Acharya, V B

Ghumman, B S

IACS Institutional Repository

tndiGn J, PhIy" 548, 242-246 (1980) Measurement of differential inc:oherent Ic:attering c:roll-sec:tions of 145 ke V photons from K-shell elec:tronl V B AchILI'Ya. a.nd B S Ghumman nepa.rtment of Physics, Punjab. Umverslty, P"tiala-147002 Received 22 May 1979 Ab.'ract, Differenti .. l cross-sectlOlll! fot' incoheront scatt"l'lng of 145 keV photon. from K-sheU electrons of tm, silver o.nd molybdonum have been mea.sured at 110D to investlgate the effect of eleotron binding on~ifferentJa.l crOS8~Beotlons in the low energy l'eglOD. The incoherent !ilcat.t.m d photons arC) selected in cJoincldence wIth X~rBrYfi whic}1 follow the va.cancies caused hy tho ojectioll of the electt'ons NaI(TI) sCllltillators are u d fol' the detectlml of Bcattorcd phot.ons a.nd emItted X.J18.ys The experimen 0.1 J'psulh~ are compared with the available theoretic,,1 data \ 1. IntrodllctioD Compton soatterlIlg is One of the basic processos of interfJ.Ction botwoon gamma raya a.nd matter _ The recent geuora.l intoTOHt in Compton sca.ttel'ing is manifold_ First, it is a. probe of electron-momentum distribution; Bocondly, it is a. l11eILn6 of determining tho polarization of photons produced in nuclear rea.ctiops and thirdly, it has provided a test of qUllontum electrodynamics. crompton sc~tt.eril1g gel10rally refers to 0. caBe ill which a. photoll is aCllottoroo from an olectron initia.lly froo and a.t rest; and is described by Klein-NishIDa. formula. However, the effect of eloctron binding hllos to be considered for low enorgy photons I1Jld inner sheJl electrons, wnoro the incidont energy is comparable with the llinding "porgy of the electrol1_ The atomic billding affects are most significant for K shell electrollS and Compton scattering from these electrons prodUCe!! significant deviations from the Klein-Nishina va.lutls_ There havo been Bomo attompts to obtain sca.ttering crosB-MOOtiollS fol' bound oloctrons using non-rela.tiviJItic trea.tment ba.sod on either atomic form fa.ctor approximations (Bloch }934, Schna.idt 1934) or incoher(lnt Hca.ttcring function approach (Shimizu et al 1966), Sujkowski a.nd Nagel 1961). The va~dity of thes(, calcula.- tiona requires the photon enorgy to be IIopprecilLbly larger than the bU'lding enorgy of the olec' '·on. Rola.tiviJItic thoories a.ro availablo only for ~Il energy of 662 koV. Thoro have b661l somlllllvol:ltiga.tions by Motz and MisHOlli (1961), Sujkowski lloIul Nliogel (1961), Pingot (1968, 19(0), Spitalo IloIld Bloom (1977) and Murty et at (1977) reporting the differontia.l Compton ijca.ttoring oroHij-sectiohs by K-ahell 242 Incoherent scatt~rinfl of 145 lee V photons 243 elootrons of varioua n.tomic tll.rget~. Most of tlle!le rneaSutoments 1L1'(1 oonfined to 662 keV photons from 0$187. The pte!lent work waH motivatoo by a dosire to investigate the effect of electron binding on diff6l'entillol aClIottering croRij·soctions in the low energy region. Tn this paper we present experimentllol results on differOlltia.l incoherent sca.ttoring croBs·sections for K .shell t;loctrons in tin, silvor and molybdenum at a. scattering a.llgle of 110° for 145 keV photons. 2. E.perimental Arrangement When a photon jij soattered incoherently by a.n eleotron in the K·shell, the electron is ejooted a.nd K X·ray is omitted with a certain probability definod by the K· shell fluoroBcent yield. The measurement of the intensity of the Rcattered photons in coincidenco with the K X.ra.ys enablos us to distinguish between tho photons incoh,erently sOll.tterod by K·shell eloctronA and photons sra.ttered by free 01' more loosely bound electrons The experimental arl'll.ngement is shown Bchemll.ticlI,lly in figure 1. A na,rrow beam of 145 Ita V phot(>n~ is obtained by pla.cing 14100 radioa.ctive source at the end of Il. lea.d oollimator. Th .. target foil is viewed by two detectors, one sensitive to charll,cteristic X·ra.ys emitted from the target and the other to the scattered gamma. rays. The scattered photons are detected by 51 mm dill.. x51 mm. thick Na,I(TI) scintillator. This detector is shielded by 80 mm thick lead and 60 mm long collimator ia pla~ed before it The K X·rays emitted from the targllt a.re detllctod by a.nother BcintillatOl' with 44·4 mm dia. X 2 mm thick NaI(Tl) crystal. The X·ray detector is pla.ced perpendicula.r to thc Bca.ttering pla,ne to minimizo dotector to detector sca.ttering. Mova.ble leuod shielding is used to prevent the gamma. ra.y and the X·ra.y detectors from directly viewing tho souroe slit. Tile gamma ra.y and thfl X·ray detectors subtelld solid angles of 0·03 and 0·08 stel'adians respl'otively at the target foil Tho inside surface of the source sht and all surfa.ceR of leo.d shiolding in view of the target and dootors a.re oovered with a grll.dod Z absorber. This absorber consists of 2 mm tin, 1 mm iron Il.nd 0·8 mm of aluminium with tin fll.cing the wa.ll. Its thickness ig sufficient to ahsorb 76·5 keV X·rays whIch are emitted from the lead shielding. A