A technique is discussed for utilizing photographic plate detectors in an evacuated camera, containing an appropriate radiator, to make precise determinations of the range distributions of the disintegration products of slow neutron reactions. The same technique is applied to the problem of measuring neutron energies by making range measurements on the forward recoil protons projected by fast neutrons from a thin polyethylene radiator. As an indication of the accuracy attainable with photographic plates when used in this manner, determinations have been carried out for theQvalues of the Li6(n,&agr;)H3reaction and the B10(n,&agr;)Li7reaction.