The Decay Scheme and Angular Correlation ofPr144

Abstract

The decay scheme and angular correlation of ${\mathrm{Pr}}^{144}$ have been studied with lens spectrometer and scintillation counter techniques. The beta-ray spectrum shows three groups with end points at 2.965±0.015, 2.3±0.1, and 0.86±0.1 Mev, the first having a relative intensity of 90 percent, the others each about 5 percent. Gamma-rays were observed by photoelectric conversion and have energies of 0.695±0.005, 1.48±0.01, and 2.185±0.015 Mev and relative intensities of 1:0.4:1.1, respectively. The data indicate that beta-emission takes place to states in ${\mathrm{Nd}}^{144}$ at zero, 0.695, and 2.185 Mev. The absorption of beta-rays in coincidence with gamma-rays shows two components with ranges of 0.34 and 1.0 g/${\mathrm{cm}}^2$ aluminum. The corresponding energies and intensities of these beta-groups confirm the above decay scheme. Gamma-gamma coincidences are also present and their angular correlation has the form 1-0.33 ${cos}^2\theta$, characteristic of either a 1-2-0 or a 1-1-0 cascade. It is suggested that the first excited state of ${\mathrm{Nd}}^{144}$ has spin 2 and even parity and the second level spin 1. Some of the features of ${\mathrm{Ce}}^{144}$ decay are described and the usefulness of this fission-product isotope as a source of homogeneous photoneutrons is discussed.