Quadrupole Collectivity in GERMANIUM-72, Palladium -110, and ERBIUM-168.
Quadrupole collective properties of three nuclei, ('72)Ge, ('110)Pd and ('168)Er have been studied by Coulomb excitation using heavy-ion beams such as ('16)O, ('40)Ca, ('58)Ni and ('208)Pb. Deexcitation gamma rays in coincidence with both the scattered projectiles and recoiling target nuclei were detected over a wide range of scattering angles, to measure the Coulomb excitation cross-sections. The Coulomb excitation code GOSIA was used to extract the E2 matrix elements in a model-independent way. Almost a complete set of E2 matrix elements for low-lying levels has been measured for the nuclei ('72)Ge, ('110)Pd and ('168)Er. A direct measurement has been performed of the lifetimes of 8 levels in ('110)Pd using the Recoil Distance Method. The excellent agreement with the Coulomb excitation results proves the correctness of the method used to analyze Coulomb excitation experiments. In ('72)Ge, 14 E2 matrix elements have been determined and limits for 7 matrix elements have been found. These include: 4 transition in-band matrix elements, 5 diagonal matrix elements and 12 inter-band matrix elements. After correcting the ground 0('+) state for mixing with an intruder 0('+) state, the E2 matrix elements in the ground and gamma bands can be explained by quadrupole collective motion, with shape parameters (gamma)(DBLTURN)28.5(DEGREES) and (beta)(DBLTURN)0.30. In ('110)Pd the measured lifetimes together with Coulomb excitation results gave new spectroscopic information about low-lying states, which now can be arranged into collective rotational bands based on the ground, 2(,2)('+), 0(,2)('+) and 0(,3)('+) states, and having deformation (gamma)(DBLTURN)18(DEGREES) and (beta) from 0.21 to 0.36. For the nucleus ('168)Er, 54 E2 matrix elements have been determined. These include: 9 transition ground -band matrix elements, 7 diagonal ground-band matrix elements, 14 transition gamma-band matrix elements, 5 diagonal gamma -band matrix elements and 21 inter-band matrix elements between the ground and gamma bands. No significant deviations from the correlations predicted by the rotational model have been found. In the three cases studied, i.e. ('72)Ge, ('110)Pd and ('168)Er, the E2 data exhibit strong correlations, which shows that collective quadrupole motion is the dominant feature of low-lying spectra in all three nuclei.
- Pub Date:
- Physics: Nuclear