Neutron capture cross sections and strength functions on 147 Sm

Cross sections and strength functions in neutron induced reactions on 147 Sm nucleus from slow neutrons up to 15-20 MeV's were evaluated. The neutron resonance parameters, transmission coefficients and the Hauser – Feshbach formalism were included in the calculations. In the MeV's region theoretical evaluations are performed by using Talys free software and author's computer programs. The obtained cross sections and strength functions are compared with experimental data in order to explain possible non-statistical effects reported previously by some authors on the alpha widths distributions. 1 Introduction Cross sections, asymmetry effects and strength functions at the EG-5 and IREN basic facilities of FLNP-JINR by using a double gridded ionization chamber were regularly measured in the last decade. By recent measurements cross sections for 5 and 6 MeV of 147 Sm (n,α) reaction were obtained. Because the values of the cross sections are very low (hundreds of microbarns) their measurements are very difficult. The cross sections experimental data are very well described by the theoretical model evaluations performed in this study [1,2]. Capture processes of neutrons with emission of charged particles, starting from thermal region up to 14 MeV, on 147 Sm, were analyzed. Cross sections for (n,α) reactions, from slow neutrons up to some MeV's, in the frame of Hauser – Feshbach formalism (HFF), were evaluated using computer codes realized by authors [3]. The main element of HFF is represented by the transmission coefficients for incident and emergent channels. Transmission coefficients were calculated by applying a quantum-mechanical approach based on reflection factor [3,4]. Starting from 0.5 MeV up to 14 MeV, a separation in the contribution of different nuclear reaction mechanisms related to discrete and continuum states were realized with the help of Talys computer codes. It was demonstrated that the main contribution to the cross sections is given by compound nucleus processes followed by direct processes. Also, nuclear data as parameters of optical potential, nuclear states densities and other were extracted. The computed cross sections and strength functions are compared with experimental data in order to explain possible nonstatistical effects reported previously by some authors on the distributions of alpha widths. 2 Theory and codes Compound processes can be described in the frame of the statistical model of nuclear reactions. Main assumptions of statistical approach are: a) by interaction of incident particle with target nucleus a compound nucleus (CN) is formed; b) CN time of life is much larger than the time necessary to incident particle to pass the target nucleus; c) CN decays on one possible channels and " forget " how it was formed (Bohr hypothesis); d) CN and residual nucleus are characterized by a great number of