Radioactivities Produced by Proton Bombardment of Palladium

Proton bombardment of Pd produces the three known Ag periods of 2.3 min. (${\mathrm{Ag}}^{108}$), 25 min. and 8 days (${\mathrm{Ag}}^{106}$), and three new periods of 16.3 min. (+), 73 min. (+) and 45 days ($K$ capture). The latter are assigned tentatively to ${\mathrm{Ag}}^{102}$, ${\mathrm{Ag}}^{104}$, and ${\mathrm{Ag}}^{105}$, respectively. Excitation functions for the isomeric 25-min. and 8-day periods give $p-n$ thresholds of 3.8 and 3.9 Mev, respectively. The former agrees with the known positron spectrum of the short period. The higher threshold for the 8-day period indicates that this state lies above the 25-min. state. This activity is accompanied by probably three gamma-rays of which two of 0.62 and 1.06 Mev have been identified with a beta-ray spectrograph. Since no positrons accompany this activity it must decay mainly by $K$-electron capture to ${\mathrm{Pd}}^{106}$ rather than to the lower isomeric state. Four gamma-rays of about 0.29, 0.42, 0.50, and 0.69 Mev accompany the 45-day period.