39Ar produced from 39K in potassium-containing rocks and minerals that is irradiated by fast neutrons in nuclear reactor is the basic of 39Ar-40Ar dating.There are few reactor resources for sample irradiation in China and lacked of irradiation parameters for different types of samples,which limits the development of high-precision 39Ar-40Ar dating.In this work,the irradiation parameters of G10 center channel with high neutron flux in High Flux Engineering Test Reactor(HFETR)were discussed for the first time.By irradiating biotite standard ZBH-25,calcium salt and potassium salt,the axial gradient of neutron flux,the production of 39ArK and the correction factor of interfering reaction were investigated.The results show that the J values of biotite standard ZBH-25 for 14 h and 35 h irradiation present a quadratic linear distribution(R2≥0.979),which is corresponding to the cosine function distribution of neutron flux,the neutron flux gradients are 0.88%·cm-1 and 0.45%·cm-1 which the variation is small,respectively indicating that the quartz tube is in the axially stable region of neutron flux and it is helpful to accurately calculate the J value of the sample.The production of 39ArK is 2.32×10-12 to 2.99×10-12(mol·h-1·%K2O),which is higher than the values of the outer channel of HFETR and other reactors.The average value of correction factor(40Ar/39Ar)K obtained by the irradiation of K2SO4 crystal is 2.96×10-3,and the proportion of induced 40Ar to the total 40Ar is(29±6)%,the average value of correction factor(36Ar/37Ar)Ca obtained by irradiation of CaF2 crystal is 2.54×10-4,the average value of correction factor(39Ar/37Ar)Ca is 7.31×10-4,and the proportion of induced 36Ar to the total 36Ar is(97±1)%.The correction factor results show that the increase of neutron flux can reduce the interference of atmospheric argon when calculating.The plateau age of biotite standard ZBH-25 is 132.89±0.93 Ma(2σ,MSWD=0.56),which is the same with the 132.7±0.6 Ma(2σ)age issued by previous studies.In summary,the G10 center channel in HFETR can satisfy the irradiation requirements of 39Ar-40Ar dating samples,especially is suitable for samples with old age and low K/Ca ratio.
HFETRG10 center channel39Ar-40Ar datingIrradiation parameters
万方数据
