abiud mI^ ^^ »ltM»#a Ilol Iwmb \o Malq

•HIT .ftllMr ttlm «f# aAktaol in ^nn a tl 4»iJv rtbS»9dm « dilv

«M»iti ;t]t»II iull 9^ •'BUm ^—ad •M lo ^Jd# callX ,a»±^«n^iw»

«rf^ 4P"Wi# #•• ft! MTzoa Ilare A ••Umtrnttm xJLImam imt tea ^ml<ia&n

-«•«? XB* ^^tnta$B ^»MwmbS rZ&tfati^ snmaa «fi wbTtsd nhft .traxf ail^

II rxvs^lt .xCdBMMaib ^ilalirp <xol stlil^vriq #i mdi mum •di &b alMv

9di teft ^sttdM aotloos «f^ && b^diut^tm mmiao ha£dhi»— «l^ MMli

•d» !• aisan ^mIm id# e# b^^Xetf si a»U«i«^ ml OrnkM Imm wmIIW

•TnrtiMlii fln#«X9f9 wit le ifool avwir

•^fti «ff .III vnrilt oi aMt ad fl»» iiiiiMHiiai la Imnmtmt «ff

to •»« al «M«f «l» !• wilt «l» 9imk —

w

Mildv «v«i)lMl ^t|

• flwdv ,#«!» M bMitfMB ai tea yni iteitit 8K1-X fen MSirf tfMi 8\e

Ml# !• MUlq «(# «iiM»ili M #i o# bmi^am al ^ai««« aladUy^ ia«l bJ\l

aaJbiaiaa ad# oi* naXiraltaaqrTaq tea Xarx^aoulb x^^^ocaa al aa^ ft^giMS

lo afetavaficv adi d^lv ifavXl mt vMod twgtMf attf lo tfo* aifT .aaatf

(iatrxat arf» it—iiii itoiihr ^-xatelXxa hml isIAt daat Al •^ •barfirroa

feaa itel#agfian aaaiai Xltaaa'aal aqeia #1 ^^anlY « aaaa<i'awn 9mi aarxaa

arf^ la iaaqpdb wdt Xf^ $9igtai idi a»^ bart9S&fav ealalcHacr barcafia

-n-

and thtis preveata obliteration of the netitrfm-caiised tracks in the

film* Second y it is the inside part of the filnhoXder^ which sup-

ports the track plates in their proper positi<m inside the cylinder

and serves as a holder for the plates during i^otographic process-

ing.

The outsicto of the filnholder is the cage irtiich aligns the

1 inch by 1/2 inch track plates in the desired radial array arotind

the target* The starting point for the BAnofacttore of this piece

vfts essentially a cylindrical cup l-lA^ Ibc^ ^^ «nd 2-1/2 inch

in dias»ter haring a 1/8 Inch thick base and sides. Slots were

illed evexy 1$ degrees arotnd the perii^ry, f!ron the top to a

depth of 1/16 Inch in the base. Then sinilar slots were provided

ersiy 7-1/2 degrees in the forward sexcLcirele to give better angi»-

lar resolntion in the forward direction. These slots were cixt so

thaty when the track plates are properly inserted ^ the plane of the

ewilsion side of the plates is exactly diaaetral, and the neutrons

fr«i Mm center of the target enter the esolsion tangentially. tbm

width of the slots is 0.080 inch, about 0.010 inch greater than tl»

average thickness of the plate, to allow for variaticsis in plate

thickness. Both the cage and the lead cylinder are provided with

a slot to perait «Kitry of the deuteron beam. A l/l6 inch thick disc,

which is attached to the t<)p of the cyliivier and cage by screws, holds

these two pieces together and completes the filnholder unit, shcnm

Bounted on the base in Figure IV. This tmit is aligned within the

cylinder by a saall aligning pin in the bottom of the cag^ which fits

-XI-

mli fit vsioant Jb«atf«>-c •

•Xiv '• aril afoxEni nc

iflDiriB Tsns Jaibw iyr'.Jtnfii f^n& rt ss"*?.!?! 7*?!*i.^ riciJl 5\I vr^' .'Irmi I

srr^ir e.toX-

f- s--V a V .V- «

•r*.t n«rii t«#99^ ffefTi 010. J^ffi;-

. osJrfc ? •;'' -i.ni: dX\j.

«i.'i^ r".-'i-,,y ..• ^ x^ova btXXipi

. irfgiiilgr

tola «

atrtr

ha£ fi'

f^ "^.o

o C^cj ?n

od v^ii^ oi fflii;'^3ct,irr^iiA XI fiat & "^ t&Uxl i ^o

-12-

a corx«8panding hole in the baa«« After exposure of the fllji insids

the cyclotron, the fUWIiolder can be removed bodily by reaoving the

cover f the entire unit ulth the plates enclosed is then eiibjeeted to

the necessary T^otographic processing*

The caosra provides for deteminaition of the distributlcms

f^B sero to 1^0 degrees on both sides; the plates at 16^ degreas

are blacksned by charged pBrtlcles scattered from the dural-foll

vindow, but thus serve to shield the other plates fr(M9i these parti-

e3»8« The l]^>ortanca of checking ihs syonetry of the distributions

will be evident in the discussion of results*

2* The FhotograiJhLic Plates

The photographic plates used were Eastoan Kodak NTA nuclear^

track plates having an eBolsioai thickness of 25|i and a developed

grain sise of about 0*6^. These plates proved advantageous for a

Binber of reasons* This type of fine-grained nuclear asolslon is

not activated appreciably by ^aBDa-radiation* Tests bj DoB^rs^

idioved that the gansBi-ray fogging is tolerable until the plate re-

ceives a total ejcposure of a fen hundoned roentgens* Fast beta-

particles have little affect on the eonlsion except to causa fog-

ging with excessive exposures; low-energy betas produce recognisable

tracks in very sensitive eoulsicnis, such as those on IfFB and Ilford

C-2 plates f but do not register appreciably in WHA enulsicsis* These

features vera particularly desirable in our work, since the only

shielding of the plates from radiations inside the cyclotron tank

v»s tha 1/8 inch thickness of the brass nails of the cylinder* When

0^ t^ti^ldbf iifiiCt &^ besoIoA* tte^tftXr OEti d^i^r #liBf irr^^d «f{^ ;19909

Wqeierv«»b ^ his i?^^' ^ escsMalolii^ Mo/«fiig» 0* ^^itJtwsd 8«#A£q if»4av(^

A "ftil VBO^aSami& t^'rorm Bt^i^i^tq lamt^ >ji^«0 ii^odJK 1b> sda ai«is

o;^ j<: -ifijjvo «d.i no liiaiii 0am 'mm iMfkt^m

., •T'3 »v.L. Aiitir',-. ^(.isv ill ssfam^

n . Ic ai ?- to -rll Aoni 'J\X »rf4r itm

-13-

HftA and IfFB plAies Here exposed •isultaneously tn test rtma, the

Wk plates had a negligible background, ti^ile the NTB eoralslons were

sufficiently fc^g^d to prefent observatlwi of the neutrwa tracks*

Tn spite of the low sensitiTlty of Wk plates to gUHB- and

beta-radiation, thej haire an eotcellent sensitivity both to priaary

charged particles, and to neutrons as eridenced by the recoil pro-

ton tracks fr<» elastic collisions nith the hydrogen nuclei in t^

SMBlsion. Slow neutrons nay also ca\]se registration of short proton

tracks fro» the K^(n,p)C'^ reaction. As far as thenal neutrcms

violin the cyclotr(m chaaiMr imre eoneemed, this roacti<m did not

appear to be inportant in our vork, since a consideratiem of the

energy-IeTsl diagraai^^ of N^ shoes that the enex^ of the recoil

proton Hill be about 700 ker. ka «ill be wemn later, this enex^

corresponds to a track length of about 1%, only sli^ly greater

than the adnisai track length observable with the Tieeing techniques

used* HonsTsr, the energy-leTsl diagram of B^ shoes that Hhen Be^

is bonbarded vith deuterons of energies between 0*92 and 1*92 Mrr

there are three thresholds for the producticn of sloe neutrons,

attributable to the decay of the compound nucleus into excited states

of B^^* This reaction can be initiated by deuterons which hare been

slewed doen in the thick target* The most energetic neutrons fron

this reaction could produce fro« the M^(n,p)C^ reaction protons

of energy approaching cxc exceeding the threshold of 2»k Ust corre-

sponding to a track length of 50|jl, the ^ortest tracks counted*

This effect, since it results froa a c<MBpound-niK:}B us type of reac-

tion, would be nearly isotropic and would be only a snail part of

^& ,w.;.' .11 YX«uoor,nilsmJt9 Jhwoepca «rr«r ««#«£<? ^^ ^"•^ ^w

wit nX X9l^n ii

^»a ottfv &mi^ mwodn -^a lo ff

:j-i*',i-

, • re,--

a*«d ©Tflri riatrfw atiotoJff»fe xieT fe©.tfil^l£t. ^ -^o rsoi^tosfyi alifT . ff 1»

