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Slide 1

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Medical Physics…read more

Slide 2

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X-ray Production
1. A cathode is heated so that it releases electrons.
2. These electrons are fired across a vacuum by a
voltage generated by the mains.
3. These electrons hit the negative anode and some
of their energy (about 1%) is converted into X-ray
4. These X-ray photons can only exit through a
window in the casing and there may be sheets of
metal either side of the window to absorb X-rays
not travelling straight, forming a collimated beam.…read more

Slide 3

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X-ray Production
· The rest of the energy of the electrons is
gained by the anode as heat, so it rotates very
fast to get rid of the excess heat.
· The energy of one X-ray photon is virtually the
same as the kinetic energy of the electrons, as
the work function is negligible.…read more

Slide 4

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X-ray Production…read more

Slide 5

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X-ray absorption ­ the photoelectric effect…read more

Slide 6

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X-ray absorption ­ the photoelectric effect
· Because the energy of X-rays is so high, the
work function is considered negligible.
· Therefore the photoelectrons produced have
virtually the same energy as the X-ray photons
that caused them.
· This is the main way that low energy X-rays
are absorbed.…read more

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