Isospin properties of electric dipole excitations in 48Ca

Abstract

Two different experimental approaches were combined to study the electric dipole strength in the doubly-magic nucleus 48Ca below the neutron threshold. Real-photon scattering experiments using bremsstrahlung up to 9.9 MeV and nearly mono-energetic linearly polarized photons with energies between 6.6 and 9.51 MeV provided strength distribution and parities, and an (\alpha,\alpha'\gamma) experiment at E_{\alpha}=136 MeV gave cross sections for an isoscalar probe. The unexpected difference observed in the dipole response is compared to calculations using the first-order random-phase approximation and points to an energy-dependent isospin character. A strong isoscalar state at 7.6 MeV was identified for the first time supporting a recent theoretical prediction.Comment: 6 pages, 5 figures, as accepted in Phys. Lett.

Decay of quadrupole-octupole1−states inCa40andCe140Derya1, Tsoneva2, Aumann3 et al. 2016Phys. Rev. CSelf Cite12120View full textAdd to dashboardCite

“…In a simple macroscopic picture, a displacement of center-of-mass and center-ofcharge of the nucleus generates a vibrational motion trying to restore the proton-neutron symmetry. Nowadays, the rapidly increasing number of experiments using different probes and techniques allow for systematic studies of the PDR over isotopic and isotonic chains from different mass regions [4,[7][8][9][10][11][12][13][14][15][16][17]. A close connection between * derya@ikp.uni-koeln.de the total PDR strength and the amount of the neutron excess of neutron-rich nuclei which on the other hand is correlated with the neutron skin thickness was proposed [6,[18][19][20].…”

1−and2+discrete states inZr90populated via theCrespi1, Bracco2, Nicolini3 et al. 2015Phys. Rev. C361120View full textAdd to dashboardCite

“…A key issue for the interpretation of the nature of the PDR states is the determination of their isospin character. In this connection extensive work [8][9][10][11][12][13] was made using the (α,α ) reaction, having a strong isoscalar character, and the general result is the presence of different excitation pattern as compared with that of the (γ,γ ) reaction. More recently, experiments performed for the nuclei 208 Pb [14], 124 Sn [15], and 140 Ce [16] to study the E1 and E2 transitions in the region 4-9 MeV have shown that the ( 17 O, 17 O γ ) reaction is a good tool to investigate the isospin properties of these states.…”

Nuclear Structure Studies with Gamma-Ray Beams

“…This mode of excitation was first observed in neutron-capture reactions [1]. Nowadays this mode has been found as a non-statistical enhanced dipole strength below the neutron-separation energy for isotopes ranging from light nuclei (8≤Z≤40) up to lead isotopes including the transitional nuclei [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. A series of nuclear experiments have shown that this is a common mode in N=82 semi-magic 136 Xe, 138 Ba, 140 Ce, 142 Nd and 144 Sm nuclei at excitation energies between 5-8 MeV [2,4,5,10].…”