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Magnetic resonance studies of atomic hydrogen gas at liquid helium temperatures

Pulsed magnetic resonance studies are reported for a gas
of hydrogen atoms at densities of 3-10¹³ X 10 cm⁻³ and temperatures
of 4.2-77 K. The gas was produced by dissociation in a room temperature R.F. discharge, and piped through glass tubing into the cryogenic apparatus for study. The magnetic resonance transition observed is between the two lowest hyper-fine levels of the 1s atom in a magnetic field of 6481 Gauss where this splitting has its minimum value of about 765.5 MHZ.
At 77 K, spin-exchange broadening of the resonance is observed. By varying the number density of hydrogen atoms, the ratio of spin-exchange broadening to atomic hydrogen density is obtained, and from this ratio the spin-exchange cross section for this transition is calculated. The cross section obtained is 60% of the theoretical value.
At liquid helium temperatures, the spin-exchange cross
section is shown to be at least 15 times smaller than that at

liquid nitrogen temperatures, as. predicted by theory. He⁴
and H₂ buffer gases . are used to limit the diffusion broadening
of the resonance, allowing the observation of small frequency
shifts of the free induction signal. A model is proposed in
which interactions of the hydrogen atoms with the flow tube walls
cause these shifts. From the diffusion broadening of the
resonance, the diffusion cross sections for H in He⁴ at 4.2 K and H in H₂ at 5-9 K
are inferred to be 500 Ų and 250 Ų respectively. / Science, Faculty of / Physics and Astronomy, Department of / Graduate
Date January 1979
CreatorsWhitehead, Lorne Arthur
Source SetsUniversity of British Columbia
Detected LanguageEnglish
TypeText, Thesis/Dissertation
RightsFor non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use

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