Ten cancer patients whose eyes were therapeutically irradiated with 6–18 MeV electrons reported visual light sensations. Nine reported seeing blue light and one reported seeing white light. Controls reported seeing no light. Additionally, tests with patients ruled out the x-ray contamination of the electron beam as being important. The photon yield due to Cerenkov radiation produced by radium and its daughters for both electrons and gamma rays was calculated; it was found to account for a turn-of-the-century human observation of the “radium” phosphene. We conclude that the dominant mechanism of this phosphene is Cerenkov radiation, primarily from betas. From our own patient data, based on the color seen and the Cerenkov production rates, we conclude that the dominant mechanism is Cerenkov radiation and that high-energy electrons are an example of particle induced visual sensations.

Observations of visual sensations produced by Cerenkov radiation from high-energy electrons.

Models developed for explaining the light flashes experienced by astronauts on Apollo and Skylab missions were used with slight modification to explain upsets observed in microelectronic circuits. Both phenomena can be explained by the simple assumption that an event occurs whenever a threshold number of ionizations or isomerizations are generated within a sensitive volume. Evidence is consistent with the threshold being sharp in both cases, but fluctuations in the physical stimuli lead to a gradual rather than sharp increase in cross section with LET. Successful use of the model requires knowledge of the dimensions of the sensitive volume and the value of threshold. Techniques have been developed to determine these SEU parameters in modern circuits.

Single-event effects experienced by astronauts and microelectronic circuits flown in space

The radiation phosphene.

Visual sensations were experienced when bursts of high-energy pions passed through the dark-adapted right eyes of three human subjects. The threshold for a visual sensation was typically 1 to 3 ..mu..rad at the retina. Data are presented to show that the mechanism is Cerenkov radiation generated within the vitreous humor. Threshold measurements agree with published optical data. A comparison is made between our observations and the light flashes observed in deep space by Apollo astronauts.

Visual Sensations Induced by Relativistic Pions

Visual Response of the Human Eye to X Radiation

The expected frequency was calculated for light flashes induced in the dark-adapted eye by Cerenkov radiation from the flux of heavy nuclei that exists in space beyond the geomagnetic field. The expected frequency of light flashes depends on the threshold number of photons that must be absorbed in a rod cluster. The results of the calculation are presented as a curve of the mean frequency of light flashes versus the threshold number of absorbed photons. The results are not sensitive to variations in the path length from 5 to 15 grams per square centimeter of water-equivalent before the nucleus reaches the retina. Calculations were based on the fluxes and energy spectra of galactic cosmic ray nuclei of helium to iron, measured at a time of minimum solar modulation. The expected light flash frequencies induced by Cerenkov radiation are consistent with the frequencies reported by the astronauts on Apollo missions 11 through 14.

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R. Madey

Papers

Frequency of light-flashes induced by Cerenkov radiation from heavy cosmic-ray nuclei