AEC Research and Development REPORT

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1 -.,- MLM (tr) DEPENDENCE OF THE YIELD OF THE ( a n ) REACTION ON ALPHA PARTICLE ENERGY E. M. Tsenter and A. B. Silin Translated by K. W. Foster AEC Research and Development REPORT MONSANTO RESEARCH CORPORATION A S U B S I D I A R Y M O U N D MlAMlSBU RG, OHIO O F M O N S A N T O C O M P A N Y L A B O R A T O R Y OPERATED FOR UNITED STATES ATOMIC ENERGY COMMISSION.. USGOVERRNMENT CONTRACT NO.AT-33-1.GEN-53 DI$TRIBUTION OF THIS DOCUMENT IS UNLtMlTED # I

2 ~ LEGAL NOTICE This repoxt was prepared as an account of Government sponsored work. Neither the United Sates, nor the Commission. nor any person acting on behalf of the Commission: A, Makes any warranty or representation, expressed or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report. or that the use of any information. apparatus. method. or process disclosed in this report may not infringe privately owned rights: or B. Assumes any liabilities with respect to the pse of, or for damages resulting from the use of any information. apparatus. method. or process disclosed in this report. As used in the above. person acting on behalf of the Cdmmission includes any employee or contractor of the Commission. or employee of such contractor. to the extent that such employee or contractor of the Commission, or employee of such contractor prepares. disseminates. or provides access to, any information pursuant to his employment or contract with the Commission. or his employment with such contractor.

3 M LM- I 378 (tr) DEPENDENCE OF THE YIELD OF THE (a,n)reaction ON ALPHA PARTICLE ENERGY E. M. Tsenter A. 6. Silin Issued: March 27, 1967 Translated by K. W. Foster From Atomnaya Energiya (SSSR) 19, 48 (July, 1965). Copyright releases have not been obtained from the publisher or the authors. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product. process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. M O N S A N T O RESEARCH CORPORATION A Subsidiary of Monsanto Company MOUND LABORATORY Miamisburg, Ohio UNITED operated for STATES ATOMIC ENERGY COMMISSION U.S. GOVERNMENT CONTRACT NO. AT-33MEN.53

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5 Neutron y i e l d s r e s u l t i n g from (a,n) reactions have a p r a c t i c a l i n t e r e s t, p a r t i c u l a r l y f o r many r a d i a t i o n monitoring p r ~ b l e m s. l - ~ Data f o r yields f o r the (a,n) r e a c t i o n of d i f f e r e n t elements a r e necessary f o r s o l u t i o n of some problems i n geochemistry and geophysics.6-10 Reference 11 contains the empirical formula n = E305" f o r the dependence of the neutron yield from beryllium on alpha p a r t i c l e energy. Formula (1)w a s developed from three values of alpha p a r t i c l e energy: E, = 5.14 MeV ( P u ~ ~ ' ), E, = 5.48 MeV (Am?41), E, = 6.11 MeV ( C d 4 ' ). and Analogous empirical formulas of the type Q=kE" a r e given f o r a number of substances i n references, 1 2 and 13. For determination of k and n, authors of these works u t i l i z e d values of Q t h a t they measured with sources of polonium-210. (E, = 5.3 MeV), radium C' (E, = 7.68 MeV), and radon radium A radium C' (E, = 5.5, 6.0, and 7.68 MeV, respectively). + + It i s not possible t o u t i l i z e these formulas with energies above the c i t e d l i m i t s without s p e c i a l v e r i f i c a t i o n. Verification i s a l s o necessary t o confirm t h a t the indicated formulas correspond t o curves with monotonically increasing f i r s t derivatives of energy. I n general, such monotonicities a r e not necessary.in the NOTE: Manuscript received by the e d i t o r, J u l y 27, I n f i n a l form, January 6, (Reference 5 not indicated i n the o r i g i n a l ). 3

6 case of resonance peaks i n the curve of rieutron dependence of r e a c t i o n cross section on the alpha p a r t i c l e energy. For beryllium, boron, carbon, magnesium and oxygen there e x i s t i n the l i t e r a t u r e curves f o r the cross section of the reaction With these c r o s s sections (a,n) f o r energies up t o 5.3 i t i s possible t o c a l c u l a t e the dependence of the neutron yield on the alpha p a r t i c l e energy. Data necessary f o r c a l c u l a t i o n of l o s s of alpha p a r t i c l e energy per u n i t track length were the r e s u l t of the conversion of energy l o s s i n a i r l ' j according t o wellknown values of r e l a t i v e stopping power, and which we considered t o be constant i n the energy i n t e r v a l s under consideration. For oxygen-18 the dependence o ( E ) i s presented i n references 14 and 15. Taking i n t o account (a,n) reactions on oxygen composed p r i n c i p a l l y of oxygen-18, i t i s possible t o compare the r e s u l t s of such c a l c u l a t i o n (See Figure l a, Curve' 1) with experimental data produced by a n a t u r a l mixture of oxygen isotopes Calculation of the value 4.5 neutrons per 10' alpha p a r t i c l e s, with an energy of 5.3 MeV (converted t o a n a t u r a l mixture of oxygen isotopes) disagrees with the 'experimental value f o r t h i s point, i. e., 7 neutrons per 108 alpha p a r t i c l e s, by -35%. The l a t e s t l v a l u e derived by the other authors a s a r e s u l t of d i r e c t experiments appears t o be more r e l i a b l e than what w a s calculated by us with cross sections from reference 15, the precision of which i s no b e t t e r than 25%. Obviously Curve 1 (Figure l a ) accurately r e f l e c t s the character of the dependence of neutron yield on the alpha-particle energy, so we derived the curve more c l o s e l y t o the t r u e curve by normalizing Curve 1 t o experimental values a t 5.3 MeV (see Curve 3, Figure l a ). Also presented i n Figure l a i s Curve 2, derived from formula ( 2 ). Calculations were likewise performed f o r beryllium, boron, carbon, and magnesium, using cross sections given i n references 14 and 15; analogous graphs were plotted (see Figures l b, IC, I d, and l e ). The numbers 1, 2 and 3, respectively, a r e designated a s i n Figure l a. Moreover, i n Figure l b i s presented Curve 4, which corresponds t o formula (1). It should be possible t o compare formula ( 2 ) f o r oxygen with data given i n reference 20. The author r e p o r t s two new neutron. sources developed by S..Amiel and A. Nier. One of these sources i s polonium-2lo/oxygen-18 (The neutron yield i s 30 neutrons per lo6 alpha p a r t i c l e s, and the average neutron energy i s approximately 2.4 MeV). 4

