Laser spectroscopy of neutron-deficient Zr isotopes with SPIRAL2

Abstract :

Technological advances in the framework of SPIRAL2 will make possible the production of intense and pure beams of short-lived nuclei located far from the stability. 

On the neutron-deficient side, for example, probing the structural properties of N = Z nuclei from ⁸⁰Zr to ¹⁰⁰Sn will become accessible. For these nuclei, the T=0 residual interaction dominates. Proton and neutron shell effects act coherently and rich structures arise from the coexistence/competition of different shapes. 

For instance, ⁸⁰Zr is well known to be deformed. It appears to be one of the most deformed nuclei known in nature, with a quadrupole deformation beta~0.4. The instability of the spherical shape of ⁸⁰Zr against deformation could be connected to the magic number N = Z = 40 for the tetrahedral shape. Additional experimental data on this nucleus could help to further elucidate the role of the single-particle behaviour in the shell model, and also that of the effective interactions. Currently, the refractory nature of zirconium isotopes prevents their efficient production at conventional high-temperature isotope separator facilities. With SPIRAL2, more specifically the S³ spectrometer, laser spectroscopy measurements on neutron-deficient zirconium fusion evaporation products could be performed for instance by using the recently developed gas catcher laser ion source system. By coupling the gas cell to the focal plane of S³, the reaction products can be efficiently thermalised and laser ionized. Furthermore, using an RF structure behind the gas cell would allow to perform laser spectroscopy measurements in the so-called ‘Laser Ion Source Trap (LIST)’ mode. The latter would results in a better resolution as no pressure broadening is expected. With the expected intensities from the SPIRAL heavy ion accelerator, the fusion-evaporation reaction of e.g. a magnesium beam on a nickel target should lead to more than ten thousands ions per second. Thus these nuclear shape investigations using in-source laser spectroscopy of these nuclei become feasible. The combination of a gas cell with a laser set-up - that brings together rapidity, efficiency and selectivity - placed after the S³ spectrometer represents a powerfull tool for these studies and might furthermore result in the production of pure short-lived n-deficient beams for decay studies.