Nuclear Structure and Dynamics in the Quasi-Continuum of ²⁴⁰Pu

Abstract

Nuclear level densities and γ-ray strength functions are essential quantities in various fields of basic and applied research involving nuclear matter. From microscopic calculations and structure research to nuclear reactor models and astrophysical applications a good knowledge of these parameters determines fundamental properties of the systems. This study analyses the level density and strength function of ²⁴⁰Pu below the particle separation threshold with the Oslo Method. The results are used to examine the effect on the fast neutron capture cross-section of ²³⁹Pu. At the Oslo Cyclotron Laboratory a ²³⁹Pu target was bombarded with a 12 MeV deuteron beam to study (d,pγ) reactions in the quasi-continuum of ²⁴⁰Pu. The particle-γ coincidences were used to obtain the primary γ-rays and extract level density and γ-ray strength function of ²⁴⁰Pu using the Oslo Method. This new experimental data reveals an increase in the γ-ray strength function on the tail of the Giant Electric Dipole Resonance, which is interpreted as a low-energy M1 scissor mode. The B(M1) strength of this resonance between about 2-4 MeV has been estimated and is compared to previous findings in the actinide region. %and it is similar to previous analyses of actinide nuclei using the Oslo method. Furthermore, these results were used to calculate the (n,γ) cross-sections for ²³⁹Pu with the TALYS reaction code. This provides predictions for neutron energy regions where previously no experimental data was available and may have a significant impact on calculations for next generation reactors.