Observation of spin-aligned secondary fragment beams ofB14

An alignment of the nuclear spin has been observed for a secondary radioactive beam of ${}_{}{}^{14}{}_{}{}^{}\mathrm{B}$ produced in the fragmentation of a 60 MeV/nucleon ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ beam impinging onto a ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ target. The fragments were separated and analyzed in momentum by means of the doubly achromatic spectrometer LISE. The spin alignment was determined through a measurement of the anisotropy of the β-delayed γ-ray emission. The alignment is found to be small in the momentum region corresponding to the peak of the fragmentation yield, whereas it takes a large negative value for the high-momentum tail. This result is discussed in terms of a simple model of projectile fragmentation. The relevance of this result for the determination of nuclear moments far from stability is considered.