Partial Atomic Stopping Power of Gaseous Hydrogen for Hydrogen Beams. I

Abstract

The stopping power of ${\mathrm{H}}_{2}$ gas for the atomic component of a hydrogen beam in charge equilibrium has been measured by placing the stopping cell in an intense transverse magnetic field. This allows only those particles to reach the exit which have entered as neutrals and have not experienced any collision, as a result of which they became electrically charged. These neutrals are partially converted to protons in a subsequent gas stripper cell, and their energy measured in an electrostatic deflector. As ${\mathrm{H}}_{2}$ gas is admitted to the stripping cell, there is a rapid decay in beam intensity, since at each charge-changing collision the particle is extracted from the beam by the magnetic field. By counting individual exit particles, however, a beam diminution factor of ${10}^{\ensuremath{-}7}$ is acceptable and a well-defined energy group is detected which has experienced a loss of approximately 1% of its energy, and for which the stopping power ${\ensuremath{\epsilon}}_{0}$ of ${\mathrm{H}}_{2}$ gas, for instance at 50 keV, is only 0.42 of the conventional $\ensuremath{\epsilon}$, measured with the field off. The values of $\ensuremath{\epsilon}$ reported agree with those of Reynolds, Dunbar, Wenzel, and Whaling. The results for ${\ensuremath{\epsilon}}_{0}$ and $\frac{{\ensuremath{\epsilon}}_{0}}{\ensuremath{\epsilon}}$ are: Above 50 keV the experimental ${\ensuremath{\epsilon}}_{0}$ values agree well with those theoretically calculated by Dalgarno and Griffing for atomic hydrogen gas; at lower energies the experimental values are somewhat higher.