Dipole strength distributions of the stable odd-massN=82isotonesLa139and

M. Scheck

¹

,

P. von Brentano

²

,

C. Fransen

³

et al.

Abstract

The low-lying dipole strength distributions of the odd-mass isotopes 139 La and 141 Pr were studied in nuclear resonance fluorescence experiments using bremsstrahlung beams. Excited states were observed at excitation energies up to 4 MeV. Spectroscopic information was obtained on excitation energies, decay widths, decay branching ratios, and transition probabilities. The states belonging to the [[2 + ⊗ 3 − ] ⊗ particle/hole] coupling were a special focus, and the results are compared with other stable odd-mass nuclei at or near the N = 82 shell closure.

Dipole strength inLa139below the neutron-separation energy

“…The nuclide 139 La with a closed neutron shell at N = 82 is also of special importance for the understanding of nuclear structure. Dipole excitations at energies below 4 MeV were investigated in photon-scattering experiments at the former Stuttgart Dynamitron [16]. The dipole strength distribution at higher energy up to S n is of particular interest because enhanced strength on the low-energy tail of the giant dipole resonance (GDR), often denoted as the "pygmy dipole resonance" (PDR), was found to be especially pronounced in neighboring N = 82 isotones [3,4] as well as in nuclides with N = 50 [6,8,9] and in 208 Pb with N = 126 [17,18].…”

Scissors mode and effects of the low-lying E1 excitations on the dipole distributions in 175Lu

“…Although the low-lying dipole excitations have also been observed in several odd-mass deformed nuclei [15][16][17][18][19][20][21][22][23][24][25][26][27][28], a limited number of theoretical attempts have been made to explore the nature and the systematics of these excitations. Pioneering calculations performed using the schematic and phenomenological models [29][30][31][32][33][34][35][36][37][38][39] reveal the existence of low-lying dipole strength in odd-mass nuclei but fail to explain the extreme fragmentation observed in dipole spectra.…”