Predictive Model of Electron Beam Induced Flashblindness

摘要

The spectral characteristics of the Cerenkov radiation have been evaluated and converted to equivalent retinal irradiance from external sources. On the basis of the conversion, electron fluxes have been estimated for 2-sec recovery times from flashblindness. The electrons are assumed to have energies greater than 6 MeV and to be delivered in one or more bursts of 1 microsecond each over 1 sec. It is important to note that very little data exists on recovery times as short as 2 sec for either photopic and scotopic conditions. This situation is a direct result of the lack of definition of the critical tasks and their sensitivity to an interruption of background adaptation. The Cerenkov radiation produced within the eye by relativistic electrons can be compared to light from external sources by the relationships: 1 rad approx. = 4.6 scotopic td-sec and 1 rad approx. = 0.55 photopic td sec. Based on these conversion factors, the following estimates can be derived by extrapolation from existing data: (1) Absolute threshold is equivalent to the Cerenkov radiation from a 4.3-microrad electron beam and to a 0.5-mrad x-ray beam. (2) For low photopic levels of adaption (approximately 10 td), 100,000-rad electron beam would be required for a 2-sec recover time for foveal or parafoveal vision. (3) For the dark-adapted eye, a dose of 10 rads may cause a 2-sec interruption in the detection of low-contrast, peripheral targets.