Magnetic dipole strength inXe128andXe134in the spin-flip resonance region

Abstract

The magnetic dipole strength in the energy region of the spin-flip resonance has been investigated in 128 Xe and 134 Xe using quasi-monoenergetic and linearly polarized γ-ray beams at the HIγS facility in Durham, NC, USA. Absorption cross sections were deduced for the magnetic and electric and dipole strength distributions separately for various intervals of excitation energy, including the strength of states in the unresolved quasi-continuum. The magnetic dipole strength distributions show structures resembling a resonance in the spin-flip region around an excitation energy of 8 MeV. The electric dipole strength distributions obtained from the present experiments are in agreement with the ones deduced from an earlier experiment using broad-band bremsstrahlung instead of a quasi-monoenergetic beam. The experimental magnetic and electric dipole strength distributions are compared with phenomenological approximations and with predictions of a quasiparticle-randomphase-approximation in a deformed basis.

E1 and M1 strength functions at low energy

“…The M1 data may indicate a resonance-like structure at about 8.5 MeV, which is the energy region of the spinflip resonance. A similar behavior is predicted by QRPA calculations [4].…”

“…[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].…”

Dipole strength inSe80forsprocess and nuclear transmutation ofSe79

“…In the past half century, the giant dipole resonance (GDR) has been investigated both experimentally and theoretically via photonuclear reactions by many researchers [1,2]. Nowadays, more precise measurements of photoneutron reactions near the neutron threshold (S n ) are performed by using quasimonochromatic γ rays [3][4][5][6]. The low-energy tail of the GDR below S n is of particular interest because of an extra enhancement of observed E1 strength.…”

Dipole strength in 80Se below the neutron-separation energy for the nuclear transmutation of 79Se

“…To obtain the correct dipole strength distribution, inelastic transitions were subtracted from the spectrum and the ground-state transitions were corrected for their branching ratios b 0 . In this study, we used the code γ DEX [5,8,11], which uses statistical methods in analogy to the code DICEBOX [21], to calculate the intensities of branching transitions to low-lying excited levels and the branching ratios of the ground-state transitions. A detailed experimental description is reported elsewhere [18,19].…”

“…In the past half century, the giant dipole resonance (GDR) has been investigated both, experimentally and theoretically via photonuclear reactions, by many researchers [1][2][3][4][5][6][7][8][9][10][11]. Recently, the behavior of the low-energy tail of the GDR below the neutron-separation energy (S n ) is paid attention for the nuclear application, because it strongly affects the estimate of neutron-capture cross sections.…”