The lifetimes of excited quantum states in the atomic nucleus give extremely important information about nuclear structure and the shape of the nucleus. For lifetimes in the picosecond regime, measurements are based on a detailed analysis of gamma-ray line shapes, which are affected by changing Doppler shifts as the decaying nucleus slows down in a solid target. In effect, the stopping of the ion in a solid becomes the clock to measure the nuclear decay rate. An example of a Doppler broadened line shape, the fit and extracted lifetime is shown in the figure.
The specific problem this project will address is that recent lifetimes measured by this Doppler Broadened Line Shape (DBLS) method disagree with those determined by other methods, particularly for the semi-magic isotopes of Ni. There are two likely reasons for the discrepancy. In the first place, the stopping powers that determine the rate of slowing of the Ni nuclei in the host material could be incorrect. Secondly, it is possible that the reaction kinematics were not treated with sufficient accuracy in the computer code used to analyse the data. Along with solving this specific puzzle, this project aims to build an up-dated computer code for Doppler Broadened Line Shape analysis, that includes general options for the type of nuclear reaction used.
As well as helping achieve the aims of the project, students can gain accelerator-based laboratory experience and develop skills in scientific programming.