A state of a nuclide is described by its energy above the ground state, by its angular momentum J (in units of ℏ ℏ ), and by its parity, i.e., its behaviour under reflection (positive + or negative −). Since the spin of nucleons is ½ (in units of ℏ ℏ ), and since orbital angular momentum has integer values, J may be an integer or a half integer number.