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Week 1 C Chapter 5 Electromagnetic Radiation A photon is the smallest element of electromagnetic energy. Photons are energy disturbances moving through space at the speed of light. Photons have no mass but they do have electric and magnetic fields.

Electromagnetic Radiation A field is an interaction between different energies, forces or masses that can not be seen but can be described mathematically. Electromagnetic Radiation can be represented by the sine-wave model. Sine-waves have amplitude.Amplitude is one half the range from crest to valley over a sine wave.

Electromagnetic Radiation The important properties of the sine-wave model are frequency(f) and wavelength(λ) and velocity. Frequency is the number of wavelengths passing a point per second. Frequency is identified as oscillations per second and measured in hertz (Hz).

Electromagnetic Radiation Wavelength is the distance from one crest to another or from any point in the wave to the next corresponding point. The wave parameters are very important. A change in one affects the value of one or both of the others.

Electromagnetic Radiation At a given velocity, wavelength and frequency are inversely proportional. The Wave Formula Velocity= Frequency x Wavelength

Electromagnetic Radiation With EMF we know the velocity so the formula is simplified. c= fλ or f= c/λ or λ= c/f As frequency increases, wavelength decreases and vice versa For electromagnetic radiation, frequency and wavelength are inversely proportional.

Electromagnetic Spectrum The electromagnetic spectrum includes the entire range of electromagnetic radiation. The frequency range is from about 10 2 to 10 24 Hz Photon wavelengths range from 10 7 to 10 -16 m. Grouped together, these radiations make up the electromagnetic spectrum.

Electromagnetic Spectrum Three important ranges. Visible light Radio frequency X-radiation Others include: –UV –IR and microwave

Electromagnetic Spectrum EMF can be measured in three formats Energy (eV) used to describe x-rays Frequency (Hz) Wavelength (m)

Visible Light Measured in wavelength. A prism is used to refract or change the direction of the photons. Only form of EMF that we can sense.

Forms of Light Visible light ranges from 700nm to 400nm wavelength. Infrared light have longer wavelength than visible light but shorter than microwaves. Ultraviolet light is located between visible light and ionizing radiation.

Radiofrequency AM radio, FM radio and Television are other forms of electromagnetic radiation. With radio, the frequency is used to identify the station. Short wavelength radiofrequency are referred to as microwaves.

Ionizing Radiation Unlike visible light or radiofrequency, ionizing electromagnetic radiation is characterized by the energy contained in the photon. When we use 70 kVp, the photon will have energy varying from 0 to 70 keV.

Ionizing Radiation The frequency is much higher and wavelength much shorter for x-rays compared to any other form of electromagnetic radiation. Visible light identified by wavelength Radiofrequency identified by frequency X-rays identified by energy

Ionizing Radiation The only difference between X-rays and gamma rays is their origin. X-rays are produced outside the nucleus. Gamma rays are produced inside the nucleus of radioactive atoms.

Wave-Particle Duality A x-radiation photon and a visible light photon are fundamentally the same except that x-radiation photons have a much higher frequency and shorter wavelength. These differences change the way they interact with matter. Visible light tends to behave as waves.

Wave-Particle Duality X-radiation tends to behave more as particles than waves. Both types of photons exhibit both types of behavior and this is referred to as the wave-particle duality of radiation. Photons interact with matter when the matter is approximately the same size as the photon wavelength.

Wave-Particle Duality Radio & television photons wavelength is measured in meters and interact with long metal rods called antennae. Microwave are measured in centimeters and react most easily with popcorn & hotdogs.

Wave-Particle Duality Visible light wavelength is measured in micrometers or nanometers, interacts with living cells such as the rods and cones in the eye. Ultraviolet light interacts with molecules. X-rays interact with atoms and electrons. All radiation with wavelengths longer than x-rays interact primarily as a wave.

Wave model: Visible Light Vision is result of specially developed organ that sense a very narrow portion of the electromagnetic spectrum. When a visible light photon strikes an object, it sets the molecule of the object into vibration.

Wave model: Visible Light The orbital electrons become excited by the higher energy. This energy is immediately irradiated as another photon of light. This is referred to as reflection. Atomic and molecular structure determine which wavelength of light are reflected.

Wave model: Visible Light Light photons not reflected are either absorbed or transmitted. There are three degrees of absorption: –Transparency –Translucency –Opacity

Degrees of Absorption If all of the light is transmitted almost unaltered, it is transparent. If only some of the light passes through, it is called translucent.

Degrees of Absorption If all of the light is absorbed, it is called opaque. Attenuation is the sum of scattering and and absorption of radiation.

Radiopaque or Radiolucent Terms used to describe the appearance of objects on the x-ray film. Objects that absorb the radiation are called radiopaque.

Radiopaque or Radiolucent Structures that attenuate the x-rays are referred to as Radiolucent. Bone is radiopaque. Lung is radiolucent.

Inverse Square Law Radiation intensity is inversely proportional to the square of the distance from the source. The reason for the decrease is the radiation is spread over a wider area.

Inverse Square Law The Inverse Square Law is used in radiography to adjust technical factors for changes in distance. It is also used for radiation protection. The farther you are away from the source, the lower the exposure.

Particle Model: Quantum Theory Unlike other forms of electromagnetic radiation, x-ray energy is measured in electron volts (eV). X-ray energies range from 1 to 50 MeV X-ray wavelengths range from 10 -9 to 10 - 12 m. X-ray frequency range from 10 18 to 10 21 Hz

Range of X-ray Energies Diagnostic Radiography uses the range of 30 kVp to 150 kVp. Grenz rays with energies of 10 to 20 kVp are used in dermatology. Therapy uses energies from 200 to 1000 kVp

X-ray Waveform X-rays have both electric and magnetic fields. One wave represents the electric field and one the magnetic field varying at right angles to each other.

Planck’s Quantum Theory X-rays are created at the speed of light or they don’t exist at all. The energy of a photon is directly proportional to it’s frequency. A photon’s energy is inversely proportional to the photon wavelength.

Matter and Energy Like the law of the conservation of matter, the law of conservation of energy states that Energy can be neither created or destroyed. Planck’s quantum physics and Einstein’s physics of relativity greatly extended these theories.

Matter and Energy According to quantum physics and physics of relativity, matter can be transformed into energy and vise versa. Although matter and energy are interchangeable, it is energy from the x-ray photon interacting with tissue and the image receptor that forms the basis of x- ray imaging.

Mass Energy Relationship Mass and energy are two forms of the same medium. This scale shows the equivalence of mass measured in kilograms to energy measured in electron volts.

End of Lecture

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