1>.'.-'J -•'i'^JA:- J.V' A*Ajk

'0I& •£!* ,i|0^ 'to <i*3««ej: 5{o»«* s o* soibiiDqt

lo rt:«cr XXmu a x^Uio ed mtfsv mis aiiisna^c'ei v-n.aw^ »« i»fc*fOw ^xi^^ls

the general i3otz>opic background resulting from other coapoiiixi-

niicleaB reactloaoa in competitioa with the stripping process* The

•liajeet is Mentioned further in the discussion of the res^dts*

Another adiraixtage of the IfTA plates vas that sufficient data

Here aTailahle on the stopping poaer of the evulsion to sake cali-

bration runs VBKBscess&ry for our purpomis. The stopping pomer is

defined as the ratio of the nean range of a particle in standard

air to the aean range in the esulsicm, and is a function of the iden-

titj and energy of the particle* Confining this function with the

relation between the energies of alpha-articles or protons and thsir

respective air ranges, deteradned Isy Livingston and Bethe^, giiw

a ealilxration eunre for tte emlsicm. For hig^ aecura^, it is

desirable to procure a large supply of plates of the sane eaxOsioa

noi^r and to obtain accurate calibration data fcr the eoulsion by

easurii^ track lei^ths of particles of known energy^' -^^9 simm

changes in cooposition between different lots of plates oay affect

the stopping power* However, the relationshiiM between range and

energy of various laDising particles in Ilford lit eamlsions have

been studied by Lattes, Fowler, and Cuer^^, who report that their

data are apolicable also to ennlBioos of other types but of siMlar

gralB sise and coi^xwition* Yagoda-^^ gives the following eoapari*

SOB between Ilford m and Kodak 8fA eaulsionss

-il-

' - ••^^ lo IK;

^ ^m, ,> ^t .8<^Kr,q'«rrr -tiro -r, ;; j,^.,^ rtr^ M aw|

-aoti edw :>'- -r.. . .r.;^ jj ^.j ^j^^^

J ^n cxjex aoj si; fA&»^}^^

ts«oi«i>rsa© AW :; ' ci? ^ frft^tXl B©5>r?*^ hob

-15-

Grain SiMm t

Uford 0.5^

WtA 0.6^

Ki]iiiii>er of AtoBst Ag Br

Ilford 1 1

WtA 1 1

R C H 3

3-2 1.6 0.3ii 0.87 0.02$

2.5 1.5 0.16 0.56 0.008

Tagoda also states (p. 91, Table 8 Note) that Xlford W plates

haire the saoe eheoioal eo^Msltlon as the Eas'^nn NTA eanlsion.

Because of the sijoilarity of the two eoulsloiui and the good agreeatnt

between aTailable calibration data on MA. plates and those for Xlford

Wt plates, the cxacra of ixroton raj^;e Tersua energy pcbllahed by

lattes. Fowler, and Oner was considered sufficiently accurate tor

our purpoees. Figtore 7, taken trca tbsir paper, is the calibraticn

curve uaed in our investigation.

The relatiTely thin eiialsion had two advantages. First, since

the thickness of the emolsion after cteTelopment was only about 12^.,

ymry little acnreaent of the oicroecope objective was zieeded to scan

all depths of the emulsion for tracks. This facilitated repid count-

ing and »ade for a niniHUH of eyestrain. Secondly, this thickness

of eMLLsion required none of the elaborate processing techniques

that Bast be used^ with thicker eBnalsiosis. Thicker enolsions are

also ST^Ject to dehydration and peeling VBoder use in a vacutou

^l^

.t^»0 ATP

V.• • 'XR 5}A « ••«««M">> 4^

O.I S.i X rfe^

3?>

-tntfco bi< '•'*^+*-C*-^<- Pi'^T ,f^^^ti rcl; fiotsXBii* eri* to wf^afc XX«

-15a-

s 4(

S (0Ul UJ

z >-

UJ <-1

Nm Q.

> <

I6URE

AN6E

z

u-oeQ

z oo ^1-o oce oQ. u.

•

ml

uoCA

(0

"T-OO

T"O o o o

AIM

T-O

-i—

r

"T"•I

oeft.

wO

u

o

0>1*1

II.

m

Nl

I

In order to facilitate cutting tAim 1 \rj^ ^ Inch plates into the

1' 1/2 inch size required, a special jig vas derised* The glass

MS were supported along their edges, eaulsicHi side dovn, over a

anel in a brass slab so that the upper side of the track plates

fleeted slightly abcve the top of the slab* Then a coyer nas placed

• the slab, claaping the p3ate tightly. This cover was slotted

•rversely at 15/32 inch intervals, the slots being just nids

«|^ to aocooraodate an ordinary saall glasscutter* In this fa^iom,

itihe scratches could be oade at oxtce, and Hm plate easily broken

•i pieces of ths required siae without exeessiye handling and with-

fttensge to the enalsion* The plates tiere cut 1/32 inch undersise

IxsTlde a nergin agitinit irregularities*

irpostce

The eorreet location of the canera ixiside the cyclotron and

uired exposure to the beam were both deter«ined by trial and

• 1 rou{^ check of the proper location nas gi-ron by the rela*

ckening of the two plates adjacent to the entrance slit,

by charged particles scattered fro© the dural-foil t»1»J0w*

r check was the position of the greatest induced activity of

itttside of the canera, as indicated by a OM counter* It was also

i feasible to locate the beaa with respect to the eaaera by cover-

lis entrance window and a saall adjacent area of tha outside of

luMra with cellophane tape; a flew seconds* booibardasnt was thsn

lient to record a charred iaage of the beaa on the tape* This

also confimed the original estinate of the beaa djjwnsions and

«dl-

«tf 9iat M#Aif nest C ^ X «l^ v^**^ •It^lXidAl o^ lafrw oZ

•Mis mn .hmtvab m» »it Xaln^g* • ,l>«i»P©^ »«i« *«* ^X

• wv» ,«w>b •Utm ml9£amm ,Mtlto t1«» j»oI» i>s^toq«pm «•» M

ifcjhr *wt W^^ *'*^X« fliil ,«I*n«*nl f(teR± StVJC *• x^ernwi

-dilw fans ^"^f*^*^ mtvmvn iirw»i:ir »afta batlMpri arf* 1© ••oslxi

Mlviafaw iltwi SC\X isro <«•» •^•Xq adT .ooIbImb® «ii o# ttMci

mr!sm

tmBLBMjH imaim^^ iM mm mmi M c^ «-ci« t^ro^P^

--aim mM ^ a**"!! »*w jmWfieoI nwnrRT w*^ ^« ia«Io ^on A

•iMtetw Xlol-X««fb ad* hdiI bwn^iMm m^oti^m berxtdo V*

lo xiXT±#ti* lM«iitol #M*««i «» -^^ xsoillw f»r» M» il»«ls» ^

lo •binAw «i* !• •«* ia^wtb* XX«« « «m3 ^««^ •««*»>» a

to toiw-tfe «i«( ad* 1» a^nid*** X«a»*ia «i# NnTteoo otX.

-17-

shape* Th» final check on the correct looatloo was of course syw-

etry of the angtilUr distributions , and this check required counting

the tracks on th© plates. In order to reduce the statistical error

in Esakinp this cheeky a fairly large nuniber of tracks, say 200,

should bf counted on two corresrxaKlin? plates on either side of the

forward direction. The nua^er of tracks should agree within the

statistical error. The iwDortance of insuring correct location

within snail Halts was not fully realised when the recording ruas

were mde, and the resultant asynaetrical distributions nade the

data difficult to evaluate*

The duT«tic>n of the exposure was too short to be aeasured quan-

titatlTely by any of the existing cyclotron instruaents. The exposure

was n&de by warning uo the cyclotron and then sweeping it through

resonance by rapidly Taiytng the Magnetic field. The total exposure

resulting from this tnrocedure was probably of the order of 1 micro-

oouloBb. For the puroose of registering the desired number of tracks

per unit area of the plates, which would Bake for the easiest counting,

the exposure was reguiUtted by varying the rate of change of the mig-

netic field. The optiana density of tracks for rapid coimting was

found to be about 1^0 tracks of all lengths per square nilliiaeter of

•Holsion. Greater densities resxilted in a considerable oTerlapoing

of tracks, which made the tracks hard to distinguish, and were also

acconpanied by greater fogging of the filn froa p iwn -radiation.

Lesser densities aade the tracks very easy to distinguish, but neces-

-rx-

5.V^9-/!-

! 10 XTJaa

' ®/tt no >do^ii «cii^

Ic t^i^if^m

'^mro btmnSHk

€;^jhViv.li.O ^'

^b^;r;r^:JiO»^D .^ii

9'X

Otis a^3^ ^-nr. .dnijrrml&^i'' o> f^?^'^^^

Itatttd scanning of larger areas in order to count sufficient tracks

to keep the statistical error at a lew valiie.

