Bresesti, M.

Cappellani, F.

Del Turco, A.

Orvini, R.

Archive of European Integration

IJWW'WWWa THE THERMAL NEUTRON CAPTURE • iiii Ju '* Λ*Ϊΐΰι.Ι.ΙΓ I CROSS-SECTION AND THE RESONANCE CAPTURE INTEGRAL OF i24Xe WFTwilMid; ¡iiii tølfi&f w : " Α · Β !w ■ '\ψ mmPPW" fciiiÄiii by yM. BRESESTI, F. CAPPELLANI, . M. DEL TURCO and E. ORVINI ¡íM' 'ñiüti ■•"'tf wfötB*­·*·» ■ w'iílíifrwlir îAlAli'ïi '«'™^« 'HK'w,MinV¡' m · "κ ιιίΛι' «'Het'ia'SSP1 i,J, ,;J..l Nuclear Research Centre lepra Establishment - Italy Materials Department Nuclear Chemistry Laboratory «Mielii Reprinted from \NIC AND Ν Vol. 26 - 1964 i v c p n u i c u " « U I JOURNAL OF INORGA I   NUCLEAR CHEMISTRY ¡ÜIII! '•2'"íifTrTS IttiUHii ¡sii WmlSSÊ^ mim. l I W i * n a i n ' , t - i r * > , g * ηΠΛ π ! fa-r*; ',*>:;-: J* ^ - í^EV- ' íJ íSSk'rra in i í í '■ Τ : Su This document was prepared under the sponsorship of the Commission of the European Atomic Energy Community (EURATOM). EURATOM Commission, its contractors nor any person acting on their behalf: Neither the WÉÊÈÈ ■ § 1° — Make any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this document, or that the use JBSam of any i formation, apparatus, infringe privately owned rights; method, or process disclosed in t o r lis document %%m w*$ Assume any liability with respect to the use of, or for damages resulting from the use may not r j f t j M ( J j »T« i fM ■m 'HiU'ŒiFenl' J. ms rej/ττ by kind -permission of the publisher, an article from "JOURNAL OF i up ψ] INORGANIC AND NUCLEAR CHEMISTRY", Vol. 26 - 1964, 9-14. For further copies please apply to Pergamon Press Ltd. - Journals Department - Headington Hill Hall, Oxford (England). Dieser Sonderdruck ist für eine beschränkte Verteilung bestimmt. Die Wiedergabe des vorliegenden in „JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY", Vol. 26 - 1964, 9-14 erschienenen I f f ."» ' - r ! : ã.~ i>»ra*in<>* 'TSfiff mmu ϊϋι»3 Ce tiré-à-part est exclusivement destine à une diffusion restreinte. Il f éprend, avec l'aimable autorisation de l'éditeur, un article publié dans le « JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY», ■i !JÌ.F"ft)4&tìtìlfil' l,e<i J UU n J V Ä J y ur JLÁ\UI\.Or¿liy±u Λ ί ν ι / ζ ν u i / i > i i n n W / Ü ¿ « Í J I I U ir, Vol. 26 - 1964, 9-14. Tout autre exemplaire de cet article doit être: demandé à Pergamon Press Ltd. - Journals Department - Headington « f f f Hall, Oxford (England). ¿tøtø'lr"'« Questo estratto è destinato esclusivamente ad una diffusione limitata. Esso è stato riprodotto, per gentile concessione dell'Editore, da «JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY V Md? lllffSHil'Üfi» ol. 26 - 1964, 9-14. Ulteriori copie dell'articolo debbono essere richieste Pergamon Press Ltd. - Journals Department - Headington Hill Hall, Oxford (England) !k;Æ Deze overdruk is slechts voor beperkte verspreiding bestemd. Het artikel is, met welwillende toestemming van de uitgever overgenomen uit „JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY", Vol. 26 -1964, 9-14. Meer exemplaren kunnen besteld worden bij Per-gamon Press Ltd. ~ Journals Department - Headington Hill Hall, " iilillillilÉllll^i t . - : 'r Lf<) t ttueMIMei! Oxford (England). EUR 5 5 1 . e REPRINT THE THERMAL NEUTRON CAPTURE CROSS­SECTION AND THE RESONANCE CAPTURE INTEGRAL OF 124Xe by M. BRESESTI, F. CAPPELLANI, A.M. DEL TRUCCO and E. ORVINI. European Atomic Energy Community ­ EURATOM Joint Nuclear Research Centre Ispra Establishment ­ Italy Materials Department Nuclear Chemistry Laboratory Reprinted from "JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY" Vol. 26 ­ 1964 ­ 9­14 pages The thermal neutron capture cross­section of m X e , its resonance capture integral (from 0.5 eV to 00) and its effective capture cross­section in a reflector position of the Ispra 1 reactor have been found to be 111 ± 11 barns, 3600 ± 500 barns and 135 ± 13 barns respectively. These values have been determined by irradiating natural Xenon and mea­suring the activity of 12δΙ, the decay product of 125Xe. EUR 5 5 1 .e REPRINT THE THERMAL NEUTRON CAPTURE CROSS­SECTION AND THE RESONANCE CAPTURE INTEGRAL OF 124Xe by M. BRESESTI, F. CAPPELLANI, A.M. DEL TRUCCO and E. ORVINI. European Atomic Energy Community ­ EURATOM Joint Nuclear Research Centre Ispra Establishment ­ Italy Materials Department Nuclear Chemistry Laboratory Reprinted from "JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY" Vol. 26 ­ 1964 ­ 9­14 pages The thermal neutron capture cross­section of 124Xe, its resonance capture integral (from 0.5 eV to 00) and its effective capture cross­section in a reflector position of the Ispra 1 reactor have been found to be 111 ± 11 barns, 3600 ± 500 barns and 135 ¡fc 13 barns respectively. These values have been determined by irradiating natural Xenon and mea­suring the activity of 125I, the decay product of 125Xe. EUR 5 5 1 . e