After a heavy nucleus fissions, the resulting fission fragments are left in a highly excited state and will then de-excite by emitting neutrons and gamma rays. The gamma rays are called prompt fission gamma rays (PFGs) as they arrive promptly after the moment of fission. These PFGs carry information about the excitation energy and angular momentum of the fragments right after fission.
If we change the mass and energy of the fissioning nucleus, how does this affect the emitted gamma rays? Two possible master projects are outlined below. They are especially suited if you want to work on new and exciting experimental data from accelerator laboratories, if you want to do numerical simulations using state-of-the-art models, and if you are interested in better understanding the fission process!
1. Excitation-energy dependent prompt gamma-ray emission from the fission fragments
In this project, we study what happens to the PFGs as the excitation energy of the fissioning nucleus changes - if we give the fissioning nucleus more energy, will that result in more PFGs being emitted? This is important both for understanding how energy is shared in the fission process, as well as nuclear reactor applications where it is important to determine if the next generation of fast reactors will experience increased gamma-ray heating.
In this project, you will be a part of running a fission experiment and then analyze the data to see what they say about how the PFGs depend on excitation energy. You will also perform simulations using a computational fission model to calculate the expected behavior, and then compare the simulation to the experimental measurements. This will test if the physics implemented in the model is right.
2. Angular momentum generation in fission
The fission fragments are known to spin after the moment of fission, i.e. they have angular momentum. This happens even when the fissioning nucleus has no angular momentum, indicating that the angular momentum must somehow be generated in the fission process. An intriguing question is therefore: How is this angular momentum generated, and which aspects of fission will impact this generation?
The population of long-lived excited states (isomers) in the fission fragments is sensitive to the angular momentum of the fragment. We can get information about the angular momentum of the fragment if we determine how often an isomer is populated compared to the ground state, a quantity we call isomeric yield ratio (IYR). In this project, you will extract the IYR of fission fragments from experimental data using a newly developed technique. Varying the mass and excitation energy of the fissioning nucleus will provide insight into the angular momentum generation in fission. You will also perform simulations with computational fission model and compare the results with the experimental data.