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发表于 2015-12-12 09:00:54
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When an X-ray or gamma ray beam
strikes a film, usually less than one
percent of the energy is absorbed. Because
the formation of the radiographic image is
governed by the absorbed radiation, more
than 99 percent of the available energy in
the primary radiation reaching the film
performs no useful photographic work.
Lead foil in direct contact with the film
has three principal effects: (1) it increases
the photographic action on the film,
largely by reason of the electrons emitted
and partly by the secondary X-rays
emitted by the lead; (2) it absorbs the
longer wavelength scattered radiation
more than the primary; and (3) it
intensifies the primary radiation more
than the scattered radiation.
資料來源 RT Handbook
簡單來說就是射線只有不到1%的能量會被底片吸收~
放增感屏可有效利用那99%的射線能量
透過光電效應轉換成電子進而提供另一個使底片感光的管道
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