Gamow-Teller decay of ${}^{142}\mathrm{Te}$ to ${}^{142}\mathrm{I}$

The $\beta$ decay of ${}^{142}\mathrm{Te}_{90}$ to ${}^{142}\mathrm{I}_{89}$ was investigated for the first time. The parent nucleus was produced by the in-flight fission of a ${}^{238}\mathrm{U}$ beam with an energy of 345 MeV per nucleon, impinging on a ${}^9\mathrm{Be}$ target at the Radioactive Isotope Beam Factory of RIKEN. Excited states in ${}^{142}\mathrm{I}$ were established by $\beta$-delayed $\gamma$-ray spectroscopy. The observed $\left(1^{+}\right)$ states in ${}^{142}\mathrm{I}$ could be interpreted to be predominantly the $\nu 0h_{9/2}\otimes \pi 0h_{11/2}$ configuration formed by a Gamow-Teller transition between a neutron in the $0h_{9/2}$ orbital and a proton in the $0h_{11/2}$ orbital. Additional features of the $\left(1^{+}\right)$ states are discussed by comparing with neighboring heavier isotones, such as ${}^{144}\mathrm{Cs}$ and ${}^{146}\mathrm{La}$. In the context of deformed shell-model calculations, the $\left(1_1^{+}\right)$ state is closely related to the $\nu [5,3,2]3/2\otimes \pi [5,5,0]1/2$ configuration, which may be related to the weak Gamow-Teller transition strength.

Figure 1

(a) $\beta$-delayed $\gamma$-ray singles spectrum of ${}^{142}\mathrm{Te}$. The numbers represent the energies of the $\gamma$-ray transitions in ${}^{142}\mathrm{I}$ following the $\beta$ decay of ${}^{142}\mathrm{Te}$ while background peaks in ${}^{142}\mathrm{Xe}$ from the $\beta$ decay of ${}^{142}\mathrm{I}$ are labeled with asterisks (*). The $\gamma$-ray transitions with ampersands (&) are candidate transitions in ${}^{141}\mathrm{I}$ from $\beta$-delayed one-neutron emission decay. (b) Half-life measurement of the ground state of ${}^{142}\mathrm{Te}$ based on $\gamma$-transition intensities in ${}^{142}\mathrm{I}$ as a function of time. A red solid line indicates the overall fit result including a single-component exponential decay curve (a red-dashed line) and a constant background (a red dashed-dotted line).

Figure 2

$\gamma \text{−}\gamma$ coincidence spectra of ${}^{142}\mathrm{I}$ with gates on the (a) 95-keV, (b) 191-keV, (c) 276-keV, and (d) 634-keV transitions. The coincident transitions are indicated with their energies.

Figure 3

$\beta$-decay scheme of ${}^{142}\mathrm{Te}$. The half-life of the ground state of ${}^{142}\mathrm{Te}$ is based on the present work. The $Q_{{\beta }^{-}}$ value is taken from Ref. [33]. Level information such as excitation energies, proposed spin parities, $\beta$-branching ratios, and log $ft$ values are provided. The widths of the arrows represent relative intensities of the $\gamma$ rays.

Figure 4

Excitation energy systematics of $\left(1_1^{+}\right)$ states of odd-odd I [20, 21, 42], Cs [43, 44], and La [45, 46, 47, 48] isotopes as a function of neutron number. The inset shows the $2_1^{+}$ state energies for neighboring even-even Te, Xe, Ba, and Ce isotopes [26].

Figure 5

Plots of the single-quasiparticle energies of (a) protons and (b) neutrons as a function of deformation parameter ${\varepsilon }_2$ for ${}^{142}\mathrm{I}$ based on the Nilsson model. Each line follows the occupied proton or neutron number as represented in the legends. At ${\varepsilon }_2=0.20$, some low-lying orbitals are marked with the Nilsson asymptotic quantum numbers.

Figure 6

Excitation energies for the components of the $\nu 0h_{9/2}\otimes \pi 0h_{11/2}$ configuration as a function of deformation for ${}^{142}\mathrm{I}$. The measured $\left(1^{+}\right)$ excitation energies are also indicated as dashed red lines.

Figure 7

Calculated excitation energies of $1^{+}$ states associated with $\nu 0h_{9/2}\otimes \pi 0h_{11/2}$ configuration at ${\varepsilon }_2=0.2$ for I, Cs, and La with $N=89$. For comparison, the experimental energies of the $\left(1_1^{+}\right)$ and $\left(1_2^{+}\right)$ states are denoted with the asterisk and diamond symbols, respectively.

Figure 8

Plots of occupancies for the neutron $0h_{9/2}$ and the proton $0h_{11/2}$ orbitals as a function of deformation.