MAGNETIC-MOMENTS OF N-17 AND B-17

The magnetic moments of N-17 and B-17 were measured by using spin-pola rized radioactive nuclear beams which were obtained from the projectil e fragmentation reaction. The observed magnetic moment of N-17, \mu(N- 17)\=(0.352+/-0.002)mu(N), where mu(N) is the nuclear magneton, falls outside the Schmidt lines. By virtue of a simplifying feature of nucle ar structure inherent in a p(1/2) valence nucleus, the deviation from the Schmidt value is attributed on firm ground to admiring of the conf igurations in which two neutrons in the sd shell are coupled to J(pi)= 2(+). This interpretation is confirmed in standard shell-model calcula tions. The calculations reproduce fairly well the experimentally infer red amount of 2(+) admixture, as well as the experimental magnetic mom ent itself. The magnetic moment for B-17 was determined as \mu((17B))\ =(2.545+/-0.020)mu(N). The result is substantially smaller than the pi p(1/2) single-particle value, and the shell-model calculations indica te that the quenching of mu largely stems from J(pi)=2(+) configuratio ns of the sd neutrons. The observed amount of quenching, however, is l arger than the shell-model predictions, suggesting an enhanced contrib ution of the 2(+) neutron configurations. This result is explained if the pairing energy for neutrons in the sd shell of a neutron-rich nucl eus is assumed to diminish by about 30%. We also find that the use of the reduced pairing energy improves agreements in the magnetic moment and low-lying energy levels of N-17 as well.