GB931515A - Improvements in devices for detecting and identifying radioactive elements, in particular for geophysical prospection - Google Patents

Abstract

931,515. Utilizing radiation detectors. COMMISSARIAT A L'ENERGIE ATOMIQUE. April 7, 1960 [April 10, 1959], No. 12429/60. Class 40 (3). An apparatus for indicating the presence, and the relative proportions, of two or more gamma-ray emissive elements comprises a scintillation counter whose output passes to a pulse height analyzer unit. This unit provides two outputs corresponding to the pulse rates in two wide bands of the gamma-ray energy spectrum, these bands being so chosen that in one there is an energy peak of one of the elements which exceeds the energies of the second element in that band and in the other the second element shows a peak which exceeds the energies of the first element in this other band. The two outputs are passed to a ratiometer or a differential circuit whose output current feeds a pen recorder. A second track on the recorder indicates the total count rate over a further wide band which includes both the bands mentioned above. Gamma rays are detected by a scintillation detector 1 and photo-multiplier 2, Fig. 1. The photo-multiplier output is amplified at 3 and feeds discriminator and integrator units 5, 6, 7, 8. Unit 5 gives a signal proportional to the count rate over one energy band and units 6 and 7 to the count rate over two other bands: the two latter bands are selected to satisfy the conditions mentioned above. The signal from unit 5 is passed to a pen recorder 10, to produce a trace 16, while the signals from units 6 and 7 pass to a ratiometer or differential circuit 9. The unit 9 gives an output which decreases for increased counting rate in one of said bands and which increases for increased counting rate in the other band. This output is recorded as trace 17, Fig. 3. As the detector 1 is passed over samples, for example as in geophysical prospecting by air, trace 16 will show peaks 18, 19, 20, Fig. 3, indicative of increased total gamma count rate. The corresponding change in trace 17 indicates the element causing the increased count and its approximate proportion relative to the other element. Thus trough 21 corresponds to an increased count rate from unit 6, showing the presence of, say, thorium deposit. Likewise, the peak 22 shows the presence of, say, uranium, while the small peak 23, and large peak 20 of trace 16, show the presence of both thorium and uranium deposits, the latter slightly predominating.