| Thermoluminescence(TL)dating is one of the main methods for geological dating,and it is the effective way to study the geological structure and geological environment for the Quaternary.The date sedimentary materials for TL dating are mainly quartz minerals,because of quartz minerals are rich in content and easy to be extracted.The 325?TL peak in quartz is main source of the OSL signal and readily bleachable.However,the higher temperature TL peak of 375?in quartz is more stable under daylight and has a much higher saturation dose than the 325?TL peak,the 375?TL peak has been widely used for TL dating.In TL dating,the single-aliquot regenerative-dose(SAR)protocol is more popular,but the measurement results of equivalent dose by SAR protocol may be not accurate,it may cause by the TL characteristics of quartz.The TL characteristics of quartz,including the shift of TL glow-curves at different irradiation doses and the reduction of TL sensitivity after repeated thermoluminescence,will cause abnormal results of TL dating measurement,it might even make incorrect result.Therefore,the researches on selecting the optimum measurement parameters and improving measurement protocol for TL dating have important significance for reducing the measurement error of TL dating.In view of the above problems about TL dating,this paper cut in from the fundamental properties of the TL characteristics of quartz,and the measurement results of the variation of the TL characteristics of quartz and their influenced on TL dating results are obtained by experiments.According to the measurement results,we propose the optimization scheme for the measurement parameters about TL dating,and then the improved protocol is proposed by the optimum measurement parameters and the conventional protocol.The following works were carried out:(1)This paper uses the experiments that include the shift of TL glow-curves at different irradiation doses and the reduction of TL sensitivity after repeat thermoluminescence to analyze variation and mechanism about the TL characteristics of quartz,and the influences for the results of TL dating.(2)According to the measurement results of the TL characteristics,this paper proposes the optimization scheme,and then the optimal pre-heat temperature and the optimal test dose for quartz with different diameter are selected by the optimization scheme and the range of regeneration dose for SAR protocol.(3)The improved protocol is proposed by the optimum measurement parameters and the conventional protocol,and is verified by verification experiment to verify whether the improved protocol is accurate and effective.Through the above research work,the following research results have been achieved:(1)This paper comprehensive investigates the TL characteristics of quartz that include mechanism and variation,and then this paper analyzes the influence of the TL characteristics for TL dating.Meanwhile,the analysis results provide theory support for the improvement of TL dating process.(2)Based on the nature doses and the regeneration doses that are in the range of100Gy?1000Gy for TL dating,this paper determines the optimal pre-heat temperature and the optimal test dose by experiments.Through those evaluation indexes of the shifts of TL peak and the loss of the intensity of TL peak,the optimal pre-heat temperature of both silt-sized grain quartz and sand-sized grain quartz are determined all as 300?.According the evaluation indexes that relative error(E_R)of the TL sensitivity is less than 5%,the optimal test doses of silt-sized grain quartz and sand-sized grain quartz separately are determined as 200 Gy and 250 Gy.(3)Based on the optimum measurement parameters and the conventional protocol,the improved protocol for TL dating is proposed,and is verified by verification experiment.The results of verification experiment show that when using the conventional protocol,the relative error of the equivalent dose 400 Gy and 700 Gy for silt-sized grain quartz are 14.74%?47.15%and 33.47%?197.71%respectively,and the relative error of the equivalent dose for sand-sized grain quartz are 7.81%?26.70%and 30.17%?100.37%respectively.And then when using the improved process,the relative error of the equivalent dose 400 Gy and 700 Gy for silt-sized grain quartz and sand-sized grain quartz are reduced in the range of-4%?4%and-6%?6%respectively.The equivalent doses that are measured by the improved protocol approximately are in agreement with the administered doses,and the improved protocol can extend the range of TL dating.(4)The geological dating of Dachaidan section is measured by the TL dating improved protocol and conventional protocol,and the results of TL dating approximately are in agreement with the presumed range of geological dating for alluvial-diluvial sandstone in this area.Meanwhile,those results prove the better applicability of the improved protocol in practical application. |
PDF Full Text Request