superthermal source

superthermal source

[¦sü·pər′thər·məl ′sȯrs]
(nucleonics)
A source of ultracold neutrons consisting of a container of liquid helium, cooled to about 1 K or less, which has walls that are good reflectors of ultracold neutrons but are transparent to electrons with energies of about 1 millielectronvolt, and which is placed in a beam of such electrons.