The bacl^roiind neutron intensity inside the cyclotron tank,

eataa^d by scattering of the boaia brjr the dees and deflector channel^

WIS BeasTired by ffsiking a run vith the caiaera inside the cyclotron

in such a poslti^i that the beam passed near the canera iRlthout

bitting it. Since the cansra nas not in the actual recording posi-

tion, this neasureaent could be considered cmly qualitati-ve but, as

will be seen later, th« stray neutron intensity was negligible

co9BKpared with the intensity frora the (d,n) reaction at the target*

Because of the short exposures required, it was poesible to

insert the camerft, naks an exposure, and renove the camera in as

short a tlias as a few minutes* Hence, the exposure of the plates

to the gamMS-backgrouxxi inside the cyclotron was veiy short, and it

was found rtossible to make successful runs Ijaar^liately after the

cyclotron had be«n in operation for several hoxirs, although the

fogging in stich cases was noticeably greater than in cases when the

ma<^ine had been idle oyBmight* After reiaoval, the outside of the

eamcra in the ricinity of the entrance window was mildly radioactiTs,

registering about 20 mr per hour of ganse-radlation on a counter at

a distance of 3 inches. In order to minimise fogging due to this

activity, the camera was imnedlstely removed to the darkroom and

dlsasseidbled I the filrdiolder unit, which was not radioactive, was

then removed and the plates, still within the holxtor, were subjected

to processing*

«*8l»

.»irlKv ?^l • " tome l£ati^<Ri»fadii «uli qe^ q&

v-i.b) 9fi^ ^---^•'t*i-* •^L^ ^?.f '^rr f- '*n' <s«aiO«

lu ^^.V,i * ,:>;. >JifnJhii tfe?

3ii n' > ?^Jlt

*1 laia ^vtiods i:*»v saw acr. ^ arii 9b,?^saJ. bti

turn ^^tio^iclb&i .for. 8s>-.?7 r:.*;,.: .

-:tnt; and" 10 iipiiUO-?' i^aj : ^^... .:..0

lo tuoti i0q, -m OS iijocfa jtr

-19-

li* Proceggif

The plates were deTeloT>ed in Kodak D-19 for 3-1/2 minutes.

This developaent appeared to giire the best coaproaise between

clearly risible trades, brought otrt by long deTslopaent, and adni-

osi fogging, accOTipliahed by short developeent. After developaent,

the plates were rinsed in water for 30 seconds and fixed in Kodak

F-5 for 30 ninntes, rinsed in running water for 30 minutes, and

dried by eTaporaticMi under an inverted beaker. All chenical solu-

iloai were filtered through cloth and kept at a uniform temperatvsre

of 72^.

5* Counting

The microscopes used were Spencer binocula r microscopes with

a 2QX objective and 12X oculars, iving an over-all magnification

of 21)0* The aechanical stage was movable by micrometer screws and

equipped with verniers having a least count of 0«02 mm in the

horisontal direction and 0.1 mn in the vertical direction* This

provided accurate resetting when the stage had to be moved in ortler

to observe long tracks that extended out of the field. A square

reticule of 100 ssbII sqtiares was superimposed on the field. The

side of each sqxiare, under the magnification used, represented a

distance in the emulsion of ^0^, Since the interocular distance

of the two observers was the sane, separate calibration was not x*e-

quired. The fine-focusing adjustw^nt was also provided with a scale

of least count 2.5n. By focusing on the grains at the extreme top

as. '^

i'lngaa Xfe-^svo ct/p r. ' &«• vrl&t>c '- £

wA* tLt mm SO.O lo d-ismrc;. -^^.-:: : .. -vr --l-i': t..*:'-^

i^^xc St.. ' o»j bod ©^G.t8 pjdi" n«' v ^c. .

"":•;

iTG bsec'- 3 9!^ «9rrrifpf IffB":*! 00.?. *to nXsroJtiin

aoi 9 «rf* i« efltri'3 »Hd- no.

'.5 vfauoo *«*"X to

-20-

«nd bottom of the eaolsion, it wis thixi possible to osasure the

arsrsge deTeloT>ed SBulsion depth as 12*^ *^ 2*^|i*

The criteria for track counting nerej

a* The track mist ha-ve a length eqtial to or greater

than a specified BiniBOi.

b« The track Bust have its origin within the grid

•iqjeriBnposed on the field.

The BiniBYBi track length that could be neasrired or easily

estiflBted nas ^0|x, the diaension of th<°* sxaall sqxeires of the grid^

and all niniaa chosen were Biiltiples of this length* Althou^ the

treeks were random in directicm, the grid allowed easy estiaation

of lengths vso to 200|j.| in dotibtful cases ^ the grid was rotated to

aid BeesiareBent* MoreasBt of t>» field was wlAam necessary except

when counting tracks orer 200^, which frequently extended out of

the grid and/or field* The randoBBiess in direction of the tracks

resulted fron the fact that the target subtended a Tsrtical angle

of UO degrees at the center of thd plates* Although due to this

effect, it is actually p<Misible for protons to recoil back toward

the target, the cosine-squared relationship between neutron and

proton energies aade the Icmgest of these tracks shorter than the

KlniBUH length coimted* The origin of any counted track was there-

fore actually the end of that track nearest ^e target*

Since the plates were of nonstandard size, duany plates were

used to assist in olABtolng tho plates on the stage* The stage

icrcnsters were used to instore, within the liaits of accuracy of

Mkt

-0^

T»^A9TS TO O^' X>Wp« •'L^J.i^l w ' 1 • «

flflrff

hius 9'-::J- fij_i..5>'•

* - !-*r '•s -'J " ' fl*v* i:

*•*<- •" y 5jV.' Ay^'

; "Xc 9^qt:i

«nt«w •»*£k£q ^^piajLrb ,"'•-: •'-<:•.,'.-: ^; ' r. -,• • - .:! la ^..Vi orvfvia

-21-

the pXata 8ls«, that the muw area of each plata nas scanned* This

largely nullified the inverse-cquare effect on the track density of

arsring distances trtm the target*

Each niniMuai track length corresTx>nded, by Figure I, to a

miniBUBi energy which ne hare called the threshold energy, since this

asthod corresponded to the iise of threshold detectors. The diffi-

culty of cotmting, ai^ the tine required, nnltiplied rapidly as the

threshold energy increased, because of the necessity of norlng the

field to Beasure long tracks and the necessity of scanning larger

areas in order to count sufficient tracks to keep the statistical

•rror low* No account vas taken of any dip angle of the tracks ia

the SMulsion.

6* Accuracy

Assuming a bean height of 1/8 inch, nAiioh corresponded rou^ly

with the bean ioage charred on the cellophane tape, it was estiiaated

that the angular resoluticm of the canera was approxinately 7 de-

grees. This was considered sufficient to resolve the peaks in iim

theoretical distribution. The statistical error was assuaed equal

to the square root of the nuaiber of coimts sade in each plate. For

ost of the rizns, at least 100 counts were nade in the forward direc-

tloOy giving an accuracy of about 10 percent in this direction and

of about 30 percent at angles greater than 70 degrees. For run D,

$00 counts were oade in the forward direction, but unfortunately the

asjfiiiitry of the distribution nullified the expected iagprovenent in

-IS-.

ai. .D9nBMc mm t^Ala d9am to »^'f^ ^"•^ <^-* +--?*.+ ,*si» •#«£q Mf#

bXcll

-*>« ^" ^^«^«BUaE>ii|v(.a »*;«• v. -.«,? tit' -v-ij- "'•o ffc^i.'^l.'XofJ^'"•"'^-'"'^ '*'

•.*-36rfJ

ai^d ax iBlJiGcr <** wrlomn oi c^nair^illca btviab? prior? afe^ e.cdl .»»»"£§

htts ffloli-oaflcib airfi nl ^a^oT:^ 01 err. ^ftffiris ,«&!*

-22-

the saoothness of the eurres. Also, the greater density of tracks

in these plates seemed to increase obsenrer error, possibly due to

fiatigue, so that the improrenent iws negligible* Since no attempt

nmm aade to conpare date on different energy spectra of the neiitrons,

it "sas not necessary to aaks any correction for the enei^y Teriation

in the neutron-scattering cross section of H.

It is of interest to estinate what ne ifill call the "arerage

probable error in niniaiHi energy" (defined later), the alniiro» energy

being that correspondii^ to a minisnm track length. This estimate

leads to conclusions regarding the extent to which one ni^t define

energy bands by obserrlng track lengths , and hence H^ extent to

nhich one conld obtain the angu3ar distribution of neutrons within

these energy bands*

In ordtor to sia^lify the calculation, it is assuaed that only

horisOTital tracks in the Ticinity of the center of the T^iotograi^ic

plate are to be counted. Mow consi^r the thin strip of the target

yxpan which the deuteron beaa is incident. (The beaa is considered

to be of unifora intensity alcmg i^e strip; dLf it is acre intense

toward the center, the error will be reduced.) This strip can be

divided along its length into eleaentary areas dl, each of which

can be considered a source of neutrons from the (d,n) reacticm. See

Figure YI.

