Experimental Determination of Cross Sections for (n,x) Nuclear Reactions

The neutron-activation method was used for obtaining new experimental data on cross sections both for Ge(n,2n)Ge nuclear reaction and for some other (n,x) reactions on zirconium and germanium isotopes. The neutron generator was used as a neutron source. The samples in a shape of foils of natural germanium and zirconium were irradiated by DTneutrons. The following sources of uncertainties are taken into account: instability of neutron flux in time, real geometry of experiment, the effect of true coincident summing of gamma-rays during activation product spectrum measurements and the effect of self-absorption of gamma-rays in a sample. The obtained results could be useful to avoid ambiguity in values of cross sections for nuclear reactions specified and to indicate the necessity of additional experiments for reduction the cross section uncertainty. Monte Carlo simulations were used in calculations of correction factors. Introduction Precise determination of nuclear reaction cross sections and investigations of interaction between neutrons and atomic nuclei have taken prevalent place in modern neutron physics. Requirements of neutron cross sections with high accuracy depend on amount of nuclear data practical applications such as: astrophysics, transmutation of radioactive waste, radiation medicine and fusion technology studies as well. Notwithstanding the fact that in the world there are exists many bases of experimental and evaluated nuclear data, but they are still incomplete and essential discrepancy at the energy range about 14 MeV observed between results obtained by others authors [1]. Moreover a discrepancy between existing results leads to errors during interpolation of experimental data and has action upon the quality of estimated data. Neutron cross sections are important for development of fusion reactor technology in the view of activation, radiation-damage and mechanical stability of construction materials as well as radiation protection etc. Furthermore, measurements of nuclear reaction cross sections in this energy range are important for testing of nuclear reaction models. Germanium and zirconium elements were selected because of significant role in nuclear spectroscopy measurements and nuclear reactor building respectively. One of the considered reactions is Ge(n,2n)Ge was chosen due to lack of such information in experimental nuclear data base [2]. Experimental method Experimental measurements have been performed at the Nuclear Physics Department of Taras Shevchenko National University of Kyiv. Activation cross section measurements were curried out using a conventional, widely used scheme: irradiation – cooling – gamma-rays counting [3]. Germanium and zirconium samples of natural composition in the shape of foil were irradiated by D-T neutrons. The neutron generator NG-300/15 was used as a source of fast neutrons. It was made two series of experimental measurements. Cross sections of Zr(n,p)Y, Zr(n,p)Y nuclear reactions were measured in the first experiment and cross sections of Ge(n,2n)Ge, Ge(n,p)Ga for 14.5 MeV neutron energy were measured in second experiment. Neutrons with energy ∼ 14 MeV are generated by T(d, n)He reaction. The maximum current of ions beam was 10 mA. For this purpose a molecular component of deuteron beam has been used. A diaphragm, which gave an opportunity of getting beam diameter 10 mm, has been used to decrease disperse of neutron energy in ion-pipe that allows to use different parts of sample after every irradiated series. Location of deuteron beam axis was defined from distribution of neutron flux density on the target by method of foil activation. 2 D + WDS'07 Proceedings of Contributed Papers, Part III, 188–192, 2007. ISBN 978-80-7378-025-8 © MATFYZPRESS