What to do when carbonate replaced water: Carb, the model for estimating the dose rate of carbonate-rich samples

Abstract

_____________________________________________________________________________________________ Introduction In 2008 we published a paper (Nathan and Mauz, 2008) where we described, calculated and modeled the impact of carbonate on the dose rate. Since then the software (called 'Carb') has been employed in several studies (Mauz et al. resulting in a clear and unequivocal impact on the accuracy of the OSL ages which allowed to improve sedimentological models on the 100 ka Milankovitch time scale (Mauz et al., 2013). This increased the confidence that the dose-rate model is a reliable tool to correct for post-depositional chemical alterations involving carbonate. Since publication, Nathan and Mauz, 2008 received some attention, but it failed to incentivise dose-rate modeling where it was-according to sample description in the relevant publications-certainly appropriate. We conclude that more attention needs to be drawn to this issue by (i) providing a clear and comprehensive description of the impact of carbonate on the dose rate and by (ii) making the code available to users. When Nathan and Mauz (2008) was published, Carb suffered from two weaknesses: (1) correction of U-series secular disequilibrium caused by post-mortem U-uptake of mollusk shells was not possible and (2) interstitial carbonate was assumed to be inert while no data were available to (dis-)prove this. With this short paper we wish to encourage users to appreciate (i) the importance of dose-deposition efficiency and its dependence on material properties and (ii) the significance of dose-rate change over time. We aim at removing doubts and misunderstandings about the impact of carbonate on dose rate, at explaining the code including its update, its assumptions and limitations and at providing instructions on how to use it. For description of the underlying physics, in particular the infinite matrix concept, calculation of attenuation factors, determination of mass stopping powers and mass absorption coefficients, the reader