ORIENTATION DEPENDENCES OF QUADRUPOLAR SPIN-LATTICE RELAXATION RATES OF SPIN-3 2 NUCLEI SUBJECT TO A RANDOM 2-SITE EXCHANGE IN A HIGH MAGNETIC-FIELD - A THEORETICAL-STUDY/

Orientational dependences of the quadrupole spin-lattice relaxation ra tes are calculated for a system of spin-3/2 nuclei in a single crystal subject to a random two-site exchange in a high magnetic field. A tec hnique with which the transition probabilities per unit time w1 (DELTA m = 1) and w2 (DELTAm = 2) can be measured with approximately equal ac curacies is proposed. The possibility of extracting the elements of th e fluctuating electric-field-gradient tensor in a crystal-fixed coordi nate system together with the exchange rate from the orientational dep endences of the spin-lattice relaxation rates w1 and w2 is discussed. Two examples - a thermal exchange between two equilibrium sites in a t emperature-independent double-potential well and an exchange between t wo sites above and below an order - disorder phase transition - are br iefly discussed.