Doorway States in the Gamma Decay-Out of the Yrast Superdeformed Band in ${}^{59}\mathrm{C}\mathrm{u}$

The decay-out process of the yrast superdeformed band in ${}^{59}\mathrm{C}\mathrm{u}$ has been investigated. The firm determination of spin, parity, excitation energy, and configuration of the states involved in this process constitutes a unique situation for a detailed understanding of the decay-out mechanism. A theoretical model is introduced that includes a residual interaction and tunneling matrix element between bands, calculated in the configuration-dependent cranked Nilsson-Strutinsky model. This interaction causes the decay to occur via a small number of observed doorway states.

Figure 1

Observed transitions in the decay-out of the SD band in ${}^{59}\mathrm{C}\mathrm{u}$ [11]. The widths of the arrows reflect the relative $B(E2)$ strengths. Energy labels are in keV and provided only for specific levels and transitions of interest. For more details and the numbering of bands, we refer to Ref. 11.

Figure 2

Occupation schemes at an arbitrary energy scale of the signature $\alpha =\pm 1/2$ single-particle orbitals of protons and neutrons assigned to the bands in ${}^{59}\mathrm{C}\mathrm{u}$: The SD band $[4\setminus 3]$ (band 5 in Fig. 1), one doorway state $[3\setminus 1]$ and typical ND bands $[2\setminus 1]$ (band 4 in Fig. 1), and $[1\setminus 1]$ (band 3 in Fig. 1).

Figure 3

(a) Calculated energies of positive parity states in ${}^{59}\mathrm{C}\mathrm{u}$ relative to a rigid rotor reference, as a function of the angular momentum [17]. Terminating states are encircled. (b) Calculated energies for the SD $[4\setminus 3]$ and the lowest $[3\setminus 1]$ and $[2\setminus 1]$ configurations at $I=33/2$ and $25/2$. The calculations are carried out along a straight line in the $({\epsilon }_2,\gamma )$ plane which to a good approximation goes through the absolute energy minima of the considered configurations starting at ${\epsilon }_2=0.18$, $\gamma \approx 30°$, and ending at ${\epsilon }_2\approx 0.41$, $\gamma =0°$ (cf. Fig. 26 of Ref. 11). The shaded areas represent the barriers between the SD and ND states above the zero point energy.

Figure 4

Experimental (black line) and simulated (grey line) $\gamma$-ray spectra at initial spins $I_i=37/2$ (a), $33/2$ (b), $29/2$ (c), $25/2$ (d), and $21/2$ (e) as a function of $\gamma$-ray energy. At $I_i=33/2$, the two curves largely overlap. Panel (f) shows the simulated and measured intensity in the SD band as a function of spin, $I_{\mathrm{i}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}}$.