Ultra-sensitive detection of hydrogen isotopes by Lyman-α RIS

An ultra-sensitive way of detecting hydrogen isotopes (muonium, H, D, and T) is described, by in which a resonant ionization scheme through the {1S-2P-unbound} transition is utilized. A time-of-flight measurement using the pulsed lasers coupled with a mass separation enables us to distinguish any hydrogen isotope with very low backgrounds. As a real demonstration of sensitive detection, H, D, and T atoms generated simultaneously by the nuclear reactions of a 500-MeV proton beam were shown to be easily distinguished and extracted without changing any experimental condition other than the corresponding Lyman-α wavelength. In the case of a laser-induced fluorescence technique using Lyman-α or Balmer-α photons, the lowest detection limit is reported to be as low as on the order of 107-109 cm-3, or 107 cm-3, respectively. In the case of two-photon induced Balmer-α emission, the detection limit is reported to be on the same order as that by three-photon ionization, 3 x 109 cm-3. The detection limit of the present method is estimated to be about 7.7 x 103 cm-3. The method of applying Lyman-α resonant ionization spectroscopy can be recognized as an ultra-sensitive and efficient mass-selection technique. (author)