(lx) Lux is the SI unit of illumination. Lux is based on lumen, and lumen is a derived unit based on candela. One lux is equal to the intensity of light on a surface that is 1 m from a uniform point source of one candle intensity or equal to one lumen (lm) per square meter.
The formula is:
1 lx = 1 lm/m²

Reflux is the backward flow of fluids.

(D) The electric flux density is a vector equal to the product of the electric field strength and the permittivity. The unit is coulomb per square meter (C/m²). The total electric flux passing through a closed surface is equal to the total charge enclosed by the surface.

Magnetic flux density is the amount of magnetic flux per unit area of a section, perpendicular to the direction of flux. The magnetic flux density is the product of the magnetic field strength and permeability. The SI unit for flux density is weber per square meter. One weber per square meter equals one tesla (T).

(NAA) Neutron activation analysis is a very sensitive analytical technique to determine even very low concentration of chemical elements, trace elements for example, in small biological samples.
NAA becomes commercial available in the USA in 1960.
In the activation process stable nuclides in the sample, which is placed in a neutron beam (neutron flux, 90-95% are thermal neutron with low energy levels under 0.5 eV), will change to radioactive nuclides through neutron capture (artificial radioactivity). These radioactive nuclides decay by emitting alpha-, beta-particles and gamma-rays with a unique half-life. Qualitative and quantitative analysis of the sample is done with a high-resolution gamma-ray spectrometer.
NAA is subdivided into the following techniques: