Nuclear magneton
The
nuclear magneton (symbol ), is a
physical constant of magnetic moment, defined by:

where:
 is the elementary charge,
 is the Dirac's constant,
 is the proton rest mass
In the
SI system of units it's value is approximately:
 = 5.050 786 6(17) × 10^{27} J·T^{1}
See also proton magnetic moment.