^^:s

9eJ!tr ........ -:>3-

'

0* jnvtx& sdj c©.ri. .* ^

^aa-s&t 0iiJ lo qitSt n.tr'Jt f^t'-.d- m: «•..:' ant';.-- ar-i" •fcadrisarcD ©tf ^'C: -stis 9^BS.q

ktn9b±fiaoo el ciAsef (MfT) ..tnv-b rai »1 sa* 't rf^tiiv aoqv

&8.:l.... .. .

riF*, -T.f^p'-,

Um "'•f <n-< r^^"

-2>

Flcm VI

Seh»BBtlo DlAgrui

for nalculpttlon of Laast ?lrobabl» '^rror 1b Mlals«i Energy

^^

Track 90«>^

dA»

dAo

Piatt Target

Bseause of the proadalty of the target and ^late, an Inreraa-

squirc intensity rule aniat be applied to obtain the relative flTix

of neutrons froa each dA* For dA< at an ax^le 6 froa the horixcm-

taly the flux, ccocpared to t^t fron dAo, will be

"ITa2

coa2«

The hoarisontal traeka prodooad by neutrons frvm. dA^ MiBt iwralt

froa head«H» collisions so that the neutrons have a ntnlmsB energy

Eno e<lual to the adjulaai reeoll proton energy corresponding to the

-^tS**

IT

^Sisrff' mmttuf-': al iot

/ki)

Cv^-^ r

r— ' " •—

T

1

i.. ..

J Q^^ l^^^if

tfe??it«^T •tfdX9

i-i ^xi.f ^c-^ rivii w<^lsJ. 9y iMi-j-A^;-.;;;!;?:^ ^JOJi;. '^i^^t ,Xjl^

«s'^

trsok length sclaeted* Since the recoil proton energ7 Tarie* as

the coaine sqxiared of the ax^le between the x«coil prot<»n track and

the incident netrtron direeticm, it is easily seen that the adnisuB

energy "tiiat a neutron from dA* oonld have in order to produce a

miniaua recoil track is EVq « Ka^/cos^O* Tte error la the minima

•nei^gr is th«Q

AKn - E'n - Eqo - Bno tan^O

or

'•no

This oust be corrected for the probability of collisions that

are due to nsutraiw from dA% that is, for the relati'ra intensities,

so that the result is

sr-^ - sin^o.^no

The arerage error e can noM be oalculated froa the usual defini-

tion; that ist

^ «1

For the scattering canem used, 9^ - 20^, and e » It percent.

-li^-.

XpM* miU'tq IljBWr. cuii t>r>ntB .httmtim lll|p»( i—i<

ftffE ^Jftjw.t fln^tf^ r*«QffiT «4t as«5iK:^«f €?faBra arf^ ^o fYSTfiu-DB SHtfEoa aft*

X-.. J. jur >i^

MMfit

0^«iOtf^ ft^*^

10

Of*

•^^Ttl-^aMo,rr'

-±Rt'!t«£» liflfcsiw dd.1 ttoul l^«#ACfr4Xa» tcf waB obo © loifie ®Bff2«vii ®rf7

v> f- + a.-) rro-W

^

,-«^

,*ifooTO<5 J - bfl» ,*'0S -J-©

^fa««f *WBMMa sAl^rc^isoe ^d* to%

TtMorvtlcally, this nMns that netitroc» of energy abotit 10

WBr could be asanlngfully defined in energy bands of UO ker* Other

considerations y howeirer, role out the possibility of such a coapara"

tiTsly good energy resolutioa with tiiis aethod* For instance, since

no allonanoe vas tasido tor the dip angle of the track in the enulsion,

only the horisontal conqposient of the track length was aeasured* The

error would be negligible for lO-lfsr nevtrons but would increase wltii

decreasing energy to a aaxisuB valne of about 12 percent for 2.li«>liBT

neutrons. Long tracks fjrequently exhibit disccsitinuities and curva-

ture caused by scattering, aaklng accurate length neasurenent dif-

ficult* Also, the practical aspects of counting require that the

inimm track length be an integral nunber of dirisions of the eye-

piece scale* This results in an energy range of 1*3 Mbt, or about $

percent, at 10 Mst* There is also the questim of the statistical

variation in track length for asutroi» of a giTen mergy* It has

been shown hj Lattes, Fowler, and Cuer^^ that, for 2- to 13-llnr

protons, the uncertainty in the energy as deduced from the track

length is not aopreciably greater than that caused by straggling

as defined by Uringston and Beths^^ (P* 326)^ which is of tte

orckir of 2 to 3 percent.

It is seen from these ccmsiderations that it is possible to

keep the ayerage probable error in the wj-nt— energy within about

8 percent* However, although the preferred track directic»i is hori-

sental, the relttiTe number of horisontal tracks is lofw because of

ficastzy* Unless the bman can be better defined so as to nake tbi

»al folvoir 4vd wnJra YHt-QX •sol « sob •(^ £>I»o«r fotr*

8»ri &J ^'

' ''

""

'

''

""

311 > ion el ':.i;:,:ic;C

-26-

nftutron soure« sobII «nd the nmber of horisontal tracks hi^, it

ia not considered practical to attesot to define neutron energy

bands by thia aethod*

Ms attempt was aads In this ezperi»snt to define energy bands

in this iiayi only threshold eiMrgies were considered , for nhich the

error T»as a coabination of the straggling, statistical, and observer

errors mentioned above* The estinated oaxlviBi error in the forward

directioi nas about 1^ percent* The experiaental results, honeTer,

shcn that the actual error was considerably less than this. aBxi»ni«

Xsn^m^ m^srtii saiftab o^ ^^^ir>*;f/i -m '... ?>:/.. eblR/^yD >?o.r 6l

elNrrfid *r^ms& 9tfJ^m> oS &tmminf*"iX%- zitit «J? mbim &B%r dcrtt-i'.^ c^

t^ tiohiy lol ^JbaTC'jbi-ftncc &tmt 8al^x«itf« Moiistj'jfli' rJCi^- y\ew eld* nl

•eaKi.ttJjLi ^LJ J. :•. -v ..-APT v-,.r'?»

I

-27-

m. RESUUS

The piijacipal result of ottr ixrreatigation iias proof of the

eapabllltj and reliability of ovar i;^otographic derice in recording

neutr(»i distributicms from reaetlouB induced inside the cyclotron

ehanber*

The capability can be beat illTietrated by reference to Figttre

TIT, which is a phot<»dcrogniph at 250EC aagnification of a plate

exposed in our device to nsutroais fron the deuteron bosbardssnt of

bexyllitn. The particle tracks giTa a aeasure of priraaxy neutron

intensity by their density and of neutron energy by their Imigth.

Of particular note is the good contrast between tracks and back-

groTSKl* Figure VXII shoes the relatively uniBQ>ortant background to

be expected nhen using exposure tiaas that give the density of

tracks shcrnn in the prsrious plate* The reliability of our dsrlce

can be shoen by a coaqsarison between curres of the angular distribu-

tion of neutrons from the Be°(d^)B^^ reaction, as emailed using

oiar device, and curves published by other inrsstigators and those

proposed in recent theory. Figure TX represents a coiroilation of

the infomation recorded by the T^tographie plates In owe device,

plotted on the same scale with the published curves of Schecter,

who used threshold reactions for neutron detection* The coapari-

Sim shoes good correlation in both the angular position of the

artw peak and the half-width at halfHMucimua. Figure X is a

eowparison between this saae run and theoretical prsdictitms by

Butler, and illustrates the general correlation of experinent with

fscntiolnvti mi* fib.

ttC"

tn ^C^lUIi^

•sxtvab lire lo t^^ij

VUwB beyUqpoo -

Mf# lo flOi^ilsoq 'I-

=: J'Eaff e<f ass ^c^illdfiaAo eri?

a^is -'. *r«? J •

- It ,i,T,, ; ?

.'7!?'

. f'siit'mcaap

.-.->

fsr.

i.^'^ai.iill'KC;

i<l

-27a-

FIGURE VH

Photomicrograph of Representative Plate, Run B, Showing Recoil Proton

Tracks from (d,n) Reaction

• A

-i^^•'^'": "-r^ - .^ *

• /*. /.v.

>^. >^.> ^

i'Vx;?;;-^7<^

Ti1

\1 /--

50 100 150 200

Scale (Microns)

The average density of tracks over 50^i long in this plate was

1^0 per square millimeter of emulsion. Because of the varying depths

of the tracks in the emulsion, not all the tracks are in focus. In

some tracks, the variation in grain spacing with particle energy is

evident. Some tracks also show scattering.

