Changes in the charge of an α-Particle passing through matter

Abstract

It is remarkable that investigations on the velocity of α -particles have hitherto failed to detect with certainty particles of velocity less than about 8 x 10 8 cm. per second (0.4V 0 , where V 0 is the initial velocity of α -particles from RaC). Geiger believed he had found a-particles with velocities as low as 0.3V 0 . However, later work of Marsden and Taylor showed that when the velocity of an α -ray beam had fallen to about 0.45V 0 , any further increase of absorption caused a rapid decrease in the number of particles; the number fell to zero when the velocity had decreased to about 0.4V 0 . Thus the minimum observed energy was that which would be acquired by the α -particle in falling through about 600,000 volts. It is surprising that particles with such enormous energy should vanish, leaving no trace. Positive rays of much less energy have of course been detected in several ways.