31 research outputs found
Development of a residency program in radiation oncology physics: an inverse planning approach
Effect of an electric field on superfluid helium scintillation produced by alpha-particle sources
We report a study of the intensity and time dependence of scintillation
produced by weak alpha particle sources in superfluid helium in the presence of
an electric field (0 - 45 kV/cm) in the temperature range of 0.2 K to 1.1 K at
the saturated vapor pressure. Both the prompt and the delayed components of the
scintillation exhibit a reduction in intensity with the application of an
electric field. The reduction in the intensity of the prompt component is well
approximated by a linear dependence on the electric field strength with a
reduction of 15% at 45 kV/cm. When analyzed using the Kramers theory of
columnar recombination, this electric field dependence leads to the conclusion
that roughly 40% of the scintillation results from species formed from atoms
originally promoted to excited states and 60% from excimers created by
ionization and subsequent recombination with the charges initially having a
cylindrical Gaussian distribution about the alpha track of 60 nm radius. The
intensity of the delayed component of the scintillation has a stronger
dependence on the electric field strength and on temperature. The implications
of these data on the mechanisms affecting scintillation in liquid helium are
discussed.Comment: 17 pages, 23 figure