Radionuclide standardization by Cherenkov counting

Rapid screening of 90Sr activity in water and milk samples using Cherenkov radiation

A method for screening 90Sr in milk samples is proposed. This method is based on a liquid scintillation technique taking advantage of Cherenkov radiation, which is produced in a liquid medium and then detected by the photomultipliers of a Liquid Scintillation Counter (LSC). Twenty millilitres of water and milk samples spiked with various concentrations of 90Sr/90Y in equilibrium were added in plastic vials and then were measured with an LSC (TriCarb 3170 TR/SL). The derived efficiencies were 49% for water samples and 14% for milk samples. The detection limit was 470 mBq L(-1)(90)Sr for water, without any pretreatment. Milk contains potassium, which also produces Cherenkov radiation due to the presence of 40K. For this reason, the interference of 40K in the measurements of 90Sr in milk samples was also investigated. The detection limit for milk was 1.7 Bq L(-1)90Sr.

Half-life determination of 40K by LSC

The long-lived radioisotope 40K is one of the isotopes applied by geologists to date rocks hundreds or even thousands of millions of years old. Knowing the half-life of 40K, the potassium-argon (K-Ar) method gives an estimate of the date of the rock's formation by measuring the quantity of the daughter stable isotope 40Ar. As in the case of other radiometric methods, the results of the K-Ar dating method are generally accompanied by an error estimate, which includes the counting process, the uncertainty in the half-life of 40K and the beta to capture branching ratio. The objectives of this paper are basically three. First, we describe a procedure to incorporate the largest amount of the potassium cations into the liquid scintillator cocktail. This time, gels are able to provide much higher counting rates than the background. Second, Cerenkov counting gives the best shapefactor for 40K beta-ray transitions. Third, the CIEMAT/NIST method determines the activity of the samples and an averaged half-life for the radionuclide.