The Argonne double lens beta spectrometer and associated coincidence circuit have been used to observe the beta transitions of ${\mathrm{Pr}}^{144}$. The validity of the spin and parity assignment, 0- to ${\mathrm{Pr}}^{144}$ is supported by a measurement of the shape of the (1.2±0.1)% abundant 2.3-Mev beta transition, observed in coincidence with the 697-kev gamma ray. Its shape is that of the unique ($\Delta I=2\mathrm{}$, yes) first forbidden transition expected if the transition goes from 0- ${\mathrm{Pr}}^{144}$ to the 2+ first excited state of even-even ${\mathrm{Nd}}^{144}$. The shape of the (1.0±0.1)% abundant 807±5-kev beta transition to the 2.19-Mev level in ${\mathrm{Nd}}^{144}$ was observed in coincidence with the 1.49 and 2.19-Mev gamma rays. Its allowed shape is consistent with a 0- assignment for ${\mathrm{Pr}}^{144}$. With this assignment the transition between the ground states is a 0- to 0+ case. The shape of this 2996±3 kev 97.8% abundant transition was obtained from the total spectrum by small subtractions of the inner groups. Its nearly allowed shape is easily explained with a pure axial vector shape factor; in contrast, the tensor-pseudoscalar formalism fails to reproduce the shape. The ratio of axial vector matrix elements $\lambda =\left(\frac{i\int {\gamma }_5}{\int \sigma ·\mathrm{r}}\right)$ can be determined from the shape; our data give $\lambda =5\mathrm{}\pm 2$. This is the same absolute magnitude as some theoretical estimates but has the opposite sign. Our experimental results are in good agreement with those of Graham, Geiger, and Eastwood who have already pointed out that this 0- to 0+ transition does not offer a sensitive measure of the relative size of pseudoscalar to axial vector coupling constants although the net relative contribution of the direct pseudoscalar part to the whole $\mathrm{AP}$ shape factor must be ≲1% (with Rose-Osborne formalism).

An incidental result of the present work is that the $H_{\rho }$ of the $K$ conversion line of the 133.5-kev transition following the $\beta$ decay of ${\mathrm{Ce}}^{144}$ has been measured as 1064.8±0.6 gauss-cm.

• Received 14 January 1959

DOI:https://doi.org/10.1103/PhysRev.114.1286