Study of the response of PICASSO bubble detectors to neutron irradiation

The objective of this work was to simulate the PICASSO experiment and to study the detector response to neutron irradiation. The results of the simulation show the rock neutron rate to be 1-2 neutrons/day for the setup used until 2009 and less than 0.1 neutrons/day for the setup used after 2010. The shielding efficiency was calculated to be 98% and 99.6% for the two setups respectively. The detector response to an AmBe source was simulated. Neutron rates differ for two AmBe source spectra from the literature. The observed data rate is in agreement with the rate from the simulation. The detector stability was examined and found to be stable. The source position and orientation affect the detector efficiency creating a systematic uncertainity on the order of 10-35%. This uncertainity was eliminated with a source holder. The localisation of recorded events inside the detector and the simulated neutron distribution agree.