Extending the maximum age achievable in the luminescence dating of sediments using large quartz grains: A feasibility study

The feasibility of extending the upper dating limit in the luminescence chronometry of sediments using centimeter size quartz grains has been investigated. In general for such large sized quartz grains, the total dose is from radioelements external to the grain and this dose gets progressively attenuated towards the grain centre. Thus, for a centimeter size grain, a finite portion of the inner volume largely receives only the gamma dose. Such a reduced dose implies a delayed onset of saturation and hence offers the prospects of a higher age limit. Monte-Carlo simulations were used to compute beta dose depth distribution inside such grains when irradiated by beta particles from 40K, 212Bi (232Th-series) and 234mPa and 214Bi (238U-series). These computations suggest that quartz grains of up to 6–10 mm diameter would have an inner core of ∼2–6 mm that receives minimal beta dose. Given that gamma dose is only a third to a fourth of the total dose, this approach offers the prospect of a three to four fold increase in the age limit obtainable by luminescence methods. This contribution discusses the conceptual formalism, computational aspects and outlines some of the practical difficulties and remedial measures for routine applications.