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

This is the authors' abstract. We don't add key points for this paper.

The electricE1 and magneticM1 dipole responses of the $$N=Z$$ N=Z nucleus ²⁴ 24 Mg 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 24 Mg( γ ,γ γ,γ′ ) reaction, were delivered by the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf. The collimated bremsstrahlung photons excited one Jπ=1⁻ Jπ=1- , four Jπ=1⁺ Jπ=1+ , and six Jπ=2⁺ Jπ=2+ states in ²⁴ 24 Mg. De-excitation γ γ rays were detected using the four high-purity germanium detectors of the γ γ ELBE setup, which is dedicated to nuclear resonance fluorescence experiments. In the energy region up to 13.0 MeV a total B(M1)↑ = 2.7(3)~μ N² B(M1)↑=2.7(3)μN2 is observed, but this $$N=Z$$ N=Z nucleus exhibits only marginalE1 strength of less than ∑ B(E1)↑ ≤ 0.61 × 10⁻³ ∑B(E1)↑≤0.61×10-3 e ² \, 2 fm ² 2 . The B( 1, 1πᵢ → 2⁺₁)/B( 1, 1πᵢ → 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 24 Mg. The use of the known ρ ²(E0, 0⁺₂ → 0⁺gs) ρ2(E0,02+→0gs+) strength and the measured B(M1, 1⁺ → 0⁺₂)/B(M1, 1⁺ → 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 β ₂² Δβ22 between the prolate ground-state structure and shape-coexisting superdeformed structure built upon the 6432-keV 0⁺₂ 02+ level.