5 types of photon interactions with matter

hi everyone my name is Julianna Frey and I'm a student here at Kaiser University in the radiology program today I'm here to discuss with you guys the five photon interactions with matter it's extremely important for a radiographer to understand why these reactions occur so one that we can reduce patient ionization from the x-ray beams by better understanding how these interactions occur we can reduce the amount of radiation and dosage to the patient and create safety for both us and the patient the second reason why this is important is to make sure that we are producing high-quality radiographic images by reducing scatter we can reduce fog and ghosting images that may interrupt or distort our images to give us a better more clear result for our diagnostic imaging so today I will go in detail and discuss with you the five ways that photon interacts with matter these include photoelectric absorption compton scattering coherence scattering photodisintegration and pair production I will explain how each of these photons interact with the item and what they produce in order to understand how x-rays are produced we need to look at a subatomic level of particles and how these photons interact with them x-ray is performed by electromagnetic radiation from photons that travel in a sinusoidal fashion the relationship between the wavelength and energy of these photons is indirectly proportional as we can see here a photon with a longer wavelength will have a low energy while a photon with a shorter wavelength will exhibit a high energy x-rays are usually in a range between 10 to the negative eight and ten to the negative ninth meters the first type of photon we can see here has a low energy and will interact with the entire atom the second type has a moderate energy with a shorter wavelength this will interact with the electrons and usually occurs at the diagnostic range for x-rays the third is a high-energy photon which possesses the shortest wavelength and interacts with the nuclei to produce nuclear argument during photoelectric absorption an incident photon will interact with an inner shell electron this electron will completely absorb the photon and create a photo electron this will result in ionization this is essential for diagnostic radiology during this interaction a characteristic cascade will occur when outer shell electrons fill an inner shell void this being the case shell L m and n shell as each outer electron jumps in to fill in the inner shell void secondary radiation will be produced these low-energy photons do not exit the patient and do not penetrate through to the image receptor in this reaction the high atomic number of the material the photon interacts with the greater the x-ray absorption will be for example fat has an atomic number of 6.3 and bone has an atomic number of 13.8 this means that fat will have less absorption and show darker on film while bone with a higher atomic number will have more absorption and show a bright white color on film however increasing the energy of x-rays decreases the probability of photo electro electric absorption from occurring if kbp is too high you will have little absorption and an image will be too dark to read accurately during compton scattering an incident photon interacts with an outer shell electron causing it to unbind from the atom this is known as ionization the outgoing photon is then deflected or scattered in a different direction with less energy than the incident photon this occurs throughout the diagnostic energy range and has a great effect on the image in a negative way the scatter causes low contrast and fog to appear in the diagnostic imaging the electron that was released from the atom is known as the recoil electron or Compton electron this and the scatter photon may have enough energy left over to cause reactions before losing all their energy this type of ionization is very harmful the scatter photon can travel in any direction when it travels back the same direction as the incident photon this is referred to as back scattering Compton scatter is the greatest source of Occupational radiation exposure for RTS especially during for fluoroscopic procedures the probability of Compton effects occurring is inversely proportional to the x-ray energy and independent to the atomic number of matter interacting with and that's a rap coherent scattering also known as unmodified or classical scattering has two distinct types that we can observe the first known as Rayleigh scattering occurs when a photon interacts with an atom by just skimming past it the incident photon will enter with a wavelength and as it passes by the atom cause excitation to the entire atom this will deflect the direction of the photon while maintaining the same wavelength this usually occurs when the photon is less than 10 kilo electronvolts and because it does not cause ionization this is not extremely important to diagnostic radiology the other type of coherent scattering is called Thompson scattering it is similar to the first in Rayleigh except that in this type it will only affect one electron instead of the entire atom as we saw before a photon will approach in outer shell electron and cause the electron to have excitation this electron will vibrate causing heat and the photon will change direction but still maintain the same wavelength just as in the interaction before this is the Thompson scattering the next type of photon interaction we will observe is called pair production in this interaction we will have 1.0 2 mega electro volts of energy that will enter the atom in a photon it will strike the atom at the nucleus this will release from the nucleus 1 positron which is positively charged and a negative which is negatively charged the positron will interact with another electron floating in the matter as these two interact it is going to cause two gamma rays to be produced in opposite directions of each other coming out in one 180 degrees opposite of each other will be our gamma rays these rays are neutrally charged and are produced in 0.5 one mega electron volts if we add each of these up it will equal the same amount of energy that was originally produced in the original photon as this reaction occurs we have going from energy into matter and back out into energy this is known as an annihilation reaction the final interaction of photons that we will observe is known as photodisintegration in this interaction a photon will enter into the nucleus with an energy level of 10 mega electron volts the strength of this photon will cause photodisintegration which is destruction of the nucleus into nuclear fragments at the nuclear force field inside of our nucleus is our subatomic particles of protons and neutrons but because of the energy in this reaction it will cause them to break down into alpha and beta particles the alpha particle is positively charged and will resemble the nucleus of helium containing 2 protons and 2 neutrons the alpha particle is containing matter and energy it is very heavy so it will only travel 5 centimeters in air although it is harmless and air and can be stopped with a piece of paper this particulate radiation is ionizing and once it enters the body it causes the most lethal radiation the other beta particles are negatively charged and resemble electrons they will travel 10 to 100 centimeters in air and can be stopped with a piece of aluminum alright guys so now that we have discussed the five types of interactions I hope you now better understand how photons interact with matter and what can occur during these interactions just to conclude we have reviewed all five types of interactions with matter these include photoelectric absorption compton scattering coherent scattering photodisintegration and pair production I hope you all enjoyed this video and learn something useful from it

Channel: Johanna Victorero

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Id: 71mhVBXZ9ng

Length: 10min 25sec (625 seconds)

Published: Thu Jun 28 2018