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A m b i e n t - B a c k g round Radiation
( e ffects on raw stock)
Ambient gamma radiation is composed of two sources: a
l o w - e n e rgy component which arises from the decay of
radionuclides and a high-energy component which is the
p roduct of the interaction of cosmic rays with the earth’s
upper atmosphere. The radionuclides responsible for the
l o w - e n e rgy photons exist in soil and rock and are carried
into earth-derived building materials, such as concre t e .
Upon exposure to ambient-background radiation, photo-
graphic negative materials can exhibit an increase in
minimum density, a loss in contrast and speed in the dark
a reas, and an increase in granularity. The changes in fil m
p e rf o rmance are determined by several factors, such as
the film speed and length of time exposed to the radiation
b e f o re the film is processed. A film with an exposure
index of 500 can exhibit about three times the change in
p e rf o r mance as a film with an index of 125. While this
e ffect on film raw stock is not immediate, it is one re a s o n
why we suggest exposing and processing film as soon as
possible after purchase. We recommend a period of no
m o re than six months from the time of film purc h a s e
b e f o re processing, provided it has been kept under spec-
i fi ed conditions. Extended periods beyond six months may
a ffect faster speed films as noted above, even if kept
f rozen. The only way to determine the specific effect of
a m b i e n t - b a c k g round radiation is with actual testing or
m e a s u rements and placing a detector in the locations
w h e re the film was stored. The most obvious clue is the
observance of increased granularity, especially in the light
a reas of the scene.
P rotection from Physical Damage
Keep films away from heating pipes and direct sunlight,
even if the room is air-conditioned. Maintain uniform
room temperature throughout the storage area by means
of adequate air circulation. If the building is not fire p ro o f ,
install an automatic fire-extinguisher system. Design
storage rooms for motion picture raw stock so that film is
at least 6 in. (15 cm) off the flo o r.
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