Study of 32Si background for CDMS II and neutron detector for dark matter search experiments

Abstract

The nature of dark matter is an open question in the area of astroparticle physics. The Super Cryogenic Dark Matter Search (SuperCDMS) is one of the leading direct low-mass dark matter search experiments in the world. The CDMS experiment looks for elastic scattering of dark matter with the detector material. These detectors measure charge and phonon signals from the interaction of dark matter with the detectors. Due to very low dark matter-nucleon interaction cross-section and the nuclear recoil energy (∼ few keV), identifying dark matter detection becomes very challenging. To detect this rare and weak signal, a rigorous understanding of backgrounds is essential. 32Si is an isotope that exists in the Si detectors right from the time of its fabrication. 32Si shows beta decay, which will be the dominant source of background in the future based experiment that employs silicon detectors. The first part of this thesis describes the analysis procedures to estimate 32Si background activity. The second part of this thesis is focused on the study of the neutron detector as a neutron is another major background in dark matter search experiments. A liquid organic scintillator detector is used for neutron studies at NISER. To characterize the detector, various gamma sources are used along with 241Am-9Be neutron source. To obtain the unfolded neutron spectrum in neutron recoil energy scale, a simulation study is needed due to unavailability of the monoenergetic neutron source. GEANT4 toolkit has been used for this purpose. Gaussian broadening is used to determine the detector resolution, which can be used further to unfold the neutron spectrum in future .