Study of the Ultra Sensitive Detection of Hydrogen Isotope by the intense Lyman-α resonant ionization

我们一直在探索一种利用{1S→2P→未结合}跃迁的共振电离方案来检测和提取氢同位素的超灵敏方法。利用脉冲激光与质量分离装置的飞行时间测量使我们能够区分具有非常低背景的任何氢同位素。通过制备一种新的“慢离子光学”装置来有效地提取氢同位素离子，提高了该方法的检测限，远优于3 × 10^3 cm^<-3>。在使用莱曼-α或巴尔默-α光子的激光诱导荧光技术的情况下，据报道，最低检测限分别低至10^7-10^9 cm^<-3>或10^7 cm^<-3>数量级。在双手机诱导巴尔默α发射的情况下，检测限据报道与三光子电离的检测限相同，3 × 10^9 cm^<-3>。目前莱曼α共振电离法的检出限可通过以下程序来评估。假设在2000 K下，在9.5 × 10^<-8> mbar的H_2气体中，W表面H_2解离的概率为10%，则约有3 × 10^7个H原子存在于约0.6 cm^3的体积中，这是沿激光通道的有效萃取体积。由于我们在2000 K下获得了时间宽度为80 ns的4.5V的MCP信号，而单事件在20 ns下获得了时间宽度为2 mV的MCP信号，因此我们可以评估在2000 K下提取的每个激光脉冲中9000个氢原子的数量。由此计算，提取和检测效率为3 × 10^<-4>。由于残余气体不可能完全由氢分子组成，估计莱曼α共振电离法的检测限优于3 × 10^3 cm^<-3>。因此，它比其他方法好3 - 5个数量级。与我们之前的报告相比，它至少改善了2.5倍以上，这是我们所知道的最高水平。Lyman-α共振电离光谱法是一种超灵敏、高效的质量选择技术。少

We have been pursuing an ultra-sensitive method for detecting and extracting hydrogen isotopes by utilizing a resonant ionization cheme via the {1S→2P→unbound} transition. A time-of-flight measurement using the pulsed lasers coupled with a mass separation device enables us to distinguish any hydrogen isotope with a very low background. By preparing a new "Slow Ion Optics" set-up to extract hydrogen isotope ions efficiently, the detection limit of the present method was improved to be much better than 3x10^3 cm^<-3>.In the case of the laser induced fluorescence technique using Lyman-α or Balmer-α photons, the lowest detection limit is reported to be as low as the order of 10^7-10^9 cm^<-3>, or 10^7 cm^<-3>, respectively. In the case of the two-phone induced Balmer-α emission the detection limit is reported to be same order as that by three photon ionization, 3 X 10^9 cm^<-3>.The detection limit of the present Lyman-α resonant ionization method can be evaluated by the following procedure … More . Assuming the probability of H_2 dissociation at the W surface at 2000 K to be 10% in 9.5 x 10^<-8> mbar of H_2 gas, about 3 x 10^7 H atoms exist in a volume of about 0.6 cm^3, which is the effective volume of extraction along the laser passage. Since we obtained an MCP signal of 4.5V with a temporal width of 80 ns at 2000 K, in contrast with that of 2 mV with 20 ns for a signle event, we can evaluate the number of 9000 H atoms per laser pulse that are extracted at 2000 K.From this, the extraction and detection efficiency is calculated to be 3 x 10^<-4>. Since the residual gas is not likely to be completely consisted of hydrogen molecules, the detection limit of the present Lyman-α resonant ionization method is estimated to be better than 3 x 10^3 cm^<-3>. It is thus 3 - 5 orders of magnitude better than the other methods. And also it is improved at least more than 2.5 times compared with that of our previous report and it is highest that we know of. The method of applying Lyman-α resonant ionization spectroscopy can be recognized as an ultra sensitive and efficient mass-selection technique. Less