In order to measure neutron flux and energy in the presence of high-intensity background gamma rays, a new nuclear emulsion based on a non-sensitized OPERA film was synthesized, which had small AgBr grain sizes of 60, 90 and 160 nm. The sensitivity of this new emulsion, which is described in terms of the stopping power and grain density, was estimated experimentally by neutron irradiation at several energies. The response of the emulsion to gamma-ray-induced electrons was also simulated and the results were compared with experimental data obtained using a 60Co gamma source. The results indicated that each AgBr grain has a threshold energy that must be deposited before the AgBr can develop into metallic Ag. Based on these results, the efficiency of the new emulsion in detecting gamma rays and neutrons was evaluated. © 2012 Elsevier Ltd. All rights reserved.