Polarized photon scattering off ${}^{52}\mathrm{Cr}$: Determining the parity of $J=1$ states

The photoresponse of ${}^{52}\mathrm{Cr}$ has been investigated in the energy range of 5.0–9.5 MeV using the photon scattering technique at the $\mathrm{HI}\gamma \mathrm{S}$ facility of TUNL to complement previous work with unpolarized bremsstrahlung photon beams at the Darmstadt linear electron accelerator. The unambiguous parity determinations of the observed $J=1$ states provides the basis needed to better understand the structure of $E1$ and $M1$ excitations. Theoretical calculations using the quasiparticle phonon model incorporating self-consistent energy-density functional theory were performed to investigate the fragmentation pattern of the dipole strength below and around the neutron-emission threshold. These results compare very well with the experimental values.

Figure 1

Nuclear resonance fluorescence ($\gamma ,{\gamma }^{\prime }$) spectra from ${}^{52}\mathrm{Cr}$ recorded in the (a) parallel and (b) perpendicular detector using a polarized photon beam of energy 7.89 MeV. Transitions in the parallel (perpendicular) detector are of an $M1\left(E1\right)$ character.

Figure 2

Same as Fig. 1, at $E_{\gamma }=9.15$ MeV.

Figure 3

Experimental azimuthal asymmetry values for $E1$ (open circles) and $M1$ (asterisks) transitions in ${}^{52}\mathrm{Cr}$. Average values for $E1$ and $M1$ transitions are drawn as dotted horizontal lines.

Figure 4

The distribution of observed $B\left(E1\right)\uparrow$ [12] strength for resonantly excited states in ${}^{52}\mathrm{Cr}$ between 5.1 and 9.5 MeV is compared with values obtained from QPM calculations. A comparison of the measured and calculated QPM cumulative $E1$ strengths is shown in the upper panel. Individual contributions and uncertainties are listed in Table 1.

Figure 5

Distribution of observed $E1$ excitation strength in several $fp$-shell nuclei. Note the range of the $y$ axis for ${}^{48}\mathrm{Ti}$.

Figure 6

Distribution of observed $B\left(M1\right)\uparrow$ [12] strength in ${}^{52}\mathrm{Cr}$ in the energy range between 5.1 and 9.5 MeV is compared with the values obtained from QPM calculations. A comparison of the measured and calculated QPM cumulative $M1$ strength is shown in the upper panel. Individual contributions and uncertainties are given in Table 1.