Seminar (セミナー)2022.9.1 Jon Kristian Dahl (Oslo Univ.)

The following seminar will be given by Jon Kristian Dahl (Oslo University, Norway), who is visiting our group in Aug. 29-Sep.2, 2022.

Title: Investigating the low energy enhancement of scandium-44, vanadium-50, and vanadium-51 with large-scale shell model calculations
Date/Place: 11:00-12:00, Sep. 1st, 2022  /  Workshop room, CCS 1F
Abstract: We live in a time where computational power is growing rapidly and is widely accessible. Large-scale shell model (LSSM) calculations are computationally heavy and benefit greatly of today’s supercomputers, making calculations which were not possible just a few years ago feasible today. Shell model calculations have historically been used to calculate the few lowest lying energy levels of nuclei, but with today’s computing power we are able to calculate thousands of energy levels and millions of transitions between the levels, opening doors to new and improved statistical analyses of LSSM calculations.
The low energy enhancement (LEE) is a feature of the gamma strength function (GSF) which was experimentally discovered by Emel Tavucku in 2002. Tavucku found that the GSFs of iron-56 and iron-57 had unexpected enhancements at the lowest gamma energies, which means that their probability of decaying as a function of gamma energy increases as the gamma energy approaches zero. The LEE has since been found in many other nuclei. It’s discovery came as a great surprise because it did not fit with any of the current models. With today’s computing power, LSSM calculations help us understand the origin of the LEE and may give important insight to the consequences of having an increased probability of decay by low energy gamma rays.
In this presentation, the GSFs of scandium-44, vanadium-50, and vanadium-51 from LSSM calculations will be discussed, with an emphasis on the LEE. The LSSM calculations were performed with the code “KSHELL”, and they will be compared to experimental data obtained with the Oslo method at the Oslo Cyclotron Laboratory. A short introduction to the generalized Brink-Axel (gBA) hypothesis will be presented, as well as a statistical approach of analysing the gBA hypothesis with the Porter-Thomas distribution.