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 powerf ul method to measure the quadrupole interaction frequency of long-live d low-spin nuclear states which decay through gamma-radiation [R. Cous sement 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 re action at a recoil mass spectrometer. The idea is to apply the LMR met hod to study some features of light exotic nuclei (e.g. initial alignm ent, radiation parameter, quadrupole moment, magnetic moment, spin, et c.). It is found that in a level mixing resonance, an appreciable amou nt of initial alignment is transferred to polarization due to a combin ed electromagnetic interaction. This transfer of alignment to polariza tion 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 immediate ly if the radiation parameter A1 is known (and vice versa). The positi on of the resonance as a function of an externally applied magnetic fi eld 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. Th e LMR method applied to recoil separated exotic nuclei produced in a f ragmentation reaction provides thus a very powerful tool to study seve ral aspects of the recoil fragments.