Development of a high-resolution large-mass cryogenic particle detector

一个专用的稀释冰箱已经建成。它能够将一公斤的吸收材料冷却到10mK。它是由特别挑选的原材料制成，以减少自然辐射背景。特别是杜瓦容器的内外瓶和冰箱的内真空室都是用无氧铜制成的。它还可以在里面安装铅辐射屏蔽。具有适合地下实验室长时间运行的规范。采用新研制的锗热敏电阻，构建了氟化锂晶体吸收体辐射粒子探测器，该探测器在20mK左右具有较高的灵敏度。它已在稀释冰箱中成功运行。为了制造许多灵敏度几乎相同的热敏电阻，采用了两种方法。一种是用锗晶体熔融掺杂锑，另一种是所谓的中子嬗变掺杂法。对于后一种方法，已经在日本原子能研究所的JRR-3反应堆上进行了中子辐照。我们还研制了含钼、氧化镍、氧化锌、硫化锌和碲化镉晶体吸收体的辐射热计，用于无中子双正电子衰变实验。结果表明，硫化锌和碲化镉适合作这种用途的测热计。

A dedicated dilution refrigerator has been constructed. It is capable of cooling one-kilogram of absorber material down to 10mK.It is made of specially selected raw materials to reduce natural radiation background from them. Especially, the inner and outer cylinders of the dewar vessel as well as the inner vacuum chamber of the refrigerator are all made of oxigen free copper.It is also made so that a lead radiation shield can be installed inside it. It has a specification suitable for a long time operation in an underground laboratory.A bolometric particle detector with an absorber of lithium fluoride crystal has been constructed with a newly developed germanium thermistor, which has a high sensitivity at around 20mK.It has been operated successfully in the dilution refrigerator.In order to manufacture many thermistors with nealy identical sensitivities, two methods were adopted. The one is to use germanium crystals melt-doped with antimony, and the other is so called neutron transmutation doping method. For the latter method, neutron irradiation has been done at the JRR-3 reactor of the Japan Atomic Energy Research Institute.We also developed bolometers with absorbers of molybdenum, nickel oxide, zinc oxide, zinc sulfide and cadmium telluride crystals for the neutrinoless double positronium decay experiment. It is found that the zinc sulfied and cadmium telluride are suitable for the bolometers of this purpose.