Abstract: A small piggy back detector system are used to study the reduction of γ-ray background induced by atmospheric neutrons in the type of active shielded γ-ray spectroscopes.The system consists of two φ1"5 ×1"5 NaI erystal units,one of which is surrounded by some neutron shield material.The results of a balloon flight in 1981 are presented.The data show that a shield of 3 cm thick pure parraffin can not reduce the γ-ray background,on the contrary,it may even cause some enhancement.