Browsing by Author "Slavkovska, Z"

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    Radio-impurity measurements for a dark matter dodium Iidide detector
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Dastgiri, F; Slavkovska, Z; Froehlich, MB; Hotchkis, MAC; Koll, D; Merchel, S; Pavetich, S; Sims, SG; Fifield, LK; Wallner, A
    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.
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    Time-resolved interstellar Pu-244 and Fe-60 Ppofiles in a Be- 10 dated ferromanganese crust
    (Australian Nuclear Science and Technology Organisation, 2021-11) Koll, D; Wallner, A; Hotchkis, MAC; Child, DP; Fifield, LK; Froehlich, MB; Harnett, M; Lachner, J; Merchel, S; Pavetich, S; Rugel, G; Slavkovska, Z; Tims, SG
    More than 20 years have passed since the first attempts to find live supernova Fe-60 (t1/2 = 2.6 Myr) in a deep-sea ferromanganese crust [1]. Within these 20 years, strong evidence was presented for a global influx of supernova dust into several geological samples around 2 Myr ago. Recently, a much younger continuous influx was found in Antarctic snow and in deep-sea sediments [2-4] and an older peak around 7 Myr in deep-sea crusts [5,6]. The long-lived isotope Pu-244 (t1/2 = 80 Myr) is produced in the astrophysical r-process similarly to most of the heaviest elements. Although the production mechanism is believed to be understood, the astrophysical site is heavily disputed. Most likely scenarios involve a combination of rare supernovae and neutron star mergers. The search for Pu-244 signatures in samples with known Fe-60 signatures allows to test for either common influx patterns or independent Pu-244 influxes disentangled from stellar Fe-60. Accordingly, this information provides a unique and direct experimental approach for identifying the production site of the heavy elements. Very recently and first reported in the AMS-14 conference, the first detection of interstellar Pu-244 was published [6]. This was only feasible by achieving the highest detection efficiencies for plutonium in AMS ever reported [7]. The achieved time resolution of 4.5 Myr integrates over the supernova influxes and is therefore not high enough to unequivocally show a correlated influx pattern of Fe-60 and Pu-244. Based on this progress, we are now aiming to measure highly time-resolved profiles of Fe-60 and Pu-244 in the largest ferromanganese crust used so far. Results on the characterization of the crust including cosmogenic Be-10 (t1/2 = 1.4 Myr) dating and a 10 Myr profile of interstellar Fe-60 including the confirmation of the 7 Myr influx will be presented along with first data on interstellar Pu-244.