Brightness Energy, Radiance

— the value of $B_{e}$, characterizing the radiation energy source of optical radiation in this direction and is equal: $$ B_{e}=\frac{d \Phi_{e}}{d \Omega d S \cos \varphi} $$ where $d \Phi_{e}$ — flux element surface luminous area $d S$ in the solid angle $d \Omega$ in a direction that makes an angle $\varphi$ with the normal to the element $d S$. Unit B. e. in SI — watts per steradian-square meter — W/(sr m2).


— the value $B_{\varphi}$, which characterizes the glow of the light source in a given direction. B. element $d S$ surface that glows in either direction determined by the ratio of intensity $d l$ of this element in the direction of spread to the area of the projection element on a plane perpendicular to this direction: $$ B_{\varphi}=\frac{d l}{d S \cos \varphi} $$ where $\varphi$ — the angle between the normal to the element $d S$ and this area. Unit B.

Nuclear Forces

— the forces acting between nucleons in atomic nuclei and determine (with electromagnetic forces) the structure and properties of nuclei. N.f. are exchange character; it is assumed that the interaction between nucleons carried by sharing pi —mezonamy; N.f. with. — short-force, their range $r_{\mathcal{я}} \sim 10^{-15}$m; they are characterized by the charge independence; N.f. depending on the relative orientation of the spins of the nucleons; N.f.

Nuclear Reaction

— the transformation of atomic nuclei, due to the interaction of elementary particles or to each other. N.r. usually carried out by bombarding heavy nuclei easier target particles (nuclei). Among N.r.

Nuclear Magnetic Resonance

— resonance absorption energy of an alternating electromagnetic field frequency range substance that is in a constant magnetic field, caused by the magnetism of atomic nuclei. N.m.r. is used to measure the magnetic moments of nuclei, the study and analysis of the structure of matter.