EXTENSION OF THE LEVEL MIXING RESONANCE (LMR) METHOD TO STUDY THE ALIGNMENT AND THE QUADRUPOLE-MOMENT OF LIGHT EXOTIC PROJECTILE FRAGMENTS

The level mixing resonance (LMR) method has proven to be a very powerful method to measure the quadrupole interaction frequency of long-lived low-spin nuclear states which decay through gamma-radiation [R. Coussement et al., Hyperfine Interactions 23 (1985) 273, G. Scheveneels et al., ibid., 52 (1989) 257, 179]. In this paper the concept of LMR has been extended for beta-decaying nuclei produced in a fragmentation reaction at a recoil mass spectrometer. The idea is to apply the LMR method to study some features of light exotic nuclei (e.g. initial alignment, radiation parameter, quadrupole moment, magnetic moment, spin, etc.). It is found that in a level mixing resonance, an appreciable amount of initial alignment is transferred to polarization due to a combined electromagnetic interaction. This transfer of alignment to polarization induces a resonant change in the beta-anisotropy as a function of the applied magnetic field. From the amplitude of the resonance, the initial alignment of the projectile fragments can be derived immediately if the radiation parameter A1 is known (and vice versa). The position of the resonance as a function of an externally applied magnetic field is extremely sensitive to the quadrupole interaction frequency of the nucleus in a host. The quadrupole frequency can be derived if the magnetic moment is known. If not, the ratio mu/nu(Q) is determined. The LMR method applied to recoil separated exotic nuclei produced in a fragmentation reaction provides thus a very powerful tool to study several aspects of the recoil fragments.