Application of zone refining to the development of NaI(Tl) detectors for SABRE North

TL;DR

This paper presents a mathematical model for zone refining of NaI(Tl) powder, aiming to produce ultra-high purity crystals for dark matter detection, and discusses how this model can optimize detector background levels.

Contribution

It introduces a new mathematical model for NaI(Tl) purification via zone refining and compares it with experimental data to improve crystal purity for dark matter experiments.

Findings

Determined distribution coefficients for impurities at ppb levels.

Validated the model against experimental zone refining results.

Provided insights for optimizing crystal purification processes.

Abstract

The SABRE North experiment is developing ultra-high radiopurity NaI(Tl) detectors to investigate dark matter. To achieve this, SABRE North utilizes the technique called zone refining for NaI powder purification. This work details the mathematical model developed to describe the purification process. By comparing this model to the results of the commissioning and production runs conducted prior to crystal growth, the distribution coefficients were determined for various impurities, contained in the powder at the parts-per-billion (ppb) level. Furthermore, the synthesis of data from both zone refining and normal freezing is discussed. These findings can be used to predict the SABRE North detectors background level in the energy region-of-interest for dark matter search and to optimize the production of ultra-high purity crystals through multiple purification strategies.