REPRINT THE THERMAL NEUTRON CAPTURE CROSS­SECTION AND THE RESONANCE CAPTURE INTEGRAL OF 124Xe by M. BRESESTI, F. CAPPELLANI, A.M. DEL TRUCCO and E. ORVINI. European Atomic Energy Community ­ EURATOM Joint Nuclear Research Centre Ispra Establishment ­ Italy Materials Department Nuclear Chemistry Laboratory Reprinted from "JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY" Vol. 26 ­ 1964 ­ 9­14 pages The thermal neutron capture cross­section of 124Xe, its resonance capture integral (from 0.5 eV to 00) and its effective capture cross­section in a reflector position of the Ispra 1 reactor have been found to be 111 ± 11 barns, 3600 ± 500 barns and 135 ± 13 barns respectively. These values have been determined by irradiating natural Xenon and mea­suring the activity of 125I, the decay product of 125Xe. Reprinted from Journal of INORGANIC & NUCLEAR CHEMISTRY P E R G A M O N PRESS OXFORD · LONDON · NEW YORK . PARIS J. Inorg. Nucí. Chem., 1964, Vol. 26, pp. 9 to 14. Pergamon Press Ltd. Printed in Northern Ireland THE THERMAL NEUTRON CAPTURE CROSS-SECTION AND THE RESONANCE CAPTURE INTEGRAL OF 124Xe M. BRESESTI , F . C A P P E L L A N I , A . M . D E L T U R C O and E . O R V I N I * Nuclear Chemistry Laboratory—C.C.R. EURATOM—Ispra {Received 13 May 1963) Abstract—The thermal neutron capture cross-section of 121Xe, its resonance capture integral (from 0-5 eV to a>) and its effective capture cross-section in a reflector position of the Ispra 1 reactor have been found to be 111 ± 11 barns, 3600 ± 500 barns and 135 ± 13 barns respectively. These values have been determined by irradiating natural Xenon and measuring the activity of 125I, the decay product of 125Xe. ALTHOUGH the nuclear reaction 124Xe(/i,y)125Xe is used for the preparation of 125I, decay product of 125Xe, the capture cross-section of 124Xe is known only imprecisely. TOBIN and SAKO11' evaluated this neutron capture cross-section by the measure-ment of the intensity of the 0-190 MeV y-ray of 125Xe. They obtained a value of 74 barns in a reactor spectrum of unspecified epithermal content. Moreover the incertainty in the value of the neutron flux was about 25 per cent. HARPER12» found in preliminary measurements that the cross-section may even be a factor of 2 or 3 higher than the value previously reported. MANN et aì.i3) have measured the total neutron cross-section of xenon from about 1 eV to about 200 eV. Irradiating various isotopie mixtures of xenon, they attributed to 124Xe a resonance peak at 5-16 ± 0Ό6 eV. For the resonance analysis a radiation width of 90 ± 20 meV was assumed. In the present work the neutron capture cross-section is determined from the activity of 125I formed through the following nuclear reactions: ^Xe(«,y)125Xe - ^ 125I ^ > 125Te (stable) The neutron capture reaction can also produce 125"'Xe. Thisisotope, never observed in the neutron irradiation of 124Xe, has been studied only as a decay product of 125Cs.(4) Since 125mXe decays to 125Xe by isomeric transition with a 55 sec half-life it is correct to evaluate the neutron capture cross-section of 124Xe, without taking into account the production of 125mXe. * Student from Nuclear Chemistry Institute of Pavia University. 111 J. M. TOBIN and J. H. SAKO, J. Appi. Phys. 29, 1373 (1958). ,2> P. V. HARPER, Proc. 5th C.N.R.N. Nuclear Congress—Vol. II, 245 ROME (1960). 131 D. P. MANN, W. W. WATSON, R. E. CHRIEN, R. L. ZIMMERMAN and R. B. SCHWARTZ, Phys. Rev. 116, 1516(1959). 141 H. B. MATHUR and E. IC. HYDE, Phys. Rev. 95, 708 (1954). IO M. BRESESTI, F . CAPPELLANI, A. M. DEL TURCO and E. ORVINI The decay scheme of 125I is the following: 125I (60 days) The data reported in literature on the electron capture and the internal conversion of the 35­5 keV transition, are summarized in Table 1. TABLE 1.—DATA ON ELECTRON CAPTURE AND INTERNAL CONVERSION IN 125I PER 100 DISINTEGRATIONS. Type of decay Κ electron capture L electron capture Κ internal conversion L internal conversion M internal conversion Unconverted y­ray Ref. (5) 77 ± 8 23 ± 8 Ref. (6) 81 ± 2 19 ± 2 Ref. (7) 80 ± 5 11 ± 2 2 ± 0 ­ 4 7 ± 2 On the basis of the data of Table 1, using the intensity ratio and the fluorescent yield reported in the Nuclear Spectroscopy Tab!es(8) the number of XKa, XKß and unconverted y­rays has been calculated (Table 2). TABLE 2.—NUMBER OF 27­4, 31­2 AND 35­5 keV PHOTONS PER 100 DISINTEGRATIONS OF 125I. Electron capture Κ capture 80% 35­5 keV transition Unconverted ;'­ray Κ conversion 80% Χχa total number Χχβ total number Unconverted /­ray Total number of photons per 100 disintegrations Χκα Χκβ Χκ* Χκβ 56­3 121 7 56­3 12­1 112­6 24­2 7 143­8 151 G. FRIEDLANDER and W. C. ORR, Phys. Rev. 84, 484 (1951). "» E. DER MATEOSIAN, Phys. Rev. 92, 938 (1953). 171 J. C. BOWE and Ρ. AXEL, Phys. Rev. 85, 858 (1952). 