Projectile Fragmentation Mechanism and Production of Aligned Spin-stretched Isomers

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The spin orientation and the isomer production ratio for ejectiles from high-energy projectile fragmentation reactions have been studied in order to clarify the reaction mechanism and to develop a method to produce spin-oriented radioactive nuclear beams, The experiments were performed (1) in the 500 MeV/u and (2) in the 100 MeV/u regions.(1) in the 500 MeV/u regin, fragments ^<43>Sc were produced through removing three nucleons from projectiles ^<46>Ti by the collision with a Be target. For the 19/2^- isomer of the ^<43>Sc, which is known to represent a spin-stretched state of a (f_<7/2>)^3 configuration, the mesurements were made of i)the isomer production ratio and ii)the spin orientation of rank 2 (i, e. the alignment). (2)In the 100 MeV/u region, projectiles of ^<15>N, ^<18>O, and ^<22>Ne were used and the rank-1 orientation (polarization) was measured for fragments produced in the fragmentation process. Also, this scheme of polarization was applied to measurents of the fragmentat … More ion process. Also, this scheme of polarization was applied to measurents of the magnetic moments and electric quadrupole moments.From the measurements described above. following results were obtained. (1)The observed isomer production ratio shows a clear momentum dependence characteristic of a behavior predicted from a participant-spectator model for the fragmentation process. (2)The spin alignment of the isomer changes from positive values at the center momentum of the Goldhaber distribution to negative values with magnitudes as large as 20% at the wing momenta, agein showing a good agreement with the participant-spectator model. (3)The polarization studied in the 100 MeV/u region showed a sytematic variation over different enegries and targets and, together with the results (1) and (2), proved general validity of the above simple model for the spin orientation observable in the 100-500 MeV/u fragmentation reactions, Utilizing the thus confirmed phenomenon of the fragment spin orientation, the magnetic moments for neutron-rich nuclei ^<14>B, ^<15>B, ^<17>N, and ^<21>F and the quadrupole moments for ^<14>B and ^<15>B were newly determined. Less