Effects of impurity atoms and molecules on the lifetime of antiprotonic helium atoms
- Institute for Nuclear Study, University of Tokyo, 3-2-1 Midori-cho, Tanashi, Tokyo 188 (Japan)
- Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113 (Japan)
- Tokyo Institute of Technology, O-Okayama, Meguro-ku, Tokyo 152 (Japan)
- Research Center for Nuclear Science and Technology, University of Tokyo, Tokai, Ibaraki 319-11 (Japan)
- Institute for Molecular Science, Myodaiji, Okazaki 444 (Japan)
- Physik Department, Technische Universitaet Muenchen, D-85747 Garching (Germany)
- CERN, CH-1211 Geneva 23 (Switzerland)
Delayed annihilation time spectra (DATS) of antiprotons in room-temperature helium gas have been studied as a function of the concentration of admixed noble gases (Ne,Ar,Kr,Xe) as well as molecular gases (N{sub 2},O{sub 2},H{sub 2}) at the low-energy antiproton ring at CERN. The DATS were a superposition of two exponential components, one with a lifetime of several 100 ns and the other with a lifetime 1{endash}3 {mu}s. They showed a shorter average lifetime ({ital T}{sub av}) than DATS of pure helium. Ne, Ar, and Kr were found to affect {ital T}{sub av} only slightly even in concentrations up to 20{percent}, while Xe showed a much stronger influence. In the case of molecular gases, the presence of N{sub 2} influenced the DATS much less than O{sub 2} and H{sub 2}, which destroyed the metastability almost completely in concentrations of 100 ppm and less. The decay rate of the slow component of DATS was found to exhibit a linear relation to the number density of the admixture. From this a collisional destruction ({open_quote}{open_quote}quenching{close_quote}{close_quote}) cross section {sigma}{sub {ital q}} was extracted. No evidence for a delayed annihilation of antiprotons in pure Ne, Kr, and Xe was observed. {copyright} {ital 1996 The American Physical Society.}
- OSTI ID:
- 285226
- Journal Information:
- Physical Review A, Vol. 53, Issue 5; Other Information: PBD: May 1996
- Country of Publication:
- United States
- Language:
- English
Similar Records
Phase and density dependence of the delayed annihilation of metastable antiprotonic helium atoms in gas, liquid, and solid helium
CROSS SECTIONS FOR THE DE-EXCITATION OF HELIUM METASTABLE ATOMS BY COLLISIONS WITH ATOMS