热电离质谱全蒸发技术在钚同位素丰度测量中的应用

Application of Total Evaporation Technique Using Thermal Ionization Mass Spectrometry in Measurement of Plutonium Isotopes

对影响热电离质谱全蒸发测量的主要因素进行研究,包括点样量、同质异位素的干扰等,并将全蒸发技术与传统测量技术测量IRMM-086的结果进行对比。结果表明,全蒸发技术可在更少的点样量下获得比传统测量法更佳的测量精度,当同位素比值大于10-4时,结果与标准值偏差小于2σ。在50 ng IRMM-086点样量下,全蒸发测量的^(240)Pu/^(239)Pu、^(241)Pu/^(239)Pu、^(242)Pu/^(239)Pu相对标准偏差分别为0.0068%、0.50%和0.83%。对于钚同位素比值分析,全蒸发测量技术可直接获得高精度、高准确度的测量结果。

When measuring the isotope ratio of plutonium by thermal ionization mass spectrometry with conventional method,the plutonium isotope standard material is usually needed to calibrate the bias caused by the isotope fractionation which is the main factor that influences the accuracy of results.Recent years,the total evaporation technique has become a good choice because of its inherent characteristics that can obtain results with no significant bias without calibrate by external standard.In this work,the main factors were investigated that influence the total evaporation measurement of thermal ionization mass spectrometry,including the amplifier current gain calibration,sample amount,and the isobaric interference ^(238)U and ^(241)Am.^(241)Am was separated from the aged plutonium by UTEVA resin,it was shown that isotopic analysis of plutonium should be completed within a reasonable time period after separation from Americium to minimize interference of ^(241)Am in-growth from decaying ^(241)Pu,and the interval limiting between sample purification and isotopic analysis was about 20 days to make sure the accuracy and precision,there would be about 2%bias after 30 days of separation.The sample lost between integration due to the necessary to adjust the filament current and the residual sample after measuring was eliminated as less than 0.3%.Measured with total evaporation technique utilizing Faraday cups only,IRMM-086 with different sample loadings were studied respectively,the results showed that sample loading between 50 and 100 ng were likely enough for good accuracy and precision,but there were also slightly biases in the ^(238)Pu/^(239)Pu and ^(242)Pu/^(239)Pu due to the low signal of ^(238)Pu and ^(242)Pu influenced by the noise of Faraday cups.The results of IRMM-086 using total evaporation and conventional techniques were compared,and showed that the total evaporation technique could obtain better accuracies than the conventional method while sample loading for total evaporation and conventional were 50 ng and 200 ng respectively.There was no significant bias between measured and certified value when isotope ratio was more than 10^(-4).For IRMM-086,the relative standard deviations of ^(240)Pu/^(239)Pu,^(241)Pu/^(239)Pu,^(242)Pu/^(239)Pu measured by total evaporation were 0.0068%,0.50%and 0.83%,respectively.Giving high precision and accuracy results without calibration,the total evaporation technique will be more widely used when we have a lower noise amplifier for Faraday collectors.In the field of spent fuel reprocessing analysis,plutonium isotope composition varies greatly due to different burn-up.Total evaporation measurement technology has a very good application prospect in the field of plutonium isotope composition measurement.