Lifetimes and transition probabilities for the low-lying states in ${}^{131}\mathrm{I}$ and ${}^{132}\mathrm{Xe}$

Lifetimes are measured for the low-lying states of ${}^{131}\mathrm{I}$ and ${}^{132}\mathrm{Xe}$ nuclei populated from the decay of radio-chemically separated Te fission fragments. The VENTURE array comprised of eight fast ${\mathrm{CeBr}}_3$ detectors is used for the lifetime measurement with $\gamma \text{−}\gamma$ fast timing technique. Large basis shell model calculations have been performed with the “nushellx” code to interpret the low-lying level structure and to calculate level lifetimes in ${}^{131}\mathrm{I}$ and ${}^{132}\mathrm{Xe}$. The measured lifetimes and absolute transition probabilities are discussed in the light of systematics with the neighboring nuclei. Single particle excitation and loss of collectivity is observed with increasing neutron number up to $N=82$, validating the double shell closure at ${}^{132}\mathrm{Sn}$. Enhanced $B\left(E1\right)$ and $B\left(E3\right)$ strengths are found for the 1646-keV, 11/$2^{-}$ level in ${}^{131}\mathrm{I}$.

Figure 1

The total projections (without any background subtraction) obtained from the ${\mathrm{CeBr}}_3$ (blue dash dotted line) and clover detectors (red solid line) are shown from ${\mathrm{CeBr}}_3-{\mathrm{CeBr}}_3$ and ${\mathrm{CeBr}}_3$-clover coincidences, respectively. The $\gamma$ rays from different isotopes are identified and marked with different colours of text for I (blue), Xe (black), and Cd (red) (contamination).

Figure 2

The ${\mathrm{CeBr}}_3$ energy gated projections of ${\mathrm{CeBr}}_3$ (blue dash-dotted lines) and clover (red solid lines) detectors are shown with gate on (a) feeder (630 keV) and (b) decay (668 keV) $\gamma$ rays of 630–668 keV cascade of ${}^{132}\mathrm{Xe}$. The photopeaks observed in (a) and (b) are marked with $★$ and # respectively, in case they arise from known $\gamma \text{−}\gamma$ coincidences or from the coincidence with the Compton background under the gating transition. The background analysis for this cascade are shown in panels (c) and (d) where $\mathrm{\Delta }{C}_{\text{BG}}$ values are shown with respect to $\text{PRD}=0$ at $E_{\text{ref}}$. The PRD curve is also shown with black dashed line by making $\text{PRD}=0$ at $E_{\text{ref}}$. The red dash-dotted line is drawn to guide the eye for $\mathrm{\Delta }C$ or $\text{PRD}=0$.

Figure 3

The ${\mathrm{CeBr}}_3$ energy gated projections of ${\mathrm{CeBr}}_3$ (blue dash-dotted lines) and clover (red solid lines) detectors are shown with gate on (a) feeder (1126 keV) and (b) decay (774 keV) $\gamma$ rays of 1126–774-keV cascade of ${}^{131}\mathrm{I}$. The background analysis for this cascade are shown in panels (c) and (d) where $\mathrm{\Delta }{C}_{\text{BG}}$ values are shown with respect to $\text{PRD}=0$ at $E_{\text{ref}}$. The PRD curve is also shown with black dashed line by making $\text{PRD}=0$ at $E_{\text{ref}}$. The red dash-dotted line is drawn to guide the eye for $\mathrm{\Delta }C$ or $\text{PRD}=0$.

Figure 4

The delayed and antidelayed TAC spectra for few cascades of ${}^{132}\mathrm{Xe}$ (a)–(d) and ${}^{131}\mathrm{I}$ (e)–(h) nuclei, used for the lifetime measurement with GCD method. The delayed and antidelayed time distributions are shown with red (solid) and blue (dotted) lines respectively.

Figure 5

The time distribution obtained for the 102–241 keV cascade with an appropriate background subtraction is shown.

Figure 6

The $B\left(E2\right)$ values for the decay of 774 keV, 11/$2^{+}$ level in ${}^{131}\mathrm{I}$ in comparison to that in neighboring nuclei is shown. The filled circles (red) represents the values calculated from the level lifetimes taken from NNDC database [26] and the open circle (blue) is for ${}^{131}\mathrm{I}$ and is measured in the present work. The branching and mixing ratios are taken from NNDC database.

Figure 7

The systematics of $E1$ decays from the 11/$2^{-}$ levels in the iodine nuclei around ${}^{132}\mathrm{Sn}$.

Figure 8

The systematics of $E1$ decays from the 13/$2^{-}$ and 15/$2^{-}$ levels in the I and Sb nuclei around ${}^{132}\mathrm{Sn}$.

Figure 9

The $B\left(E2\right)$ values for the decays of ${}^{132}\mathrm{Xe}$ levels in comparison to that in neighboring nuclei. The filled circles represents the values calculated from the level lifetimes taken from NNDC database [26]. The open circle is for ${}^{132}\mathrm{Xe}$ and are measured in the present work. The branching and mixing ratios are taken from NNDC database.