J.I. Lee

Distillation of Liquid Xenon to Remove Krypton

A high performance distillation system to remove krypton from xenon was constructed, and a purity level

First limit on WIMP cross section with low background CsI(Tℓ) crystal detector

Abstract The Korea Invisible Mass Search (KIMS) Collaboration has been carrying out WIMP search experiment with CsI ( T l ) crystal detectors at the YangYang Underground Laboratory. A successful reduction of the internal background of the crystal was done and a good pulse shape discrimination was achieved. We report the first result on WIMP search obtained with 237 kg days data using one full-size CsI ( T l ) crystal of 6.6 kg mass.

Self-shielding effect of a single phase liquid xenon detector for direct dark matter search

Liquid xenon is a suitable material for dark matter search. F or a future large scale detector, single phase detectors are attractive by their simple detector configuration and sc alability. But in order to reduce backgrounds, they need to fully rely on the self-shielding. A prototype detector was d eveloped at Kamioka Observatory to establish vertex and energy reconstruction methods and to demonstrate the self-shielding power against the gamma rays from outside of the detector. Suffi cient self-shielding power for future experiments was obta ined.

Scintillation yield of liquid xenon at room temperature

The intensity of scintillation light emission from liquid xenon at room temperature was measured. The scintillation light yield at 1 � C was measured to be 0:64 � 0:02 (stat.) � 0:06 (sys.) of that at � 100 � C. Using the reported light yield at � 100 � C (46 photons/keV), the measured light yield at 1 � C corresponds to 29 photons/keV. This result shows that liquid xenon scintillator provides high light yield even at room temperature.

Measurement of the thermal neutron capture cross section of W 180

We have measured the thermal neutron capture cross section for w-180 nucleus. There is only one previous data on this cross section with a value of 30

Production of low radioactivity CsI(Tl) crystals for WIMP searches

^{+300%}_{-100%}

Development of CaMoO4 crystal scintillators for a double beta decay experiment with Mo100

barn. To consider w-181 as a low energy neutrino source, the thermal neutron capture cross section should be measured more precisely to estimate the production rate of w-181 inside a nuclear reactor. We measured the cross section of w-180 with a natural tungsten foil and obtained a new value of 21.9

The development of a cryogenic detector with CaMoO4 crystals for neutrinoless double beta decay search

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Measurement of the neutron flux in the CPL underground laboratory and simulation studies of neutron shielding for WIMP searches

2.5 barn

Development of low-background CsI(Tℓ) crystals for WIMP search

We have extensively studied the mechanism of the 137Cs and 134Cs contamination in CsI compounds. The nuclei 137Cs and 134Cs in various samples have been studied using a HPGe detector at deep underground. The main source of the 137Cs contamination in CsI powder was desolved 137Cs in the water used in the chemical process of cesium extraction at company side. We also found that 134Cs was produced mainly from 133Cs by neutron capture. We have successfully produced CsI powder containing no more than 2 mBq/kg of 137Cs by using only ultra‐pure water for whole extraction process from raw ore(pollucite).