[en] A search for the 0 νββ is one of the most promising ways to clarify the nature and the mass of neutrinos. A high sensitivity to ¹⁰⁰Mo 0νββ search can be achieved by using a CaMoO₄ crystal. We have studied the energy resolution of a small CaMoO₄ crystal coupled with a large area avalanche photo diode(LAAPD) photo sensor recording the full waveform of the signal. The energy resolution for 662 keV gammas measured at low temperature was 4.2 ± 0.2% in standard deviation. The contamination from 2νββ decay events in the 0 νββ search window is studied by using a Monte-Carlo simulation. With the expected energy resolution of 4.5% (FWHM) at 3 MeV and 15 kg year data, we can confirm the claim of m_ββ = 0.32 ± 0.03 eV, even after considering the uncertainties of the nuclear matrix elements from the current theoretical calculations.

[en] The King AbdulAziz City for Science and Technology (KACST) in the Kingdom of Saudi Arabia has a plan to build a 10 MeV, 15kW linear accelerator (LINAC) for electron beam and X-ray, which is to be supplied by EB Tech in Republic of Korea. The design and construction of the accelerator building will be carried out jointly between EB Tech and KACST. Recommendations for the design and installation of radiation shielding for x-ray and gamma-ray can be found in NCRP No. 49(1976) and for accelerators with energies over 10 MeV in NCRP No. 151 (2005). Monte Carlo calculations were conducted using the MCNP6 code to determine photon fluxes and doses at the point detectors locations around the accelerator building. The problem was run as an electron, photon and neutron transport problem to account for all reactions including the (γ,n) reaction. The detectors where the DXTRAN spheres were used are indicated in the table. The computation was continued until electrons reached a total of 1x10"+"8 histories

[en] Low Level Counting techniques using low background facilities are continuously under development to increase the possible sensitivity needed for rare physics events experiments. The CUP (Center for Underground Physics) group of IBS is developing, in collaboration with Canberra, a ultra low background instrument composed of two arrays facing each other with 7 HPGe detectors each. The low radioactive background of each detector has been evaluated and improved by the material selection of the detector components. Samples of all the building materials have been provided by the manufacturer and the contaminations had been measured using an optimized low background 100% HPGe with a dedicated shielding. The evaluation of the intrinsic background has been performed using MonteCarlo simulations and considering the contribution of each material with the measured contamination. To further reduce the background, the instrument will be placed in the new underground laboratory at YangYang exploiting the 700m mountain coverage and radon-free air supplying system. The array has been designed to perform various Ultra Low background measurements; the sensitivity we are expecting will allow not only low level measurements of Ra and Th contaminations in Copper or other usually pure materials, but also the search for rare decays. In particular some possible candidates and configurations to detect the 0νECEC (for example "1"0"6Cd and "1"5"6Dy) and rare β decays ("9"6Zr, "1"8"0"mTa , etc ) are under study

[en] The Center for Underground Physics has developed in collaboration with CANBERRA a low background instrument composed of 14 HPGe detectors divided in two arrays facing each other. The performance and the background of a single detector of the array have been studied in order to improve the array final configuration. An accurate material selection, through the measurements of building material samples and Monte Carlo simulations based on Geant4, has been performed to reach the lowest possible intrinsic background. Alternative materials and configurations have been considered for the final design of the array simulating the expected intrinsic background of the instrument considering the needed changes. The expected sensitivity of the improved array configuration, concerning the low background material selection for rare events physics experiments, has been evaluated through Monte Carlo simulations considering ²³²Th concentration in a Copper sample. Since the array can also be used for rare decays searches, the expected sensitivity on the ¹⁵⁶Dy resonant double electron capture has thus been calculated. (paper)

[en] We measured the thermal neutron capture cross section for the ¹⁸⁰W nucleus. There is only one previous measurement with regard to this cross section, and it yielded a value of 30 -100%+300% b. To determine whether ¹⁸¹W is an appropriate low energy neutrino source, the thermal neutron capture cross section should be measured more precisely to estimate the production rate of ¹⁸¹W inside a nuclear reactor. We measured the cross section of ¹⁸⁰W using a natural tungsten foil and obtained a value of 22.6±1.7 b