-27b-

FIGURE VIII

Photomicrograph of Representative Plate, R\m A, Showing Recoil Proton

Tracks from Neutron Background Within the Cyclotron

^0 100 150 200

Scale (Mcrons)

The average density of tracks over 50|j, long in this plate -was

about 2 per square millimeter of emulsion. One such track is visible

near the center.

-2 Te-

rn

lu

u.

oif.

1-

3 z

z

fe O-J

zooX

K UJ

CD X1-

OC

\h zoo Hq:<-I

8UJ

O cl2OD

"T" T" -r -1-lO

-8

oM

ID•lO

-r^3 Y 80» 00

8X9VU1 iO U38MnN 3AI1V~IBU

-27d-

8X9VU1 dO USeMON 3AllV~l3tl

-27e-

SXdVUl JO MBflMnN 3AIIV13U

-27f-

I I I I I I I

Q o> a> 1^ <p in t."'

SMOvtii do uaannN BAiiviau

-27g-

I T

o o> CO r^ (O lo 00TM

-28-

thfiory. Rtm D, in Figure XI^ was complicated by alsallgiineiit be-

tween the geoaetrlcal center line of our deTice and the plane of

the incident deuteron beaa: btrt deapite the asyraetry the cur?e

froa nm D ahoea qualitative agreeaant ulth the other cunrea.

Figure XII lllustratea the change in the character of the dlatrlbii-

tloDZ with increasing neutron energy. The broadening of the T^eak^

as shown in our distributions, agrees ulth the obsertatlons of

Sohecter, and the appearance of the double peak at energies above

9«U Ifev is In accord itith the neasuresents of Falk. The asyift-

atry of our eunres can be attributed to the same type of niaallgn-

aent noted in run !)• Tn Figure Xiri, there is a conparison among

our curves for iMsutron energy above 9.<b Mbt, the vork of Falk, and

the exoerinMital predictions of Butler for an angular aoaentua

change of 1. Despite soas differences, the over-all correlation

Is good, and the reliability of our dsvloe is STldent.

lo mulq mU bam Mirab «ro \c mil "c«la«» Ifial<ztaBD«9 ui^ nmimt

mv9 wi^ 11 till ill Mtf miUiwtti ^4 iommj a»?fij£rftfi> ^naltlasi acU

• •rxtfo T«l#* «<# iUlir icMMMSB mwl^niilmp wmmdm (I an aotl

-•dl^iib wl^ lo n*#8mrfi nU aI itnMlD M» M#ivrwIXl HI mrslir

^tfiiq id# to yidtaifeio^ «iT •XB«*> ontois nOiavnai OAtm wakti

lo usol^ffmidb Mft tiSt^ 9Bm^» , pfwlistfiiteib ram at oimIi h

indJi ML^rnoi ^« XAoq •£<!?(» aojT id MfliVM^n* *^ ^* ^ii#oirflt

.«XM idT •iUi^ lo i#iMinBWi «& if^lw Mmh fU il €> jU^

-i^JtlMjM !• 1^^ muMM »M 0^ bltodl^^l itf AM ICTOd WO lo Tt^«B

^Hi Mlivi^is 1 si Ka<f^ «inX ewBlt ol -a ib?i ox koioo ^omi

Am ,iCn li *nm odi ^v* ji.^ wmdA xyiiM 8fx#ir« i»l mptbto «•

f^infff iflXiyii on ^ol ttliiff lo moi^ftttrtwo Ii#nHiiiicixi idt

ml^alvnoo IXa-titd «1# «iMe«i»lllb tsoi •iUsua .1 lo 9:safino

•iiMbIn li Mlnl^ wo lo xiilldAilsi oitf tei «tooa li

-29-

17. DISGUSSIOlff CT RESULTS

1* Results

fbB Boat funda»mtal question of our thesis was of the gen-

eral faasibllity of photographically recording neutron distrlbutloitf

in the high backgroimd of t}m cyclotron chaidser. Hence, the eape->

bllity of our photographic device , a» illustrated by the i>icr(^oto-

graphs of Figures VJI and VIII, ^sas one of the «o»t inportant results

of our inrestieation. Figure VII illt»trates that neutron-caused

tracks can be successfully recorded, and Figure VIII shoes that tte

bfickgrouod present as these tracks are recorded is almost insignifi-

eaat.

The density of tracks, as shosn in Figtrre VII^ is high enou^

to alios a sufficient nuijber of counts to be nade to give a fairly

low statistical error. In our preliminary work, up to 100 tracks

per olate of length ^OOrj. (9«lt *) i»re nade, giving a statistical

error of 10 percent. Of particular helo in the rather az^uous task

of icroscopic exaadnatlon of the plates, is the good contrast be-

tween tracks and background oTldeneed by our developed plates. When

ieved isader the Bicroscope using dark>-field iUuaination, the rela-

tiTS shadings are reversed, background black and tracks white, and

the contrast is even better than shown by the sicrophotographs •

The backgrotsid, illustrated by Figure VIII, is not a cosqpletely

accurate Dortxvyal of conditions as they exist durii^ boitordoent of

the target by the detxbercn beaa. It is pl^raioally iqpossible to

separate background tracks fron stripped neutron tracks imder these

«cc.

';

-it«8 mit To «2. ;t 1UC iro . ^np Tr,

•BOJt#W(fl't^ftlb iJO-fcTi.' r45 S«lb*sooi ; u.A9jL»Js3[BiAVJ-...

:

nndit&Gi £&i%

««qSO id;!' (VOIm! '\xsids' r i^ri.t no f:p -c • V." ri^M arf-t Kl

-o^orkjoioLi III »:- rffl tr '

nrXtftvt icr«^!ccw.:-Mj . .J t •.:'k .'^ / Bs-w§ii xc aoqjfcia

'iii^.' - j^sml -vro lo

«» .1.: T :^rf fi^o

t\fJJ^i.^r , Oi to -ranm

I

-30-

conditions. To picture the backgrmnd as closely ae hum hunanly

poeflibla, a run i«» nade with ovr device retracted joat enou^

from its nomal position to allow the dettteron boaa to sweep by

without obstruction* Expoaure tine iras eli^tly longer than uaual

in an attevtpt to correct fisr the atoomal condition* "Hie remits

shomsd the bQckgroimd so lifflignificantlj' snail that no ed^tfflt»!*nte

"Were necessary in the tabulation of track cotnte*

Althou^ the capability of our deyice was a neceasazy condi-

tion of success in our investigation, it vas the proof of its re-

Itabili-ty that provided the sufficient. c<M)dition* Its faithfulness

in reeofrdlng nsutrcm distributions txxm the deuteron boiribard»^ of

bexylliuB is illustrated by Figures n through XIII, although ad-

fldttedly sonsirtuit laEperfect3y. It nas not our purpose to purarus

the esqperlMBaisal teohniques to the fineness that ccoqpletely aocu~

rate curves (laithin the limits of our device) naiild deoand*

fiathar^ proof of the general reljjibility and potentialities of

our device nas our ain*

Figure IX is pei*aps onougji to indicate this. It itas prepared

by microscopioally counting all tracks over 50ji (2*li ?fev) an indi-

vidual plates, tabulatijag results, and presentijog then in the fora

of the curve* laufaediately evident is the peakinf, in the forward

direction, characteristic of neutrons from deuteron-induced reac-

tions* Our experi»»ntal distrlbation coraparee favorably in general

shape and half-^idth at half-audjaaa with the observations of

-<st-

-^s

.'-O'fl

-JLTfU'; ii

* If 3 '"•"V^

> ..• dflv is ii^.?:R^l'

-31-

Schecter, who used threshold reactions for neutron detection. Hia

dlstribitticms -were only carried to a point 60 degrees frois the for-

nard direction beyond which he asstoed an Isotropic netttron distri-

bution from the decay of the cca^sotrnd macletai B^^ into B^^ n«

Our observations tend to confirm the geoerftl Talldity of this as8tag>-

tloUf but they sees to indicate the isotropic distribution assuoes

ijcpartanee at 90 degrees and beyond*

Figure X is a comparison of this sane run with the theoretical

predictions of Butler for a zero angular sooentini change. The

ratios of »ero to 90-<tegre« intensities show fair airo^Bisnt while

there is a larger discrepancy in peak width. This can probably be

attribttted to the fact that, at these neutron energies, there is

likely to be a mixt-jire of ©Ten A/ chances rather than sianly that

of aZ * 0. Higher iwniBntnia changes in Butler's theory lead to

major peaks displaced from the forward direction, and a snail aaoimt

of these chains ccKsblned with the iiJL « transfonsation could

Xsad to a distribution shape such as shown by run B*

Run D, oicttm^d in T±gur9 XI, while showing qtMitltatlTS

agreenent with the predicted shape, is comollcated by the fact that

all intensities cm one side of the target are lower than those of

corresponding plates on the (^^poslte side* This asyanetry cannot

bo justified by any theory of strinoed neutron behaTlor and araart

bo a ccMQsequsnce of systenatic errors in technique. A closer exaai-

natlcn of run B reyeals the sans discrepancies to a less noticoablo

doftreo*

• "Hid t^^$9 9ti toJ. tr:- \fi^ btiWf OJfir ,?«?tf ?jfjiB

,-.;,., ..-nis -a.-iA'- «;. '!'''tfi eofiiJiJx.v '.-

Ijft©l;f'5»-i:c9Hi' «vf* /i;fi:iv run: s?a>;-a sldd' to nc?5.i:*r..««r.-> 8 rsi X. «rEf'ji1[

