Interaction with Electromagnetic Field: Electromagnetic Moments

Abstract

As mentioned in Chap. 1, by measuring the magnetic moment of proton, Stern showed that the proton is not an ideal point particle which can be described by the Dirac equation. Also, we learnt in Chap. 3 that the magnetic moment of deuteron tells that deuteron is in the spin-triplet and isospin-singlet states, and that one can get information on the magnitude of the tensor force through the admixture of the D-state in deuteron. In this way, the electromagnetic properties of nuclei provide valuable information on the structure of nucleons and nuclei. Also, the interaction of nuclei with the radiation field leads to the emission and absorption of a $\gamma$-ray, governs the lifetime of each energy level, and provides information on the nuclear structure as well as nuclear collective motions through the strength of the electromagnetic transitions between nuclear levels. Furthermore, the measurement of the angular correlation between the cascade $\gamma$-rays enables us to determine the spin of each energy level. The electromagnetic transitions play an important role also in the synthesis of elements through, e.g., the radiative neutron capture (see Cottingham and Greenwood, An Introduction to Nuclear Physics, 2nd edn. (Cambridge University Press, Cambridge, 2001); Thompson and Nunes, Nuclear Reactions for Astrophysics: Principles, Calculation and Applications of Low-Energy Reactions (Cambridge University Press, Cambridge, 2009) [1, 2]). In this chapter we learn the electromagnetic moments such as the magnetic dipole moment and the quadrupole moment which provides important information on the nuclear shape. The electromagnetic transitions by emitting $\gamma$-rays will be discussed in Sect. 8.3 after we learn about nuclear structure in Chaps. 5 and 7.