The LMV now has an analytical facility – unique in France – dedicated to the measurement by counting or nuclear spectrometry of all the radioactive isotopes of the natural chains of 238U and 232Th. By combining a alpha spectrometry, gamma spectrometry, and global alpha-beta counting, all the isotopes, from the shortest to the longest periods, can be analyzed in geological and/or atmospheric samples.
a Spectrometry :
Model : Alpha-assembly spectrometer, AMETEK (Ortec), 8 counting channels equipped with 300 mm² silicon diodes.
Acquisition date : June 2012
Main usage : the alpha spectrometer is almost exclusively used today to measure the 210Po activity in geological samples by isotopic dilution (addition of a 209Po tracer) or, more rarely, the isotopic composition of uranium (ratio 234U/238U) or thorium (ratio 230Th/232Th). Analytical precision is proportional to the counting statistics, imposing de facto very long analysis times, between 0.5 and 3 months per sample.
gamma Spectrometry :
Model : Well type gamma spectrometer with Germanium detector, ITECH-Instruments, single counting channel.
Acquisition date : October 2013
Main usage : The gamma spectrometer is mainly used to measure the 210Pb and 226Ra (238U chain) as well as 228Ra and 228Th (232Th chain) activities in geological samples. The analytical precision is proportional to the counting statistics, imposing de facto very long analysis times, between 1 and 4 months per sample
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alpha-beta Counter :
Model : Global alpha-beta low background IN20 counter, Canberra (now Mirion), with 8 counting channels equipped with gas flow detector, 56 mm diameter.
Aquisition date : November 2003
Replacement cost : 78 k€ (NB: this IN20 meter no longer exists in the current range of products offered by Mirion (ex-Canberra); the price indicated is for a LB4200 (Mirion) meter with 16 56 mm detectors. Such a device is currently on order on ClerVolc credits for commissioning in the second half of 2019, to replace the IN20 which has reached the end of its life).
Main usage : the global counter is used for the analysis of 210Pb, 210Bi, 210Po in volcanic gas (filter sampling) or hydrothermal water (evaporated dry residue). It can also be used for the analysis of the volumetric activities of 222Rn (via its very short-lived descendants 218Po-214Pb-214Bi-214Po) in air samples (outdoor or domestic samples for radiation protection monitoring).
Contact : Pierre-Jean Gauthier
