High spin $\gamma$-ray spectroscopy in ${}^{41}\mathrm{Ca}$

High spin states in ${}^{41}\mathrm{Ca}$ have been investigated by using $\gamma$-ray spectroscopic techniques following the ${}^{27}\mathrm{Al}({}^{16}\mathrm{O},pn){}^{41}\mathrm{Ca}$ fusion-evaporation reaction. Around twelve new transitions belonging to ${}^{41}\mathrm{Ca}$ have been observed and placed in the level scheme, which now has been extended up to $E_x\sim 9$ MeV. The spin-parity assignments for the observed levels were arrived at following the analysis of both the coincidence intensity anisotropies and linear polarization measurements. The established 5p-4h band was extended up to $J^{\pi }=19/2^{-}$. The observations of Doppler shape and shifts facilitated the estimation of the level lifetimes by using the Doppler shift attenuation method. The lifetimes were validated with respect to previous measurements and lifetime of a few levels has been arrived at for the first time. Shell-model calculations were carried out to explain the observed level structure of the nucleus and are indicative of both single-particle and collective degrees of freedom in this $N\sim Z\sim 20$ nucleus.

Figure 1

Projection spectrum of ${}^{16}\mathrm{O}+{}^{27}\mathrm{Al}$ reaction at an incident beam energy of 34 MeV. Nuclei in the $A\sim 30$ region were populated from the reaction of ${}^{16}\mathrm{O}$ beam with the ${\mathrm{Ta}}_2{\mathrm{O}}_5$ target (please see text for details).

Figure 2

Plot of $R_{\text{DCO}}$ values for transitions in ${}^{38}\mathrm{Ar},{}^{41}\mathrm{K},{}^{41}\mathrm{Ca}$ when the gate is on quadrupole and dipole transitions. New transitions in ${}^{41}\mathrm{Ca}$ are marked by asterisks.

Figure 3

Plot of experimental and calculated polarization values as a function of $\gamma$-ray energy for transitions in ${}^{41}\mathrm{Ca},{}^{41}\mathrm{K},{}^{38}\mathrm{Ar}$ populated in the present experiment. The new transitions in ${}^{41}\mathrm{Ca}$ are marked by asterisks.

Figure 4

Level scheme of ${}^{41}\mathrm{Ca}$ obtained from the present work. The levels of the $K^{\pi }=3/2^{-}$ band are marked in red.

Figure 5

Coincidence spectrum with gate on 460 and 4014 keV transitions in ${}^{41}\mathrm{Ca}$. The new transitions are marked by asterisks.

Figure 6

Representative fit of Doppler shape for 1389 and 1509 keV $\gamma$ rays in ${}^{41}\mathrm{Ca}$.

Figure 7

Comparison of experimental and shell-model calculated level energies in ${}^{41}\mathrm{Ca}$.

Figure 8

Plot of excitation energy against $J(J+1)$ for negative-parity states in ${}^{41}\mathrm{Ca}$. The $K^{\pi }=0^{+}$ deformed bands in ${}^{40,42}\mathrm{Ca}$ and the $K^{\pi }={3/2}^{-}$ bands in ${}^{43}\mathrm{Ca}$ are also shown for comparison. New levels in ${}^{41}\mathrm{Ca}$ are marked by asterisks.