Comprehensive Gamma-ray Spectroscopy of 62Zn and Studies of Nilsson Parameters in the Mass A=60 Region

All ordinary matter around us is made out of atoms. In turn, the building blocks of the atoms are nowadays known to be three types of particles:electrons, protons and neutrons. The latter are called nucleons, as they together form the positively charged nucleus of the atom, around which the electrons are moving. The radius of the nucleus is about three orders of magnitude smaller than that of the atom, while it comprises almost all its mass. The name of a chemical element relates to the number of protons inside the nucleus, while different numbers of neutrons can give rise to various isotopes of a certain element. To overcome the Coulomb repulsion amongst the protons inside the nucleus, there is the need for another fundamental force — the strong nuclear force. To explain the properties of atomic nuclei, one needs an understanding of the forces acting between the nucleons. However, these forces are very complicated and still not known in all aspects. Here, the study of nuclei at extreme conditions, like, high excitation energy, high angular momenta, or at unusual proton to neutron ratios, can contribute to a better understanding of specific aspects of the nuclear force. It is also important to understand that nuclei can become deformed, i.e. nuclei at large deformation (or funny shapes like bananas or pears rather than spheres) is another example of extreme conditions. Ultimately, the deformation of nuclei are mainly determined by the quantum mechanical shell structure of the protons and neutrons which are described as moving in specific orbitals inside the nucleus. The shell structure is closely related to symmetries and becomes particularly strong at the highly symmetric spherical shape. However, the shell structure can be partly restored at specific deformations, for example at superdeformation corresponding to an axial shape with a 2:1 ratio between the long axis and the perpendicular axes. To describe and simulate the outcome of experiments, it is necessary to compare experimental results with theoretical calculations, and thereby test and improve the present nuclear models. In this work, the level scheme of 62Zn (with 30 protons and 32 neutrons) has been observed in great de-119 tail, leading to one of the most complex and comprehensive excitation scheme ever deduced. It includes few hundreds of excited states with a ‘world record’ discrete quantum state at 42.5 MeV excitation energy. This energy is mainly stored as rotational energy, and it makes the nucleus 62Zn rotate with a frequency of f = 500000000000000000000 revolutions per second(f = 5 · 10^20/s).
The experimental results are probed with the ‘Cranked Nilsson Strutinsky model’, where the nucleons move in an anisotropic harmonic oscillator potential generated by the other nucleons, and with two additional terms which are dependent on the orbital and internal motion of the nucleons.
A more global assessment of rotational bands in nuclei near 62Zn leads to a modification of parameters, i.e. a change of the strengths of these two terms. This leads in turn to an improved knowledge of the energies of various proton and neutron orbitals and thus contributes to the improved understanding of atomic nuclei.