131 A. H. WAPSTRA, G. J. NiJGH and R. VAN LIESHOUT—Nuclear Spectroscopy Tables-Holland Publishing Company, Amsterdam (1959). ­North­The thermal neutron capture cross­section and the resonance capture integral of l21Xe 11 The 125I activity was evaluated by measuring the intensity of the 35­5 keV y­ray, 27­4 keV XKa and 31­2 keV ΧΚβ. EXPERIMENTAL (a) Irradiations High purity natural xenon, containing 0096 per cent of 124Xe, supplied by "Air Liquide", was sealed in silica ampoules. Each ampoule was filled at a pressure of about 1 atm with an amount of xenon exactly measured in a high vacuum line. The samples, closed in rubber capsules, were irradiated by a pneumatic carrier in the graphite reflector, close to the heavy water tank, of the Ispra 1 reactor. The irradiation time was about 2 hr. To evaluate the epithermal activation some xenon ampoules were enclosed in 1 mm thick cadmium boxes. In the irradiations under the cadmium silica ampoules had a volume of about 2 ml, in the other ones the volume was about 4 ml. In all the irradiations a 1 mm in diameter wire of Al/Co alloy (1 per cent Cobalt) was added to the sample to evaluate exactly the neutron flux. (b) Chemical separation The ampoules were opened in a glove­box 10 days after the end of the irradiation, when 125Xe had totally decayed to 125I. About 80 per cent of 125I activity was recovered from the walls of the ampoule by washing with CCI4. This fraction of 125I is presumably present in the elementary form. The remaining 20 per cent was recovered by a Nal aqueous solution. The main impurity present on the walls of the ampoule was 137Cs, daughter of 137Xe produced by 130Xe neutron capture. The whole 137Cs activity was found in the aqueous solution. To eliminate I3,Cs and to obtain 125I in iodide form, suitable for the preparation of the sources, the following procedure was adopted: a few milligrams of NaN02 and one drop of concentrated HN03 , added to the aqueous solution, oxidize the iodide to iodine that is separated by repeated extractions with 1 ml fractions of CC14. The whole 137Cs activity remains in the aqueous fraction. The CCI4 fractions are added to the carbon tetrachloride used for washing the capsule. By adding to the whole solution 1 ml of alkaline solution of Na2S03, obtained by dissolving 30 mg of Na2S03 and 10 mg of NaOH in 10 ml of water, elementary iodine is reduced to iodide that is separated by repeated extractions with 2 ml fractions of water. The aqueous solution is utilized for the preparation of the sources on aluminium discs. Losses of 125I in the purification process have been controlled and corrections have been introduced. (c) Counting methods The chemical separation of 137Cs and the purity of the final solution of 1251 were tested by /­spectroscopy using a 3 in χ 3 in NaI(Tl) crystal and a multichannel pulse analyser. Due to the short irradiation periods (2 hr) no trace of 120I, produced by (η, γ) reaction on I25I, was found, although the neutron capture cross section of 125I seems to be of several hundred barns from measurements in progress. The quantitative analysis of l25I was performed by a proportional counter filled with an argon + 10 per cent methane mixture. The efficiency curve of the proportional counter was previously determined in the energy range of our interest. A typical spectrum of 125I is shown in Fig. 1. By assuming the total number of Xjca, Χκβ ar>d 35­5 keV y­rays equal to 143­8 for 100 disintegra­tions as reported in Table 2 the following values were obtained: Χκα = 114­8; Χχρ =24­0; γ = 5­0. The data for the XKa and Xgß intensities agree very well with those of Table 1 while the value for the 35­5 keV y­ray is quite different. However, this value which is within the experimental error indicated by BOWE,171 seems to be more reliable for the better resolution of the proportional counter. The G0Co intensity of the flux monitors was determined by a 3 in χ 3 in Nal(TI) crystal which had been calibrated previously. 12 M . BRESESTI , F . C A P P E L L A N I , A . M . D E L T U R C O a n d E . O R V I N I 15.000 5.000 100 150 200 channels FIG. 1—'251 photon spectrum by the proportional counter. CROSS­SECTION AND RESONANCE INTEGRAL CALCULATION The results were calculated following the procedure of EASTWOOD et α/.,<9) based on the convention described by WESTCOTT et al.ao) The data for 59Co used in the calculation of the conventional flux were taken from WESTCOTT(11) and are the following: σ0 = 37­3 barns RI = 75 barns s0= 1­736 No self­shielding correction had to be applied to the thermal and epithermal activities induced in 59Co. The general expression for calculating the effective cross­section from the 125I activity is the following: A, Νην0σ λ1 — λ2 LAe­^O ­ e""**) ­ Å2e-'i'(l -;·ιΌ' )] ''■" Τ. Α. EASTWOOD, A. P. BAERG, C. Β. BIGHAM, F . BROWN, M. J. CABELL, W. E. GRUMMITT, J. C. ROY, L. P. R O Y and R. P. SCHUMAN, Proceedings of the Second International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1958 Vol. 16, p . 