Radioactive zirconium isotopes of mass number <90 have been prepared by bombardment of niobium with 100-Mev protons. These isotopes and their decay products have been extensively studied in the beta-ray spectrometer and by radiochemical methods. ${\mathrm{Zr}}^{87}$ is shown to be a 94±6-minute activity, emitting positrons of 2.10±0.02-Mev energy and decaying into ${\mathrm{Y}}^{87m}$. Accompanying its 14-hour decay into ${\mathrm{Y}}^{87}$, ${\mathrm{Y}}^{87m}$ has a complex gamma-ray spectrum. The most prominent conversion electrons correspond to a 0.389±0.004-Mev gamma-ray. ${\mathrm{Y}}^{87}$ decays by orbital electron capture into ${\mathrm{Sr}}^{87m}$ which decays by emission of a 0.394±0.004-Mev gamma-ray with a 2.80±0.03 hour half-life into stable ${\mathrm{Sr}}^{87}$. ${\mathrm{Zr}}^{86}$ is a 17±2-hour orbital electron capturing isotope decaying into ${\mathrm{Y}}^{86}$, which in turn disintegrates into stable ${\mathrm{Sr}}^{86}$ with a half-life of 14.6±0.2 hours by the emission of positrons. This positron spectrum is complex, with two components of approximately equal intensity. The energies are 1.80±0.02 and 1.19±0.02 Mev. The latter appears to have a forbidden Fermi-Kurie plot corresponding to a first-forbidden transition with a spin change of two units and a change of parity.

The energy of the ${\mathrm{Zr}}^{89}$ positron is redetermined as 0.910±0.010 Mev. Conversion electrons corresponding to previously unreported gamma-rays of energy 0.027, 0.396, 0.917, and 1.27 Mev are observed. Preliminary evidence for ${\mathrm{Zr}}^{88}$ is presented which indicates that this isotope decays, by the capture of orbital electrons with a half-life of the order of 150 days, into 105-day ${\mathrm{Y}}^{88}$. Conversion electrons of a 0.406-Mev gamma-ray are prominent in the decay of ${\mathrm{Zr}}^{88}$.

• Received 7 February 1951

DOI:https://doi.org/10.1103/PhysRev.82.944