Multiple Scattering of Low-Energy Alpha Particles in a Gas

Abstract

Alpha particles from a polonium source were slowed down and allowed to enter a cloud chamber containing a mixture of hydrogen, water, and ethyl alcohol at pressures of 12.25 cm, 1.50 cm, and 2.25 cm, respectively, during the sensitive time. Eighty-four sharp tracks of particles which stopped in the illuminated part of the chamber and which did not show any sharp bends due to single scattering were selected for study. Starting at the termini of the projected tracks, the angles between successive chords of three millimeters length were measured, the energies at the first three intersections of the chords being approximately 18, 45, and 85 kev. The magnitudes of the angles at which the tails of the distributions could be distinguished from the Gaussian parts were determined to be 10°, 6° to 8°, and 4°, respectively. The total standard deviations (which included the experimental error of 2.2°) for the Gaussian part of the distributions at these energies were 8.0°, 4.3°, and 3.0°, respectively, so that the standard deviations due to multiple scattering were, respectively, 7.7°, 3.7°, and 2.0°.