SEARCH FOR DARK MATTER USING THE SUPERHEATED SUERCONDUCTOR

点击翻译按钮获取中文摘要

We have carried out a project of constructiog a cryogenic particle detector, which can be applied for the detection of dark-matter particles in cosmic rays and/or neutrinos, using a collection of superheated superconducting tin micro granules as a target set up in the detector.1.Responses of tin granules in 200micron diameter to alpha rays at 2 kelvins :It turned out that the single granule is sensitive to several-million-electron-volt energies deposited by an incident alpha particle.2.Responses of tin granules in 30micron diameter to gamma rays at 30mK :We were able to measure spectre lines of the energy absorption due to the photoelectric effect for the K-and L-shell electrons in tin atoms irradiated with gamma rays of 60keV.The absorption rates are consistent with roughly-calculated values. The heat energy induced by ionized electrons in the single granule was detected up to less than lkeV.3.Measurements of the flip-flop phenomenon :It is expected that a granule not only flips from a superconduting state to a normal conducting state receiving a sufficient heat energy, but also flops vice versa at a sufficiently low temperature. In this case, the state of a granule traces along a hysteresis curve in the phase diagram in magnetic field-magnetization. Precise measuremets showed that the condition for the phenomenon to take place depends critically on the thermal property of the material of a granule. The phenomenon turned out not to manifest itself in the case of tin of which thermal property is explained on the basis the local-heating picture.4.A prototype detector :The detector has a l-gram target consisting of a collection of 30micron tin granules set up set up at a temperature of a dilution refrigerator. A test run will start soon.