Search for isospin effects on nuclear level density

A. Brondi¹, A. Di Nitto¹, G. La Rana^1a, R. Moro¹, P.N. Nadotchy², E. Vardaci¹, A. Ordine¹, A. Boiano¹, M. Cinausero³, G. Prete³, V. Rizzi³, N. Gelli⁴ and F. Lucarelli⁴

¹ Istituto Nazionale di Fisica Nucleare and Dipartimento di Scienze Fisiche, Universitá di Napoli ”Federico II”, Via Cinthia, 80126 Napoli, Italy
² Istituto Nazionale di Fisica Nucleare, Via Cinthia, 80126 Napoli, Italy
³ Laboratori Nazionali di Legnaro dell’Istituto Nazionale di Fisica Nucleare, Legnaro (Padova), Italy
⁴ Istituto Nazionale di Fisica Nucleare and Dipartimento di Fisica, Firenze, Italy

^a e-mail: giovanni.larana@na.infn.it

Abstract

Studies on the isospin dependence of the level density have been recently reported in the literature for nuclei with 20 ≤ A ≤ 110. Corrections to the level density have been deduced which would imply a significant reduction of this quantity for nuclei far from the valley of stability. Isospin effects on the level density are also expected through the symmetry energy contribution to the nuclear masses, which is predicted to increase with the temperature. According to these findings, we have implemented the statistical model in order to account for isospin effects on the level density parameter a and on the temperature-dependent symmetry energy. We present the results of calculations for the decay of a variety of neutron-rich composite systems. We found that isospin produces sizable eïňĂects on difierent observables, this result being promising for future experiments with the second generation RIB facilities SPES and SPIRAL2. We report the results of a first experiment aimed at searching for isospin effects in the decay of 139 Eu composite nuclei produced by a stable beam at E x =90 MeV.