HIGH SENSITIVITY GAMMA RAY SPECTROMETRY
The ultimate sensitivity provided by activation analysis depends on the sensitivity of the counting equipment used in measuring the product nuclei. Gamma spectrometric methods were investigated with the aim of optimizing both sensitivity and selectivity in radioisotope measurements. The response of three high-sensitivity gamma spectrometer systems is discussed. The first system is a summing coincidence spectrometer which uses two large opposing crystals as detectors. The crystals sandwich the sample between them for the measurements. The signals from the two detectors are summed to provide a sum spectrum'' and are also coincidence analyzed to determine if the pulse has resulted from two or more gamma rays striking the two crystals. The spectrometer system thus permits a sum spectrum and a coincidence sum spectrum to be recorded simultaneously. The sum spectrum is due mainly to radioisotopes emitting one gamma ray per disintegration while the coincidence sum spectrum is due to radioisotopes which emit two or more gamma rays per disintegration. This system aids in the analysis of a mixture of radioisotopes by separating them into two groups characteristic of their decay mode and providing a very low counting background in the coincidence sum mode of operation. The second type of spectrometer system employs a large phosphor surrounding the principal detector and operating in anticoincidence with it. The sample to be measured is placed on top of the principal detector (or in its well). The gamma rays which strike the principal detector but are not completely absorbed are seen'' by the anticoincidence guard phosphor and are canceled. This type of detector system results in a large reduction in the Compton response and in the background. The third spectrometer system employs the same two detectors as in the system described above, in addition, the sample is sandwiched in a small plastic phosphor (or in a scintillating gel medium) which is located in the well of the principal detector and is viewed with a small phototube. For an event to be stored by the analyzer, a pulse must be received from the small plastic phosphor (indicating that a beta particle was emitted) and there must not be a pulse from the guard crystal. In addition to the advantages provided by the second system, this system discriminates against non-beta emitters and provides approximately a hundred-fold background reduction over that available with the second system. (auth)
- Research Organization:
- General Electric Co., Richland, Wash.
- NSA Number:
- NSA-17-039001
- OSTI ID:
- 4657365
- Report Number(s):
- HW-SA-2344
- Journal Information:
- Proc., Intern. Conf., Mod. Trends Activation Anal., College Station, Tex., Other Information: HW-SA-2344. Orig. Receipt Date: 31-DEC-63
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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