N-trimethyl B-tri(diphenyl), N-triphenyl B-tri(diphenyl), N-triphenyl B-tri(alphanaphtyl) borazines, and hydroxiborazaro phenanthrene and bis 2-1 borazaro-2-naphtyl ether, were assayed in benzene solution and as solid films for scintillation counting of thermal neutrons moderated with paraffin from the reaction Li7(d,n) Be8 . A background of gamma radiation was present, partly from the reaction Li7(p,gamma)Be8. Absolute gamma and neutron flux measurements of the source were made, using gamma ray spectrometry and foil activation. Characteristic counting curves and absolute counting efficiencies were obtained for several liquid and solid scintillators. Also, studies of the concentration effects, geometrical and dimensional factors, etc. were made using a Po-Be and a Ra-Be source and several gamma ray sources. Finally, actual tests based on the aforementioned experiments were made in a nuclear critical facility and excellent results were obtained.