54. United Nations (1959). I 1 0 ) C. H. WESTCOTT, W. H. WALKER and T. K. ALEXANDER, Proceedings of the Second International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1958 Vol. 16, p. 70 United Nations (1959). 1111 C. H. WESTCOTT, Report, AECL-1101 (1960). The thermal neutron capture cross­section and the resonance capture integral of 124Xe 13 where At = 125I activity at time t after the end of the irradiation N = number of 124Xe atoms nv0 = conventional flux σ = effective cross­section AT = decay constant of 125Xe λ2 = decay constant of 125I ta = irradiation time t = time after the end of the irradiation In the present experiment, the irradiation time was 2 hr and the 125I activity was measured about 10 days after the end of the irradiation. Under these conditions the term A2e"Ali(l — e^'1'») can be neglected and the expression simplifies to At = Νην0σ Κ λι — λ2 ,<(1 _ e­'='o) The reaction rates for 124Xe and 59Co measured without cadmium cover are reported in Table 3. These reaction rates are conventionally defined*9·10' as R = ην0σ. The data utilized for the calculation of the conventional flux nv0 and the results obtained have been assembled in Table 4. The average value for Ä59Co reported in TABLE 3.—REACTION RATES OF 124Xe AND 59CO WITHOUT CADMIUM COVER Experiment 1 2 3 Average value Λΐ24Χ ο (sec-1) 2-93 x IO"9 2-98 χ 10-9 2-98 χ IO"9 2-96 χ 10"° /?59Co (sec 1 ) 8-18 χ IO"10 8-24 χ 10"1" 8-35 χ IO' '" 8-26 χ IO""1 TABLE 4.— Experiment under cadmium 4 5 6 7 8 -CONVENTIONAL NEUTRON FLUX MEASURED WITH COBALT Ä59Q0(Cd) (sec­1) 1­17 x IO ­11 1­17 χ IO"11 1­16 χ 10­11 1­04 χ 10­11 109 χ IO"11 CRs*co 70­6 70­6 71­2 79­4 75­8 Æ) 00066 00066 00065 00059 00061 < 7 5 9 C o (barns) 37­73 37­73 37­72 37­68 37­70 MONITORS nv„ (neutron c m 2 sec ­1) 219 χ 1013 219 χ 10" 219 χ 1013 2­19 χ 10la 2­19 χ 1013 14 M. BRESESTI, F . CAPPELLANI, A. M. D E L TURCO and E. ORVINI Table 3 has been utilized in the calculation of the Cadmium Ratio CR^Cu. R^Co (Cd) is the reaction rate of 59Co under cadmium, <J59CO the effective cross­section. The calculated values of the effective cross­section <Xi24Xe, of the thermal cross­section σ0 and of the resonance integral RI are assembled in Table 5. The average TABLE 1 Experiment under cadmium 4 5 6 7 8 ' .—CAPTURE CROSS­SECTION AND RESONANCE CAPTURE INTEGRAL OF 12J ¿124Xe (barns) 135­2 135­2 135­2 135­2 135­2 i?124Xc(Cd) (sec­1) 5­95 χ IO"10 5­40 χ IO"10 4­73 χ IO"10 4­96 x IO"10 5­87 χ IO"10 0 ? 1 2 4 X e 4­97 5­48 6­26 5­97 5-04 ■*o124Xe 37­6 33­3 28­7 33­6 40-2 σ0 (barns) 108 111 114 113 109 Xe RI (barns) 3810 3470 3060 3590 4050 value of Ri24Xe reported in Table 3 has been utilized in the calculation of the Cadmium Ratio CRiuXa and the effective cross­section oi24Xe. We have made a liberal estimate of possible errors, mainly systematic errors in the evaluation of the 125I activity and of the neutron flux, as ±10 per cent for a and σ0 and as ±15 per cent for the resonance integral RI. This error does not take into account the uncertainties in the decay scheme of 125I and in the values of σ0 and RI for 59Co. The average of the five determinations, including the estimated errors, gives values of a = 135 ± 13, σ0 = 111 ± 11 and RI = 3600 ± 500 barns. The value obtained for the resonance integral is in good agreement with the value calculated from the expression RI = 277a0£o1/2£r1/2/r where σ0 = thermal cross section (111 barns) E0 = 0­0253 eV ET = resonance energy of 124Xe (5T6 eV) Γ = radiation width (90 meV) Taking into account the uncertainty of the radiation width, the value obtained is RI = 2800 ± 600 barns. The expression reported above is valid when the epithermal activation is almost exclusively due to a single resonance with the following parameters : Γ < Er ; Er > ECd. This enables us to conclude that the epithermal activation of 124Xe is mainly due to the resonance at 5­16 eV. Acknowledgements—The authors wish to thank Prof. G. BERTOLINI of this Laboratory and Prof. A. M. ROLLIER of the Nuclear Chemistry Institute of PAVIA University for the helpful discussions. ÏÏOÊM täüäs&towmmm 

THE THERMAL NEUTRON CAPTURE CROSS-SECTION AND THE RESONANCE CAPTURE INTEGRAL OF i24Xe. EUR 551.e

IJWW'WWWa 
THE THERMAL NEUTRON CAPTURE 
• iiii Ju '* Λ*Ϊΐΰι.Ι.ΙΓ 
I 
CROSS-SECTION AND THE RESONANCE 
CAPTURE INTEGRAL OF i24Xe 
WFTwilMid; ¡iiii tølfi&f w : " Α · Β !w ■ '\ψ mmPPW" 
fciiiÄiii by y
M. BRESESTI, F. CAPPELLANI, 
. M. DEL TURCO and E. ORVINI 
¡íM' 
'ñiüti ■•"'tf wfötB*­·*·» ■ w'iílíifrwlir 
îAlAli'ïi '«'™^« 
'HK'w,MinV¡' m · "κ 
ιιίΛι' «'Het'ia'SSP1 i,J, ,;J..l 
Nuclear Research Centre 
lepra Establishment - Italy 
Materials Department 
Nuclear Chemistry Laboratory 
«Mielii Reprinted from 
\NIC AND Ν 
Vol. 26 - 1964 
i v c p n u i c u " « U I 
JOURNAL OF INORGA I   NUCLEAR CHEMISTRY 
¡ÜIII! 
