Abstract
The Sudbury Neutrino Observatory experiment was built to measure the total flux of 8B solar neutrinos via the neutral current disintegration deuterium nuclei. This process can be mimiced by daughter isotopes of 232Th and 238U which can photodisintegrate the deuterium nucleus. Measurement of the concentration of such radioisotopes in the heavy water was critical to the success of the experiment. A radium assay technique using Hydrous Titanium Oxide coated filters was developed for this purpose and it was used in conjunction with a delayed beta-alpha coincidence counting system. The design, calibration and operation of this counting system are described in this paper. The counting efficiency for 232Th (224Ra) and 238U (226Ra) were measured to be 50 ± 5% and 62 ± 7%
Highlights
Dawson, M, Doucas, G, Fergani, H, Jelley, N A, Majerus, S, O'Keeffe, H M, Peeters, S J M and Perry, C (2016) A beta-alpha coincidence counting system for measurement of trace quantities of 238U and 232Th in aqueous samples at the Sudbury Neutrino Observatory
: The Sudbury Neutrino Observatory experiment was built to measure the total flux of 8B solar neutrinos via the neutral current disintegration deuterium nuclei
A radium assay technique using Hydrous Titanium Oxide coated filters was developed for this purpose and it was used in conjunction with a delayed beta-alpha coincidence counting system
Summary
The beta-alpha system was designed to measure the number of beta-alpha coincidences arising from the decay of daughter nuclei in the 232Th and 238U chains. Toward the end of the 238U chain, 214Bi decays by beta emission to 214Po which subsequently alpha decays with a half-life of 164 μs The signature of this coincidence is a beta decay with a Q-value of 3.27 MeV followed many μs later by a 7.7 MeV alpha (Q = 7.83 MeV). A similar coincidence exists in the 232Th chain, where 212Bi decays with a 64% branch by beta emission to a short lived state of 212Po which alpha decays to 208Pb with a 0.3 μs half life. The signature for this decay is a beta decay with a Q-value of 2.25 MeV followed a fraction of a μs later by an 8.78 MeV (Q = 8.95 MeV) alpha. This technique is commonly referred to as pulse shape discrimination and it was used as the basis for this beta-alpha counting system, an overview of which is given
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