par- 2 février 2011 - ( maj : 2 février 2011 )
Alpha / Beta Counting using :
Ten separate flow counter tubes (proportional counter chambers) with high detection sensitivity, allowing the simultaneous measurement of the alpha and beta activities of 10 samples ensuring a high sample throughput. A special mixture of 90% argon and 10% methane (P10 gas) is used to initiate the charge multiplication process in the counter tubes. The 10 ultra-flat measuring counters (60mm diameter, 8mm height) are protected at the top by a large-area flow counter tube acting as common guard counter. The guard counter operates in anticoincidence with the sample detectors for nearly complete elimination of cosmic radiation ; events occurring simultaneously in the guard and measuring counter are detected and eliminated. This system is designed for the detection of very low concentrations of alpha and beta radiation. It allows to benefit of background level less than 15 pulses per hour at mean beta energies corresponding to Sr-90 and Cs-137 detection. The counting efficiency ( 40%) is checked by Sr-90 and Cs-137 standard at 195.7 and 174.3 keV (mean beta energy), respectively.
In our laboratory, the alpha / beta counting system is commonly used for the determination of Total Beta Concentrations (comprising fission products as Sr-90 and Cs-137, as well as natural radionuclides issued from uraniuma and thorium series) in snow/firn/ice samples for dating purposes.
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