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Electromagnetic Spectrum

Ionizing Radiation Chapter 10 HS 432 Students please read chapter 10, focusing on the topics covered in this presentation. Electromagnetic Spectrum. Ionizing Radiation. Radiation that ionizes atoms Ionization is an energy transfer process that changes the electrical balance of an atom.

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Electromagnetic Spectrum

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  1. Ionizing RadiationChapter 10HS 432Students please read chapter 10, focusing on the topics covered in this presentation

  2. Electromagnetic Spectrum

  3. Ionizing Radiation • Radiation that ionizes atoms • Ionization is an energy transfer process that changes the electrical balance of an atom. • Model of the atom (Fig. 10-3, p. 262) • When ionization of body tissues occurs, some of the electrons surrounding the atoms are forced out of their orbits. • The greater the intensity of the radiation, the more ions are created and the greater the damage to the cells. • Types:alpha particles, beta particles, gamma rays, X-rays and neutrons.

  4. Ionizing Radiation The amount of energy a particular kind of radioactive material possesses is defined in terms of MeV (million electron volts). The greater the number of MeV, the greater the energy and the potential damage it can cause to living tissue. Each radioactive material emits its own particular kinds of radiation, with energy measured in MeV.

  5. Types of Ionizing Radiation 1. Alpha particles = Helium atom = 2 protons + 2 neutrons • Massive particles with the most energy • Least penetrating • Internal radiation hazard: if ingested or inhaled • Shield? • Paper, clothing or human skin 2. Beta particles = electron • More penetrating than alpha radiation • Can penetrate only ½ inch into the skin • Internal radiation hazard: if ingested or inhaled • Shield? • Layer of clothing, 1/4 inch of aluminum or other substances, a wall

  6. Types of Ionizing Radiation 3. Neutrons • No electrical charge • Released when certain radioactive material (fissionable isotopes) disintegrate. • They have short or long ranges in air depending on their kinetic energy, which depends on how they were produced • Depth of penetration in human tissue varies from ¼ to several inches depending on its energy • Exposure sources include reactors, accelerators and neutron generators.

  7. Types of Ionizing Radiation 4. Gamma rays • Most penetrating type of ionizing radiation • External radiation hazard • Shield? - dense material such as lead or concrete 5. X-rays • Similar to gamma rays but slightly less penetrating.

  8. Ionizing Radiation: Half-life Half-life is the time it takes for half of the amount of radioactive material to decay and be transformed into something else. Example p.264

  9. IONIZING RADIATION: Health Impacts • Somatic effects (injury to individual) and genetic effects (damage to chromosomes) • Tissues with a high turnover rate are more susceptible • High-sensitivity tissues: thyroid, lung, breast, stomach, colon and bone marrow • Leukemia is the most common cancer associated with radiation exposure • Mutations, cancer, birth defects • High-level radiation exposures can cause cell death • Low-level radiation exposure over time can cause mutations and cancers • Fetuses and children are very sensitive to radiation-induced damaging effects.

  10. IONIZING RADIATION: Dosage Radiation Effective Dose = Absorbed dose x Relative Biological Effectiveness Sievert (Sv) Gray (Gy) rad rem 1 Sv = 100 rems 1Gy = 100 rads Relative Biological Effectiveness (RBE): • 1 for X-rays and gamma rays • 1-5 for beta-particles • 10 for alpha particles. Greatest tissue damaging potential.

  11. IONIZING RADIATION: Dosage and Health Effects Dose rate largely affects the potential for health effects from exposure to radiation.   Damage to living tissue is generally assumed to be entirely due to the ionization process which destroys the capacity of cell division in some cells and causes mutations in others. The body has cell-damage-repairing capabilities. But these capabilities have limitations. There is no radiation exposure level below which no health effect can be detected, therefore levels should always be kept As Low as Reasonably Achievable (ALARA). National Council on Radiation Protection Recommendations (Table 10C, p. 267)

  12. Basic Safety Factors • Time • The longer the exposure, the greater the chance for radiation injury. • Fig. 10-14, p.271 • Distance • Inverse square law: the intensity of radiation falls off by the square of the distance from the source. • Fig. 10-15, p. 272 • Shielding • The higher the density of the shielding material the less thickness is needed.

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