Program - Brookhaven National Laboratory

Investigation of (n,α) and (n,p) cross sections averaged over the fission neutron spectrum is important to
estimate radiation damage due to helium and hydrogen production, nuclear heating and transmutations
in the reactor structural materials. On the other hand, systematical analysis of neutron cross sections is of
interest to study nuclear reaction mechanisms. In addition, it is often necessary in practice to evaluate the
neutron cross sections of the nuclides, for which no experimental data are available, using the systematics.
Analysis of the experimental (n,α) and (n,p) cross sections in the energy range of 14-15 MeV was carried
out by Levkovsky [1,2] and a certain systematical dependence of the cross sections on the asymmetry
parameter of neutron and proton numbers (N-Z)/A was observed which in literature is termed as the
isotopic effect. We also have obtained a similar dependence for the (n,α) and (n,p) cross sections of 6 to 20
MeV [3] and for wide energy range suggested the statistical model [4-6] to explain the dependence of the
(n,α) and (n,p) cross sections on the parameter (N-Z+0.5)/A and (N-Z+1)/A, respectively. In this paper
the statistical model based on the Weisskopf-Ewing theory is used for systematics of known experimental
(n,α) and (n,p) cross sections averaged over the fission neutron spectrum. A regular behaviour in the
fission neutron spectrum averaged (n,α) and (n,p) cross sections was observed. It was shown that the
experimental data is satisfactorily described by the statistical model. In addition, the average effective
neutron energy for (n,α) and (n,p) reactions induced by fission neutrons was found to be around 5 MeV.
[1] V.N. Levkovsky, Journal of Experimental and Theoretical Physics. 45, N8, 305(1963) (In Russian) [2]
V.N. Levkovsky, Yadernaya Fizika, 18 705 (1973) (In Russian) [3] G. Khuukhenkhuu, G. Unenbat, Yu.M.
Gledenov, M.V. Sedysheva, Proceedings of the International Conference on Nuclear Data for Science and
Technology (19-24 May 1997), Trieste, Italy, Bologna, Editors: G.Reffo, A.Ventura, C.Grandi, part 1, 934
(1997) [4] G. Khuukhenkhuu, G. Unenbat, Scientific Transactions of the National University of Mongolia,
159, N7, Ulaanbaatar, 72 (2000) [5] G. Khuukhenkhuu, G. Unenbat, Yu.M. Gledenov, M.V. Sedysheva,
Proceedings of the International Conference on Nuclear Data for Science and Technology, Oct. 7-12, 2001,
Tsukuba, Journal of Nuclear Science and Technology, Supplement 2, 1 782(2002) [6] G. Khuukhenkhuu,
G. Unenbat, M. Odsuren, Yu.M. Gledenov, M.V. Sedysheva, B. Bayarbadrakh, JINR Communication,
E3-2007-25, Dubna (2007)
HC 8 5:45 PM
Evaluation of Non-Rutherford Alpha Elastic Scattering Cross-Section for Silicon
A.F. Gurbich
Institute for Physics and Power Engineering, Obninsk 249033, Russia
C. Jeynes
University of Surrey Ion Beam Centre, Guildford GU2 7XH, England
The analysis of silicon samples by Ion Beam Analysis (IBA) methods is widely used in numerous laboratories.
IBA exploits the interactions of rapid charged particles with matter to determine the composition
and structure of the surface regions of solids, the differential cross-section data being needed to derive
element concentrations through computer simulation of measured spectra. There are a number of benefits
in use for IBA of 4 He elastic backscattering at elevated energies where the elastic scattering cross-section
is non-Rutherford and consequently has to be determined through measurements and evaluation. A procedure
applied in order to obtain an evaluated differential Si( 4 He, 4 He)Si cross-section resembled a standard
approach in all respects save one. Generally established steps starting from a compilation of relevant experimental
data followed by their examination and critical selection were made. The R-matrix theory was
employed in order to calculate the Si( 4 He, 4 He)Si cross sections. In the calculations the phases obtained
in the frameworks of the optical model with Saxon-Woods real potential well and a surface absorption
were taken instead of hard sphere ones in order to take into account broad single particle resonances. The
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