[en] For the study of astrophysically important states in ¹⁸Ne, the ¹⁴O(α, α)¹⁴O cross section was measured in inverse kinematics using a radioactive ¹⁴O beam. This reaction was investigated for properties of resonant states of ¹⁸Ne for determining the ¹⁴O(α, p)¹⁷F reaction rate, which is one of the most important reactions for understanding the breakout mechanism from the Hot CNO cycle to the rp-process. Alpha-induced elastic scattering on ¹⁴O was performed using the low energy radioactive ion (RI) beam separator at the Center for Nuclear Study (CNS) in the RIKEN Accelerator Research Facility. The energy range E_x = 7.2 ∼ 13.1 MeV of ¹⁸Ne was scanned with the thick target method. Recoiled alpha particles were measured with Si dE-E telescopes. Spins and widths of three resonances at E_x = 8.6, 9.22, and 10.06 MeV were calculated using the R-matrix analysis, and a new state of ¹⁸Ne at E_x = 12.0 MeV was found in this experiment.

[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] 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] The Korea Invisible Mass Search (KIMS) experiment presents new limits on the weakly interacting massive particle (WIMP)-nucleon cross section using data from an exposure of 3409 kg·d taken with low-background CsI(Tl) crystals at the Yangyang Underground Laboratory. The most stringent limit on the spin-dependent interaction for a pure proton case is obtained. The DAMA signal region for both spin-independent and spin-dependent interactions for the WIMP masses greater than 20 GeV/c² is excluded by the single experiment with crystal scintillators

[en] Astrophysical stellar reactions at extremely high temperatures involve a variety of problems both in nuclear reactions and nuclear structures. Specifically, the problems in the νpprocess were discussed in this talk based on our recent experimental results with low-energy RI beams and a simulation study. The νp-process is one of the key processes for investigating the mechanism of type II supernovae, and the process could be possibly responsible for 'the excess production' of p-nuclei around mass 90-100. Alpha cluster resonances have been discovered experimentally to play a crucial role for the stellar (α, p) reactions just above the alpha threshold. Neutron induced reactions in the proton-rich nuclear regions in the νp-process are also suggested to play an important role, which involve nuclear structures of high level density at high excitation energies, probably giant resonances. The discussion also covered the p-nuclei production through the νp-process at around mass 100.

[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)