The LUX-ZEPLIN (LZ) radioactivity and cleanliness control programs

LUX-ZEPLIN (LZ) is a second-generation direct dark matter experiment with spin-independent WIMP-nucleon scattering sensitivity above $${1.4 \times 10^{-48}}\, {\hbox {cm}}^{2}$$ 1.4 × 10 - 48 cm 2 for a WIMP mass of $${40}\, \hbox {GeV}/{\hbox {c}}^{2}$$ 40 GeV / c 2 and a $${1000}\, \hbox {days}$$ 1000 days exposure. LZ achieves this sensitivity through a combination of a large $${5.6}\, \hbox {t}$$ 5.6 t fiducial volume, active inner and outer veto systems, and radio-pure construction using materials with inherently low radioactivity content. The LZ collaboration performed an extensive radioassay campaign over a period of six years to inform material selection for construction and provide an input to the experimental background model against which any possible signal excess may be evaluated. The campaign and its results are described in this paper. We present assays of dust and radon daughters depositing on the surface of components as well as cleanliness controls necessary to maintain background expectations through detector construction and assembly. Finally, examples from the campaign to highlight fixed contaminant radioassays for the LZ photomultiplier tubes, quality control and quality assurance procedures through fabrication, radon emanation measurements of major sub-systems, and bespoke detector systems to assay scintillator are presented.

Natural radioactivity content in Italian bottled mineral waters

Bottled water consumption has a long history but nowdays bottled water industry is a fast-growing sector of the world industry. Most of the water in bottles comes from springs or underground aquifers. The mineral content of the aquifer is diluted in small amounts into the water and although consuming mineral water is thought to be a healthy practice, there are several cases where radioactivity is also present. Monitoring the bottled water natural radioactivity is very important especially for the cases people consume mainly this kind of water. Radioactivity accumulation in the human body if exists in excess, can pose a threat for the health. In the present work, thirty brands of Italian bottled water were measured for gross alpha and beta radioactivity, uranium, radium and polonium radioisotopes. Radioactivity content was determined using the LSC method and sorbtion on polyamide pieces covered with thin film of MnO2. The analysis using the MnO2 thin films showed that the radium activity in waters varied from 4.7-69.3 mBqL-1 and the polonium activity varied from 5.9-26.8 mBqL-1. The measurements with the LSC method showed uranium concentrations varying from 0.7- 93.1 mBqL-1, while the radium activities exhibited variations from 1.6-34.1 mBqL-1. Finally the gross beta activity values varied from 13.1-1584.9 mBqL-1 and the gross alpha from 2.4- 305.2 mBqL-1.

Investigation of chemical composition and moisture content for different materials on the attenuation of γ rays

In the present work, materials, namely mud, sand mud, ferruginous sandstone and sandstone with different densities are used to evaluate the effect of chemical composition and moisture content on the self-attenuation coefficient factor at γ-energy range from 59.5 to 1332.5 keV. The results revealed that the attenuation coefficient increases with increasing the moisture content until the material saturate with moisture. The average value of increasing linear attenuation coefficients based on increasing moisture content are 14.3%, 16.0%, 18.2%, 28.1% and 24.8% at γ-energies 59.5, 356.0, 661.7, 1173.4 and 1332.5 keV, respectively. Chemical composition of material affected on the values of attenuation, i.e. the elements with high density have high attenuation coefficient. Significant effect of self-attenuation correction factor was observed at low γ-energies up to 500 KeV. Application of the calculated correction of environmental sample with low radioactivity content has been carried out.