Background: In ESR and luminescence archaeological dating

the assessment of external radiation dose rate is one of the constant sources of uncertainty because of its variation in the past time and it cannot be determined accurately using the present-day measurements.Purpose: ESR isochron protocol was proposed to solve this uncertainty for the tooth samples.This protocol is applicable wherever multiple samples with different internal doses have all experienced a common external dose.The variable uranium concentration of tooth samples makes it possible to plot the equivalent dose versus the internal dose rate of each sample

and the slope of isochron line gives hence the age.For isochron dating of teeth

combined ESR/U-series dating analysis must be done together with isochron protocol.Methods: In this study

we try to use combined ESR/U-series isochron method on 5 tooth samples collected from immediate adjacent square in layer C III’6 of Longgupo archaeological site

Chongqing

China.Combined ESR/U-series analysis with in situ external dose rate shows recent uranium uptake of all the samples.Results: The time-averaged external dose rate was iterative calculated by isochron protocol

and gives an isochon age of 1.77±0.09 Ma for layer C III’6

which consistent with the mean US-ESR ages of 5 samples(1.64+0.16/ 0.21 Ma) in the error range.The calculated time-averaged external dose rate(~807 μGy/a) was basically in agreement with the in situ measured gamma dose rate value(850 μGy/a) in 2006

indicating the geochemical alterations may not occurred or do not affect the environmental dose rate obviously during the burial history.Conclusions: This study indicates the potential of solving both internal and external dose rate problems of ESR dating of fossil teeth by combining with U-series analysis and isochron protocol.