From the coincidence rates it may be concluded that gamma-rays are in cascade and that the high energy beta-rays are followed by 0.55 Mev of gamma-radiation. A gamma-gamma coincidence rate of (0.59+/-0.03)×10 -3 coincidence per gamma-ray was also observed. Beyond that point, the coincidence rate remains constant.

(4) Antimony (124): Coincidence experiments show a decrease in the beta-gamma coincidence rate from 0.92×10 -3 coincidence per beta-ray at zero absorber thickness to 0.38×10 -3 coincidence per beta-ray at 0.110 g/cm 2. The coincidence experiments show that gamma-rays are emitted in cascade and that 2.3 Mev of gamma-radiation follow each beta-ray. A strong gamma-gamma coincidence rate, (0.85+/-0.03)×10 -3 coincidence per gamma-ray, was also observed. (3) Lanthanum (140): The beta-gamma coincidence rate is 1.63×10 -3 coincidence per beta-ray and seems to be independent of the beta-ray energy. The coincidence experiments show that on the average, each beta-ray is followed by 0.6 Mev of gamma-radiation.

The gamma-gamma coincidence rate is (0.23+/-0.01)×10 -3 coincidence per gamma-ray recorded in the gamma-ray counter. The beta-gamma coincidence rate is 0.41×10 -3 coincidence per beta-ray, independent of the beta-ray energy, suggesting a simple spectrum. (2) Iridium (192): The beta-rays have a maximum energy of 0.56 Mev as measured by absorption in aluminum and Feather analysis. A disintegration scheme is given for Ir 194. The momentum distribution of secondary electrons ejected from a thick aluminum radiator in a magnetic spectrograph gives an energy of 1.35+/-0.03 Mev. Coincidence absorption experiments revealed the presence of a gamma-ray of quantum energy 1.43 Mev. The gamma-gamma coincidence rate is (0.54+/-0.05)×10 -3 coincidence per gamma-ray, indicative of cascade emission of gamma-rays in the nineteen-hour period. (1) Iridium (194): The beta-gamma coincidence rate decreases from 0.06×10 -3 coincidence per beta-ray at zero absorber thickness to zero at 0.150 g/cm 2, corresponding to 0.48 Mev, indicating a soft beta-ray spectrum of low intensity, and that the hard beta-rays of energy 2.2 Mev are non-coincident with gamma-radiation. The beta- and gamma-radiations of radioactive isotopes of iridium, lanthanum, antimony, and zirconium, prepared by slow neutron bombardment in the Clinton pile, have been investigated by absorption and coincidence methods.

Iridium 192