A Study of the Radiations from Iridium (194), Iridium (192), Lanthanum (140), Antimony (124), and Zirconium (95)

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. The results are given in summary below.(1) Iridium (194): The beta-gamma coincidence rate decreases from 0.06\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ coincidence per beta-ray at zero absorber thickness to zero at 0.150 g/${\mathrm{cm}}^{2}$, 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 gamma-gamma coincidence rate is (0.54\ifmmode\pm\else\textpm\fi{}0.05)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ coincidence per gamma-ray, indicative of cascade emission of gamma-rays in the nineteen-hour period. Coincidence absorption experiments revealed the presence of a gamma-ray of quantum energy 1.43 Mev. The momentum distribution of secondary electrons ejected from a thick aluminum radiator in a magnetic spectrograph gives an energy of 1.35\ifmmode\pm\else\textpm\fi{}0.03 Mev. A disintegration scheme is given for ${\mathrm{Ir}}^{194}$.(2) Iridium (192): The beta-rays have a maximum energy of 0.56 Mev as measured by absorption in aluminum and Feather analysis. The beta-gamma coincidence rate is 0.41\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ coincidence per beta-ray, independent of the beta-ray energy, suggesting a simple spectrum. The gamma-gamma coincidence rate is (0.23\ifmmode\pm\else\textpm\fi{}0.01)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ coincidence per gamma-ray recorded in the gamma-ray counter. The coincidence experiments show that on the average, each beta-ray is followed by 0.6 Mev of gamma-radiation.(3) Lanthanum (140): The beta-gamma coincidence rate is 1.63\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ coincidence per beta-ray and seems to be independent of the beta-ray energy. A strong gamma-gamma coincidence rate, (0.85\ifmmode\pm\else\textpm\fi{}0.03)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ coincidence per gamma-ray, was also observed. The coincidence experiments show that gamma-rays are emitted in cascade and that 2.3 Mev of gamma-radiation follow each beta-ray.(4) Antimony (124): Coincidence experiments show a decrease in the beta-gamma coincidence rate from 0.92\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ coincidence per beta-ray at zero absorber thickness to 0.38\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ coincidence per beta-ray at 0.110 g/${\mathrm{cm}}^{2}$. Beyond that point, the coincidence rate remains constant. A gamma-gamma coincidence rate of (0.59\ifmmode\pm\else\textpm\fi{}0.03)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ coincidence per gamma-ray was also observed. 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.(5) Zirconium (95): The 63-day activity was found to emit 0.40-Mev beta-rays. The maximum energy of the gamma-rays was 0.91 Mev as measured by coincidence absorption. The beta-gamma coincidence rate was 0.21\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ coincidence per beta-ray, independent of the beta-ray energy. The gamma-gamma coincidence rate, greater than the beta-gamma coincidence rate, was (0.29\ifmmode\pm\else\textpm\fi{}0.02)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ coincidence per gamma-ray. The coincidence experiments suggest that the 0.91-Mev gamma-ray is non-coincident with the beta-rays and may be related to some other decay process.Chemical purification was carried out in all cases, except that of antimony (124). The calibration curve for the coincidence absorption counting set is given as well as a short discussion of some previously measured beta-ray spectra.