TY - JOUR
T1 - Internal U, Th and Rb concentrations of alkali-feldspar grains
T2 - Implications for luminescence dating
AU - Smedley, Rachel
AU - Pearce, N. J. G.
N1 - This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.quageo.2016.05.002
PY - 2016/10/1
Y1 - 2016/10/1
N2 - This study assesses whether internal U, Th and Rb concentrations of single grains of alkali-feldspar can impact upon luminescence dating. Internal alpha dose-rates determined for two sedimentary samples calculated from mean U and Th concentrations accounted for ∼10% of the total dose-rates, while internal beta dose-rates from mean Rb concentrations accounted for ∼2%. Depth profiles of measurements penetrating into each grain show that internal U and Th concentrations varied between grains, where some grains had effective internal alpha dose-rates up to 1.8 Gy/ka (32% of the total dose-rate). K concentrations inferred from Rb (KRb) for individual grains suggest that internal U and Th concentrations are related to the feldspar composition. Grains with KRb > 6% had low U and Th, and grains with KRb < 6% had higher U and Th concentrations. Internal alpha and beta dose-rates of the perthitic and Na-rich grains contaminating the density-separated K-feldspar separates had a significant impact upon the single-grain De distributions, which was estimated to be equivalent to overdispersion values of ∼10–15%. The scatter in the De distributions arising from internal alpha and beta dose-rates for both samples could be reduced by selecting only the brightest 20% of grains for luminescence dating.
AB - This study assesses whether internal U, Th and Rb concentrations of single grains of alkali-feldspar can impact upon luminescence dating. Internal alpha dose-rates determined for two sedimentary samples calculated from mean U and Th concentrations accounted for ∼10% of the total dose-rates, while internal beta dose-rates from mean Rb concentrations accounted for ∼2%. Depth profiles of measurements penetrating into each grain show that internal U and Th concentrations varied between grains, where some grains had effective internal alpha dose-rates up to 1.8 Gy/ka (32% of the total dose-rate). K concentrations inferred from Rb (KRb) for individual grains suggest that internal U and Th concentrations are related to the feldspar composition. Grains with KRb > 6% had low U and Th, and grains with KRb < 6% had higher U and Th concentrations. Internal alpha and beta dose-rates of the perthitic and Na-rich grains contaminating the density-separated K-feldspar separates had a significant impact upon the single-grain De distributions, which was estimated to be equivalent to overdispersion values of ∼10–15%. The scatter in the De distributions arising from internal alpha and beta dose-rates for both samples could be reduced by selecting only the brightest 20% of grains for luminescence dating.
UR - http://hdl.handle.net/2160/42997
U2 - 10.1016/j.quageo.2016.05.002
DO - 10.1016/j.quageo.2016.05.002
M3 - Article
SN - 1871-1014
VL - 35
SP - 16
EP - 25
JO - Quaternary Geochronology
JF - Quaternary Geochronology
ER -