Half-life and magnetic moment of the first excited state in ${}^{132}\mathrm{I}$

The half-life and the magnetic moment were measured for the first excited state in ${}^{132}\mathrm{I}$, of which the inconsistent results on the half-life have been reported by several other groups. This time, measurements were performed on ${}^{132}\mathrm{I}$ obtained as a decay product of a ${}^{132}\mathrm{Te}$ radioactive beam from the ion guide at Tohoku University. The half-life of this level was determined to be $T_{1/2}=1.120\pm 0.015$ ns using a conventional coincidence technique with a pair of BaF${}_2$ detectors. The time-differential perturbed angular correlation technique was successfully applied to the first excited state in ${}^{132}\mathrm{I}$ implanted into nickel foils. The magnetic moment of this state was determined to be $\mu =+(2.06\pm 0.18){\mu }_N$. The present results are consistent with values reported by Gorodetzky et al. and Singh et al.

Figure 1

Simplified decay scheme of the relevant $A=132$ mass chain. Transient radioactive equilibrium is realized in the ${}^{132}\mathrm{Te}\to {}^{132}\mathrm{I}$ decay by populating ${}^{132}\mathrm{Te}$ as the parent nuclei. Only the 277.9-keV state in ${}^{132}\mathrm{I}$ is populated by the ${\beta }^{-}$ decay of ${}^{132}\mathrm{Te}$, and the 228.2- to 49.7-keV cascade is dominant in ${}^{132}\mathrm{I}$.

Figure 2

Comparison of typical energy spectra of nickel foils in which ${}^{132}\mathrm{I}$ were implanted. “Selected” corresponds to the energy spectrum for a piece used for the measurements and “Not Selected” for a discarded piece, respectively. In this selection procedure, no background shield for the Ge detector was used. The $\gamma$-ray peak at 140 keV was identified as a background from other than the foil pieces, possibly from another radioactive source in the laboratory.

Figure 3

Typical energy spectrum of ${}^{132}\mathrm{I}$ implanted into aluminum foil observed by one of the BaF${}_2$ detectors in the present measurement system. $\gamma$-ray peaks corresponding to 228 and 49.7 keV were successfully observed. Other peaks were identified as $\gamma$ rays from ${}^{131}\mathrm{I}$, ${}^{133}\mathrm{Xe}$, and the x ray from lead bricks that were used for background reduction.

Figure 4

(a) Time spectrum of the 228.2- to 49.7-keV cascade. A single exponential curve with a constant term was applied as a fitting function to the data. The data within the HWHM from the prompt position was excluded from the fit. The solid line is the best fit to the experimental data. (b) Time spectrum taken with the $\gamma$-gates shifted slightly above to miss the 228.2- to 49.7-keV cascade. A Gaussian function with a constant term as the fitting function was applied to the data.

Figure 5

Appearance of the “cage type” magnet (left) and the set up of this magnet for the TDPAC measurement (right). Three return yokes were prepared every ${120}^{\circ }$ for suppressing the fringing field. Three BaF${}_2$ detectors were placed 3 cm away from the center.

Figure 6

Energy spectra of the 59.5-keV $\gamma$ ray of an ${}^{241}\mathrm{Am}$ source placed in different magnets taken by a BaF${}_2$ detector at 3 cm away from the source. “C type” denotes a conventional C-type magnet with the gap of 11 mm, “cage type” for the present cage-type magnet with a gap of 13 mm. Each magnet had the same magnetic field of 0.3 T at the gap center. “No magnet” is the spectrum without a magnetic field for comparison.

Figure 7

TDPAC spectrum of ${}^{132}\mathrm{I}$ in nickel. The data within HWHM determined in the half-life measurement from the prompt position was excluded for the fit.