Design of a neutron calibration source for the SNO+ experiment

Abstract

SNO+ is a multipurpose detector situated at the SNOLAB facility located at Creighton mine 2 km deep. The SNO+ experiment will have three phases: water, pure scintillator and Te-loaded scintillator. With the detector filled with scintillator, solar neutrinos, geo and reactor anti-neutrinos, and supernova neutrinos can be studied. To analyze the data collected by the detector, it is important to have detailed knowledge of the detector response. This is why calibration is a crucial part of the experiment. The detector response to neutrons will allow us to study the anti-neutrino flux coming from reactors in Canada. Anti-neutrinos can be detected via the inverse beta decay reaction which can be tagged using the neutrons it produces. This thesis will discuss the radioactive calibration source Americium Beryllium (AmBe) which produces neutrons and gammas. The existing AmBe source - inherited from the SNO experiment - that will be used in water phase has to be modified for the scintillator and loaded scintillator phases. Simulations were carried out to determine the optimal additional shielding required for the scintillator phase. The optimal shielding was determined to be 2 mm of lead surrounded by 1 mm of stainless steel for the encapsulation. The new design for the AmBe source was finalised. The estimated neutron capture event detection efficiency is 74.22%. The analysis of the source deployment at various positions within the detector and the shadowing effects are discussed as well.