The reorientation effect in Coulomb excitation was used to measure the static electric quadrupole moments of the first excited (2+) states in 48Ti and 56Fe. These measurements yielded the following values: Q2 + (48Ti) = -13.5 ± 8.8 e · fm2 and Q2 + (56Fe) = -24.9 ± 5.8 e · fm2. Comparison with other measurements indicates that nuclear interaction effects produce spurious quadrupole moments if the distance of closest approach for 180° scattering is much less than 1.25(AP 1 3 + AT 1 3) + 6.0 fm. In the present measurements, the 2+ states were excited by means of 32S projectiles and the de-excitation γ-rays were observed in coincidence with scattered particles, using a multiple detector system. The angular distribution of de-excitation γ-rays was found to be significantly attenuated (deorientation effect) and it was crucial to include this effect in analysing the reorientation data. Measurements of the attenuation were consistent with a magnetic-dipole hyperfine interaction between the excited nuclear state and a randomly fluctuating atomic environment for ions recoiling into vacuum. The effective magnetic hyperfine field was observed to have a velocity dependence consistent with the form H ∞ βx, where β = recoil velocity/c and x = 0.66±0.13. The static quadrupole moments and other E2 properties of 56Fe are characteristic of a relatively stiff prolate rotor, while 46, 48Ti exhibit properties of nuclei soft to collective quadrupole motion. Pure (f 7 2)n shell-model calculations for the even titanium isotopes cannot explain the E2 properties of the low-lying levels, and predict static quadrupole moments of the wrong sign. The inclusion of configurations with one nucleon excited into the upper (1f-2p) shell yields a dramatic improvement, compared with the pure (f 7 2)n shell-model results, in explaining the experimental E2 properties of 48Ti. A similar, though not so striking, improvement holds for 46Ti. The E2 properties of the ground state band in 56Fe are adequately described by a 2p-2h shell-model configuration, assuming an inert 56Ni core. However, the calculation fails to reproduce the magnetic moment of the first excited state, as well as the electromagnetic properties of other low-lying levels, indicating the presence of appreciable admixtures of core-excited configurations in 56Fe.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Nuclear reactions