"Nuclear Quadrupole Moment" is a quantity that characterizes the deviation from spherical symmetry of the electrical charge distribution in an atomic nucleus.
$Q = (\frac{1}{e}) \int (3z^2 - r^2)\rho(x, y, z)dV$, in the quantum state with the nuclear spin in the field direction $(z)$, where $\rho(x, y, z)$ is the nuclear electric charge density, $e$ is the elementary charge, $r^2 = x^2 + y^2 + z^2$, and $dV$ is the volume element $dx$ $dy$ $dz$.
Applicable units are those of quantitykind:NuclearQuadrupoleMoment
Nuclear Quadrupole Moment