Radiation detector assembly for formation logging apparatus

摘要

A detector assembly which is particularly well suited for detecting gamma rays in a formation density logging tool employs a sodium iodide crystal and glass phototube; and is housed in a novel mounting arrangement which provides appropriate gamma ray shielding as well as protection from shock and vibration. The actual crystal is mounted in a hermetically sealing housing. The outer configuration of the housing allows for rigid attachment to a magnetic shield. This shield provides magnetic protection for the phototube so as to avoid undesired disturbances in the tube output signal during operation. A layer of elastomeric material provided with voids for volumetric expansion is interposed between the crystal housing and the magnetic shield. An outer insulating tube is then ruggedly secured to one end of the mumetal shield by an adhesive. This tube, in combination with a protective end cap, serves to environmentally protect the dynode electronics assembly (having a novel circular arrangement) required for phototube operation. The entire detector package described thus far is encapsulated in an elastomer, which has a specified geometry using a construction of molded ribs to give the desired rigidity and vibration characteristics. This technique creates a small, rugged package, which can then be inserted into a hatch in a formation evaluation tool sub wall without resorting to standard fasteners for mounting.