Three element triple coincidence compton spectrometer

摘要

908,485. Radiation detectors. SOCONY MOBIL OIL CO. Inc. May 27, 1959 [June 2, 1958], No. 18120/59. Class 40 (3). A gamma ray detector comprises three scintillation crystals 24, 25, 26 (Figs. 1, 2 and 3), housed in a thin casing 50 (e.g. of aluminium) and optically screened from each other by means of thin aluminium baffles 51, 52, the arrangement being such that scintillations produced in all three crystals by a Compton recoil electron (produced by an incident gamma ray 21 and travelling along path 45) fall on a photo-multiplier 30 whilst the scintillations produced in crystals 24 and 26 fall on respective photomultipliers 40, 42. By giving the crystals suitable (thickness) dimensions such that only Compton recoil electrons have sufficient energy to traverse all three crystals and by utilizing, as a control effect, the coincidence of output signals from all three photo-multipliers. Compton recoil electrons (which are distinctive of the energy of the original gamma rays) may be identified separately from gamma ray conversions produced by other than the Compton effect since the range of such other conversion products will be insufficient to produce triple coincidence. Thus, as shown in Fig. 1, the output signals from each photo-multiplier are supplied, after amplification, to a triple coincidence circuit 32 the output signal from which opens a gate circuit 34 and allows the output from photomultiplier 30 (which is indicative of the total energy of the recoil electron) to pass to a recorder 16. The energy of the incident gamma ray may then be computed. The invention may be employed in a well logging system in which an exploring unit 10 (Fig. 1) lowered into the borehole carries the detector and a suitable radiation source 20 which may be of the neutron type. In a modification of the detector unit the three crystals have different widths each being associated with a respective photomultiplier in addition to the photo-multiplier which is common to all crystals (Fig. 9, not shown).