Studies of isochron luminescence dating with sand-sized grains
STUDIES OF ISOCHRON LUMINESCENCE DATING WITH SAND-SIZED GRAINS
Submitted by Zhao Hui
for the degree of Doctor of Philosophy at The University of Hong Kong
in September 2002
The study was focused on isochron luminescence dating with sand-sized grains of quartz and K-feldspar. The proposed isochron approaches do not require any assumptions concerning the stability of the external dose rate. These approaches can be applied to samples for which K-feldspar has a significant underestimation of the equivalent dose (De). It was observed that the De values of both quartz and K-feldspar change linearly with grain size, supporting the assumption that all K-feldspar grainsize fractions from the same sample have a constant underestimation factor. This underestimation factor can be estimated by extrapolating the trend line of De values against with the grain-size to zero. The calculated isochron ages with all grain-size fractions are consistent with the values expected from quartz separates, and have smaller uncertainty than using two grain-size fractions.
The internal dose rate is very important for the isochron dating method. Internal radioactivity in K-feldspar grains indicated that the K-content of individual K-feldspar grains is about 13%. This content is higher than the estimation from routine measurements of bulk samples. Concentrations of uranium (U), thorium (Th) and rubidium (Rb) in K-feldspar were obtained using the inductively coupled plasma mass spectrometry (ICP-MS) analysis. U and Th concentrations of K-feldspar are higher than expected. The dose rate contributions, especially the alpha dose from U and Th, should be considered in the K-feldspar dating.
In the isochron approach with sand-sized grains, the internal dose rate from U, Th and Rb hardly affects the results because their internal dose rates are almost
independent from grain sizes.
The single aliquot additive dose (SAAD) method was compared with the single aliquot regenerative dose (SAR) method for quartz, and it was found that the luminescence correction SAAD method can only be applied to samples for which the natural signal is in the linear part of the growth curve. A growth function correction (GFC) was applied to the SAAD data sets and improved growth curves were obtained.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:quartz feldspar thermoluminescence dating
Date of Publication:01/01/2003