In-beam spectroscopic study of ${}^{244}\mathrm{Cf}$

The ground-state rotational band of the neutron-deficient californium ($Z=98$) isotope ${}^{244}\mathrm{Cf}$ was identified for the first time and measured up to a tentative spin and parity of $I^{\pi }={20}^{+}$. The observation of the rotational band indicates that the nucleus is deformed. The kinematic and dynamic moments of inertia were deduced from the measured $\gamma$-ray transition energies. The behavior of the dynamic moment of inertia revealed an up-bend due to a possible alignment of coupled nucleons in high-$j$ orbitals starting at a rotational frequency of about $\hslash \omega =0.20\mathrm{MeV}$. The results were compared with the systematic behavior of the even-even $N=146$ isotones as well as with available theoretical calculations that have been performed for nuclei in the region.

Figure 1

Energy spectra of $\alpha$ particles from the ${}^{48}\mathrm{Ca}+{}^{198}\mathrm{Pt}$ reaction measured in the DSSDs and vetoed with the gas counter (MWPC) and the planar detector: (a) all $\alpha$-like events, (b) $\alpha$-like events following a recoil implantation at the same position in the DSSDs within $100\min$.

Figure 2

Energy spectrum of prompt $\gamma$ rays measured with the JUROGAMII array at the target position associated with the recoils tagged with ${}^{244}\mathrm{Cf}\alpha$ decays in the DSSDs and the escaped $\alpha$ particles observed in the PIN detectors. The inset shows the $\gamma$ rays with energies up to 1 MeV.

Figure 3

The measured ER-$\alpha$ times corresponding to (a) ${}^{244}\mathrm{Cf}$ and (b) ${}^{243}\mathrm{Cf}$ with a search time of up to $12\times {10}^3\mathrm{s}$. The dashed lines in blue (real) and red (random) correspond to the two components of the fitted decay curve that is shown in black (see text for more details).

Figure 4

Energy spectrum of $\alpha$ particles from the ${}^{48}\mathrm{Ca}+{}^{202}\mathrm{Hg}$ reaction measured in the DSSDs and vetoed with the gas counter (MWPC) from an earlier study of ${}^{248}\mathrm{Fm}$ [30] that was used to determine the $\alpha$ decay branching ratio of ${}^{244}\mathrm{Cf}$. Note that the energies plotted on the $x$ axis have not been corrected for the partially detected recoil energy of the daughter nucleus ($\approx 70\mathrm{keV}$ due to the pulse-height defect).

Figure 5

The measured cross sections for the $2n$ and $3n$ evaporation channels in the ${}^{48}\mathrm{Ca}+{}^{198}\mathrm{Pt}$ fusion reaction as a function of the excitation energy $E^{*}$ at the center of the target of the compound nucleus ${}^{246}\mathrm{Cf}^{*}$. The solid lines are fits to guide the eye. See text for details.

Figure 6

The (a) kinematic ${\mathcal{J}}^{\left(1\right)}$ and (b) dynamic ${\mathcal{J}}^{\left(2\right)}$ moments of inertia of the ground-state rotational bands as a function of rotational frequency ($\hslash \omega$) in the even-even $N=146$ isotones ${}^{238}\mathrm{U}$ [4], ${}^{240}\mathrm{Pu}$ [5], ${}^{242}\mathrm{Cm}$ [6], ${}^{244}\mathrm{Cf}$ (from this work), and ${}^{246}\mathrm{Fm}$ [7]. The lines represent (a) fits to the low-spin part of the ${\mathcal{J}}^{\left(1\right)}$ data using the $\gamma$-ray transition energies with Eq. (2) and (b) ${\mathcal{J}}^{\left(2\right)}$ plotted using Eq. (3) and the Harris parameters obtained in panel (a). See text for details.

Figure 7

The kinematic ${\mathcal{J}}^{\left(1\right)}$ moment of inertia of the ground-state rotational band in ${}^{244}\mathrm{Cf}$ as a function of the rotational frequency ($\hslash \omega$). The measured values from this work are compared with calculations from Afanasjev et al. [43] using the $\mathrm{NL}{3}^{*}$ parametrization (dash-dotted red line) with the inset showing the calculated neutron (blue) and proton (red) contributions. Calculations performed in a similar way as described in Shi et al. [49] (dashed black line) are also included. The solid line represents a fit to the low-spin part of the ${\mathcal{J}}^{\left(1\right)}$ data using the measured $\gamma$-ray transition energies with Eq. (2). See text for details.