par- 2 février 2011
Gamma Ray Spectrometry using :
1. A very low background specified High Purity coaxial detector of 20.6% relative efficiency. This type of detector exhibits an excellent efficiency down to low energies as for the 46.52 keV line of Pb-210. The respective resolutions of 0.847, 1.36 and 1.75 keV are specified at 122, 662 and 1332 keV with a peak to Compton ratio of 56 at this latter energy. The detector (95 cm3) is mounted with an Anti-Compton annulus which combines 9x8 and 3x3 inch plug NaI (Tl) scintillators. The latter device system provides a lower detection threshold, especially for the main isotopes of interest such as Be-7, Pb-210 (+ Pb-214 and Bi-214), Cs-137 and Am-241. The continuous baseline is highly reduced in the Anti-Compton mode : the integrated counting rate between 10 and 1500 keV decreases from 0.5 to 0.05 counts per second. The high resolution spectrometer can be used as a non-destructive technique for measuring filters (snow and atmosphere), soil and sediments.
In our laboratory, this analytical system is commonly used for the determination of Pb-210, Cs-137 and Am-241 in snow/firn/ice samples, as well as natural gamma emitters in atmosphere particulates. Above, schematic picture of N-type gamma spectrometer
Above, schematic picture of N-type gamma spectrometer
2. A low background specified High Purity well detector of 40.8% relative efficiency. The respective resolutions of 1.35 and 2.08 keV are specified at 122 and 1332 keV with a peak to Compton ratio of 59.6 at this latter energy. The detection device system provides a low detection threshold, especially for the main isotopes of interest such as Be-7, Pb-210 (+ Pb-214 and Bi-214), Cs-137 and Am-241.
In LGGE, this high resolution spectrometer is commonly used for the determination of latter radionuclides in sediment and soil samples. As for the coaxial spectrometer, the well detector requires little sample preparation and is then used as a non-destructive technique for measuring radionuclides.
Photo of P-type gamma spectrometer Photo of P-type gamma spectrometer
For both gamma ray spectrometers, the absolute efficiency curves, from 40 to 1500 keV are obviously established thanks to several standard solutions and calibrated materials (LEA-CERCA, Amersham).
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