slow·fa.et ooinciden(>(l set up of 30 n.sec reRolving time is used for recording events. In uodditioll to tht> desired coill~idences between the photons aCllottered from the K·shell eleotrons Ilond X·rays whioh follow the ejection of the electrons, other events may contribute to the reoorded counting ra.te. These oonsists of (i) K·shell photoelectl'OllS may ionize the \;a.rget atoms Ilond the characteristio X.rays produced be deteoted in gammllo detector; (ii) Compton electrons ma.y proo.uce K X·rays during slOWing down prooe.ss; (iii) photo and OomptoJl. elec· trons produoing bremestrahlul1g r3diatiol1 in the. target; (iv) mUltiple sOllottering of photolls from air, target holder and other surroundings; (v) detector to detector 244 V B AMarya and B 8 Gkmmrm soattering; (vi) cosmic ray ba.okground and (vii) the f~o ooincidences. Ma.ny of these effects can be a.ocountod for by replaoing the target 'with aluminium foil of equivaJent thickness (containing same number of oleot~on~ por om- M the target a.nd then recording the coinuidonoe rate). '" ... o F.1Ift 1. Expel'imental B8t up. X-source of 145 keV photons, D,-gammEl rEly detector, D...-X-rElY detBctor, S.--Salltte .... Determination of Compton scattering cross-section from K-shl'>ll eloctrons requires an absolute measurement of incident photon flux at the ta,rget and the detector efficiency. To a.void these measurements the bound electron or08s-SHOtion ill determined relative to the croBB-section due to 8. stationary and free electron whioh is given by Klein-Nishina formula. 3. .....It ..... dUeu .. lo. The experimental results for the K.,shell to free electron soattering cross-section ratio for 146 keV photons at a scattering angle of 110° are IIhown in oe]uzan 3 (If table 1, Incoherent Bcattering of 145 keY photon8 245 I Relativistic theories whioh IUC expected to give better agroomont with ex,lltlrime;ntal results aro a few and no ~uch caloulations aro available fOl' 145 keV Most of the theoretical invostigations on inoohorent sca.ttering of' photons by a.tomic electrons uso nOll-I'elativiatic tl'oo.tment based on either a.tomio form faotor a.pproximations or inoohorent function approa.oh Approximatulg ifFj by a non-relativistic wa.ve function of 0. K·shell eleotron in a hydrogen like Ilotom dO"k and ifFl by 0. plane wave, Shimizu et al (1965) have calculated the va.lue-d 0"1 which is given by (1) whore Z is tho atomio number of tho target, mo the eloctron ma.sB, c tho velocity of light, Po = y'2moB is the initial momentum of the electron, b = ~n, B is a. tho binding onergy of the olectron. ao iR the first Bohr radiu~. I£ma. = T + B-I·2y'TB, Eml" = T+B-2y'TB, T = [I~)'o"y(l-[\os 0))/[1 +1'(1-0080)], () is tho scattering anglo. "y = h"o. and h"o is the incident photon energy. moe TheoroticaJ. vaolues calculated by using equa.tion (1) are shown in column 4 of t,able 1. Lenz (1952) deriv6d a rela.tion between the incohorent scattering function 8(v) a.nd dia.magnlltio susceptibility of the sca.ttering o,tom by to,king into account the oleot-ronic charge distribution basM. on the Wentzel model of aotom. This expression is given as (2) whero p ill the density of the scattering material, A is the atomic weight, v = q(Jo![31tZ i / 3] a.nd Vrltle is the dia.magnetic susceptibility of the atom. Uamg equation 2, the values calculo,ted for the preaent energy a.re shown in column Ii of'ta.ble 1. The errors shown in the experimentaJ va.lues are sta.ndard deviations. ThtIBII include oounting statistics, efror in the meo,surement of solid angle and target thiokness Mld the errors aasocia.ted with the absorption ooeffioients, detector efficiency and ftuorescont yield etc. For molybdenum t.he mea.sured oross-sectiolt 246 V B Acharga and B 8 Ghumman rlLtio dUI:/dup is in agreement with the theoretiolLl vaiu(lobtlLineti from equation (1) j for tin ILnd SilV(lf the oxperimental results are highel'. T.ble l. Differential aroaa·seotion ratio dC1~/dC1 F for 145 ke V photons at scattering angle of 11 0' . Theoretioal Results Element E>;perimental baaed on based on: eq.(I) oq.(2) Tin 50 0·1i06±O·070 0·369 1·00 Silver 47 0·560±O·078 0·414 1·00 Molybdenum 42 0·521 ±0'070 O'~ll 1·00 Reference. Bloch F 1934 PhyB. Rev. 46 668 Grodstein G W 1967 X-.a.!I Attenuation aoeffleientB NaiiOMI Bureau oj Sta.n(/a.rd. ( · ... la.· 583 Lenz F 1952 NaturwiB. 39 265 Motz J W and Missoni G 1961 Phy •. Rev. 11M 1458 Murty D S R, Reddy V G and Rao C N 1977 Phy.iea. gSe 137 Pingot 0 1968 Nucl. Ph" •. AU9 667; 1069 ibid AU8 334 S.hnaidt F 1934 Ann. Ph" •. 21 89 Shinuzu S, Nakayams Y, snd MukoyslD8 T 1965 Phy" nev. ltoA 806 Spitalo G C .. nd Bloom S D 1977 Ph" •. Rev. lOA 221 Sujkowski Z and Nagel B 1961 Ark. Py •. 20 323 

Measurement of Differential Incoherent Scattering Cross-Sections of 145 KeV Photons from K-Shell Electron

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Measurement of Differential Incoherent Scattering Cross-Sections of 145 KeV Photons from K-Shell Electron

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