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. 2021 Jul 5;14(13):3757.
doi: 10.3390/ma14133757.

Hybrid Ultra-Low-Radioactive Material for Protecting Dark Matter Detector from Background Neutrons

Marina Zykova  1 , Mikhail Grishechkin  1 , Andrew Khomyakov  1 , Elena Mozhevitina  1 , Roman Avetisov  1 , Nadezda Surikova  2 , Maxim Gromov  2   3 , Alexander Chepurnov  2 , Ivan Nikulin  4 , Igor Avetissov  1
Affiliations

Hybrid Ultra-Low-Radioactive Material for Protecting Dark Matter Detector from Background Neutrons

Marina Zykova et al. Materials (Basel). .

Abstract

A laboratory technology for a new ultra-low background hybrid material (HM) which meets the requirements for neutron absorption with simultaneous neutron detection has been developed. The technology and hybrid material can be useful for future low background underground detectors designed to directly search for dark matter with liquid noble gases. The HM is based on a polymethylmethacrylate (PMMA) polymer matrix in which gadolinium nuclei are homogeneously distributed up to 1.5 wt% concentration in polymer slabs of 5 cm thickness. To determine the 65 impurity elements by the inductively coupled plasma mass-spectrometry (ICP-MS) technique in the Gd-based preparations in 100-0.01 ppb range, the corresponding method has been developed. Limits of determination (LD) of 0.011 ppb for uranium, and 0.016 ppb for thorium were achieved. An analysis of Gd raw materials showed that the lowest contents of U and Th (1.2-0.2 ppb) were detected in commercial Gd-based preparations. They were manufactured either from secondary raw materials (extraction phosphoric acid) or from mineral raw materials formed in sedimentary rocks (phosphogypsum). To produce the Gd-doped HM the commercial GdCl3 was purified and used for synthesis of low-background coordination compound, namely, acetylacetonate gadolinium (Gd(acac)3) with U/Th contents less than LD. When dissolving Gd(acac)3 in methylmethacrylate, the true solution was obtained and its further thermal polymerization allowed fabrication of the Gd-doped PMMA with ultra-low background.

Keywords: dark matter; gadolinium; hybrid material; inductively coupled plasma mass spectrometry; low-radioactivity; neutron background; polymethylmethacrylate; thorium; uranium.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Mass spectra of the sample with a Gd concentration of 0.001 wt% obtained in different modes: (a) standard; (b) KED for m/z 168–177; (c) standard; (d) KED for m/z 192–200.
Figure 2
Figure 2
The determined concentration of thorium and uranium in commercial Gd-based preparations.
Figure 3
Figure 3
The impurity composition of gadolinium-based preparations of various manufacturers according to the results of ICP-MS analysis: (a) Gd2O3, American Elements; (b) Gd2O3, Party No. 1 (2018) Yeemeida Technology Co. Ltd.; (c) Gd2O3, Stanford Advanced Materials; (d) Gd2O3, Party No. 2 (2019) Yeemeida Technology Co. Ltd.; (e) Gd2O3 IoLiTec (20–80 nm); (f) Gd2O3, FSUE “IREA”; (g) Gd(NO3)3, FSUE “IREA”; (h) Gd2O3, “LANHIT” Ltd.; (i) GdCl3, “LANHIT” Ltd.; (j) Gd2O3 Shin ETSU (Japan). The empty bars show the limits of determination of the elements.
Figure 4
Figure 4
Setup for chlorination of powder preparations: 1—Drexel vessel; 2—quartz-glass reactor valve; 3—outlet pipe system with fungal seal; 4—glassy carbon container for GdCl3; 5—glassy carbon container for NH4Cl; 6—double zone resistive furnace with cerablanket thermoinsulation; 7—inlet pipe system with fungal seal; 8—capillary tube connector for gas inject; 9—dual channel temperature controller; 10 and 11—mass flow controller; 12—control block for mass flow controllers; 13—HCl cylinder; 14—argon cylinder.
Figure 5
Figure 5
The impurity composition of Gd-05 (a), Gd-06 (b) GdCl3 preparations and PMMA of various manufacturers (c) Voxeljet AG, (Germany); (d) RND Polymer (Russia) measured by ICP-MS. The empty bars present the limits of determination of the corresponding elements.
Figure 6
Figure 6
The determined concentration of thorium and uranium in commercial polymers. The empty cubes correspond to the limits of determination.
Figure 7
Figure 7
IR absorption spectra of Gd(acac)3 preparations after stepwise annealing (ID samples see in Table 7).
Figure 8
Figure 8
Gd distribution along the HM width determined by EDAX analysis.
Figure 9
Figure 9
Stress–strain test of nominally pure PMMA and Gd-doped PMMA (HM-03) at room (a) and liquid nitrogen (b) temperatures.
See this image and copyright information in PMC

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