【摘要】 铱（Ir）同位素组成可作为理想的核燃料燃耗指示信息。提高Ir待测离子的电离效率,以获得足够强度且稳定的离子流是精确测量痕量Ir同位素组成的关键。因Ir电离电位较高,极难形成稳定的正离子,因此需采用负离子模式。本研究通过对比不同的灯丝材料、灯丝结构、涂样条件、电离温度等因素,建立并优化了Ir的负离子转化条件。通过采用Pt单带、Ba（OH）₂为发射剂涂样,并缓慢提高灯丝电流,50 ng的Ir电离效率可达9.8×10^-4。经氧同位素校正后,Ir涂样量10 ng以上的n(¹⁹¹Ir)/n(¹⁹³Ir)同位素比值与标准溶液的参考值在误差范围内一致,且相对标准偏差优于0.2%,能够满足痕量Ir同位素组成的测量精度要求。更多还原

【Abstract】 The isotopic ratio of iridium is a useful tool for the identification of burn-up of nuclear fuel in nuclear industry. The key issue for precise measurement of isotopic ratios of iridium in trace amount is to improve ionization efficiency, in order to generate sufficient ion intensity and stable ion beam. Negative thermal ionization mass spectrometry（N-TIMS） is proven to be a powerful method for the analysis of nuclides with relatively high ionization potentials. In this work, a novel method was established based on N-TIMS for the precise measurement of Ir isotopes. The optimized condition was developed after comparing IrO₂^- ion beams under different circumstances. The ionization efficiency of 50 ng Ir could reach up to 9.8×10^-4 when employing Pt single filament and Ba（OH）₂ as ionization activator. The iridium isotope ratios of n(¹⁹¹Ir)/n(¹⁹³Ir) obtained after oxygen isotopic correction agree well with the certified values in the range of the analysis error, and the external precision for 10 ng Ir sample loads is better than 0.2%, which can fulfill the requirements for applications in nuclear industry.更多还原