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In this paper, we demonstrate the use of physical models to evaluate the production of $^{39}$Ar and $^{40}$Ar underground. Considering both cosmogenic $^{39}$Ar production and radiogenic $^{40}$Ar production in situ and from external sources, we can derive the ratio of $^{39}$Ar to $^{40}$Ar in underground sources. We show for the first time that the $^{39}$Ar production underground is dominated by stopping negative muon capture on $^{39}$K and ($alpha,n)$ induced subsequent $^{39}$K(n,p)$^{39}$Ar reactions. The production of $^{39}$Ar is shown as a function of depth. We demonstrate that argon depleted in $^{39}$Ar can be obtained only if the depth of the underground resources is greater than 500 m.w.e. below the surface. Stopping negative muon capture on $^{39}$K dominates over radiogenic production at depths of less than 2000 m.w.e., and that production by muon-induced neutrons is subdominant at any depth. The depletion factor depends strongly on both radioactivity level and potassium content in the rock. We measure the radioactivity concentration and potassium concentration in the rock for a potential site of an underground argon source in South Dakota. Depending on the probability of $^{39}$Ar and $^{40}$Ar produced underground being dissolved in the water, the upper limit of the concentration of $^{39}$Ar in the underground water at this site is estimated to be in a range of a factor of 1.6 to 155 less than the $^{39}$Ar concentration in the atmosphere. The calculation tools presented in this paper are also critical to the dating method with $^{39}$Ar.
Energy resolution, alpha/beta ratio, and the pulse shape discrimination ability of the ZnWO_4 crystal scintillators were studied. The radioactive contamination of a ZnWO_4 crystal was investigated in the Solotvina Underground Laboratory. Possibilitie
The discovery of argon from underground sources with significantly less 39Ar than atmospheric argon was an important step in the development of direct-detection dark matter experiments using argon as the active target. We report on the design and ope
Several experiments have been conducted in the YangYang Underground Laboratory in the Republic of Korea such as the search for dark matter and the search for neutrinoless double-beta decay, which require an extremely low background event rate due to
One IGEX 76Ge double-beta decay detector is currently operating in the Canfranc Underground Laboratory in a search for dark matter WIMPs, through the Ge nuclear recoil produced by the WIMP elastic scattering. A new exclusion plot has been derived for
The LUNA (Laboratory Underground for Nuclear Astrophysics) facility has been designed to study nuclear reactions of astrophysical interest. It is located deep underground in the Gran Sasso National Laboratory, Italy. Two electrostatic accelerators, w