Formation of high-spin neodymium and mercury isomers in neutron and charged particle induced nuclear reactions

Abstract

The isomeric pairs 195m,g Hg, 197m,g Hg, 139m,g Nd and 141m,g Nd constitute interesting cases since the ground state has a low spin and the isomeric state a relatively high spin. Their formation was studied in several reactions induced by n, p, 3 He, and α-particles. The four projectiles were produced at the Jvariable-energy compact cyclotron (CV 28); for neutron production the 2 H(d,n) 3 He reaction was used. The cross sections were measured by the activation technique. From the available experimental data, isomeric cross-section ratios were determined. Nuclear model calculations using the code STAPRE, which employs the Hauser-Feshbach and exciton model formalisms, were undertaken to describe the formation of both the isomeric and the ground states of the products. The calculations were compared with the results of the EMPIRE-II code. The total reaction cross section of a particular channel is reproduced fairly well by the model calculations, with STAPRE giving slightly better results. Regarding the isomeric cross sections, the agreement between the experiment and theory is only in approximate terms. A description of the isomeric cross-section ratio by the model was possible only with a very low value of η (η = Θeff/Θrig) for the mercury isotopes, while slightly larger η values were needed for neodymium isotopes. An exponential mass dependence of η is proposed.