RADD 2501 Interactions - Lecture 3 Lecture 3: The...

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Lecture 3 Lecture 3: The interaction of radiation with matter In this Lecture ¾ What happens when x-rays hit something ¾ Learn about photoelectric and Compton interactions ¾ Understand why scatter is your enemy ¾ Learn one simple way to decrease scatter and improve film quality ¾ Understand the terms absorption and attenuation So far in our story we have a generator, and an x-ray tube that makes x-rays. Now it is time to set them free to the world and use them medical purposes. When radiation hits some form of matter, three things can happen 1. It can go right through an not interact at all - transmission 2. It can be absorbed - absorption 3. It can scatter off like billiard balls - scatter Which one of these interactions predominates depends on 1. The energy of the x-ray : When you take a radiograph you select the energy of the x-ray beam that will be produced. The unit of electricity applied to the anode is the killovoltage potential or kVp. The unit of the x-ray energy is the killivolt electron potential. Think of it like this…when we bomb Osama Bin Laden in his caves we can shoot bullets at the cave or we can drop bunker busters. The bunker busters will go through the side of the cave and the bullets will bounce off. 2. Atomic number of the absorber : More interactions will occur with matter of a higher atomic number. Using our analogy. if Osama was in a cave made of carbon our bullets are more likely to go through than if his cave was made of steel.
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3. Thickness and density of the object : Thicker or denser objects will stop more radiation. As far as Osama and his cave…A cave made out of lead foil would stop fewer bullets than a cave made out of thick lead blocks. This business about Osama is pretty general. What really happens when x-rays interact with matter? Interactions, Interactions, Interactions W hen x-rays interact with matter (and don’t just pass through to hit the radiographic film) there are a few different things that can happen. The two important ones at this point are Photoelectric absorption Compton Scattering Photoelectric Absorption: This type of interaction occurs when x-ray enters an atom and imparts all its energy to an inner shell electron which is ejected from its orbit. The ejected electron is called a photoelectron. The energy of the photoelectrons is so low
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This note was uploaded on 11/22/2011 for the course RADD 2501 taught by Professor Sandyeverage during the Winter '11 term at Life Chiropractic College West.

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RADD 2501 Interactions - Lecture 3 Lecture 3: The...

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