Abstract
We present the first experimental evaluation of the alpha efficiency value for electron spin resonance (ESR) dating of coarse quartz grains, which is used for the evaluation of the internal and external alpha dose rate components. Based on our results, we recommend the use of an a-value of 0.07 ± 0.01 (1σ) for both the Al and Ti centres. Although we acknowledge that quartz ESR alpha efficiency may be sample dependent, and could also be impacted by other sources of uncertainty, this potential variability is presently impossible to evaluate given the absence of other experimental a-values available in the ESR dating literature. Measured radioactivity of quartz grains from the Moulouya catchment (NE Morocco) provides an internal dose rate in the range of 50–70 µGy/a when using an a-value of 0.07. The use of this empirically derived a-value for the evaluation of the internal and external alpha dose rate has a limited overall impact on the final ESR age results: they change by <2% and <3%, respectively, in comparison with those obtained with an assumed a-value. However, the large variability observed among the broader sample dataset for quartz internal radioactivity and hydrofluoric acid (HF) etching rates underscores the potential importance of undertaking experimental evaluations of alpha dose rate parameters for each dated sample.
Highlights
We present the first experimental evaluation of the alpha efficiency value for electron spin resonance (ESR) dating of coarse quartz grains, which is used for the evaluation of the internal and external alpha dose rate components
The gamma-irradiated aliquots exhibit systematically higher ESR intensities than their alpha-irradiated equivalents for both the Al and Ti centres, the alpha irradiation doses were chosen to be approximately ten times higher (~2230 and ~4460 Gy) than the gamma dose values (~200 and ~395 Gy) (Table S1). This is a good illustration of the lower efficiency of alpha irradiation in producing ESR signals when compared to gamma rays
As the mean a-value results obtained for the Al and Ti centres are statistically indistinguishable, it is appropriate to calculate a mean value of 0.073 ± 0.003 for the combined dataset as a reliable estimate of the true alpha efficiency for the ESR Al and Ti signals measured in these quartz samples
Summary
We present the first experimental evaluation of the alpha efficiency value for electron spin resonance (ESR) dating of coarse quartz grains, which is used for the evaluation of the internal and external alpha dose rate components. Measured radioactivity of quartz grains from the Moulouya catchment (NE Morocco) provides an internal dose rate in the range of 50–70 μGy/a when using an a-value of 0.07 The use of this empirically derived a-value for the evaluation of the internal and external alpha dose rate has a limited overall impact on the final ESR age results: they change by
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