5:15 PM - 6:45 PM
[HQR06-P02] ESR equivalent dose evaluation of sediments using a partial annealing procedure
Keywords:ESR, quartz, sediments, bleach
The most serious problem in applying electron spin resonance (ESR) dating to sediment samples is the overestimation of the equivalent dose (De) due to incomplete bleaching. However, this is a more complex issue because the Al center signals have an unbleachable component that is not attenuated by long time exposure to sunlight. A reliable De can be obtained by subtracting the unbleachable Al signal from the apparent De of the dating sample or by subtracting the incomplete dose of the modern sediment sample. Both of these methods require that the De values be correctly evaluated. These considerations must also account for time constraints due to long time exposures and the influence of the difference in thermal stability between the Al and Ti centers. We have examined the thermal stability of these related ESR signals and have confirmed that (1) the unbleachable signal of the Al center is more thermally stable than the bleachable signal, and (2) the sensitivity of the Ti center to radiation does not change after either annealing or bleaching. These findings suggest that the bleaching to obtain the signal intensity of unbleachable Al centers can be reproduced by partial annealing, and that the zero resetting of Ti centers can be done by annealing for the equivalent dose evaluation.
In this study, we confirmed the validity of the protocol which replaced the procedure of bleaching with heating in the dating protocol by the dose recovery test. All of the following four protocols were successful, with a recovery ratio within 10 %: the MAR protocol for Al center employing partial annealing, the MAR protocol for Ti center employing annealing, the MAR protocol employing bleaching and with the MAAD protocol. This showed that hundreds of hours of ESR signal bleaching could be replaced by heating for less than one hour. It will also discuss the effect of preheating and thermal transfer ESR signals.
In this study, we confirmed the validity of the protocol which replaced the procedure of bleaching with heating in the dating protocol by the dose recovery test. All of the following four protocols were successful, with a recovery ratio within 10 %: the MAR protocol for Al center employing partial annealing, the MAR protocol for Ti center employing annealing, the MAR protocol employing bleaching and with the MAAD protocol. This showed that hundreds of hours of ESR signal bleaching could be replaced by heating for less than one hour. It will also discuss the effect of preheating and thermal transfer ESR signals.