Reactions with relativistic radioactive beams and gamma multiplicities

Licentiate thesis, 2016

Experiments with relativistic radioactive beams are used to study the properties of exotic nuclei. The experimental setup used in this thesis is a complex system of detectors for identifying and measuring the 4-momenta of all incoming nuclei and products created when the nuclei impinge on a reaction target. The high spatial resolution of the tracking detectors makes it impossible to align all the detectors with sufficient mechanical precision. Instead the measured tracks are used to calculate the exact detector positions during the data analysis. In this thesis a simplified and improved method is presented for the detector alignment. In the target different types of reactions can take place. The reactions of most interest in this thesis are fragmentation and knockout reactions. In these reactions nucleons are removed from the nuclei, creating new isotopes which typically are in their excited state. If the excitation energy is lower than the particle emission threshold, the excitation energy is emitted as gamma radiation. The gamma multiplicity gives information about the excited states populated and the reaction mechanism. In this thesis radioactive beams ranging from proton-rich Li to neutron-rich F isotopes have been created and studied. The wide range of isotopes offers the possibility to compare the gamma multiplicities between different reaction channels and the different isotopes. The analysis showed that the background contribution to the gamma multiplicity was too large to obtain any reliable results. Different approaches of reducing the background and possible explanations of the large contributions are discussed in the thesis.