röntgen in polymers

https://dx.doi.org/10.1351/goldbook.R05404
Non-SI unit of exposure to X- or γ-radiation: R = 2.58 × 10 −4 C kg.
Source:
PAC, 1996, 68, 957 (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 991