Radio-impurity measurements for a dark matter dodium Iidide detector
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Date
2021-11-17
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Nuclear Science and Technology Organisation
Abstract
The first dark matter detector is being built in the Stawell gold mine in south-eastern Australia, as
the southern hemisphere arm of an international collaboration SABRE (Sodium Iodide with Active
Background Rejection). This experiment employs ultra-low background sodium iodide (NaI)
detectors placed in highly shielded vessels across both hemispheres. The aim is to confirm or refute
annual modulation claims attributed to dark matter particles by the DAMA/LIBRA collaboration at
the Laboratori Nazionali del Gran Sasso in Italy. This requires the lowest possible concentration of
radio-contaminants that can be achieved, to minimise the potential for radiation signals that can
mimic dark matter particles signals.
We report on the techniques employed for the detection of potentially problematic contaminants in
the NaI material from which the crystals will be grown. We focus on the establishment of the
measurement techniques of ⁴ ⁰ K and ²¹⁰ Pb at the Australian National University and ANSTO.
For the measurement of ⁴ ⁰ K, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used
to measure the concentration of ³⁹ K, and from the well-known natural abundance ratios of
³⁹ K/⁴ ⁰ K, the concentration of ⁴ ⁰ K was inferred. The challenges associated with measuring ultraprecise
levels of ³⁹ K, and the techniques of minimising the introduction of potassium in the sample
preparation will be discussed.
210-Lead was measured using AMS. The ²¹⁰ Pb concentration in the NaI powder is very low, which
necessitates that large amounts (~ 1kg) of the powder need to be processed to result in sufficient
atoms for an AMS measurement. This low concentration requires the additions of a Pb-carrier (~
1mg), which itself needs to contain minimal ²¹⁰ Pb. Several lead materials have been investigated
and will be reported. In addition, we will discuss the different lead compounds and cathode
materials used to optimise the beam current and minimise the background.
Other contaminants of potential interest such as ³H, ²³²Th and ²³⁸ U; especially those identified in
DAMA/LIBRA and other NaI detectors will be presented.
Description
Keywords
Nonluminous matter, Universe, Mines, Underground facilities, Australia, Sodium iodides, Particles, Modulation, Crystals
Citation
Dastgiri, F., Slavkovska, Z., Froehlich, M. B., Hotchkis, M. A. C., Koll. D., Merchel, S., Pavetich, S., Tims, S. G., Fifield, K., & Wallner, A. (2021). Radio-impurity measurements for a dark matter dodium Iidide detector. Paper presented to the 15th International Conference on Accelerator Mass Spectrometry. ANSTO Sydney, Australia. November 15th – 19th, 2021. (pp. 150). Retrieved from: https://ams15sydney.com/wp-content/uploads/2021/11/AMS-15-Full-Program-and-Abstract-Book-R-1.pdf