There are many ways how an atomic nucleus can form excited quantum states when we increase its energy. It is for example possible to excite an individual proton or neutron to a higher orbital. We call this a single-particle excitation. It is also possible to excite the nucleus as a whole, for example by making the protons and neutrons vibrate. If the mass distribution of a nucleus is not spherical but deformed, it is also possible to make it rotate. We call vibrations and rotations of a nucleus collective excitations. To understand the nature of excited states, whether they are based on collective or single-particle excitations, tells us a lot about the forces between the protons and neutrons in the nucleus.
Collective states have shorter lifetimes than single-particle states because gamma-ray transitions between collective states are much more likely. Measuring the lifetime of excited states gives us therefore important information about the nature of the excitation and for example the underlying shape of the nucleus. There is only one problem: Lifetimes of excited states are typically very short in the range of picoseconds (10e-12 s), and such short time intervals are not easy to measure. Here is how we do it: When we produce excited nuclei in accelerator experiments, they move with high velocity. Gamma rays are therefore shifted in energy by the Doppler effect. If we manage to slow the nuclei down over the course of a few micrometers, we change the energy of the gamma rays over the time span of a few picoseconds. We can then measure the lifetime of excited states by measuring the energy of gamma rays as a function of the distance that the nucleus has traveled.
If you choose this topic for your master project, you will be involved in experiments at international accelerator laboratories. You will analyze data from such experiments, which involves writing code to correlate the signals from various types of detectors and separate the interesting signals from a large amount of background. At the end, you will compare the experimental lifetimes with theoretical calculations to interpret the results and learn more about the nature of the excited states. Such results will also be used to test and improve theoretical models of atomic nuclei. Depending on your interests, we can emphasize the experimental, theoretical, or computational aspects of the project.