[en] Cu-based amorphous (Cu₅₄Zr₂₂Ti₁₈Ni₆) coating was produced through cold spraying as a new fabrication process. The microstructure and macroscopic properties of the amorphous coating layer were investigated and compared with those of the cold-sprayed, pure Cu coating. Amorphous powder was prepared via gas atomization, and Al 6061 was used as the substrate plate. The X-ray diffraction results showed that Cu-based amorphous powder could be successfully deposited through cold spraying sans any crystallization. The Cu-based amorphous coating layer (300-400 μm thick) had 4.87% porosity. The hardness of the Cu-based amorphous coating was 412.8 H_v or 68% of the hardness of the injection-casted bulk amorphous material. The wear resistance of the Cu-based amorphous coating was found to be three times higher than that of the pure Cu coating. The results of the 3-point bending test showed that the adhesion strength of the Cu-based amorphous coating layer was higher than the pure Cu coating. The hard Cu-based amorphous particle was also observed to be able to deform soft substrate easily through particle collisions; thus generating strong adhesion between the coating and substrate. Note, however, that the amorphous coating layer unexpectedly showed lower corrosion resistance than the pure Cu coating, possibly due to the higher porosity of the cold-sprayed amorphous coating.

[en] 180mTa, which is the second excited state of 180Ta at Ex = 77 keV, is naturally occurring and is the only known stable isomer. The half-life of 180mTa is considered to be an important parameter for nuclear synthesis models for heavy elements. However, the decay of 180mTa has never been observed even though several groups tried to measure it. We will search for gamma transitions from 180mTa decays in a tantalum sample by using an array of fourteen HPGe detectors recently installed in an underground laboratory at Yangyang, Korea. In preparation for the measurement, Monte-Carlo simulation studies were conducted to optimize the tantalum sample configuration. Based on the simulation study, we decided on a configuration composed of a 2 mm thick disk with diameter of 200 mm and six 2 mm thick rectangular plates with dimension of 158 × 195 mm2. The finalized tantalum sample configuration gives 2.0 and 7.5 coincidence events per year for the EC and the β-decay of 180mTa, respectively. In this study, we used T1/2 = 2.0 × 1017 years and T1/2 = 5.8 × 1016 years for the EC and β-decay which are the present best lower-limits as reported by B. Lehnert et al.

[en] ^180mTa, which is the second excited state of ¹⁸⁰Ta at E_x = 77 keV, is naturally occurring and is the only known stable isomer. The half-life of ^180mTa is considered to be an important parameter for nuclear synthesis models for heavy elements. However, the decay of ^180mTa has never been observed even though several groups tried to measure it. We will search for gamma transitions from ^180mTa decays in a tantalum sample by using an array of fourteen HPGe detectors recently installed in an underground laboratory at Yangyang, Korea. In preparation for the measurement, Monte-Carlo simulation studies were conducted to optimize the tantalum sample configuration. Based on the simulation study, we decided on a configuration composed of a 2 mm thick disk with diameter of 200 mm and six 2 mm thick rectangular plates with dimension of 158 × 195 mm². The finalized tantalum sample configuration gives 2.0 and 7.5 coincidence events per year for the EC and the β-decay of ^180mTa, respectively. In this study, we used T_1/2 =2.0 × 10¹⁷ years and T_1/2 = 5.8 × 10¹⁶ years for the EC and β-decay which are the present best lower-limits as reported by B. Lehnert et al.

[en] KIMS is a dark matter search experiment using low background CsI(TB) crystals at Yangyang Underground Laboratory in Korea. With a total exposure of 3409 kg·d data, we set a new limit on WIMP-nucleon cross section. We achieved the most stringent limit on the spin-dependent interaction for a pure proton case. We were able to exclude the DAMA signal region for both spin-dependent and spin-independent interaction for the WIMP mass greater than 20 GeV/c². KIMS experiment is upgraded with 12 CsI(TB) crystals corresponding to a total mass of 104 kg and accumulating data since Jan. 2008.

[en] The DAMA experiment has reported an annual-modulation signal in an array of low-background NaI(Tl) scintillating crystals that may be caused by WIMP-nucleon interactions. However, to date there has been no direct confirmation of this result that uses the same taget nuclides. The Korea Invisible Mass Search (KIMS) collaboration has been engaged in an extensive R and D program to grow ultra-low background NaI(Tl) crystals for use as a direct test of the DAMA result using same nuclide targets. Six crystals were grown from different powders in order to understand mechanisms of internal background contaminations and to reduce their effects. Studies of internal backgrounds in these crystals were performed with the ultimate goal of reducing internal background contamination levels to 1 dru at 2 keV. (paper)