Comparison between positron and electron emission from aluminium in the keV region

Positrons and electrons are injected by radioactive sources in aluminium absorbers, whose thicknesses are of the order of half range. The emitted particles are counted as a function of their energy, in the interval between 1.5 keV and 3.5 keV. The ratio between position and electron emission probabilities decreases very rapidly with decreasing energy; in the interval of the measurements a variation of this ratio of at least 100 is measured. Some speculations are given in connection with this experimental result.