'•2'"íifTrTS 
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This document was prepared under the sponsorship of the Commission of the European 
Atomic Energy Community (EURATOM). 
EURATOM Commission, its contractors nor any person acting on their behalf: Neither the WÉÊÈÈ ■ 
§ 1° — Make any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this document, or that the use JBSam of any i formation, apparatus, infringe privately owned rights; method, or process disclosed in t o r lis document %%m w*$ 
Assume any liability with respect to the use of, or for damages resulting from the use 
may not r j f t j M ( J j 
»T« 
i fM 
■m 
'HiU'ŒiFenl' J. ms rej/ττ 
by kind -permission of the publisher, an article from "JOURNAL OF 
i 
up 
ψ] 
INORGANIC AND NUCLEAR CHEMISTRY", Vol. 26 - 1964, 
9-14. For further copies please apply to Pergamon Press Ltd. - Journals 
Department - Headington Hill Hall, Oxford (England). 
Dieser Sonderdruck ist für eine beschränkte Verteilung bestimmt. Die 
Wiedergabe des vorliegenden in „JOURNAL OF INORGANIC AND 
NUCLEAR CHEMISTRY", Vol. 26 - 1964, 9-14 erschienenen 
I f f ."» ' - r ! : ã.~ i>»ra*in<>* 'TSfiff mmu 
ϊϋι»3 
Ce tiré-à-part est exclusivement destine à une diffusion restreinte. Il 
f éprend, avec l'aimable autorisation de l'éditeur, un article publié dans 
le « JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY», 
■i !JÌ.F"ft)4&tìtìlfil' 
l,e<i J UU n J V Ä J y ur JLÁ\UI\.Or¿liy±u Λ ί ν ι / ζ ν u i / i > i i n n W / Ü ¿ « Í J I I U ir, 
Vol. 26 - 1964, 9-14. Tout autre exemplaire de cet article doit être: 
demandé à Pergamon Press Ltd. - Journals Department - Headington 
« f f f Hall, Oxford (England). 
¿tøtø'lr"'« 
Questo estratto è destinato esclusivamente ad una diffusione limitata. 
Esso è stato riprodotto, per gentile concessione dell'Editore, da 
«JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY 
V 
Md? lllffSHil'Üfi» 
ol. 26 - 1964, 9-14. Ulteriori copie dell'articolo debbono essere richieste 
Pergamon Press Ltd. - Journals Department - Headington Hill Hall, 
Oxford (England) !k;Æ 
Deze overdruk is slechts voor beperkte verspreiding bestemd. Het artikel 
is, met welwillende toestemming van de uitgever overgenomen uit 
„JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY", 
Vol. 26 -1964, 9-14. Meer exemplaren kunnen besteld worden bij Per-
gamon Press Ltd. ~ Journals Department - Headington Hill Hall, 
" iilillillilÉllll^i 
t . - : 'r Lf<) t ttueMIMei! 
Oxford (England). 
EUR 5 5 1 . e 
REPRINT 
THE THERMAL NEUTRON CAPTURE CROSS­SECTION AND THE RESONANCE CAPTURE INTEGRAL OF 124Xe by M. BRESESTI, F. CAPPELLANI, A.M. DEL TRUCCO and E. ORVINI. 
European Atomic Energy Community ­ EURATOM Joint Nuclear Research Centre Ispra Establishment ­ Italy 
Materials Department Nuclear Chemistry Laboratory 
Reprinted from "JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY" Vol. 26 ­ 1964 ­ 9­14 pages 
The thermal neutron capture cross­section of m X e , its resonance capture integral (from 0.5 eV to 00) and its effective capture cross­section in a reflector position of the Ispra 1 reactor have been found to be 111 ± 11 barns, 3600 ± 500 barns and 135 ± 13 barns respectively. 
These values have been determined by irradiating natural Xenon and mea­suring the activity of 12δΙ, the decay product of 125Xe. 
EUR 5 5 1 .e 
REPRINT 
THE THERMAL NEUTRON CAPTURE CROSS­SECTION AND THE RESONANCE CAPTURE INTEGRAL OF 124Xe by M. BRESESTI, F. CAPPELLANI, A.M. DEL TRUCCO and E. ORVINI. 
European Atomic Energy Community ­ EURATOM Joint Nuclear Research Centre 
Ispra Establishment ­ Italy Materials Department Nuclear Chemistry Laboratory 
Reprinted from "JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY" Vol. 26 ­ 1964 ­ 9­14 pages 
The thermal neutron capture cross­section of 124Xe, its resonance capture integral (from 0.5 eV to 00) and its effective capture cross­section in a reflector position of the Ispra 1 reactor have been found to be 111 ± 11 barns, 3600 ± 500 barns and 135 ¡fc 13 barns respectively. 
These values have been determined by irradiating natural Xenon and mea­suring the activity of 125I, the decay product of 125Xe. 
EUR 5 5 1 . e 
REPRINT 
THE THERMAL NEUTRON CAPTURE CROSS­SECTION AND THE RESONANCE CAPTURE INTEGRAL OF 124Xe by M. BRESESTI, F. CAPPELLANI, A.M. DEL TRUCCO and E. ORVINI. 
