Possible overestimation of the external standard quench parameter on Wallac 1220 Quantulus™ with high energetic beta-emitters

Abstract

The 1220 Quantulus is equipped with an ¹⁵²Eu external source used to determine an external standard quench parameter SQP(E). The relationship between ⁹⁰Sr/⁹⁰Y counting efficiency and SQP(E) was found linear in a defined range of SQP(E) values. This function was fixed after many counting experiences made with ⁹⁰Sr/⁹⁰Y standards. The sasme equation is used for the measurement of ⁹⁰Sr in environmental samples. The first goal of this paper is to objectify an overestimation of the SQP(E) when high energetic beta-emitters like ⁹⁰Y are present (1 to 4% in routine conditions). The second one is to show how this artefact could induce a bias in the calculation of ⁹⁰Sr activity in environmental samples. The median of this overestimation is estimated around 6%. Another approach using ⁸⁵Sr standard is suggested to avoid this overestimation. Provided the chemical composition — and thus the quenching — is similar for the two standards, the counting efficiency measured with the ⁹⁰Sr/⁹⁰Y standard could be related to the SQP(E) value of the ⁸⁵Sr standard. Indeed this one appears to be more robust regarding to the range of activity and to the counting time of the external source.