nuclear magneton

https://doi.org/10.1351/goldbook.N04236
Electromagnetic fundamental physical constant $$\mu _{\text{N}}=\frac{m_{\text{e}}}{m_{\text{p}}}\ \mu _{\text{B}}=5.050\ 7866(17)\times 10^{-27}\ \text{J T}^{-1}$$, where $$m_{\text{e}}$$ is the electron rest mass, $$m_{\text{p}}$$ the proton rest mass and $$\mu _{\text{B}}$$ the Bohr magneton.
Source:
CODATA Bull., 1986, 63, 1. (https://doi.org/10.6028/jres.092.010)