7 . n U m s > e C z 4. C v n U Y) 53 > C a 4. al C Y U U h 1.o Y) o, '0.8 > C c - a 0 E. U a E, 4 5 (Mev) a O12 5 Figure 1 0 5

8 In reference 17 the neutron yield for the polonium-2lo/oxygen-18 source is given as 31 neutrons per lo6 alpha particles. In 1959 data were published on the gamma radiation21 and neutron specof the neutron source polonium-2lo/oxygen-18. The maximum of the energy curve was at 2.4 MeV. In reference 20 the data of the neutron yield from the source thorium-228/oxygen-l8 are questionable (1500 neutrons per 10" alpha particles). Energies of alpha particles from thorium-228 and its decay products are equal to 5.4, 5.7, 6.3, 6.8, 6.08, and 8.8 MeV;23 the last group occurs in a portion of approximately 13%. For alpha particles of radium C (Ea = 7.68 MeV) the yield from (a,n) conversion on oxygen-18 is 280 neutrons per lo6 alpha particles.i2 Judging from the spectrum of alpha particles, the neutron yield from the source thorium-228/oxygen-l8 must be smaller than the neutron yield from the source radium C'/oxygen-18. Thus, the value of 1500 neutrons per 10" alpha particles reported in reference 20 is overestimated by approximately one order of magnitude. 6

9 REFERENCES 1. V.'V. 2. I. N. Plaksin, V. N. Smirnov, and L. P. Starchik, Dokl. Akad. 127, 618 (1959). Nauk SSSR, - 3. I. N. Plaksin, V. N. Smirnov, and L. ' P.. Nauk SSSR, 128, 1208 (1959). 4. I. N. Plaksin, V. N. Sinirnov, and L. P. Starchik, A t. Enerq., 9, 361 (1960). 5. A. Blanc e t a l., Proceedings of the Second I n t e r n a t i o n a l Conference on Peaceful Uses of Atomic Energy, V o l. 23, , (1959) , 6. Ivanov'et a l., A t. Energ.,L, Starchik, Dokl. Akad. p , D. Cartwright, M. Todd, and B. Ukaea, Nucl. Power, ' 7 9 (1961). 66, G. V. Gorshkov, N. M. Lyatkovskaya, Dokl. Akad. Nauk SSSR, 92 (1960). 133, G. V. Gorshkov, N. M. Lyatkovskaya, Dokl. Akad. Nauk SSSR, 745 (1939). 25, L e L. Kashkarov, V. V. Cherdyntsev, Geokhimiya, 632 (1958). I, I. Pine, and P. Morrison, Phys. Rev., 86, 606 (1952). 11. J. B. Marion and J. L. Fowler, Fast Neutron Physics, I n t e r science, N. Y., 1960, p G. V. Groshkov, V. A. Zyabkin, and 0. S. Tsvetkov, A t. Enerq., 475 (1962). 13, 13. G. V. Groshkov and 0. S. Tsvetkov, A t. Enerp;.,l&, 14. T. Bonner e t a l., Phys. Rev., 15. J. Bair and H. Willard, Phys. Rev., 128, 299 (1962). 102, (1963). (1956). - 7

10 16. E. Segre, Eksperim. Yadernaya Fiz., Vol. 1, Foreign Literature Press, MOSCOW, 1955, p I. A. Serdyukova, A. G. Khabakhpashev, and E. M. Tsenter, Press. Akad. Nauk SSSR, Phys. Ser., - 21, 1017 (1957). 18. E. Segre, op. cit., Vol. 11, p G. V. Groshkov, V. A. Zyabkin, and 0. S. Tsvetkov, At. Energ., - 13, 65 (1962). 20. G. Ben-David, Neutron Dosimetry, Vol. 11, IAEA, Vienna, 1963, p E. M. Tsenter, A. G. Khabakhpashev, and I. A. Pyrkin, - Zh. Eksperim. i Teor. Fiz., 37, 1138 (1959). 22. A. G. Khabakhpashev, At. Energ.,L, 71 (1959). 23. D. Strominger, J. Hollander, and G. Seaborg, Rev. Mod. Phvs., - 30, Pt. 11 (1958). 8

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