European Atomic Energy Community ­ EURATOM Joint Nuclear Research Centre 
Ispra Establishment ­ Italy Materials Department Nuclear Chemistry Laboratory 
Reprinted from "JOURNAL OF INORGANIC AND NUCLEAR CHEMISTRY" Vol. 26 ­ 1964 ­ 9­14 pages 
The thermal neutron capture cross­section of 124Xe, its resonance capture integral (from 0.5 eV to 00) and its effective capture cross­section in a reflector position of the Ispra 1 reactor have been found to be 111 ± 11 barns, 3600 ± 500 barns and 135 ± 13 barns respectively. 
These values have been determined by irradiating natural Xenon and mea­
suring the activity of 125I, the decay product of 125Xe. 

Reprinted from 
Journal of 
INORGANIC & NUCLEAR 
CHEMISTRY 
P E R G A M O N PRESS 
OXFORD · LONDON · NEW YORK . PARIS 

J. Inorg. Nucí. Chem., 1964, Vol. 26, pp. 9 to 14. Pergamon Press Ltd. Printed in Northern Ireland 
THE THERMAL NEUTRON CAPTURE CROSS-SECTION 
AND THE RESONANCE CAPTURE INTEGRAL 
OF 124Xe 
M. BRESESTI , F . C A P P E L L A N I , A . M . D E L T U R C O and E . O R V I N I * 
Nuclear Chemistry Laboratory—C.C.R. EURATOM—Ispra 
{Received 13 May 1963) 
Abstract—The thermal neutron capture cross-section of 121Xe, its resonance capture integral (from 
0-5 eV to a>) and its effective capture cross-section in a reflector position of the Ispra 1 reactor 
have been found to be 111 ± 11 barns, 3600 ± 500 barns and 135 ± 13 barns respectively. 
These values have been determined by irradiating natural Xenon and measuring the activity 
of 125I, the decay product of 125Xe. 
ALTHOUGH the nuclear reaction 124Xe(/i,y)125Xe is used for the preparation of 
125I, decay product of 125Xe, the capture cross-section of 124Xe is known only 
imprecisely. 
TOBIN and SAKO11' evaluated this neutron capture cross-section by the measure-
ment of the intensity of the 0-190 MeV y-ray of 125Xe. They obtained a value of 
74 barns in a reactor spectrum of unspecified epithermal content. Moreover the 
incertainty in the value of the neutron flux was about 25 per cent. HARPER12» found 
in preliminary measurements that the cross-section may even be a factor of 2 or 3 
higher than the value previously reported. MANN et aì.i3) have measured the total 
neutron cross-section of xenon from about 1 eV to about 200 eV. Irradiating various 
isotopie mixtures of xenon, they attributed to 124Xe a resonance peak at 5-16 ± 0Ό6 
eV. For the resonance analysis a radiation width of 90 ± 20 meV was assumed. 
In the present work the neutron capture cross-section is determined from the 
activity of 125I formed through the following nuclear reactions: 
^Xe(«,y)125Xe - ^ 125I ^ > 125Te (stable) 
The neutron capture reaction can also produce 125"'Xe. Thisisotope, never observed 
in the neutron irradiation of 124Xe, has been studied only as a decay product of 
125Cs.(4) Since 125mXe decays to 125Xe by isomeric transition with a 55 sec half-life 
it is correct to evaluate the neutron capture cross-section of 124Xe, without taking 
into account the production of 125mXe. 
* Student from Nuclear Chemistry Institute of Pavia University. 
111 J. M. TOBIN and J. H. SAKO, J. Appi. Phys. 29, 1373 (1958). 
,2> P. V. HARPER, Proc. 5th C.N.R.N. Nuclear Congress—Vol. II, 245 ROME (1960). 
131 D. P. MANN, W. W. WATSON, R. E. CHRIEN, R. L. ZIMMERMAN and R. B. SCHWARTZ, Phys. Rev. 
116, 1516(1959). 
141 H. B. MATHUR and E. IC. HYDE, Phys. Rev. 95, 708 (1954). 
IO M. BRESESTI, F . CAPPELLANI, A. M. DEL TURCO and E. ORVINI 
The decay scheme of 125I is the following: 
125I (60 days) 
The data reported in literature on the electron capture and the internal conversion 
of the 35­5 keV transition, are summarized in Table 1. 
TABLE 1.—DATA ON ELECTRON CAPTURE AND INTERNAL CONVERSION 
IN 125I PER 100 DISINTEGRATIONS. 
Type of decay 
Κ electron capture 
L electron capture 
Κ internal conversion 
L internal conversion 
M internal conversion 
Unconverted y­ray 
Ref. (5) 
77 ± 8 
23 ± 8 
Ref. (6) 
81 ± 2 
19 ± 2 
Ref. (7) 
80 ± 5 
11 ± 2 
2 ± 0 ­ 4 
7 ± 2 
On the basis of the data of Table 1, using the intensity ratio and the fluorescent 
yield reported in the Nuclear Spectroscopy Tab!es(8) the number of XKa, XKß and 
unconverted y­rays has been calculated (Table 2). 
TABLE 2.—NUMBER OF 27­4, 31­2 AND 35­5 keV PHOTONS 
PER 100 DISINTEGRATIONS OF 125I. 
Electron capture 
Κ capture 80% 
35­5 keV transition 
Unconverted ;'­ray 
Κ conversion 80% 
Χχa total number 
Χχβ total number 
Unconverted /­ray 
Total number of photons 
per 100 disintegrations 
Χκα 
Χκβ 
Χκ* 
Χκβ 
56­3 
121 
7 
56­3 
12­1 
112­6 
24­2 
7 
143­8 
151 G. FRIEDLANDER and W. C. ORR, Phys. Rev. 84, 484 (1951). 
"» E. DER MATEOSIAN, Phys. Rev. 92, 938 (1953). 
