MR. STRETCH1 objects to the use of the term ‘neutron flux’ because the entity specified is a scalar, the movement of neutrons involved being random instead of a directed flow ; he contrasts this with the usage of the word ‘flux’ for a vector quantity. This usage, as in ‘heat flux’, is, however, already a degenerate form. Though now often used with a vectorial meaning, ‘flux’ was originally a scalar, albeit derived from a vector. The original meaning, which is still the customary one in electrical theory, is ‘the surface integral of the normal component of a vector’, and this is a scalar. It is this mathematical concept, surely, that should be the standard of orthodoxy.
Stretch, K. L., Nature, 191, 60 (1961).