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Introduction to Radiation

Introduction to Radiation. The classical atom. All radiation is a byproduct of the decay of the atom … specifically the nucleus of the atom. Terminology. Radiation : energy in transit High energy results in ionization Low energy results in non-ionization

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Introduction to Radiation

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  1. Introduction to Radiation

  2. The classical atom • All radiation is a byproduct of the decay of the atom … specifically the nucleus of the atom

  3. Terminology • Radiation : energy in transit • High energy results in ionization • Low energy results in non-ionization • Radioactivity : the characteristic to emit energy capable of ionization • Ionization : the removal of electrons from an atom (changing the overall charge on the atom) by high energy radiation

  4. 3 types of radiation • Alpha radiation • Beta radiation • Gamma radiation

  5. Alpha Radiation • Occurs when a particle consisting of 2 neutrons and 2 protons is ejected from a nucleus • The ejected particle is essentially the nucleus of a helium atom

  6. Alpha decay occurs only in heavy, neutron rich atoms such as Uranium, Thorium and Radium • Neutron rich means that there are many more neutrons than protons in the nucleus • 235U92231Th90 + 4a2

  7. Properties of alpha radiation • Positively charged • Very heavy • Most energetic of all of the radiation • Can cause many ionizations in a short distance • Travels a few centimeters in air • Stopped by a sheet of paper • Only dangerous if ingested

  8. Applications of alpha radiation • Smoke detectors • Alpha source ionizes the air to allow for the passage of small currents through an air gap. Smoke obstructs this flow … setting the alarm off • Power source • Used in space probes and pace makers • Ion engines

  9. Beta Radiation • Ejection of an electron from the nucleus of an atom • How can a nucleus eject an electron?

  10. The electron is created out of the nucleus for beta decay • The nuclear weak force causes a neutron to decay into an electron, a proton and an anti-neutrino • 1n01p1 + 0e-1 + v-

  11. Beta decay occurs in neutron rich atoms • A common radiation type in all nuclear reactors • Decay of rhenium into osmium • 187Rh75187Os76 + 0e-1 + v-

  12. Properties of Beta radiation • Negatively charged • Nearly massless • React less readily compared to alpha radiation • Can travel several meters in air • Stopped by thin sheets of plastic or metal • Travels faster than light in certain materials (water) resulting in Cherenkov radiation

  13. Applications of Beta radiation • Radiation therapy used to destroy cancer cells • Radioactive tracers • Used to check thickness of materials such as paper

  14. Gamma Radiation • Present in most of the other forms of decay processes • After a radioactive decay the daughter nuclei is fairly energetic and will release some of this excess energy as a gamma ray pulse / burst

  15. Properties of gamma radiation • Similar in nature to light or microwaves • Only higher in energy • No mass • No charge • Travels at / near the speed of light • Interact through collisions with electrons • Lose energy slowly • Can travel hundreds of meters in air

  16. Application of Gamma Radiation • Used in cancer surgery • Gamma ray knife • Sterilization of food products • Irradiation • Scanning • CT scans • Container scans at airports • Molecular changes in materials • Turns white topaz into blue topaz

  17. summary • Charge • Alpha = positive • Beta = negative • Gamma = neutral • Mass • Alpha = heavy • Beta = nearly massless • Gamma = massless

  18. Half life • Describes the time required for nuclear material to be reduced by half • Each radioactive isotope has different half lives • Carbon-11 = 20 minutes • Uranium-238 = 4.5 x 109 years

  19. Half life game • Everyone tosses one coin • Heads leave the game • Tails continue to toss until no one is left in the game • Questions • What does your graph resemble? • Why is this?

  20. Predicting the quantity remaining

  21. Applications of half life • Dating • Carbon-14 decays to carbon-12. The ratio can be used to date archeological artifacts • Toxicology • Predict the effects of certain toxins in the human body over time

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