When atomic nuclei are excited to high energy, the number of possible quantum states increases exponentially. At some point the density of states becomes so high that we cannot resolve individual states anymore and can only describe average properties. The gamma-strength function (GSF) describes the average probability of a nucleus to emit or absorb gamma rays of a given energy. Besides being important for reaction calculations, the GSF exhibits characteristic features that can be associated with various types of excitations, for example a collective vibration of the protons against the neutrons in the nucleus.
The GSF can be broken down into different multipolarities of the radiation (dipole, quadrupole etc.), which in turn can have either electric or magnetic character. In most cases, electric dipole (E1) radiation is dominating, but some modes of excitation are based on magnetic dipole (M1) excitations. To understand the features in the GSF it is important to determine the multipolarity and electric or magnetic character of the gamma rays.
We are interested in finding out how well the Oslo Scintillator Array (OSCAR) can distinguish M1 from E1 gamma radiation. To find out, we will excite a specific excited state in 6Li in an experiment at the Oslo Cyclotron Laboratory. This state is known to be a source of strong M1 radiation. You will play a leading role in this experiment and be responsible for the data analysis. You will then compare the experimental results with numerical simulations of the detector response using the GEANT4 software toolkit that simulates the interaction of radiation with matter. The goal of the project is to develop a new technique through a combination of calculations, simulations, and data analysis.