We measured the decay time of the scintillation pulses produced by electron and nuclear recoils in CaF2(Eu) by a new fitting method. In the recoil energy region 5-30 keVee, we found differences of the decay time between electron and nuclear recoil ev
ents. In the recoil energy region above 20 keVee, we found that the decay time is independent of the recoil energy.
A new search result of the Tokyo axion helioscope is presented. The axion helioscope consists of a dedicated cryogen-free 4T superconducting magnet with an effective length of 2.3 m and PIN photodiodes as x-ray detectors. Solar axions, if exist, woul
d be converted into X-ray photons through the inverse Primakoff process in the magnetic field. Conversion is coherently enhanced even for massive axions by filling the conversion region with helium gas. The present third phase measurement sets a new limit of g_{agammagamma}<(5.6--13.4)times10^{-10} GeV^{-1} for the axion mass of 0.84<m_a<1.0 eV at 95% confidence level.
We propose a new method of alpha($alpha$)-ray measurement that detects helium atoms with a Quadrupole Mass Spectrometer(QMS). A demonstration is undertaken with a plastic-covered $^{241}$Am $alpha$-emitting source to detect $alpha$-rays stopped in th
e capsule. We successfully detect helium atoms that diffuse out of the capsule by accumulating them for one to 20 hours in a closed chamber. The detected amount is found to be proportional to the accumulation time. Our method is applicable to probe $alpha$-emitting radioactivity in bulk material.
