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

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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