Experimental determinations of beta attenuation in planar dose geometry and application to ESR dating of tooth enamel

Two experiments were performed to determine the distribution of beta dose i n a target medium as a function of distance from a planar source (2 pi geom etry). In Experiment #1 planar absorbers were used to simulate depth in the target medium, and the attenuated dose that penetrated the intervening abs orbers was detected using thermoluminescence from CaSO4:Tm. In experiment # 2 pellets of powdered tooth enamel were situated in a cavity in solid tooth enamel. Dose response of the electron spin resonance (ESR) signals in the pellets allowed direct detection of dose distribution within the target med ium. The dose distributions were found to agree more closely with Monte Car lo calculations and with one-group transport theory (Prestwich er al., 1997 and Brennan ct al., 1997) than with approximations used widely in ESR dati ng applications (Grun, 1986); Although the latter were supported by experim ents by Aitken el al. (1985), the results of experiment #1 provided data to suggest that departure from 2 pi geometry was,unacceptably large in the Ai tken et al. (1985) configuration. The beta doses obtained by one-group theo ry in typical target volumes of enamel were 17 to 40% lower than those obta ined using the Grun approximation. It was concluded that one-group transpor t theory provides the best available routine tool for calculations of beta dose attenuation in near-planar target materials (e.g. tooth enamel and she ll) irradiated by natural sources, although Monte Carlo methods are better and could eventually be introduced into-the ROSY ESR dating program (Brenna n el al., 1997). It was also concluded that a revision of previously publis hed ESR ages using one-group transport for beta dosimetry will be needed. F or cases where the U concentrations in enamel are generally low (less than a few ppm), previously published ESR ages on tooth enamel are systematicall y too young by 5-30%. (C) 1998 Published by Elsevier Science Ltd. Air-right s reserved.