The Nuclear Magnetic Moment ofLi7by Perturbation Theory

Under the assumption that the intrinsic magnetic moments of protons and neutrons are not destroyed by the nuclear binding process, and with the adoption of a rather general exchange interaction, the same between all pairs of heavy particles, the magnetic moment of ${\mathrm{Li}}^7$ is calculated by a perturbation theory which develops from the approximation in which the particles move independently in a central field. The first-order result is that the orbital part of the magnetic moment has a value between $0.26{\mu }_N$ and $0.30{\mu }_N$, depending on the details of the interaction, and that the spin part can differ from the proton magnetic moment by not more than $0.03{\mu }_N$, because of the exchange nature of the like-particle interaction and the small spin dependence of the unlike-particle interaction allowed by the data on scattering. The second-order modification is very small ($0.01{\mu }_N$ from the doubly excited states) and is due principally to the excitation of the $s$ shell, since states involving only the excitation of the three $p$ particles annual one another in their second-order effect. The modification is positive, corresponding to a limited participation of three protons and four neutrons in the orbital part, rather than one proton and two neutrons as in first order. Cancellation of positive and negative higher order contributions facilitates rapid convergence. If our result is to agree with experiment, the value of the proton magnetic moment must be near the upper limit ($3{\mu }_N$) of the rather wide range suggested experimentally, which seems unlikely. Such a discrepancy may be associated with the inadequacy of the symmetrical interaction apparent in calculating binding energies.