Background: In combined Electron spin resonance(ESR)/U-series dating of tooth fossil

annual dose is comprised of the dose rate contributed by α-rays

β-rays and γ-rays. A correction factor(called alpha-efficiency or k-value) is applied to the measured or calculated alpha dose rate. However

due to the experimental difficulty

k-value could not be measured very precisely. Purpose: In order to investigate the effects of the two commonly used k-values and the variation on the dating results

we analyzed the tooth enamel samples from Longgupo

a hominid archaeological site in Chongqing. Methods: Five tooth fossils from Longgupo site were analyzed using combined ESR/U-series method

and their ages were calculated with DATA program. Results: The study showed that the sample ages decreased as k-value increased from 0 to 0.3. For the samples of low uranium concentration

the ages only had small changes(~2%)

while for those of high uranium concentration

the ages decreased obviously(up to 50%)

and 20% decrement appeared when k-value increased from 0.13 to 0.23. For dating results of samples of similar uranium concentration

those of higher 230Th/234U ratio were affected more obviously with the k-value variation. Conclusion: The difficulty of measurement makes it hard to obtain a very precise k-value

and different k-values indeed cause considerable uncertainty to the fossil dating results. In addition

k-value may vary according to the uranium content of the tooth tissues

which will be investigated in further study.