Updated $\beta$-decay measurement of neutron-rich ${}^{74}\mathrm{Cu}$

The $\beta$ decay of neutron-rich ${}^{74}\mathrm{Cu}$ has been studied at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. By using a high-resolution mass separator a purified ${}^{74}\mathrm{Cu}$ beam was obtained, thus allowing decay through its isobar chain to stable ${}^{74}\mathrm{Ge}$ without any decay chain member dominating. A total of $170\gamma$ rays were associated with ${}^{74}\mathrm{Cu}\beta$ decay with 111 placed in the ${}^{74}\mathrm{Zn}$ level scheme. Updated $\beta$ feeding intensities and estimated $log\left(ft\right)$ values are presented, and new $J^{\pi }$ assignments are proposed using shell model calculations. The progression of simulated total absorption $\gamma$-ray spectroscopy (TAGS) based on proposed levels and $\beta$-feeding values from previous measurements to this evaluation are presented and demonstrate the need for a TAGS measurements for this and similar decays.

Figure 1

Example of selective background gates used to isolate the coincidence spectrum of the 1133-keV transition. The peak gate is labeled by “pk + bg” and the background gates are labeled with “bg.” Peaks are labeled with $\gamma$-ray energy in keV; peaks belonging to the nuclide ${}^{74}\mathrm{Ga}$ are labeled with (#). Inset is the compound 606-keV peak, to which this technique was applied to obtain the reasonably clean coincidence spectrum shown in Fig. 3.

Figure 2

Coincidence spectra of the three peaks seen in Fig. 1 using the split-background technique described in the text. Numbers above the peaks give the coincident $\gamma$ ray energy, with parentheses indicating only a possible coincidence. All definite peaks in the 1132-keV gate (top panel) belong to the decay of ${}^{74}\mathrm{Ga}$, while all definite peaks in the other two gates are distinct, clean, and are only ${}^{74}\mathrm{Cu}\gamma$ rays.

Figure 3

The $\gamma \gamma$-coincidence spectrum for the 606-keV peak. Probable coincidences are indicated in parentheses, and $\gamma$ rays associated with ${}^{74}\mathrm{Zn}$ (*) and ${}^{74}\mathrm{Ga}$ (#) are indicated.

Figure 4

Proposed decay scheme for ${}^{74}\mathrm{Cu}$ determined in this analysis in the energy region below 3.1 MeV. See Sec. 3 for discussion. Solid dots indicate definite coincidences, while open dots indicate possible coincidences based on the statistical tests mentioned in the text.

Figure 5

Proposed decay scheme for ${}^{74}\mathrm{Cu}$ determined in this analysis in the energy region above 3.1 MeV. See Sec. 3 for discussion. Solid dots indicate definite coincidences, while open dots indicate possible coincidences based on the statistical tests mentioned in the text.

Figure 6

Comparison of both positive and negative parity states predicted by the shell model for ${}^{74}\mathrm{Zn}$ with the experimental level energies reported in this work.

Figure 7

Comparison of $I_{\beta }$ profiles of each experiment. Bin widths were set to 200 keV.

Figure 8

Fission yields and $Q_{\beta }$ windows in ${}^{74}\mathrm{Zn}$ region centered near $N_{\text{magic}}=50$, captured from the NNDC [16]. Top: The lower-mass region of fission yield for both ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$, the principal fuels used in nuclear power plants. The dark red regions (yield probability $\sim {10}^{-1}–{10}^{-3}$) contain the nuclides from the Yoshida et al. [3] list of heaviest influence on the pandemonium problem. The orange and yellow regions have yield probabilities $\sim {10}^{-4}-{10}^{-8}$ and the green regions have $\sim {10}^{-9}–{10}^{-15}$. Bottom: $Q_{\beta }$ window for nuclides in the same region, where green represents $Q_{\beta }\sim 60\text{keV}–3.6$ MeV, yellow represents $Q_{\beta }\sim 5.3–10$ MeV, and orange/red represents $Q_{\beta }>10$ MeV. The open black square indicates ${}^{74}\mathrm{Zn}$ while the solid black square indicates ${}^{74}\mathrm{Cu}$.

Figure 9

A modular total absorption spectrometer (MTAS) simulated response for each of the three decay schemes performed to date. The black trace is based on the scheme from Winger et al., the cyan trace is from the work by Van Roosbroeck et al., and the brown trace reflects the experiment reported here. See text for discussion.