^ftit ^^iiT;; 'e :o s'U'. ">ci od- "\;i

ttBJ&s& litem JS bnB ,rfi->;-:tr;f-*'" *^v:^.>'-j';'^ —^ •:?»?>* frrp ^-h mf?;f-'

ifirtt ^c -:&

u" ;- . . « . rjt,- /,: .-A-."' i'.r. -. ,

-. •• •''•

-^.n-aaTj^foo

-32-

Th» tsost prolaable source of this error irss • lalsallgnnsat

betiteen the gec»9etrioal center lin» of owr device and th*» plane of

the incident deutez'oai bean. Th« distributi«i cwrves indicate that

^e beaia did not strike the target along its center line but sone-

what to on© eidc| that is^ on the upper half of the target at it «ac

oriented in the cjrclotron. Thia Tipould lead to a l/r^ diainytion of

nexitron intenaity on the opi^osite side and would, in part, aeeount

for the asyametry*

Ho'^Tir, a closer exaadnation of the ratio beiareen intensi-

tljes of equal-angle plates on opposite sides of the target shews

that these ratios have a peak value at a ooint somewhere around h^

degrees and a decrease at smaller and larcer angles. Clearly a

l/r^ correction alonrs cannot aceo^nt for this. Because of internal

construction features of our cajosra, hcwever, there are other ad-

justjosnta to be aRjlied that, in con.iunction T»ith the 1/r^ corroc-

tian, give a cooposite adjustaent eurre vith a peak close to h$

degrees*

There are two features to be considered. The first is the

shape of the brass target holder baeklng up the beryllius target*

Since its shape is semicircular (see Figure ITT), a neutron eaanat-

ing from a collision on one side of the target center "would havo

less brass to pass throng before reaching the photographic plates

than vould a neutron leaving at an equal opoosit© angle. The ad-

justaent to neutron intensity on the photographic plates would havs

a BBxiinn at apprcodjaitely 7^ degrees, disinlshing slcwly at soalXsr

ftfiv d-J «i^ if'!*'!!:* -^'.^ "^^^ ir<5ri t^y & :t isri-t ji3>l:>r8 ?>rfe oJ- u-

lo fro" '

' - "

T»4 ot ©roin 7Ji::'>c. fi ti.fiw vrmo .*JjtaoqBro « wjts ^atii

»r^«S^&^ Bffriff^-'t'^'-' ^.^^» ^.s/ ^ aMssrf T-3ri'od .t':5;,T::i.' r.-»eTi frfJ" "^r^ «?«*»

-ba ni{T »eXso« »v)-x^ ' -» tt& iB .

'''<^^'' --'-'

-33-

tagiBB, but going effectivsly to Mro at 90 degroes^ as the strip-

ping reaction can be considered as alaost exelnaiTsly a surfiace

inosi*

The second feature is the relative position of the enrulsioa

surfaces <m the photograjfdiic plates as arranged in otzr device. Thegr

are placed back to baek| that is^ with the eamlsion an the left sur-

faee of the plates on one side of the sero-degree plate and ewnlslnm

SB the right side on the other side of the niddle plate* Again

aanBtag an off-center collision, a netxtron laaring at such aa angle

that it viU be recorded on a gi-ven plate on one side of the sero-

degree plate can reach the enulsion directly nithout passags throogk

ths glass plate* On the other hand, a neutron leaving at an equal

spposite angle vill have the glass plate interposed betveen its

Morce and the emalsion* To reach the emlsion on the opposite

plates and be reeorcted, the neutron oust pass throu^ a greater or

lesser length of glass, depending upon its obliquity* The correc-

tion to be applied to neutron intensitgr viU be a wjawn at snail

Mglss and decrease to zero at 90 degrees*

It is to be noted that all three of these adjtistasnts to

HButron Intensi^ are in the sifls direction and in each case Hill

insrease intensity on the plates on the opposite side of the tarfst

on -Bhich the off-center collision is assiaed* Rou^ ealnulatioiis,

considering the neutrons as point sources and the scattering cross

Motion as 2irr2 in the fomala I (Intensity) - I^e^^^^^^ with

n • nnclei/oait toIuibb and x • the distance of travel throu^ the

-^x-

no * a£.ufi-:i& O'

^BH™1^ »

'

"•

rtt) fi;.

rf^i/*']!''^^ fe^fisaaq *:«G£i3-^,:i

08

fti e-

. . f^'S '<• ' ' ' '.-T' r. '.'je

^tiX ii'&.ui \.-'JiW} < J" .'iiJ'

€».ii.t '

r .T, -rj- •. :' T{*f, x.-f

,:c-

, ^o :(;^-iT-.!:

o.t t.

ixtMf no

^ «'!'>

^in ^^-'V .-f'-Jf Tl* .'=>''^^ fT^ ^'^-r'^ *S ':

V ic sortdd'iixfe «{:> * X iiii;

I

-3U-

absorbisg laeditDB^ indicate that the saxiBtm corrections ariaing froB

^b« internal construBtion fysaturea are of tht saae order of nagnittida

as the naxlBUB l/r^ eorrecti(m, assuMjie an eccentricity of approxi-

ately 1*.^ BdUiaeters* The coatbination of comBctiona tioiild lead

to neutron intensity ratios of approximately 1.25 at 15 degrees,

1*7 at k^ (tegrees, and 1.2^ at 90 degrees. This is roughly in agree>

ent iiith the pattern of observed intensity ratios and indicates

that the asyaaetry, as shown hj runs B and D, is aeet probably due

to a very slight nisalignaent between the gexxnstrical center line

of our device and the plane of the deuteron beaa*

Further corroboration Is offered by experlaental runs oacto

irith the position of our photc^i^ohic ctevice pr^jressively raised in

rslatioi to the deuteron beas* Run B had a ratio of intensities on

plates U and 13 (at * 1$ degrees to the incident bean) of 1«2^.

Successive x*uns reduced this ratio to 1*09 and finally down to l.Ol.

Accurate experijentatioa, hcmever, imis isade difficult becatuw of

technical cyclotron probleas Miioh necessitated alsost daily shifts

in the lateral and vertical position of the beas. These shifts of

couriM invalidated our reference points and cosplicated controlled

ezperinents. However , the investigation showed to the authors* sat-

isfiftoticm that the asyagoetry of runs B and D was due to adsalignaent

and that careful technique would eliadnate this source of error*

The plots of Figure XII indicate a broadening of the aajor

forward peak with increases of neutron energy* Schecter*s curves

also Indicate this fact, as will be noted "bj reference to his work

-iit-

-III fa r-,_r

'O aO iVisiil-d'; lid-in' ^ftMK

J.' ^'\i ^

L

t^D-r ,•/ - It,""?^

5S.X ^'

aoxv

v'f?*«•

^ "A-

i^lirie x^ia!) ^scmCe bd^a^Lir, ........ .,...-..-., .affXdcn.^ a,.,..-.,*., ,.v. XaoloEtoo^

lo •jfiJxfB ••mIT •ffMtf fliii lo noJt^isocT w hnsi ImLf^nS, siiS al

baXXoi^ewo boieoilqiaoo bofk m$09^, •xi^rr^-'^.m. -nro b«&abtltral mrbtoo

&s(maqi±limJtK oi airib saw d JbaA £[ bovi to x^tmmv^sk <ad^ i-fify^ iify.tta«nai

•^»T» Tt» mrmea rJ-j*]^ ^mxtstti^ Mjew wptafd^t Xtft«Tfo i«iU bB»

3^'!^^ »a*!< fii ftaffiw^^^ vrf h*»Jt^cr s«f Xf%?r e« ,l^*i ftlrt?- ai'ssltel oafa

I

as skom 1a Figtcre IZ« Of aajor interest Is the appearftnce of the

doii^Ie peak at odutron snergles above 9»k Usr* Schecter does not

report this peak \»tll 20 Vbr la reached , but Falk, uslxig both

threshold detectors and proportloiaal counters, reported ths double

peak at 9 Mbt. His curve is shewn in Figure im^ along vith the

theoretical predictions of Butlsr for an angular nosentui change of 1.

