Photo-response of the $$N=Z$$ nucleus $$^{24}$$Mg

Abstract

AbstractThe electricE1 and magneticM1 dipole responses of the$$N=Z$$N=Znucleus$$^{24}$$24Mg were investigated in an inelastic photon scattering experiment. The 13.0 MeV electrons, which were used to produce the unpolarised bremsstrahlung in the entrance channel of the$$^{24}$$24Mg($$\gamma ,\gamma ^{\prime }$$γ,γ′) reaction, were delivered by the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf. The collimated bremsstrahlung photons excited one$$J^{\pi }=1^-$$Jπ=1-, four$$J^{\pi }=1^+$$Jπ=1+, and six$$J^{\pi }=2^+$$Jπ=2+states in$$^{24}$$24Mg. De-excitation$$\gamma $$γrays were detected using the four high-purity germanium detectors of the$$\gamma $$γELBE setup, which is dedicated to nuclear resonance fluorescence experiments. In the energy region up to 13.0 MeV a total$$B(M1)\uparrow = 2.7(3)~\mu _N^2$$B(M1)↑=2.7(3)μN2is observed, but this$$N=Z$$N=Znucleus exhibits only marginalE1 strength of less than$$\sum B(E1)\uparrow \le 0.61 \times 10^{-3}$$∑B(E1)↑≤0.61×10-3 e$$^2 \, $$2fm$$^2$$2. The$$B(\varPi 1, 1^{\pi }_i \rightarrow 2^+_1)/B(\varPi 1, 1^{\pi }_i \rightarrow 0^+_{gs})$$B(Π1,1iπ→21+)/B(Π1,1iπ→0gs+)branching ratios in combination with the expected results from the Alaga rules demonstrate thatKis a good approximative quantum number for$$^{24}$$24Mg. The use of the known$$\rho ^2(E0, 0^+_2 \rightarrow 0^+_{gs})$$ρ2(E0,02+→0gs+)strength and the measured$$B(M1, 1^+ \rightarrow 0^+_2)/B(M1, 1^+ \rightarrow 0^+_{gs})$$B(M1,1+→02+)/B(M1,1+→0gs+)branching ratio of the 10.712 MeV$$1^+$$1+level allows, in a two-state mixing model, an extraction of the difference$$\varDelta \beta _2^2$$Δβ22between the prolate ground-state structure and shape-coexisting superdeformed structure built upon the 6432-keV$$0^+_2$$02+level.