171 J. C. BOWE and Ρ. AXEL, Phys. Rev. 85, 858 (1952). 
131 A. H. WAPSTRA, G. J. NiJGH and R. VAN LIESHOUT—Nuclear Spectroscopy Tables-
Holland Publishing Company, Amsterdam (1959). 
­North­
The thermal neutron capture cross­section and the resonance capture integral of l21Xe 11 
The 125I activity was evaluated by measuring the intensity of the 35­5 keV y­ray, 
27­4 keV XKa and 31­2 keV ΧΚβ. 
EXPERIMENTAL 
(a) Irradiations 
High purity natural xenon, containing 0096 per cent of 124Xe, supplied by "Air Liquide", 
was sealed in silica ampoules. Each ampoule was filled at a pressure of about 1 atm with an amount 
of xenon exactly measured in a high vacuum line. The samples, closed in rubber capsules, were 
irradiated by a pneumatic carrier in the graphite reflector, close to the heavy water tank, of the 
Ispra 1 reactor. The irradiation time was about 2 hr. 
To evaluate the epithermal activation some xenon ampoules were enclosed in 1 mm thick cadmium 
boxes. In the irradiations under the cadmium silica ampoules had a volume of about 2 ml, in the 
other ones the volume was about 4 ml. 
In all the irradiations a 1 mm in diameter wire of Al/Co alloy (1 per cent Cobalt) was added to the 
sample to evaluate exactly the neutron flux. 
(b) Chemical separation 
The ampoules were opened in a glove­box 10 days after the end of the irradiation, when 125Xe 
had totally decayed to 125I. 
About 80 per cent of 125I activity was recovered from the walls of the ampoule by washing with 
CCI4. This fraction of 125I is presumably present in the elementary form. The remaining 20 per 
cent was recovered by a Nal aqueous solution. 
The main impurity present on the walls of the ampoule was 137Cs, daughter of 137Xe produced 
by 130Xe neutron capture. The whole 137Cs activity was found in the aqueous solution. To eliminate 
I3,Cs and to obtain 125I in iodide form, suitable for the preparation of the sources, the following 
procedure was adopted: a few milligrams of NaN02 and one drop of concentrated HN03 , added 
to the aqueous solution, oxidize the iodide to iodine that is separated by repeated extractions with 
1 ml fractions of CC14. The whole 137Cs activity remains in the aqueous fraction. The CCI4 fractions 
are added to the carbon tetrachloride used for washing the capsule. By adding to the whole solution 
1 ml of alkaline solution of Na2S03, obtained by dissolving 30 mg of Na2S03 and 10 mg of NaOH 
in 10 ml of water, elementary iodine is reduced to iodide that is separated by repeated extractions 
with 2 ml fractions of water. The aqueous solution is utilized for the preparation of the sources 
on aluminium discs. 
Losses of 125I in the purification process have been controlled and corrections have been 
introduced. 
(c) Counting methods 
The chemical separation of 137Cs and the purity of the final solution of 1251 were tested by 
/­spectroscopy using a 3 in χ 3 in NaI(Tl) crystal and a multichannel pulse analyser. 
Due to the short irradiation periods (2 hr) no trace of 120I, produced by (η, γ) reaction on I25I, 
was found, although the neutron capture cross section of 125I seems to be of several hundred barns 
from measurements in progress. 
The quantitative analysis of l25I was performed by a proportional counter filled with an argon + 
10 per cent methane mixture. The efficiency curve of the proportional counter was previously 
determined in the energy range of our interest. A typical spectrum of 125I is shown in Fig. 1. 
By assuming the total number of Xjca, Χκβ ar>d 35­5 keV y­rays equal to 143­8 for 100 disintegra­
tions as reported in Table 2 the following values were obtained: Χκα = 114­8; Χχρ =24­0; 
γ = 5­0. 
The data for the XKa and Xgß intensities agree very well with those of Table 1 while the value 
for the 35­5 keV y­ray is quite different. However, this value which is within the experimental 
error indicated by BOWE,171 seems to be more reliable for the better resolution of the proportional 
counter. 
The G0Co intensity of the flux monitors was determined by a 3 in χ 3 in Nal(TI) crystal which 
had been calibrated previously. 
12 M . BRESESTI , F . C A P P E L L A N I , A . M . D E L T U R C O a n d E . O R V I N I 
15.000 
5.000 
100 150 200 channels 
FIG. 1—'251 photon spectrum by the proportional counter. 
CROSS­SECTION AND RESONANCE INTEGRAL CALCULATION 
The results were calculated following the procedure of EASTWOOD et α/.,<9) based 
on the convention described by WESTCOTT et al.ao) 
The data for 59Co used in the calculation of the conventional flux were taken 
from WESTCOTT(11) and are the following: 
σ0 = 37­3 barns 
RI = 75 barns 
s0= 1­736 
No self­shielding correction had to be applied to the thermal and epithermal 
activities induced in 59Co. 
The general expression for calculating the effective cross­section from the 125I 
activity is the following: 
A, 
Νην0σ 
λ1 — λ2 LAe­^O ­ e""**) ­ Å2e-'i'(l 
-;·ιΌ' )] 
''■" Τ. Α. EASTWOOD, A. P. BAERG, C. Β. BIGHAM, F . BROWN, M. J. CABELL, W. E. GRUMMITT, 
J. C. ROY, L. P. R O Y and R. P. SCHUMAN, Proceedings of the Second International Conference on 
the Peaceful Uses of Atomic Energy, Geneva, 1958 Vol. 16, p . 54. United Nations (1959). 