Our curve ^cras an asymetry which is probably due to the saas ids-

allg|BD»nt exTor noted preriously* However^ the appearance of this

doi:yble peak, even thot^ distorted, was of the greatest iioport in

proving the reliability of our device. Recent experiaental noric

with stripped protons, which obey the sane lass and have di.?tribu->

tiofi curve similar to those of stripped neutrtxis, has gone far in

proving the aain pointe of Butler's theory* Failure of over device

to shoe the double peak might raise serious dotftrts about its relia*

bill^« Komrrer, in the authors' opinion, our owe, as shown in

Figure XIII, does eidiibit this doid>le peak, although scwihst iaper-

fectly* It is to be regretted l^hat ftirther experinantal work could

not be done to better illustrate this point, but a cyclotron shut*

down aloi^ with the tias deadline of this report corabined to curtail

any further investigation*

?• CoeelusioiMi

It should be rearaJbersd that none of the foregoing distribution

curves are clained as highly accurate portrayals of neutron distri-

bution* As previously noted, experiamtal techniques were not car*

risd to ths point that msneh a stateaent would require. It is felt^

"^t-*

9Ai lo Bdttmr

,7. 'V r7f>,r,h 'r'-.f ••,':

••'^ u ^*

tdtdirob art* fc

9ft; ,..,.: -^ff^rr ,J"*'"7 '>-"--.f'"T .:• :<-.... 5 -:

-8lB mum eii& of &v' t ei xft^jfe/ \

bjiii

.•••, •: FV

«..^,

ff-^t

'>o ti.

.'Yo ii J'Jjtf .inlo'j ihU ^ 11 ti»^im o& floeb sd Joa

snicfeco S^mi'ys - mH.be.i^ tsKi;t !^* itiln scbdIa asset) I

?^ir

)lJBtfh•:^:^.?:^ " r? ro*-! *'rr * •^1 tc 'r»>fi[ ,t«tit .bgifK^^scY M fc.r.rri-.?fE .f'

-xiJ^iD iJO'^Jiinn lu ii:.xi:;--*i;r'ic;q eo-^rsroox:.•"

i.i5 D'XLlIc'.

-36-

howsTer^ l^t the results as pictured by tho Bterefjhotogrsphs and

dlstribxition curves justify the clains of both the capability and

OTsr-all reliability of oxxr t*otographic derice* m the authors*

opinion, this is the nost iiQ>ortant conelnsion to be derived fren

our investigation.

Hoveter j trends can be discerned by an axaidnation of our dis-

tributions. Frora the results, as pictured, it can be conelucted that

neutrons fron the reaction Be9(d,n)B^ are sharply peaked in the for-

nard direction aix! tall off to an Isotropic distribution at 90

degrees to the direction of the incident deutercn beaa* It can ba

further ccmcluded that neutrons froa this aaas reaction ha^e a

broader peak for increased energies and hsve a dorible-peaked distri-

bution for all neutron ^aergies in excess of apr»rozlaat(^ly 9 Mbt*

3* RseoaasirfatloBB

Despite the fact that our curves can only shonr aajor trends

in neutron distribution, this does not aean that our dmrtce is

Incapable of nixing ]Kn*e accurate rwralts. &Mnrgy errors of B per-

cent and an angular definition of 7 degrees are adequate to iHlTe

distribution curves con^rable in accuracy to those of Falk,

Sahseter, and other investinters prosdnently aentioned in this

report. The sijsplicity of our derloe ^ould aaks it a valuable tool

if axperlawital techniques v»re delreloped to a clegree that viould

kMp errors in detemjjnlnp angular position and er»rgy of stripped

neutrons 'ifithln these limits. It is rccoawnded that additional

tlas be spent on this phase of our InvBstigatlons

.

JM iMM^»iif»<fc|Hi'iiiJM 9{ii Iff M«Miitq «» «^l(r9«rr <ld^ .^

jp '^'jsH ooid'ti.^.'.'i fc")e!*ie ai<ifJ mn'i. i^eso^ '''': '^'t ?>i5rfjirf?w«o» i-'siiv'J'xrrl

,:i£fi^ "fee StSOdj ct Y^PTtroO.^ fli' ©IcfjEi1?C,aO'> ^-•'vrtr. r'o^+^ff ^'7.•t^:^^.

g •><> ! ffi Mfyr-x© qMoI

afff "^ 's^ tr * •ff*^'1[.+ nMif^' enc'iJ?7*n

-37-

Otsr preliulnRry t»ork shoved that the r>osltion of the targst

in relation to the deiiteron bea« was a rery aeBSitlTe ad^ttstaftnt

and reqtiirsd careftil all^maent. Additiooal tiaa eoold ba spent with

profit on thia rxjtnt. On the other hand, if atritable factors cotxld

be theoretically and axperi«Bntally T>rov«Ki that would M»lng intan-

aitios rasnlting fnm an eccentricity into aqtiality with those on

the other side of the zero-degi«e plate, then deliberate adsaligTi-

nenb could be toed to dctemlne points on the distribntion cwrm

that were displaced in angular position froa the fixed position of

the slots in the filnholder* Doetead of being V> degrade en both

aides of the incident beam, the plates night represent perhape 12

degrees on one side and 19 degrees en the other, and so forth*

This v?ould effectively double the Boiber of «s«ftil plates In our

derioe and therefore lead to wrre reliable eurres*

If ccHxsistently reliable curves could be obtaiasd with onr

(^aaray it is further recoinended that additional wozit be done on

the problea of dtetermlnlnp: spin and parity Talues of tmknown nuclear

states with the aid of the distribution cucnns* Aaau«iag that tim

spin and parity of the ground state of a particular target nucleus

were knoan, distribution curres for Tariota energies of neutrons

trait a deuteron-induced rmictioa with the chosen target ooold be

prepared. These could be cosEpared with the theoretical ctnrTss of

Butlar for different changes in angular neaaenta, and throu^ corre-

latlen between thea spin and parity Taluss could be aaaignad to

ttng^ta^ 9d$ te mU±e€>q at^ SkM *Wf •fO

:^ • -

•. . . --j-.c

1,0 ^'.'T-^TVlT

U b^

^otisv Tol: fWfnuTo ^t'i.t!fd^^»tB-t.'

wiU' ciJ"X«- b, fed felwos -, - .

Tn.. -•+^,.i^v f..vii nice afirld- rt«»«vf«:f itoid-Rl"

-38-

exeited leirelt in th» coapound ouelevs* Thi« infony&tion Mould \m

of grsat aid in the study of the eoaplez internal atruotars of

Bttclai*

-se-

ed ;.;I?ro« rmiSsivmlnj: »'"ftT ^'ss^mm ^ir^^mzsn miS nf ^fstsf htitl UJUi

lo ©-f.t?»J»inJ's Xemft^it.t Xi'^lq^ico mvr "i .

-39-

^* CQMSLTJSIOTiS AND RECQMIBHDATIOIB

1, Conc lttslona

From ovar Inyestlgatlran, It 1» concltrfed that:

a* Th# plbotogx^phlc d«Tice, as illtuitratecl In FisnJi^a

IT, HI, and TV, and the ©xp«rl»»i!tal technlqt»c c!escrib©d are

capable of recording reliable ctnrves of the angular dtstrl-btttion of

etttrans tvom denterott-lndnced roaction»«

b. Ifetrtrona from the reaction B«9(<}^n)BlO n^i* sharply

peaked in the forward direction and tail off to an Isotropic dis-

tribution at ^ 90 degrees to the direction of the incident deuteron

bean for nexitron eoerglGS below ?.6 W&v,

c* There is an increase of rwak width in the neutron

diatribtition ctnrvps frosi the reacti«ai Be9(d,n)B^ as neutron energy

Is increased frora 2,h to ^.6 Hbv,

d* Mentrons from the reaction Be9(d,n)B^® have a doxible-

peaksd dlstribtiticm ctnrve when the ei»i»gy of the atripoed netitrons

exceeds 9«b ^tev*

£• Rec OBBPsmlatiepS

It is recoHwnded thatt

a« Additlooal tias be spent in refining ezperi»ental

technlqrtes to redwse errors in neutron distribution to those iiaooaed

by the rAyslcal lljBlts of the apparatus*

•^4-

Aji:.,-^

c^lri-^ •£

rt.»ii«iJ 'ig'..'g'? •^''.'t hr* ,Tr hrr** ^ITI jTT

IT !: ^' f.-: 1

.<!!

• icr^»«9qrii erf* t© i&^iwil laoicirrfcr ?^vt vrf

"^dtfob B 9waA ^a(n,b)^«9 nel^nfi^w arid"

EfTo*f^*ffl bdarr.t^t^& set* !to yffftUBHb 'toA n

b. Additional tiiB be spent in defining the Misalign*

neat that prodttces an aajmmtxy in nexitran distribution and in

deterinining the practicability of t»ing a deliberata eccentricity

effective2y to do^uble the madber of T^otographic plates in Uw

derice.

c* If Vm corres of neutron distribution dsteralned by

this photograi^ic technique are proved consistently reliable, the

feasibility of determining spin and parity -values of tmknown nuclear

states vith the aid of this technique be investigated.

