By an ingenious example of lateral thinking, she applied a similar method to make the first ever observation of the impact of neutrons in nuclear emulsion. Being electrically neutral the neutron cannot, of course, be directly detected in a photographic emulsion, but if it strikes a proton in the emulsion, that recoiling proton can be detected. She used this method to determine the energy spectrum of neutrons resulting from specific nuclear reaction processes. She developed a method to determine proton energies by measuring the exposed grain density along their tracks (fast minimum ionising particles interact with fewer grains than slow particles). To record the long tracks of fast protons more accurately, she enlisted British film manufacturer Ilford (now Ilford Photo) to thicken the emulsion on its commercial plates, and she experimented with other emulsion parameters — grain size, latent image retention, development conditions — to improve the visibility of alpha-particle and fast-proton tracks.