Untersuchung von (n, 2n) anregungsfunktionen

Abstract

Investigation of (n, 2n) excitation-functions. The activation method was used to measure (n, 2n) excitation-functions in the energy region 12.6–19.6 MeV for 52Cr, 75As, 85Rb, 106Cd, 112Sn, 121Sb, 140Ce, 142Ce, 141Pr, 144Sm, 165Ho and 181Ta. Further isomeric (n, 2n) cross-section ratios were obtained for 85Rb and 121Sb in the energy region stated above and for 123Sb and 144Sm at 14.1 MeV. The total (n, 2n) excitation-functions were compared with results from statistical theory calculations using optical model absorption cross sections and the Fermi-gas model nuclear level density ω(E) = C(E+t) −2 exp(2(aE) 1 2 ) . Particularly at lower excitation energies (near reaction thresholds) better agreement between theoretical and experimental cross sections has been obtained when the pairing effect in the level density was accounted for by using appropriate values for the factor C according to Brown and Muirhead instead of shifting the nuclear ground state by the pairing energy δ as usually is done in the literature. In most cases good agreement has been obtained with level density coefficients a from Abdelmalek and Stavinsky. From the isomeric cross section ratios spin cut-off factors σ were deduced applying the theory of Vandenbosch and Huizenga. These values of σ lead to moments of inertia for the nuclei considered which only amount to 20–50% of the rigid body values.