An investigation of pulsed-irradiation regeneration of quartz OSL and its implications for the precision and accuracy of optical dating (Paper II)

Abstract

An essential part of the laboratory procedure associated with optical dating is the irradiation of sample aliquots with known doses of ionizing radiation. Only if laboratory irradiation faithfully reproduces the effects (within the dating sample) of natural irradiation (during burial) will the dates obtained be accurate. Modelling of quartz luminescence suggests that the usual practice of administering laboratory doses at room temperature, and in single exposures, may lead to both equivalent-dose overestimation and increased levels of scatter in individual age estimates for samples with palaeodoses greater than ∼ 40 Gy. In the model, this effect is due to the large differences between laboratory and natural dose rates. A modification to standard irradiation practices is suggested as a remedy to this problem, whereby laboratory regeneration doses are administered in 10 Gy pulses, with the aliquot then being heated to 240 °C following each pulse. Empirical measurements of 12 sedimentary samples support the theoretical findings, with significant differences in dose response being observed between single-irradiation and pulsed-irradiation OSL regeneration data. Results are also presented in which the problem of the laboratory dose response failing to reach the level obtained through natural irradiation is remedied by the pulsed-irradiation procedure. It is possible that the application of pulsed-irradiation regeneration may in future lead to a more accurate means of dating the deposition of quaternary sediments, although this remains to be demonstrated empirically by the dating of known-age samples.