RTEC A - WEEK 4 GENERAL SCIENCE REVIEW

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RTEC A - WEEK 4GENERAL SCIENCE REVIEWX-RAY
PRODUCTION IN THE TUBE
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Objectives

• General Science review
• Atomic interactions in the tube

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Atomic Models

• BOHR model of the atom.
• Electrons orbit around a nucleus (center)

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ATOM
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Differences in Binding Energy
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K L M Shells
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Electrostatic Laws

• Repulsion/attraction
• Like charges repel
• Unlike charges attract
• Inverse square relationship
• Electrostatic force is very strong when objects
  are close together
• It decreases rapidly as objects separate

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How X-rays are created

• TO PRODUCE X-RAYS
• YOU NEED
• A SOURCE OF ELECTRONS
• A FORCE TO MOVE THEM QUICKLY
• SOMETHING TO STOP THEM SUDDENLY

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How X-rays are created

• Power is sent to x-ray tube via cables
• mA (milliamperage) is sent to filament on cathode
  side.
• Filament heats up electrons boil off
• Negative charge

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How X-rays are created

• Positive voltage (kVp) is applied to ANODE
• Negative electrons attracted across the tube to
  the positive ANODE.
• Electrons slam into anode suddenly stopped.
• X-RAY PHOTONS ARE CREATED

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Electromagnetic Energy Spectrum

• Spectrum
• Continuous range of energy
• Although there are precise ranges defined, they
  often overlap
• 3 most important to Radiologic technology
• Visible light
• X-radiation
• Radiofrequency

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Electromagnetic Radiation

• Photon is the smallest quantity of any type of EM
  radiation
• It is a small bundle of energy traveling at the
  speed of light
• Only visible light is naturally apparent to us
• May be described as wavelike fluctuations of
  electric and magnetic fields.

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Electromagnetic Radiation

• These bundles of electric and magnetic fields
  travel at the same velocity
• Travel at the speed of light
• 3 x 108 m/s or 186,400 miles per sec
• The Photons of EM radiation differ only in
  frequency and wavelength

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General Characteristics of EMSX-ray photons

• Have no mass or physical form
• Travel in a linear path (until interaction
  occurs)
• Dual nature wave vs. particle
• Unaffected by
• electric or magnetic fields
• gravity

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Wavelength and Frequency

• Wavelength is the difference between
• Crest to Crest
• Valley to Valley
• Frequency is the number of wavelengths passing a
  point of observation per second
• Wavelength frequency are inversely proportional
• As Wavelength increases frequency decreases
• As wavelength decreases frequency increases

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Wavelength and Frequency

• Frequency and wavelength are closely associated
  with the relative energy of electromagnetic
  radiations.
• More energetic radiations have shorter
  wavelengths and higher frequency.

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Wavelength
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Frequency
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The shorter the wavelength the higher the
frequency
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The Electromagnetic Spectrum

• X-rays have wavelengths much shorter than visible
  light, but longer than high energy gamma rays.

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What is Ionization?
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When an electron is added or removed from the
atom- it is ionized
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Kinetic energy

• Energy of motion
• The electrons KINETIC energy is converted to
  electromagnetic or PHOTON energy

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X-ray production begins at the atomic level
Energy (photons) are released when the electron
collides with another electron,or passes close
to the nucleus of the atom the change in energy
of the shells produces photons
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X-ray Production in the TUBE
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INTERACTIONS IN THE TUBE

• BREMS (Bremsstrahlung)
• CHARACTERISTIC
• HEAT

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Tube Interactions

• Heat 99
• X-ray 1
• Bremsstrahlung
• (Brems) 80
• Characteristic 20

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Bremsstrahlung Radiation

• Heat Characteristic produces EM energy by e-
  interacting with tungsten atoms e- of the target
  material
• Bremsstrahlung is produced by e- passing by
  closely with the nucleus of a target tungsten
  atom the change in direction of the electron
  releases a photon of energy

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Heat

• Most kinetic energy of projectile e- is converted
  into heat 99
• Projectile e- interact with the outer-shell e- of
  the target atoms but do not transfer enough
  energy to the outer-shell e- to ionize

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Heat
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1. Projectile electrons from cathode
2. Pass by the electrons in the target
3. Causing the electrons to vibrate (excitation)
4. Excitation produces small amounts of heat

HEAT
e
e
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Heat is an excitation rather than an ionization
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Bremsstrahlung

• German
• word meaning
• slowed-down
• or braking
• radiation

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Bremsstrahlung Radiation
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X-ray Photons BREMS
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Energy (photons) are released when the e passes
close to the nucleus, then changes direction
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BREMS RADIATION

• Electron
• Passes by nucleus
• Changes direction
• Energy released as a PHOTON

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Brems Radiation Animation

• http//www.coursewareobjects.com/objects/mrophysic
  s_v1/mod08/0816a.htm

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Characteristic Radiation

• Projectile e- with high enough energy to totally
  remove an inner-shell electron of the tungsten
  target
• All tube interactions result in a loss of kinetic
  energy from the projectile e-
• Characteristic x-rays are produced when
  outer-shell e- fills an inner-shell void

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Characteristic Radiation (Tube)
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CHARACTERISTIC (in tube)

• Electron hits inner shell e in orbit knocked
  out creates a hole
• Other Es want to jump in
• Energy released as PHOTONS

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• It is called
• characteristic
• because it is
• characteristic of
• the target element
• in the energy of
• the photon
• produced

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Characteristic Radiation Animation

• http//www.coursewareobjects.com/objects/mrophysic
  s_v1/mod08/0808a.htm

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Tungsten Atom