resonance neutrons 

https://doi.org/10.1351/goldbook.R05342
Neutrons whose energy corresponds to the resonance energy of a specified nuclide or element. If the nuclide is not specified, the term refers to resonance neutrons of 239U.
Source:
PAC, 1994, 66, 2513. (Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)) on page 2522 [Terms] [Paper]