x rays

1. X-RayRobert Eshun
S.L.T. Dept.
Accra Polytechnic

2. Introduction
 E. m. Radiation.
 Wavelengths in the range of 10 to 0.01 nm [frequencies
30 petahertz (+15) to 30 exahertz (+18)].
 Also known as Rontgen rays.
 Energies ranging from 120eV to 120keV.
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3.  Bounded by gamma rays on the left and U.V. on the
right.
 Shorter in wavelength than U.V. rays.
 Longer in wavelength than gamma rays.
 X-rays are emitted by electrons outside the nucleus,
while gamma rays are emitted by the nucleus.
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5.  X-rays penetrate easily through materials such as fat
and muscle but not bones.
 This makes them useful in medicine.
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6.  Ionizing radiation and as such can be dangerous.
 X-rays collide with atoms and knock out electrons.
 Ionizing radiation is radiation with enough energy to
remove tightly bound electrons from the orbit of an
atom, causing the atom to become ionized.
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7.  Exposure is the measure of X-rays ionizing ability.
 The SI unit is coulomb per kilogram (C/kg).
 It measures the amount of radiation required to create
1 coulomb of charge of each polarity in 1 kilogram of
matter.
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8.  Absorbed dose measures more appropriately the
effect of ionizing radiation on matter .
 This is the amount of energy deposited rather than the
charge created.
 The Gray (Gy) which has units of (J/kg), is the SI unit
of absorbed dose.
 This is the amount of radiation required to deposit 1
Joule of energy in 1 kilogram of any kind of matter.
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9.  Equivalent dose is the measure of the biological
effect of radiation on human tissue.
 The sievert (Sv) is the SI unit of equivalent dose, which
for X-rays is equal to the gray (Gy)
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10. INSTRUMENTATION of an x-ray equipment
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11.  Electrons ejected from filament (cathode) through
thermionic emission.
 Released electrons accelerated by H.T. voltage towards
the target (anode).
 These high-energy electrons are sharply decelerated as
they collide with a metal target, usually tungsten.
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12.  Deceleration of charged particles (electrons) produces
a radiation (X-rays).
 Only about 1% of the electrons energy is converted to
x-ray production.
 The rest is heat in the anode.
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13.  X-rays created by two different atomic processes.
 X-ray fluorescence:
 Electron knocks an orbital electron out of the inner shell
of a metal atom.
 Vacancy filled by electrons from higher energy levels
emitting X-ray photons.
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14.  Produces discrete spectrum of X-ray frequencies
(spectral lines).
 Lines generated are characteristic of the target element
(anode).
 Transitions from upper shells into K shells (producing K
lines), into L shells (producing L lines) etc.
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16.  Bremsstrahlung:
 Given off by electrons decelerated by strong electric
fields.
 Continuous spectrum X-rays.
 Increase linearly with decreasing frequency.
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18. Radiation protection
Three accepted standards. Controls the amount (or dose)
received.
 Time: Reduction in duration of exposure reduces the
effective dose proportionally.
 Distance: Increasing distance reduces effective dose.
(Inverse square law)
 Shielding: Reduces radiations to safe levels.
 Radiation falls exponentially with thickness of shield.
 Operators of x-ray eqmnt stay behind leaded glass screens
and wear lead aprons.
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19. National regulatory authorities set the ff. requirements
based on international recommendations for ionizing
radiation:
 Justification: Unnecessary use not permitted
 advantages must outweigh disadvantages.
 Limitation: Individuals must be protected through
individual radiation dose limits.
 Optimization: Radiation doses should be kept as low
as possible. Actual radiation dose should be much
lower than the permitted limit.
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20. Detectors
 Photographic plate were used to produce radiographic
images. The images were produced right on the glass
plates.
 Film replaced the plates.
 Now computed and digital radiography is replacing
film in medicine.
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21.  Photo-Stimulable Phosphors (PSP)
 Excited electrons in phosphor material remain trapped
in colour centres in the crystal lattice.
 Stimulation by laser beam.
 Light given off during laser stimulation is collected by a
PMT.
 Resulting signal is converted into a digital image.
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