Developing Ultra-low Background Sodium-Iodide Crystal Detector for Dark Matter Searches

Abstract

Astronomical and cosmological observations have established that dark matter makes

up about a quarter of the Universe. While the majority of underground experiments

have failed to directly detect dark matter in laboratories, DAMA/LIBRA saw an

annual modulation in event rate in an array of high-purity NaI (Tl) scintillation

detectors, a phenomena expected from change in the relative velocity between the

Earth and the dark matter halo as the Earth orbits around the Sun.

SABRE experiment aims to use ultra-high purity NaI (Tl) crystals and an active

liquid scintillator veto to search for the annual modulation with sufficient sensitivity

to confirm or refute the DAMA/LIBRA result. Through many years of R&D, we

have successfully achieved crystal purity that has never been achieved before. We

have also set up a liquid scintillator veto detector at Laboratori Nazionali del Gran

Sasso (LNGS), Italy as part of a prototype detector to demonstrate the performance

of low-background NaI (Tl) crystals.

In this thesis, I will present in detail the key steps and processes required to grow

ultra-high purity NaI (Tl) scintillating scintillator crystals and preparation of SABRE

prototype detector, including assembly of crystal detector module, commissioning of

the veto detector, the trigger and the data acquisition system and a detailed analysis

of projected background.

Although ultra-high purity NaI (Tl) crystals are developed as an essential

component in resolving the annual modulation controversy, the techniques de-

veloped throughout this thesis have general implications for the development of

low-background detectors.