Fine Structure of the GiantM1Resonance inZr90

Abstract

The M1 excitations in the nuclide 90Zr have been studied in a photon-scattering experiment with monoenergetic and linearly polarized beams from 7 to 11 MeV. More than 40 J(π)=1+ states have been identified from observed ground-state transitions, revealing the fine structure of the giant M1 resonance with a centroid energy of 9 MeV and a sum strength of 4.17(56) μ(N)(2). The result for the total M1 strength and its fragmentation are discussed in the framework of the three-phonon quasiparticle-phonon model.

E1 and M1 strength functions at low energy

“…The correction of the data for branching ratios was applied separately to the two sets and allowed us to extend the correction of the photoabsorption cross section to low energy. There is a good agreement between the (γ, γ ) and ( 3 He, 3 He') data in the transition-energy region from about 4 to 9 MeV. The uncertainties of the (γ, γ ) data become very large below about 3 MeV even for the 7 MeV experiment.…”

“…The strength function is deduced from the photoabsorption cross section σ γ determined in (γ, γ ) experiments using the relation f 1 = σ γ /[g(π c) 2 E γ ] with g = (2J i + 1)/(2J 0 + 1), where J 0 and J i are the spins of the ground state and the excited state, respectively. The strength function derived in this way for 74 Ge is compared with the one obtained from ( 3 He, 3 He') experiments in Fig. 6.…”

“…We have studied . Dipole strength functions of 74 Ge based on (γ, γ ) data measured at two electron energies of 7 MeV (red circles) and 12 MeV (blue circles) and based on ( 3 He, 3 He') data (black squares). The M1 strength function deduced from shell-model calculations is also shown (blue solid line).…”

“…74 Ge via the (γ, γ ) reaction at γ ELBE [27]. Besides, the dipole strength function of 74 Ge was extracted from experiments using the ( 3 He, 3 He') reaction at the cyclotron of Oslo University [8] and relative cross sections were obtained from an (α, α ) experiment at the cyclotron of iThemba LABS Somerset [28]. The strength function is deduced from the photoabsorption cross section σ γ determined in (γ, γ ) experiments using the relation f 1 = σ γ /[g(π c) 2 E γ ] with g = (2J i + 1)/(2J 0 + 1), where J 0 and J i are the spins of the ground state and the excited state, respectively.…”

“…[1]. In the energy region, where the spin-flip resonance is expected to occur [2], few examples of an M1 resonance were found in NRF experiments [3,4]. Strong M1 excitations around 3 MeV observed in various NRF studies are considered as the scissors mode [2].…”