Magnetic Moments Of N-17 And B-17

The magnetic moments of N-17 and B-17 were measured by using spin-polarized radioactive nuclear beams which were obtained from the projectile 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 nuclear structure inherent in a p(1/2) valence nucleus, the deviation from the Schmidt value is attributed on firm ground to admiring of the configurations in which two neutrons in the sd shell are coupled to J(pi)=2(+). This interpretation is confirmed in standard shell-model calculations. The calculations reproduce fairly well the experimentally inferred amount of 2(+) admixture, as well as the experimental magnetic moment 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 indicate that the quenching of mu largely stems from J(pi)=2(+) configurations of the sd neutrons. The observed amount of quenching, however, is larger than the shell-model predictions, suggesting an enhanced contribution of the 2(+) neutron configurations. This result is explained if the pairing energy for neutrons in the sd shell of a neutron-rich nucleus 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.