Cryostat for photon detector and its use in a borehole logging tool.

摘要

A borehole logging tool having a semiconductor detector (22) includes a cryostat (24) to maintain the detector at cryogenic temperatures. The cryostat has an elongate aluminium heat sink (46) on one end of which the detector is removably mounted. The other end of the heat sink is arranged to receive a liquid cryogen or the cold finger of a helium refrigerator, which is removed before a logging run, the detector being maintained at cryogenic temperatures during the logging run by absorption and retention of heat in the solid, single-phase heat sink. An aluminium tube (42) having similar thermal capacity and similarly pre-cooled to cryogenic temperatures, surrounds but is spaced from the heat sink, and carries it by means of low thermal conductivity supports. The tube is itself carried within an evacuated stainless steel housing (30) by similar supports, which are arranged to permit substantial differential changes in length of the tube and the housing.