Application Of LA-ICPMS Method On Apatite Fission Track Analysis

Apatite fission track analysis has significant meaning in the field of geology.Informations such as age and annealing got from fission track analysis providing a basis for the ancient strata inversion and palaeogeothermal evolution.In the Apatite fission track analysis,the 238 U content of apatite grains is a important parameter of grain age calculation.The average content of 238 U in the earth's crust is about 2.5 ?g/g,so we need instrumental analytical method with higher sensitivity and precision.The present analytical method for trace elements analysis in kinds of sample include: inductively coupled plasma mass spectrometry(ICP-MS),neutron activation analysis,inductively coupled plasma atomic emission spectrometry(ICP-AES),spectrophotometry,fluorescence method,et al.ICP-MS method has been used for trace elements analysis since its high sensitivity and speed,low detection limit,and the capacity of multielement analysis at the same time.In apatite fission track analysis,we need to analysis 238 U content at the home position of apatite grains.NAA method often used for analyzing 238 U content,but its procedures is complex,and its precision is not very high.In recent years,LA-ICPMS which has united the advantages of laser ablation(LA)and ICP-MS is a new hot point in this field.This research has discussed effects of different LA conditions on signal to achieve the aim of direct analysis of glass samples and rock slice samples by LA-ICPMS.By comparing the reproducibility and fractionation factor of trace elements in standard glass samples NIST SRM 612 and NIST SRM 610.The result shows that when the aperture of the ablation is 32 ?m,carrier gas flow rate is 400 mL/min,the laser energy density is 7 J/cm2,laser pulse rate is 12 Hz,the content of 208 Pb,232Th,238 U,55Mn,88 Sr and 205 Tl in NIST SRM 612 have good consistency with the reference value(RSD less than 16%).Content of 232Th?238U?55Mn and 88 Sr in apatite was measured by this LA-ICPMS method and using NIST SRM 612 and NIST SRM 610 as external standard,the results of these elements are 240~390 ?g/g,8~15 ?g/g,80~120 ?g/g and 440~570 ?g/g,and the RSD is less than 22%.The age result calculated by the content of 238 U in apatite grains has a good consistency,that means LA-ICPMS method can be applied in apatite fission track analysis.