Experimental measurements have been carried out to study the effect of cadmium on the distribution and attenuation of reactor thermal neutrons emitted from a reactor core and the new thermal neutrons produced in a heterogeneous shield of water, iron, iron + B4C and ordinary concrete. Measurements were performed using a reactor beam of neutrons filtered with cadmium emitted from one of the horizontal channels of ET-RR-1. It was found that the presence of cadmium sheet at channel exit causes a marked decrease in the thickness of the shield required to attenuate the thermal neutron flux by a certain factor.