<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _nelec(self):
 """ Particles per unit lorentz factor """

        pd = self.particle_distribution(self._gam * mec2)
        return pd.to(1 / mec2_unit).value