Following on from those developments, after World War II, Powell and his research group at Bristol University collaborated with Ilford (now Ilford Photo), to further optimise emulsions for the detection of cosmic ray particles. Ilford produced a concentrated ‘nuclear-research’ emulsion containing eight times the normal amount of silver bromide per unit volume (see External Link to 'Nuclear emulsions by Ilford'). Powell's group first calibrated the new ‘nuclear-research’ emulsions using the University of Cambridge Cockcroft-Walton generator /accelerator, which provided artificial disintegration particles as probes to measure the required range-energy relations for charged particles in the new emulsion.