@property
def numberOfCoreParticles(self):
    'Count the number of core particles. Returns None if the electronic\n        configuration has no core.'
    if (not self.hasCore):
        return None
    (core_shell, _) = self.shells
    (core_occupancy, _) = self.occupancies
    return self.countParticles(core_shell, core_occupancy)
Count the number of core particles. Returns None if the electronic
configuration has no core.
@property
def numberOfCoreParticles(self):
    'Count the number of core particles. Returns None if the electronic\n        configuration has no core.'
    if (not self.hasCore):
        return None
    (core_shell, _) = self.shells
    (core_occupancy, _) = self.occupancies
    return self.countParticles(core_shell, core_occupancy)