Observations by Human Subjects on Radiation-Induced Light Flashes in Fast- Neutron, X-Ray, and Positive-Pion Beams. Page: 6 of 23
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OBSERVATIONS BY HUMAN SUBJECTS ON RADIATION-INDUCED LIGHT FLASHES
IN FAST-NEUTRON, X-RAY, AND POSITIVE-PION BEAMS
C. A. Tobias, T. F. Budinger, and J. T. Lyman
Lawrence Radiation Laboratory
University of California
Berkeley, California 94720
In order to examine the hypothesis that light flashes seen by astro-
nauts on lunar missions are the result of primary cosmic particles, two
human subjects were exposed to a fast neutron beam (20 MeV to 640 MeV)
at the Berkeley 184-inch cyclotron. Both subjects saw 25 to 50 discrete
pinpoint bright momentary light flashes in response to a flux of 1U4 neu-
trons cm-2 sec-1 (1 mrem dose). The star-like phosphene phenomenon
in the neutron exposure is different from x ray induced radiophosphenes
and from electrically produced visual flashes. No visual phenomenon
was noted on positive pi meson exposure at 200 neutrons cm-2 sec-1. We '
believe that bright flashes seen by astronauts are from primary cosmic
particles traversing the retina. The mechanism is probably ionization,
although light from Cerenkov effect has not been ruled out.
During the space flights of 1969 that car-
ried man to his first lunar landings, Edwin
Aldrin and other astronauts on Apollo 11, 12,
and 13 observed a series of light flashes and
streaks when they were in darkness at great
distances from the earth. It has been known
for many years that relatively low doses of
x rays impinging on the retina can cause light
scnoation and alteratiun of light sensitivity
threshold;2 however, the astronauts' de-
scriptions of discrete flashes and streaks do
not conform to the homogeneous flood of light
cIadaictcriotic of x-ray phocphenes.
During surveys of the radiobiological
hazards of high-altitude flight and manned
space exploration, one of us suggested that
heavy cosmic ray particles might cause light
sensations (" . . . it would seem that a dark
adapted person should be able to ' see' very
heavily ionizing single tracks as a small
light flash, since they would pass through
several retinal receptors, enough to corre-
spond to a visual object of greater than 1'
angular aperture. . If a track travels within
the plane of the retina, several rods and
conc may be inactivated " - " " ), 3, 4 Although
these suggestions were made in 1952 and
1958, it was not until after light flashes were
seen by the astronauts that definitive experi-
ments were commenced to elucidate the mech-
anism of the phenomenon and the validity of
the above hypothesis.
It is possible that these flashes were due
to ionization or some other form of interac-
tion of primary cosmic particles with tissues.
The streaks might be principally due to heavy
primaries, and double points could be ac-
counted for by one cosmic particle intersec-
ting the retina at two points. Energy trans-
ferred to tissue by these particles is propor-
tional to the square of their atomic number,
and it also depends on their velocity (~ 1/v2).
It is important for the safety of long inter-
planetary flights to understand such effects
and the potential hazard they may cause. Fur-
ther, knowledge about induction of light sen-
sation by charged particles may also lead to
a better understanding of the process of vi-
Other studies that bear on these effects
include cosmic meson interactions, ioniza-
tion from low energy protons, and the
Cerenkov effect. On the basis of statistical
analysis of coincidences in cosmic-ray
counts and light sensations reported by sub-
jects, mesons have been reported to cause
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Tobias, C. A.; Budinger, T. F. & Lyman, J. T. Observations by Human Subjects on Radiation-Induced Light Flashes in Fast- Neutron, X-Ray, and Positive-Pion Beams., report, January 1, 1970; [Berkeley, California]. (https://digital.library.unt.edu/ark:/67531/metadc872480/m1/6/: accessed May 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.