Search

The N = 52 Ga 83 β decay was studied at ALTO. The radioactive 83 Ga beam was produced through the ISOL photofission technique and collected on a movable tape for the measurement of γ -ray emission following β decay. While β -delayed neutron emission has been measured to be 56–85% of the decay path, in this experiment an unexpected high-energy 5–9 MeV γ -ray yield of 16(4)% was observed, coming from states several MeVs above the neutron separation threshold. This result is compared with cutting-edge QRPA calculations, which show that when neutrons deeply bound in the core of the nucleus decay into protons via a Gamow–Teller transition, they give rise to a dipolar oscillation of nuclear matter in the nucleus. This leads to large electromagnetic transition probabilities which can compete with neutron emission, thus affecting the β -decay path. This process is enhanced by an excess of neutrons on the nuclear surface and may thus be a common feature for very neutron-rich isotopes, challenging the present understanding of decay properties of exotic nuclei. [ABSTRACT FROM AUTHOR]

Excited states in the mirror nuclei 31P and 31S were populated in the 1p and 1n exit channels of the reaction 20Ne + 12C, at a beam energy of 33 MeV. The 20Ne beam was delivered for the first time by the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. Angular correlations of coincident γ -rays and Doppler-shift attenuation lifetime measurements were performed using the multi-detector array GASP in conjunction with the EUCLIDES charged particle detector. In the observed B(E1) strengths, the isoscalar component, amounting to 24% of the isovector one, provides strong evidence for breaking of the isospin symmetry in the A = 31 mass region. Self-consistent beyond mean field calculations using Equation of Motion method based on a chiral potential and including two- and three-body forces reproduce well the experimental B(E1) strengths, reinforcing our conclusion. Coherent mixing from higher-lying states involving the Giant Isovector Monopole Resonance accounts well for the effect observed. The breaking of the isospin symmetry originates from the violation of the charge symmetry of the two- and three-body parts of the potential, only related to the Coulomb interaction. [ABSTRACT FROM AUTHOR]

We present the first experimental evidence of the scissors mode in the superheavy nucleus 254No produced in the 208Pb(48Ca, 2 n γ))254No reaction. The spectrum of γ rays emitted by the excited 254No nuclei shows an enhanced γ -ray yield for transition energies of ≈2.5 MeV. By measuring the linear polarization properties of the emitted γ rays, we confirm that the transitions in the enhancement region are predominantly of magnetic-dipole character, characteristic for the scissors mode. To further characterize the enhanced γ -ray yield, simulations of the electromagnetic decay of 254No were performed. The observed enhancement is reproduced by including an M 1 component in the γ strength function with total strength B (M 1 ↑) = 11.8 (19) μ N 2. This is in good agreement with the integrated M 1 strength from sum-rule estimates and new calculations within the quasi-particle random-phase approximation presented here. Our results provide a stringent test of phenomenological formulae for the scissors mode currently used in stellar nucleosynthesis calculations. We find that those formulae are not satisfactory, and we recommend using sum-rule estimates assuming a rigid-body moment of inertia instead for describing the scissors mode in superheavy nuclei. [ABSTRACT FROM AUTHOR]