The Disintegration ofAs72

The spectra of the various radioactive arsenics produced by high energy alpha-particle bombardment of gallium have been studied using a magnetic lens spectrograph. These isotopes consist of ${\mathrm{As}}^{72}$ (26 h), ${\mathrm{As}}^{74}$ (19.5 d), ${\mathrm{As}}^{73}$ (90 d) and ${\mathrm{As}}^{71}$ (60 h). The main investigation concerns ${\mathrm{As}}^{72}$. This element is found to emit five positron groups of end-point energies 3.339 (19.3 percent), 2.498 (64.6 percent), 1.844 (12.1 percent), 0.669 (5.0 percent) and 0.271 (2.0 percent) Mev. A strong gamma-ray of energy 0.835 Mev together with many weak gamma-rays with energies up to 3 Mev have been found. The levels of the product nucleus ${\mathrm{Ge}}^{72}$ agree well with those found from a study of ${\mathrm{Ga}}^{72}$. The highest energy positron group has a forbidden shape. The spectrum of ${\mathrm{As}}^{74}$ consists of one gamma-ray of energy 0.593 Mev, two negatron groups of energies 1.45 and 0.82 Mev together with a positron group of energy about 0.96 Mev. ${\mathrm{As}}^{73}$ disintegrates by $K$-electron capture and the emission of an internal conversion line corresponding to a gamma-ray of 0.052 Mev. An internal conversion line corresponding to a gamma-ray at 0.162 Mev is ascribed to ${\mathrm{As}}^{71}$.