The lunar surface is directly and continuously exposed to Galactic Cosmic ray (GCR) particles and Solar energetic particles (SEPs) due to the lack of atmosphere and lunar magnetic field. These charged particles interact with the lunar surface materials producing secondary radiations such as neutrons and gamma rays. In a departure from precise GCR and SEP data, we estimated the effective dose equivalent at the lunar surface and in a lunar lava tube in this paper by using PHITS, a Monte Carlo simulation tool. The effective dose equivalent due to GCR particles at the lunar surface reached 416.0 mSv yr−1 and that due to SEPs reached 2190 mSv/event. On the other hand, the vertical hole of the lava tube provides significant radiation protection. The exposure by GCR particles at the bottom of the vertical hole with a depth of 43 m was found to be below 30 mSv yr−1 while inside a horizontal lava tube, the value was less than 1 mSv yr−1 which is the reference value for human exposure on the Earth. We expect that the lunar holes will be useful components in the practical design of a lunar base to reduce radiation risk and to expand mission terms.

Measurements of the mobility and longitudinal diffusion coefficient of electrons under external electric fields were performed in high-density gaseous xenon at room temperature. The xenon density and reduced electric field ranges were from 2.55 ×1020 to 1.73 ×1021 cm-3 and from 0.027 to 0.19 Td, respectively. The electron transport parameters of the density-normalized mobility, density-normalized longitudinal diffusion coefficient, and the ratio of the longitudinal diffusion coefficient to the mobility were found to increase with increasing density for reduced electric fields at around 0.04 Td. This result indicates the density-dependent variation of the effective momentum-transfer cross section for electron–atom scattering. It was also found that the density-dependent variations are different depending on the electron transport parameters, which can be attributed to the difference in parameter sensitivity to the momentum-transfer cross section.

The longitudinal diffusion coefficient of electrons and the ratio of the longitudinal diffusion coefficient to the mobility of electrons were measured for the first time in high-density gaseous xenon in the extensive density range of 4.19×1019–4.82×1020 cm-3. The density dependence of the longitudinal diffusion coefficient was observed in the reduced electric field range of 0.025–0.055 Td.

Abstract. The XENON experiment searches for dark matter particles called WIMPs using liquid xenon (LXe) as the active target. The detector is a 3D position sensitive Time Projection Chamber optimized to simultaneously measure the ionization and scintillation produced by a recoil event of energy as low as 16 keV. The distinct ratio of the two signals for nuclear recoils arising from WIMPs and neutrons and for electron recoils from the dominant gamma-ray background determines its event-by-event discrimination. With 1 ton of LXe distributed in ten identical modules, the proposed XENON1T experiment will achieve a sensitivity more than a factor of thousand beyond current limits. A phased program will test a 10 kg detector (XENON10) followed by a 100 kg (XENON100) one as unit module for the XENON1T scale experiment. We review the progress of the XENON R&D phase before presenting the status of XENON10. The experiment will be based at the Gran Sasso Underground Laboratory and is expected to start data taking in early 2006.