Some experiments on the production of positive electrons

This paper describes work curried out during the last year on the production of positive electrons, or positrons. by various radiations. Although it is probable that the positrons found in conjunction with cosmic raw have their origin in the interaction of some penetrating radiation with matter, these experiments gave no direct information about their mode of origin. In order to throw light on this and to have a method of studying their properties more closely it was necessary to seek a means of producing positrons under easily controlled conditions. Our first experiments directed to this end were those which showed that the radiation from beryllium bombarded by polonium α-particles, a radiation consisting of γ-rays and neutrons, could eject positrons from lead. A preliminary notice of these results was given by us in a letter to ‘Nature.’ Almost at the same time Meitner and Philipp and Curie anti Joliot reported the same effect.