Abstract
DURING Apollo 11–15, astronauts observed randomly occurring light flashes and streaks1. Among the explanations offered is that they are caused by direct interaction of fast, heavy primary cosmic rays with the retina2–6. Other suggestions include the assumption that Cerenkov light from relativistic cosmic ray particles7,8 or fluorescence of the lens9 causes the effect. Previously we demonstrated that flashes are observed in single recoil events from fast neutrons in the hundred MeV energy domain2,3 and by actions in the eye from fast neutrons of 25 MeV maximum kinetic energy6. Discrete flashes are generated by neutrons with energy ranges between 3 and 8 MeV (ref. 10), but not by neutrons of fission spectrum energies6. Recently, it was demonstrated that flashes and streaks are seen when single nonrelativistic helium ions (about 240 MeV) stop in or cross the retina of the human eye11,12. These particles, with a linear energy transfer greater than 10 keV µm−1, were seen by two subjects (T.F.B. and C.A.T.) with a 40% detection efficiency in a 4 mm diameter beam of 10 particles s−1.
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