Multipolarity of gamma radiation

Each of these, being electromagnetic radiation, consists of an electric and a magnetic field.

[note 1] Similarly, magnetic dipole, quadrupole, octupole… radiation (generally: 2

[1] In quantum mechanics, angular momentum is quantized.

The various multipole fields have particular values of angular momentum: E

To make a simple classical comparison, consider the figure of the oscillating dipole.

It produces electric field lines travelling outwards, intertwined with magnetic field lines, according to Maxwell's equations.

This system of field lines then corresponds to that of E1 radiation.

Similar considerations hold for oscillating electric or magnetic multipoles of higher order.

), and by its parity, i.e., its behaviour under reflection (positive + or negative −).

(i.e., dipole, or quadrupole...) carry the same angular momentum

:[1] The designation "electric multipole radiation" seems appropriate since the major part of that radiation is produced by the charge density in the source;[1] conversely, the "magnetic multipole radiation" is mainly due to the current density of the source.

[1] In electric multipole radiation, the electric field has a radial component; in magnetic multipole radiation, the magnetic field has a radial component.

Clearly, this must carry away an angular momentum of 2, without change of parity.

The case of the 1.17 MeV transition is a bit more complex: going from J = 4 to J = 2, all values of angular momentum from 2 to 6 could be emitted.

But in practice, the smallest values are most likely, so it is also a quadrupole transition, and it is E2 since there is no parity change.