Artificial Production of Neutrons
It has been shown by Curie and Joliot that [alpha]-particles of energy as low as 1,300,000 electron-volts are capable of disintegrating beryllium with the production of neutrons, and that the efficiency of the excitation follows roughly that predicted on the basis of the Gamow theory. The present writers have constructed an apparatus for accelerating helium ions up to 1,000,000 volts, with the object in view of obtaining a strong artificial source of neutrons, and of investigating the fficiency of production of neutrons in the region below 1,000,000 volts. This region does not seem to be accessible with the available radioactive sources of [alpha]-particles, due to the low efficiency and consequent large number of [alpha]-particles which would be required to produce a measurable effect. Theoretically, the probability of a 1,000,000 volt [alpha]-particle penetrating the beryllium nucleus is about 10^-4 times that of a full range polonium [alpha]-particle. At 750,000 volts this factor becomes 10^-5, and at 500,000 volts it is 10^-7. It is therefore necessary in this energy range to have a positive ion current of the order of 10 or 100 microamperes to produce an appreciable effect.