Further considerations on "Towards the origins of over-dispersion in beta source calibration" by Hansen et al., radiation measurements, 2018

Highlights: • Accurate calibration of dose rate during laboratory irradiations of the aliquots using a⁹⁰Sr/⁹⁰Y beta source mounted on the reader system is a key factor in luminescence dating of geological samples. • The Z-dependent backscatter and build up effects are the major concerns which result into variation in apparent dose rate from aliquot to aliquot. • High Z substrates may not be of much use although they facilitate higher dose rates due to beta backscattering and bremsstrahlung production. • It is recommended that while performing beta irradiations in RISO readers, the low Z substrates like Al (Z ≤ 13) may be preferred over high Z substrates like stainless steel or Pt, to minimize the bremsstrahlung contribution. • The use of low Z substrates like Al also does not pose any serious operational problems while recording OSL or TL except at higher temperatures preferably above 500 °C. This is due to the fact that heating the aluminum disc above 500 °C, there will be risk of melting and the heating element may be damaged. -- Abstract: Accurate calibration of dose rate during laboratory irradiations of the aliquots using a ⁹⁰Sr/⁹⁰Y beta source mounted on the reader system is a key factor in luminescence dating of geological samples. The Z-dependent backscatter and build up effects are the major concerns which result into variation in apparent dose rate from aliquot to aliquot. Recently it has been proposed that there may be a practical advantage in using a high Z substrate because of the higher dose rate. In this regard, the author would like to add that use of high Z substrates may not be of much use although they facilitate higher dose rates due to beta backscattering and bremsstrahlung production. Since the typical radioactivity of ⁹⁰Sr/⁹⁰Y source in RISO readers is ~(10-50) mCi or so, the bremsstrahlung radiation associated with higher Z substrates/cups may be substantial and leads to large errors because over-response corrections are generally not included while establishing standardization and calibrating the beta doses. In view of this, it is recommended that while performing beta irradiations in RISO readers, the low Z substrates like Al (Z ≤13) may be preferred over high Z substrates like stainless steel or platinum, so as to minimize the bremsstrahlung contribution. The use of low Z substrates like Al also does not pose any serious operational problems while recording OSL or TL except at higher temperatures preferably above 500^oC.