I 1 0 ) C. H. WESTCOTT, W. H. WALKER and T. K. ALEXANDER, Proceedings of the Second International 
Conference on the Peaceful Uses of Atomic Energy, Geneva, 1958 Vol. 16, p. 70 United Nations 
(1959). 
1111 C. H. WESTCOTT, Report, AECL-1101 (1960). 
The thermal neutron capture cross­section and the resonance capture integral of 124Xe 13 
where 
At = 125I activity at time t after the end of the irradiation 
N = number of 124Xe atoms 
nv0 = conventional flux 
σ = effective cross­section 
AT = decay constant of 125Xe 
λ2 = decay constant of 125I 
ta = irradiation time 
t = time after the end of the irradiation 
In the present experiment, the irradiation time was 2 hr and the 125I activity was 
measured about 10 days after the end of the irradiation. Under these conditions 
the term A2e"Ali(l — e^'1'») can be neglected and the expression simplifies to 
At = Νην0σ Κ λι — λ2 ,<(1 _ e­'='o) 
The reaction rates for 124Xe and 59Co measured without cadmium cover are 
reported in Table 3. These reaction rates are conventionally defined*9·10' as R = 
ην0σ. 
The data utilized for the calculation of the conventional flux nv0 and the results 
obtained have been assembled in Table 4. The average value for Ä59Co reported in 
TABLE 3.—REACTION RATES OF 124Xe AND 59CO 
WITHOUT CADMIUM COVER 
Experiment 
1 
2 
3 
Average value 
Λΐ24Χ ο 
(sec-1) 
2-93 x IO"9 
2-98 χ 10-9 
2-98 χ IO"9 
2-96 χ 10"° 
/?59Co 
(sec 1 ) 
8-18 χ IO"10 
8-24 χ 10"1" 
8-35 χ IO' '" 
8-26 χ IO""1 
TABLE 4.— 
Experiment 
under 
cadmium 
4 
5 
6 
7 
8 
-CONVENTIONAL NEUTRON FLUX MEASURED WITH COBALT 
Ä59Q0(Cd) 
(sec­1) 
1­17 x IO ­11 
1­17 χ IO"11 
1­16 χ 10­11 
1­04 χ 10­11 
109 χ IO"11 
CRs*co 
70­6 
70­6 
71­2 
79­4 
75­8 
Æ) 
00066 
00066 
00065 
00059 
00061 
< 7 5 9 C o 
(barns) 
37­73 
37­73 
37­72 
37­68 
37­70 
MONITORS 
nv„ 
(neutron c m 2 sec ­1) 
219 χ 1013 
219 χ 10" 
219 χ 1013 
2­19 χ 10la 
2­19 χ 1013 
14 M. BRESESTI, F . CAPPELLANI, A. M. D E L TURCO and E. ORVINI 
Table 3 has been utilized in the calculation of the Cadmium Ratio CR^Cu. R^Co 
(Cd) is the reaction rate of 59Co under cadmium, <J59CO the effective cross­section. 
The calculated values of the effective cross­section <Xi24Xe, of the thermal cross­
section σ0 and of the resonance integral RI are assembled in Table 5. The average 
TABLE 1 
Experiment 
under 
cadmium 
4 
5 
6 
7 
8 
' .—CAPTURE CROSS­SECTION AND RESONANCE CAPTURE INTEGRAL OF 12J 
¿124Xe 
(barns) 
135­2 
135­2 
135­2 
135­2 
135­2 
i?124Xc(Cd) 
(sec­1) 
5­95 χ IO"10 
5­40 χ IO"10 
4­73 χ IO"10 
4­96 x IO"10 
5­87 χ IO"10 
0 ? 1 2 4 X e 
4­97 
5­48 
6­26 
5­97 
5-04 
■*o124Xe 
37­6 
33­3 
28­7 
33­6 
40-2 
σ0 
(barns) 
108 
111 
114 
113 
109 
Xe 
RI 
(barns) 
3810 
3470 
3060 
3590 
4050 
value of Ri24Xe reported in Table 3 has been utilized in the calculation of the Cadmium 
Ratio CRiuXa and the effective cross­section oi24Xe. 
We have made a liberal estimate of possible errors, mainly systematic errors in the 
evaluation of the 125I activity and of the neutron flux, as ±10 per cent for a and σ0 
and as ±15 per cent for the resonance integral RI. This error does not take into 
account the uncertainties in the decay scheme of 125I and in the values of σ0 and RI 
for 59Co. 
The average of the five determinations, including the estimated errors, gives 
values of a = 135 ± 13, σ0 = 111 ± 11 and RI = 3600 ± 500 barns. 
The value obtained for the resonance integral is in good agreement with the 
value calculated from the expression 
RI = 277a0£o1/2£r1/2/r 
where σ0 = thermal cross section (111 barns) 
E0 = 0­0253 eV 
ET = resonance energy of 124Xe (5T6 eV) 
Γ = radiation width (90 meV) 
Taking into account the uncertainty of the radiation width, the value obtained 
is RI = 2800 ± 600 barns. 
The expression reported above is valid when the epithermal activation is almost 
exclusively due to a single resonance with the following parameters : Γ < Er ; Er > 
ECd. This enables us to conclude that the epithermal activation of 124Xe is mainly 
due to the resonance at 5­16 eV. 
Acknowledgements—The authors wish to thank Prof. G. BERTOLINI of this Laboratory and Prof. 
A. M. ROLLIER of the Nuclear Chemistry Institute of PAVIA University for the helpful discussions. 


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