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radiography

radiography   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
864 words
Illustration(s):
1

...of the attenuation with the atomic number (Z) of the medium substance Energy range in which this kind of attenuation is dominant simple scattering ∝ 1/ E ∝ Z 2 1–20keV photoelectric effect ∝ 1/ E 3 ∝ Z 3 1–30keV Compton scattering falls gradually with E independent 30keV–20MeV pair production rises slowly with E ∝ Z 2 above 20 MeV Air has a higher average Z than soft tissue, which consists of mostly carbon ( 6 C) and hydrogen ( 1 H). However, the low average density of air means that it does not attenuate...

quantum mechanics

quantum mechanics   Quick reference

A Dictionary of Physics (8 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Physics
Length:
1,612 words
Illustration(s):
3

...based on quantum theory , which arose out of the failure of classical mechanics and electromagnetic theory to provide a consistent explanation of both electromagnetic waves and atomic structure. Many phenomena at the atomic level puzzled physicists at the beginning of the 20th century because there seemed to be no way of explaining them without making use of incompatible concepts. One such phenomenon was the emission of electrons from the surface of a metal illuminated by light. Einstein realized that the classical description of light as a wave on...

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