Cross Polarization of Unstable Nuclei and Its Application

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New method of polarizing unstable nuclei has been developed, which is applicable to the projectile fragments produced in the high-energy heavy-ion reaction. The method consists of the following four stages : 1.Production of polarization in Rb atoms by means of the laser optical pumping, 2.transfer of the Rb polarization to ^<129>Xe nuclei through the hyperfine interactions inthe course of Rb-Xe atomic collisions, 3.production of a polarized Xe solid by freezing the polarized gas of Xe, and 4.implantation of projectile fragments in the polarized Xe solid and subsequent cross polarization of the implants by the host Xe spins. Results obtained untilnow in the present investigation are :1.Agaseous Xe was successfully polarized in a pyrex glass cell, 22 mm in diameter, 40 mm in length. Polarization P_<Xe>=60% was attained at the Xe gas pressure of p=10torr. P_<Xe> was found to decrease with increasing p. The whole behavior of P_<Xe> as a function of p was well explained by theory based on t … More he consideration of Rb-Xe and Xe-Xe collisios and Xe spin-wall interaction as sources of spin transfer and relaxation.2.Efforts were made to eliminate the wall relaxation in order to achieve a high value of P_<Xe>. As a result, a wall relaxation time T_w as long as 11 min was attained by coating the inner surface of the cell with dichlorodimethylsilane. With such a value of T_w,10^<21> atoms of Xe, amounting to a solid Xe of 5*5*1mm^3 volume, can be polarized to P_<Xe>=7.5-11%.3.Apolarized gas of Xe thus obtained was transported from the pumping station to a high-field region, cooled there, and frozen into a solid under an applied field of 90 mT.Observed NMR signals from the solid indicated that about 35% of the initial polarization was retained through the transportation and freezing. Further investigation is needed to reduce loss of polarization in these procedures.4.Development was made of the beta-NMR measurement technique on implanted projectile fragments. Heavy-ion beams at E/A=70-100 MeV/u were used to produce several light neutron-rich isotopes, and the beta-NMR measurements were made. In the course of development, results were obtained for magnetic moments and electric quadrupole moment of those nuclei which could be polarized by the fragmentation reaction itself.Based on the outcome presented above, the cross polarization experiment of ^<11>Be and its application to the magnetic moment measurement are now under consideration. Less