K. Ichihara

MOON for spectroscopic studies of double beta decays and the present status of the MOON-1 prototype detector

The MOON (Molybdenum Observatory Of Neutrinos) project, as an extension of ELEGANT V, aims at spectroscopic studies of double beta decays from 100Mo with a sensitivity of the Majorana neutrino mass around 30 meV. Measurements with good energy and position resolutions enable one to select true signals and to reject background ones. A prototype MOON detector (MOON Phase-1A) with 142 g 100Mo was built and is running at the Oto underground laboratory. The present report describes briefly the outline of the MOON project and the present status of MOON-1.

WIMPs search by means of the highly segmented scintillator

The highly sensitive method to search for WIMPs dark matter particles is proposed. An array of thin NaI(Tl) plate has the great selectivity for distinguishing the WIMPs events and background ones. The principle of signal selection for WIMPs is described. The high sensitivity for SD (spin-dependent) type WIMPs is expected by applying multi-layer system of NaI(Tl) detector. A method of highly sensitive measurement is strongly needed to study nuclear and particle rare processes. The need for highly sensitive radiation detector has been increased in the fields of particle astrophysics and nuclear physics. Particularly, the search for dark matter candidates and the search for neutrino-less double beta decay need to select the signal events from the huge number of background ones. In the case of WIMPs search, the groups such as ELEGANT, 1 DAMA 2 applied the huge volume of NaI(Tl) scintillator. The new project with the huge volume scintillator are proposed with hundreds kg of scintillators by XMASS 3 group, ZEPLIN group 4 and so on. The many groups are trying to enhance the sensitivity by developing a large volume and low background detectors. However, to reduce the background events becomes more difficult for the larger detectors because of its poor position resolution. We propose highly selective detector system to extract the signals of WIMPs. The segmentation of a detector results good position resolution, which enhances the sensitivity for WIMPs.The highly sensitive method to search for WIMPs dark matter particles is proposed. An array of thin NaI(Tl) plate has the great selectivity for distinguishing the WIMPs events and background ones. The principle of signal selection for WIMPs is described. The high sensitivity for SD (spin-dependent) type WIMPs is expected by applying multi-layer system of NaI(Tl) detector.

CANDLES for double beta decay of 48Ca

CANDLES is the project to search for neutrinoless double beta(0νββ) decay of 48Ca by using CaF2 scintillators. The observation of 0νββ decay will prove existence of a massive Majorana neutrino. The expected performances of the CANDLES system for lightsignal detection and background rejection are presented here. The current status of development for the detector system is also described.

PICO-LON project for WIMPs search

Highly segmented inorganic crystal has been shown to have good performance for dark matter search. The energy resolution of ultra thin and large area NaI(T1) scintillator has been developed. The estimated sensitivity for spin-dependent excitation of 127I was discussed. The recent status of low background measurement at Oto Cosmo Observatory is reported

The Performance of Thin NaI(Tl) Scintillator Plate for Dark Matter Search

A thin (0.05 cm) and wide area (5×5 cm 2 ) NaI(Tl) scintillator was developed. The performance of the thin NaI(Tl) plate, energy resolution, single photoelectron energy and position sensitivity wer...A thin (0.05cm) and wide area (5cmX5cm) NaI(Tl) scintillator was developed. The performance of the thin NaI(Tl) plate, energy resolution, single photoelectron energy and position sensitivity were tested. An excellent energy resolution of 20% (FWHM) at 60keV was obtained. The single photoelectron energy was calculated to be approximately 0.42 0.02keV. Position information in the 5cmx5cm area of the detector was also obtained by analyzing the ratio of the number of photons collected at opposite ends of the detector. The position resolution was obtained to be 1cm (FWHM) in the 5cmx5cm area.

The MOON-1 detector construction and the study of backgrounds from radioactive isotopes

MOON is a multilayer system of plastic scintillators and 100Mo films for 100Mo 0νββ decays. A prototype detector MOON-1 was built with 6 layers of plastic scintillators and 142g of 100Mo films for background (BG), energy and position resolution studies of the MOON detector. No serious BG from natural radioactive isotopes (RI) for 0νββ detection was found.

WIMPs search by means of thin NaI(Tl) array

A thin plate of NaI(Tl) with the dimension of 5cm×5cm×0.05cm has been developed for WIMPs search. The thin NaI(Tl) showed the good performance for energy resolution and low energy threshold. The advantages for WIMPs search, especially, inelastic excitation of nuclei by spin-dependent interaction between WIMPs and 127I is discussed.

Low Radioactivity in CANDLES

CANDLES is the project to search for double beta decay of 48Ca by using CaF2 crystals. Double beta decay of 48Ca has the highest Q value among all nuclei whose double beta decay is energetically allowed. This feature makes the study almost background free and becomes important once the study is limited by the backgrounds. We studied double beta decays of 48Ca by using ELEGANTS VI detector system which features CaF2(Eu) crystals. We gave the best limit on the lifetime of neutrino‐less double beta decay of 48Ca although further development is vital to reach the neutrino mass of current interest for which CANDLES is designed. In this article we present how CANDLES can achieve low radioactivity, which is the key for the future double beta decay experiment.