The radiation phosphene.

A low flux of X-rays below the Cerenkov energy threshold generates a phosphene by direct action on the retina without a fluorescence in the ocular media. X-rays above the Cerenkov threshold can generate only a faint luminescence in the lens and cornea. From experimental work on humans in 1905 with unencapsulated radium, it is known that approximately 80% of the intensity of the radium phosphene is from the beta-ray component and approximately 20% from the gamma-ray. From calculations of the photon yield due to Cerenkov radiation in the eye from radium, one finds intensities of approximately 90% and approximately 10% for beta and gamma-rays, respectively, if only Cerenkov radiation is considered. Thus, one may conclude that the dominant mechanism of the radium phosphene is Cerenkov radiation, primarily from electrons and not fluorescence as previously speculated. The term "radium phosphene" is a misnomer and should be subsumed along with the X-ray phosphene and particle induced visual sensations under the name "radiation phosphene".