Structure of the high-spin, $\beta$-decaying state in the neutron-rich nucleus ${}^{146}\mathrm{La}$

Excited structures in ${}^{146}\mathrm{Ce}$ were populated in $\beta$ decay of the high-spin state in the neutron-rich nucleus ${}^{146}\mathrm{La}$. The beam was produced by the Californium Rare Isotope Breeder Upgrade (CARIBU) facility at Argonne National Laboratory, reaccelerated by the ATLAS accelerator, and implanted on a moving-tape system in the middle of the GAMMASPHERE array. The decay scheme of the high-spin, $\beta$-decaying state in ${}^{146}\mathrm{La}$ was revised with respect to previous studies and evaluated nuclear data. The structure of ${}^{146}\mathrm{La}$ is discussed in the framework of the deformed Nilsson model and systematics of known quasiparticle structures in the region.

Figure 1

Time spectra produced by gating on (a) 410-, 503- and 515-keV $\gamma$ rays, depopulating the $4^{+}$, $6^{+}$, and $5^{-}$ levels at 669-, 1172-, and 1184-keV, respectively; (b) the 925-keV $\gamma$ ray, depopulating the $1^{-}$ level at 925 keV. The solid lines represent least-squares fits using a single-exponential decay and a constant background.

Figure 2

Partial decay scheme of the high-spin, $\beta$-decaying state of ${}^{146}\mathrm{La}$, showing levels up to 1956 keV in the daughter nucleus ${}^{146}\mathrm{Ce}$. It was constructed using data from the CARIBU and the ${}^{252}\mathrm{Cf}$ source experiments. The $J^{\pi }=1^{-}$ level in ${}^{146}\mathrm{Ce}$ is populated only from the decay of the low-spin ${}^{146}\mathrm{La}$ isomer, and indicated in red color, together with the depopulating 666- and 925-keV $\gamma$-ray transitions. All levels and $\gamma$-ray transitions were known from previous studies [5], except those indicated in blue color, which were observed for the first time in the present work. The $Q_{\beta }$ value is from Ref. [29].

Figure 3

Sample $\beta \text{−}\gamma \text{−}\gamma$ coincidence spectra from the CARIBU experiment; (a) $\gamma$ rays in coincidence with the 410-keV transition, depopulating the $4^{+}$ level at 669 keV; (b) and (c) $\gamma$ rays in coincidence with the 503-keV transition depopulating the $6^{+}$ level at 1172 keV. The peak labeled with an asterisk corresponds to the 511-keV positron annihilation line.

Figure 4

Sample $\gamma$-ray coincidence spectrum from the GAMMASPHERE experiment with the stationary ${}^{252}\mathrm{Cf}$ source produced by double gating on the 410- and 515-keV $\gamma$ rays.

Figure 5

(a) The experimentally observed, one-quasiparticle proton ($p$) and neutron ($n$) states in ${}^{145}\mathrm{La}$ ($Z=57,N=88$) and ${}^{145}\mathrm{Ba}$ ($Z=46,N=89$), respectively; $p_0$: $\pi 5$/2[413] and $p_1$: $\pi 3$/2[411]; $n_0$: $\nu 5$/2[523] and $n_1$: $\nu 1/2\left[530\right]$. (b) Predicted low-energy, two-quasiparticle states in ${}^{146}\mathrm{La}$; $p_0{n}_0$: $\pi 5/2\left[413\right]\otimes \nu 5/2\left[523\right]{}_{K^{\pi }=5^{-},0^{-}}$, $p_1{n}_0$: $\pi 3/2\left[411\right]\otimes \nu 5/2\left[523\right]{}_{K^{\pi }=1^{-},4^{-}}$, and $p_0{n}_1$: $\pi 5/2\left[413\right]\otimes \nu 1/2\left[530\right]{}_{K^{\pi }=2^{-},3^{-}}$.