Selection Rules in Nuclear Radiation

Abstract

In the first part of this paper we discuss the radiation from a single charged particle moving in an arbitrary central field of force and obeying Dirac's equation. We consider the electric quadripole and magnetic dipole radiation as well as the electric dipole. We derive the selection rules for the magnetic dipole radiation and collect together for reference the corresponding selection rules for the electric dipole and quadripole radiations. In the second part we discuss the relative intensities of the various types of radiation, treating in detail the cases where the selection rules for magnetic dipole and electric quadripole are simultaneously satisfied. Finally we show that these results have an important bearing on the theory of internal conversion of γ-rays. The internal conversion of soft γ-rays occurs with such high probability that the theory is unable to account for the experimental results unless it is assumed that the radiation is largely magnetic dipole in character. On the other hand, Fisk and Taylor (loc. cit.) were unable to account for the presence of magnetic dipole radiation in appreciable amounts. We show that this is due to the fact that, of the two possible transitions (a and e of § 2) in which both magnetic dipole and electric quadripole radiation can be emitted, Fisk and Taylor considered only the second. In the case of the second, corresponding to a transition between two distinct terms, we show that Fisk and Taylor were correct in predicting a negligible amount of magnetic dipole radiation, but in the case of the first, corresponding to a transition between two levels of one multiplet term, we find that there is indeed a high percentage of magnetic dipole radiation.

Photo‐Induced Electric Field Effects on Water Droplets Generated in a LiNbO3 Opto‐Microfluidic Platform

“…The interaction of different kind of electric field geometries with fluids has been studied for decades starting from the pioneering work of Taylor. [ 47 ] In literature, specific geometries have been studied to describe the effect of applied electric field on interacting fluids and explain the induced deformation. Static spherical droplet or cylinder with a circular cross‐section have been investigated under a uniform electric field, showing that a prolate or oblate ellipsoidal form (or ellipsoidal cross‐section) is achieved according to the electrohydrodynamic (EHD) properties of the system.…”

Substrate‐Independent Electrohydrodynamic Jet Printing with Dual‐Ring Electrostatic Focusing Structure

“…The mutual coulombic repulsion between these mobile charges induces a tangential electrical force on the surface of the ink, thereby deforming the meniscus into a Taylor cone. [ 48 ] When the electric field is high enough, the electrical force overcomes the surface tension, viscous force, and gravity, then a droplet or a jet of ink is ejected from the microtip and moved toward the substrate relying on its own motion inertia. The force balance of the electrical force, surface tension, viscous force, and gravity determines the stable jet.…”