激光剥蚀-多接收电感耦合等离子体质谱法测定含钚颗粒物中^(240)Pu/^(239)Pu比值

Determination of^(240)Pu/^(239)Pu in Plutonium-containing Particle by Laser Ablation Multiple Collector Inductively Coupled Plasma Mass Spectrometry

为高精度、准确地获取含钚颗粒物中具有核保障监督意义和核取证价值的钚同位素比值,建立了激光剥蚀-多接收电感耦合等离子体质谱(LA-MC-ICP-MS)测定含钚颗粒物中^(240)Pu/^(239)Pu的分析方法。采用检漏、安装排风罩和擦拭剥蚀池内壁等方式有效降低激光剥蚀产物沾污实验室和危及人身安全的潜在风险。联用扫描电迁移率粒径谱仪(SMPS)与激光剥蚀-多接收器等离子体质谱(LA-MC-ICP-MS)研究了激光剥蚀玻璃基体标样产生气溶胶的分布特性,结果表明,剥蚀产物的主要粒径是40~500 nm,应尽量采用水平管道连接激光剥蚀进样系统与MC-ICP-MS,含钚颗粒物分析后剥蚀池持续吹扫时间应大于15 min。采用外标归一化法离线校正质量分馏效应和离子计数器检测效率,建立了含钚颗粒物中^(240)Pu/^(239)Pu的LA-MC-ICP-MS分析方法,固定束斑直径30μm、脉冲重复率5 Hz、剥蚀时间5 s,调节能量密度使含钚颗粒物模拟样品中239Pu的信号强度分别达2×104cps和2×105cps,本方法对^(240)Pu/^(239)Pu测量的相对实验标准不确定度小于1.4%(n=6),测量结果与参考值的相对偏差小于4.7%,仪器调试时间和单个样品测量时间分别为9.0和0.5 h。含钚颗粒物模拟样品分析结果表明,本方法精度高、结果准确、分析速度快,可满足核保障监督、禁产核查和核取证中含钚颗粒物直接分析的需求。

The isotopic fingerprints of plutonium are extremely important for nuclear safeguards and nuclear forensics. An analytical method was developed for direct determination of240Pu/239Pu ratio in plutoniumcontaining particles by laser ablation multiple collector inductively coupled plasma mass spectrometry（ LAMC-ICP-MS）. The risk of ablated particles leakage was reduced by leak detection,exhaust hood,and swiping the laser cell. Scanning mobility particle sizer（ SMPS） was used to measure the effect of ablation parameters on the size distribution of ablated particles. The results showed that the majority of ablation material presented as particles from 40-500 nm and the sweep time after laser ablation should be longer than 15 min. The particle size was evaluated to guide LA-MC-ICP-MS system. By using external normalization method for correction of the mass fractionation correction factor and ion counter efficiencies measured by nebulizer-coupled MC-ICP-MS,a LA-MC-ICP-MS method was established for analysis of 239Pu/240Pu ratio in plutonium particles. Spot size,ablation rate and laser dwell time were set at 30 μm,5 Hz and 5 s,respectively. Laser energy density was controlled to ensure that the intensities of239 Pu for plutonium-containing particles were about 2 × 104 cps and 2×105 cps,respectively. The analytical results showed that the relative uncertainties for239 Pu/240 Pu was less than 1.4%（ n = 6）,and the measured value deviated by less than 4. 7% from the reference value. The time for adjusting system and determining 239Pu/240Pu ratio in single plutonium particle was 9 h and 0. 5 h,respectively. The results demonstrated that this technique was rapid,precise and accurate,and could be used for determination of 239Pu/240Pu in plutonium-containing particles.