Do light nuclei display a universal γ-ray strength function?

¹ Department of Physics, University of Oslo, N-0316 Oslo, Norway
² Institute of Nuclear Physics, NCSR "Demokritos", Athens, Greece
³ Institute of Nuclear Physics PAN, Kraków, Poland
⁴ Institute of Particle and Nuclear Physics, Charles University, Prague, Czech Republic
⁵ Department of Physics, Åbo Akademi University, FIN-20500 Åbo, Finland
⁶ Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA

^a e-mail: magne.guttormsen@fys.uio.no

Abstract

In this work we focus on properties in the quasi-continuum of light nuclei. Generally, both level density and γ-ray strength function (γ-SF) differ from nucleus to nucleus. In order to investigate this closer, we have performed particle-γ coincidences using the reactions (p, p'), (p, d) and (p, t) on a ⁴⁶Ti target. In particular, the very rich data set of the ⁴⁶Ti(p, p')⁴⁶Ti inelastic scattering reaction allows analysis of the coincidence data for many independent data sets. Using the Oslo method, we find one common level density for all data sets. If transitions to well-separated low-energy levels are included, the deduced γ-SF may change by a factor of 2 – 3, due strong to Porter-Thomas fluctuations. However, a universal γ-SF with small fluctuations is found provided that only excitation energies above 3 MeV are taken into account. The nuclear structure of the titaniums is discussed within a combinatorial quasi-particle model, showing that only few Nilsson orbitals participate in building up the level density for these light nuclei.