Probing Shell Structure and Shape Changes in Neutron-Rich Sulfur Isotopes through Transient-Field $g$-Factor Measurements on Fast Radioactive Beams of ${}^{38}\mathrm{S}$ and ${}^{40}\mathrm{S}$.

The shell structure underlying shape changes in neutron-rich nuclei near $N=28$ has been investigated by a novel application of the transient-field technique to measure the first-excited-state $g$ factors in ${}^{38}\mathrm{S}$ and ${}^{40}\mathrm{S}$ produced as fast radioactive beams. There is a fine balance between proton and neutron contributions to the magnetic moments in both nuclei. The $g$ factor of deformed ${}^{40}\mathrm{S}$ does not resemble that of a conventional collective nucleus because spin contributions are more important than usual.

Figure 1

Schematic view of the experimental arrangement from above. Only the four SeGA detectors perpendicular to the magnetic field axis are shown. There are ten other SeGA detectors (see text) which are not shown for clarity.

Figure 2

Doppler-corrected $\gamma$-ray spectra at $\theta =40°$ for ${}^{38}\mathrm{S}$ (left) and ${}^{40}\mathrm{S}$ (right). The sulfur and iron peaks are labeled. The broad feature to the right of the 1292 keV line is mainly its Doppler tail, due to decays within the target.

Figure 3

Angular correlations for ${}^{38}\mathrm{S}$ and ${}^{40}\mathrm{S}$ in the frame of the projectile nucleus. Data are normalized to the calculated angular correlation. The difference in anisotropy stems from the alignment produced by Coulomb excitation, which depends on the ratio of $E(2^{+})$ to the beam velocity.

Figure 4

Theoretical $g$ factors compared with experiment. The previous results for ${}^{38}\mathrm{Ar}$ and ${}^{40}\mathrm{Ar}$ are from Refs. 22, 23, respectively.