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38 Cards in this Set
- Front
- Back
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What are:
-Alpha particles? -Beta- particles? -Beta+ particles? |
-Helium nuclei
-Electrons -Positrons |
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How to calculate half life?
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T½=0.693/λ
λ=decay constant |
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1Bq represents?
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1 desintegration/s
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How does alpha decay occur?
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When a heavier element decays into another element and helium.
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Where does beta- decay occur?
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In nuclei with excess of neutrons.
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Where does beta+ decay occur?
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In nuclei of excess of protons.
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Alpha particles
Their range in air, water and tissue? How do they interact with matter? How do their tracks look? How does contamination occur? |
Air=2-9 cm
Water or tissue=10-100 µm Through electric fields. Straight lines. Intake of contaminated food, by air or by surface contamination of skin. |
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Beta particles
Their range in air, water and tissue? How do they interact with matter? How do the tracks look? How do they contaminate? |
Air=several centimeters to a few meters
Water and tissue=Several centimeters Electric fields Strongly twisted and irregular Through a medium at a distance |
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What does radiation emitted from an X-ray tube consist of?
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-"Breaking radiation": bremstrahlung with continous energy spectrum
-Characteristic radiation (characteristic to anode/target material) |
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How do emitted neutrons interact with matter?
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Fast neutrons
-Through elastic collisions with nuclei Slow neutrons -Through capture by nuclei |
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The linear attenuation/absorption coefficient (µ):
-is? -related to absorbent's atomic number how? -Decreases in energy up to? |
-Is proportional to density of the material
-Energies increase with an increase of absorbent's atomic number (Z). This holds true for low and high energies. -A few MeV. |
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What is the mass attenuation/absorption coefficient independent of?
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Density
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What are the values of mass attenuation coefficients dependent upon?
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-Rayleigh scattering
-Compton effect -Photoelectric effect -Pair creation -Photonuclear reaction |
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Rayleigh scattering
Also called? Explain it. How does it contribute to the radiation dose? |
Thomson scattering/coherent scattering/classical scattering.
An x-ray photon interacts with an atom without changing the internal energy of the scattering atom or the energy of it self. What changes is the direction of the x-ray photon. It does not contribute to the radiation dose because no energy is transferred. |
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How does the probability of Rayleigh scattering relate to:
-Photon energy? -Atomic number (Z)? -Biological materials? |
-The higher the photon energy the less probable.
-The higher the atomic number the more probable. -Negligible above 100keV. |
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Photoelectric effect
What occurs? |
An x-ray photon is absorbed resulting in the ejection of electrons from the shell of the atom. This ionizes the atom.
Subsequentlyt, the ionized atom returns to a neutral state with the emission of an x-ray characteristic to the atom. |
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How does the photoelectric effect relate to:
-The energy of the photon? -The atomic number of the atom? -Biological materials? -The photon beam? |
-The PE decreases with a decrease in energy of the photon.
-The PE increases with an increase in atomic number (Z). -The effect dominates for low energy radiation (below 30-40 keV). -Photoelectrons are ejected mainly at directions perpendicular to the photon beam. |
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Compton scattering
-Is also known as? -What occurs? |
-Incoherent scattering
-When a x-ray photon ejects an electron from an atom, a x-ray photon of lower energy is scattered from the atom. The x-ray has lower energy but greater wavelength than the photon. This occurs because relativistic energy and momentum are conserved in this process. |
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How does the compton effect realte to:
-Atomic number (Z)? -Biological materials? -Ejection of Compton electrons? |
-Atomic number is not a factor.
-The effect dominates for medium energy radiation (50 keV). -Mainly in the forward direction; especially for high energy photons. |
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Pair production
-What occurs? |
A x-ray photon of greater energy than 1.02 MeV creates an electron and a positron with the anihilation of the x-ray photon.
The positron is very short lived and undergoes anihilation with an electron, forming two photons of 0.511 MeV energy. |
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How is pair production realated to:
-Energy of the x-ray photon? -Atomic number? |
-The thereshold is 1.02MeV and the probability increases with energy.
-The probability increases with atomic number. |
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Photodisintegration
-What occurs? -How much does it contribute to energies in radiography? -Why? |
A x-ray photon transfers all of its energy to the nucleus of an atom, ejecting a praticle from the nuceus.
Nothing, because of the enormously high energies involved. |
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In mammography, how much does coherent scatter account for?
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12%
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How is the interaction of ionizing particles with matter related to the speed af the particles?
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The energy transferred by slow particles is larger than the energy transferred by fast particles.
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How are interactions between charged particles and matter related to:
-The velocity of the particle? -The charge of the particle? -The desity of the absorbent? |
-The higher velocity the lower the energy transfer.
-Increased charge results in incresed energy loss. -The greater the density, the higher the energy absorption. |
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What are the benifits of proton/hadron therapy?
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-Favourable spatial dose distribution in beam axis (with significant reduction of dose behind the tumor)
-Favorable lateral dose distribution (negligible lateral dose scattering) -Favourable LET distribution in irradiated region. |
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Name some current methods of detection and measurment of radiation.
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-Ion chamber, Geiger-Muller counters
-Film -Chemical dosimetry -Thermoluminescent dosimetry -Semiconductor probes -Biological dosimetry |
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Exposure?
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One roesntgen (R) of gamma or x-ray radiation = the amount of radiation that produces 2.58*10^-4 C of ionizing charge for each kologram om air at STP.
1R = 2.58*10^-4 C/kg-air |
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Kinetic energy released in matter (KERMA)?
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The amount of energy transferred from the primary radiation into kinetic energy of electrons in a region divided by the mass of the region.
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Absorbed dose?
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The amount of energy deposited into a region of the body divided by the mass of that protion of the body that absorbed the radiation.
1 Gy = 1J/kg |
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Is KERMA and dose the same?
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No, they do not occur in the same place in the medium.
Under conditions of no electronic equilibrium, they are not the same. |
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How are broad beams related to depth dependance of radiation intensity?
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They do not follow an exponential behaviour.
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Quality factor?
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Reflects the effectiveness of radiation in induction of biological effects resulting from the deposition of radiation energy.
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Effective dose
Define it. When is it used?` |
It expresses the risk from an exposure of a single organ or tissue in terms om equivalent risk from an exposure of the whole body.
If the exposure to the body is not uniform. |
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Deterministic effects (non-stochiastic)
-Are due to? -What is the threshold? -How long after radiation do they occur? |
-Killing of cells.
-1-2 Gy. 100-200 mGy during fetal development. -Immediately. |
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Interdeterministic effects (stochastic)
-Are due to? -What is the threshold? -How long after radiation do they occur? |
-Mutations
-There is no threshold but the probability of occurance increases with dose. -They have a latent period from 2 to 20 years. |
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What is the Linear Nonthreshold (LNT) hypothesis?
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An official approach in radiation protection.
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Explain "radiation hormesis".
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It is the theory that suggests that low levels of exposure and natural background radiation are benign due to stimulatory effects on the immune system, reparation processes at the cellular level and other adaptive processes.
This is in contrast the LNT theory which suggests that the negative health effects of ionizing radiation are proportional to the dose. |