-C'j.^

'4^'

yi. APPRIffilX

-liw

)cr'js?^» .IV

-12-

A. ORTGIHAL DATA

A recanitulatitm of all recorded rtms, with the indicated

purpose of each, follows;

Rial A - determination of baclqpround

Run B ~ neiitr<»i diatributl<»Mi fr<» Be9(d,n)B^^ reaction

Run C - neutron distributions froa Be9(d,n)B^^ reaction

Run D - neutron distributicma tram Be9(d^)B^^ roactitai

Rvn E - effects of eccentricity-

Run F • effects of eccentricitj

Rim G - effects of eccentricity

The data taksn from these iikliTidual runs is as indicated belout

1. Ricm A

No counts itere aade as background tracks nere insignificant

In nmiber*

2« Rub B'Nator of Tracks

PlateWmbmr

Position(Degrees)

150

Over

26

Orer

200u

Oter

500u

2 •

135 17 - •

120 13 - -

105 17 - m

90 15 10 -

r$ 2li 15 m

6S0 28 27 7

kS 52 35 ft

XitldJhE$a»09« to 8^9«tl» •> 8 art

t«il«rf b«#aiillfldb t« •! IwlilTltel

JBOtlh^lMf vtwr OCOAft

A sut^ •L

T

01

rs

5€

vx

atx

S5

osx

5a

£ nog .S

e

T

8

-13-

Run 6 (contlxraed)

10 10 73 88 $0

n V$ 111 151 m12 152 iia 6t

13 15 89 100 ^111 JO 55 hh n1$ k$ 39 31 13

16 40 29 19 •

17 n 19 10 -

18 90 16 - «k

19 10? 16 - -

20 120 17 - -

21 135 17 - -

22 150 16 m •

3« Rua C

Angtilarnalw Position of TracksMvAmr (Bogr—g) or»er 50^

11 15 117

11.5 7-5 lUj

It • 137

12.5 7.5 116

Coi»t abandonid bocanoo of low track (tensity.

timtt ^o

dJLL

uVl 88 v'' OJl or

08 I?J[ III II

ra loil s^x S.C

8d r-- '^ '*

<?r. >I u

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a IC ^l ^;- n

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- ex ^x ^v TX

- - d£ Of ai

- - dl "-'-- ^.» « n OS

•• - n za IS

«» ax o^x ss

'£M "^

sx

I

U* Run D

AngularPMition(Degreo*)

90

Of»r

Hunber of Traeks

Orep OrerlOOti 350u

Over

200u

4 71 36 - -

7 n m ttl T -

1 00 11,9 H 32 -

$> IS 208 Ik U i

30 30 lOh 60 n 12

XL %S $18 U8 IS 29

32 3li5 90 IS 22

ai 1^ 222 99 n Ui

^ » 125 A 30 f

3$ IS 112 It IS -

u tfo If IT f -

XI t^ ^ 3^ T •

u 90 19 3i •» .

t3t9«tT 1q 'xocGavS

-iia-

C nuH »d

10^„ 4^1 -

- - IT

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** SI I£ ':•'

« hi aa 805

SI ss od ill.(

ff« ^ii PXI Ik ».

ss ?.li otj ^ie

ic ^s ^> ss?

^ 01 ilc ^11

• n ^L. SIX

• ^ TS ^- T U T^

^^ ^ ^J

0r iNfaDT

( z^nc%^ ; ^9(feag

OQ ^

^' T

06 8

H ^

(K OX

?I XI

u^I tl

oc lU

^ ^I

•ft ac

^ XI

09 31

$• Rtm E-US'

PUt«

6

9

10

11

12

13

lU

15

18

AagularPosition^Degrees)

90

30

15

15

30

U5

90

of Trftcks

s

25

It

lib

1$

f

6, Rtrn F

Plate

9

10

11

12

13

AngularPosition(D»gree«)

li5

30

n5

15

Vwberof Traekaover 5Qu

i»

It

n

;^

as

^

'H-

c

i«r

itacbRiA

01

U

a

81:

ntoiKT l:o

or

^5

•its!*!

IX

a

-16-

Run G

AngularPlate Fwiition of TracksSumber (Degrees) over 50u

6 90 Ub

9 m 33

10 JO Hi

11 :i^ 1$

12 61

13 %? (^

Ih JO Id

1? Ib^ J?

16 10 ty

13 90 lb

»'

-bd-

XI

c

Od

0^

01

XI

21

CX

-hi-

B« RKTERgKSg

«

1* R. £• Bell and L» Q* Elliott, GaMja-Baya from the Reactiop

H-^(p,y)D^ and the Binding Enercf of the Detiteron , Ftiys. Rer.

79, 282 (1950)

2* L. Sehecter, Angular DlatrlbTitlcm of tfeutrona froa Targets Boj-

barded b^ 20 Jter Degterona. Fbya. Rer. 8^, 69? (1951)

3. C. £• F^lk, (d,n) Raactlona ulth 15 Mbt Deuterwia ^ Phya. Rev.

83, li99 (1951)

k» S. ?• Butler, Qa Angular Distrllmtions froM (d,p) and (d,B)

Ittclear Reactiona , Phya. Rer. 80, 1095 (1950)

5* J* CSiadwiek, A* H* Wky, T* 0. Pieka'vance, and C* F* Powell,

An Inveatigatlon of the Scattering of High-Fjiergy Partielea

from the Cyclotron "b^ the T^otograi^le ifethod , Proc • Roy.

Soc, A183, 1 (19Ui)

6« H. T. Richarda, A PhotograiAic Plate ST)ectnni of the Metitropa

firom the Disintegration of IlthiiBi hj; DaTiterons , Fliys. Rer.

52, 796 (191*1)

7* W. M. Oibaon and D. L. li^raaay, Sautrona Eaitted in the Diala-'

tegration of Nitrogen b^ De^teraiM. Psroe* I^ya. Soc. 60, 5^

(1S«48)

8« J» C. Qroaskreuts, iteutrwM froai C(d.n)!t and Cn(d,n)Zn . Fhya»

Rev. 76, 182 (I9I49)

9. R. A. Peek, Jr., A f^otographie Study of Weutrona froa Al H ,

Biya. Rer. 76, 1279 (191^9)

(elf?!)

-h8-

10. S. Rvdbin, A Photographic Auparatta for Angtilar Distribution

Iteaauroaants , aiys. Hav. 72, 1176 (1917)

11. L. Roaan, F. K* Tallaad^^ &ni J. H. WiUlana, Range Diatribtrbion

of tha Charged Particlea fro« tha D-D Reactiona for 10 Iter

Deuterons^ Phys. Rav. ]6, 1283 (19li9)

12* S. Htbin, W. A* Fowler, and C« C* lAiiritaan, Angular DiatribTition

fi£ j^ I^'^(P.a)a Raaction. T>hys. Rer. 71, 212 (19li7)

13* F. L« Talbott, private conavmication vitfa H. Yagoda reported in

Reference 18, p. 267

lit* P. D«asrB, Han Photographic Eanlaiops Showing Iirorored Tracka of

lonialng f^orticlea , Can. J. Reaearch A2$. 223 (19U7)

15. M. S. LLrlBgaton and H. A. Batha, !ftxclear SypaMJoa . Exoerlaental.

Bar. Modem Phya. £, 268 (1937)

16* C. F. Powell, a. ?. S. Ooehialinl, D. L. liTaaej, and L. 7.

Chiltcm, A Sew Photographic F.Hnilslon for the Detection of Faat

Charged Patrtieles . J. Sd. Inatr. 23, KK (1^6)

17. C. M. 0. Xattea, P. H. Fowler^ and P. Cuer, A Study of the

Iteclaar Tranawifeatiopa of Lif^t Elaaanta by the Photographic

Ifcthod . Proc. Phya. Soc. 5^, 883 (19U7)

18. H. Tagoda, Radicactirity Measureaenta with Wuclaar Eaqlaions »

John viley and Sana, Inc. New York (I9ii9)

19. W. F. HomcTak, T. lamritaen, P. Morriaon, and W. A. Fowler,

Energy LErvela of Llg^t Huclei . Rey. Modern FliyB. 22, 321

(1950).

..p,]-

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to SjJojantT l>»w?';qKl ysiwoKS J^£^-^"' iiflL^'il^"' •.l;^^'-'_*'^ t

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• jl

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(Ti^X) C35 Jg ••c

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AP ^56 U 5 28

ThesisB232

AH

17138Barnes I

A photographic techni-que for the determinatioof the angular distri-butionof neutrons ,,,2 56 i+ 5 2 8

i

ThesisP232 Barnes

17138

A photographic tech-nique for the determinationof ^the angular distributionof neutrons from deuteron-induced reactions.

Librr.ry

U. S. Naval Postgraduate SchoolMonterey, California

1