lecture26 - Physics 102: Lecture 26 X-rays Make sure your...

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X-rays Physics 102: Lecture 26 Make sure your grade book entries are correct.
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Photons with energy in approx range 100eV to 100,000eV . This large energy means they go right through you (except for your bones). What are the wavelengths?    λ = hc E = 1240 eV nm E    1240 eV nm 100000 eV .01nm    1240 100 10 nm X-Rays .01 nm to 10 nm 10
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X-Ray Production Black Body Radiation Would require temperature over 10 times hotter than surface of sun Excitation of outer electrons Typically have energy around 10 eV Radioactive Decays Hard to turn on/off How do you produce 100 eV photons? 15
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Electron Tubes Accelerate an electron through a voltage difference to give it some energy. .. An electron is accelerated through a potential difference of 70,000 V. How much energy does it emerge with? Recall from Lecture 3: EPE = V q KE = EPE = (70,000 V) (1 e - ) = 1.6 x 10 -19 C = 70,000 eV = 11.2 x 10 -14 J EPE of voltage gap becomes K.E. for electron. 18
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From Electrons to X-Rays Now take these high energy electrons (up to 100,000 eV) and slam them into heavy atoms - any element. 2 kinds of X-Rays are produced: “Bremsstrahlung” “Characteristic” VIS 21
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Bremsstrahlung X-Rays Electron hits atom and slows down, losing kinetic energy. Energy emitted as photon If all of electron’s energy is lost to a single photon, photon has maximum energy (minimum wavelength) . Minimum X-Ray wavelength = λ o . Electron hitting atom makes many photons (X-Rays), all with different energy. Many different wavelengths.
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This note was uploaded on 01/25/2012 for the course PHYS 102 taught by Professor Lee during the Spring '08 term at University of Illinois, Urbana Champaign.

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lecture26 - Physics 102: Lecture 26 X-rays Make sure your...

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