Nuclear Pairs from the 3.4-Mev State inCa40

A thick calcium metal target was bombarded with 4.84-Mev protons and a search was made with a magnetic lens pair spectrometer for pairs from the 3.35-Mev state of ${\mathrm{Ca}}^{40}$. A peak was observed in the spectrometer at an energy of 3.46±0.1 Mev. In a second experiment with a 1 mm Al absorber between the calcium target and a 2-mil lead converter, no external pair peak was observed, indicating that the pairs coming from the target were nuclear pairs and not internally converted gamma-ray pairs. The existence of pairs and the absence of gamma radiation establish the angular momentum of the first excited state of ${\mathrm{Ca}}^{40}$ as zero.