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Activity calibration of $^{222}$Rn in water by TDCR method in LSC and determination of the half-life of $^{214}$Po

Abstract : Liquid scintillation counting is a well-suited method for the activity calibration of 222Rn sources, as the geometrical efficiency is 4 Pi sr and the detection efficiency is close to 5 at equilibrium with the progenies. In the past we have developed a method to calculate this detection efficiency for the Triple to Double Coincidence Ratio (TDCR) method, considering some simplifications, like assuming 100% detection efficiency of alpha radionuclides and high-energy beta radionuclides of the radon progenies. A correction was applied for the disintegration of 214Po, as its half-life is not negligible versus the counter dead-time and leads to a reduction of its detection probability. In this work we revisited these simplifications in order to develop a more accurate model. In the new model, we did not assume a unity detection efficiency for the high-energy beta radionuclides, but we calculated it using the free parameter model in LSC, by considering the energy spectrum transferred to the scintillator, from up-to-date beta spectra calculation and Monte Carlo simulation of the energy transferred to the scintillator. Radon in water LS sources were measured using a miniature TDCR counter and an acquisition system based on a fast digitizer. The offline processing of acquisition files was made using several dead-time base duration values from 5 µs to 1000 µs, and the counting rates were corrected for blank measurement, accidental coincidences and dead-time evolution during the measurement. The analysis of the relationship between the triple and double coincidence counting rates versus the base dead-time duration allows a new type of determination of the half-life of 214Po. This half-life was found to be slightly smaller, albeit coherent with the evaluated DDEP value. This new value was integrated to a computer program, allowing an accurate determination of the detection efficiency of 222Rn in equilibrium with its progenies, without the need of an extrapolation to zero dead-time measurement. The results obtained in this work will largely facilitate the calibration of 222Rn sources and the calibration of LSC counters for 222Rn-in-water measurements.
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https://hal-cea.archives-ouvertes.fr/cea-03853852
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Submitted on : Monday, November 21, 2022 - 11:39:19 AM
Last modification on : Tuesday, November 22, 2022 - 11:20:51 AM

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  • HAL Id : cea-03853852, version 1

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Philippe Cassette, Chavdar Dutsov, Benoit Sabot, Krasimir Mitev, Vladislav Todorov. Activity calibration of $^{222}$Rn in water by TDCR method in LSC and determination of the half-life of $^{214}$Po. ICRM LLRMT 2022 - The 8th international conference on radionuclide metrology - Low-level radioactivity measurement techniques, May 2022, Gran sasso, Italy. pp.87. ⟨cea-03853852⟩

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