Projectile Fragmentation Mechanism and Production of Aligned Spin-stretched Isomers

本文研究了高能弹丸破片反应中抛射物的自旋取向和异构体生成比，以阐明反应机理，并建立了一种产生自旋取向放射性核束的方法。实验分别在500 MeV/u和100 MeV/u区域进行。(1)在500 MeV/u区域，弹丸^<46>Ti与Be靶的碰撞使3个核子脱落，产生了^<43>Sc碎片。对于^<43>Sc的19/2^-异构体（已知代表（f_<7/2>）^3构型的自旋拉伸状态），测量了i)异构体产生比和ii) 2阶自旋取向（i，即排列）。(2)在100 MeV/u区域，采用^<15>N、^<18>O和^<22>Ne的弹丸，对破碎过程中产生的破片进行了秩1取向（极化）测量。并将该偏振方案应用于离子破碎过程的测量。同时，将该极化方案应用于磁矩和电四极矩的测量。从上面描述的测量。得到以下结果：(1)观察到的同分异构体生成比显示出明显的动量依赖特征，这是由破碎过程的参与者-旁观者模型预测的行为。(2)同分异构体的自旋排列由Goldhaber分布中心动量处的正值变为翼动量处的负值，其幅度可达20%，与参与者-旁观者模型吻合较好。(3)在100 MeV/u区域所研究的极化在不同的能量和目标上呈现出系统的变化，并与结果(1)和(2)一起证明了上述简单模型在100-500 MeV/u分裂反应中观察到的自旋取向的一般有效性。利用由此证实的碎片自旋取向现象，富中子核的磁矩为^<14>B, ^<15>B, ^<17>N，和^<21>F和^<14>B和^<15>B的四极矩是新的。少

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