Arnold Wolfendale conducted research on cosmic rays — immensely energetic particles from sources mainly beyond our Solar System. Arnold became, in particular, a world expert on muons — an elementary particle similar to the electron. His expertise was important in accounting for cosmic ray background effects in experiments that successfully detected neutrinos emitted by nuclear fusion within the Sun.
Arnold developed the neon flash tube and the solid iron spectrograph to improve cosmic ray detection and measurement of their energies. As well as helping us to understand their origin, cosmic ray research has bearing due to the damage that these charged particles can inflict on electronic circuits and living organisms — directly in those sent into space, and indirectly in those on Earth through secondary radiation.