Artificial Production of Neutrons

A porcelain vacuum tube capable of producing currents of positive ions up to 30 microamperes and with energies up to ${10}^6$ electron-volts has been constructed and used for artificial disintegration experiments. Neutrons have been produced by bombarding beryllium with helium ions, and by bombarding lithium and beryllium with the ions of the heavy isotope of hydrogen. The curve obtained for the efficiency of production of neutrons by helium ions as a function of voltage is in agreement with the curve obtained by a downward extrapolation of curves known from work with polonium $\alpha$-particles. The present paper is mainly a discussion of the apparatus and methods of measurement, since brief reports of the results have already been presented.