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Radioactive Materials Safety Training

Radioactive Materials Safety Training. Massachusetts Institute of Technology Radiation Protection Program. Outline. Introduction Delegation of Authority Radiation Physics Units and Quantities Background and Occupational Radiation Doses Biological Effects of Ionizing Radiation

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Radioactive Materials Safety Training

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  1. Radioactive Materials Safety Training Massachusetts Institute of Technology Radiation Protection Program

  2. Outline • Introduction • Delegation of Authority • Radiation Physics • Units and Quantities • Background and Occupational Radiation Doses • Biological Effects of Ionizing Radiation • Minimizing Radiation Exposures - ALARA • General Radiation Safety and Surveys

  3. + - - - - + + + + - - - + - + + - - - + - + Radiation • Radiation: Energy in the form of particles or electromagnetic waves • Ionizing Radiation: Radiation with sufficient energy to remove an electron from an atom or molecule.

  4. $- Radioactivity • The process by which unstable atoms spontaneously transform to new atoms* and in the process emit radiation. * The “new atom” may be the same atom in a lower energy state.

  5. Units of Activity • Curie (Ci): 37 Billion transformations per second. (2.22 trillion per minute) • Bequerel (Bq): 1 transformation per second. mCi and uCi are common quantities used in the lab (10 uCi up to 50 mCi). 0.0013 uCi (48 Bq) - Ra-226 in a 1 kg rock 0.12 uCi (4400 Bq) - K-40 in your body 330 pCi - C-14 in ¼ lb of beef

  6. t T1/2 1 f l t f e 2 ln ( 2 ) l T1/2 Half-Life • Half-life is the amount of time needed for the activity to reach one half of the original amount. Days

  7. ExposureR (roentgen): Amount of charge produced per unit mass of air from x-rays and gamma rays. Absorbed Dose rad: Amount of Energy deposited per unit mass of material. 1Gy = 100 rad. Dose Equivalentrem: Risk adjusted absorbed dose. The absorbed dose is weighted by the radiation type and tissue susceptibility to biological damage. 1 Sv = 100 rem. Radiation weighting factors: alpha(20), beta(1), n(10). Tissue weighting factors: lung(0.12), thyroid(0.03), and gonads(0.25). For whole body x or gamma-ray exposure 1 R  1 rad  1 rem Definitions

  8. Alpha Decay • Helium Nucleus – Very massive and doubly ionized • Only a hazard via ingestion or inhalation of alpha emitter • Not usually an external radiation hazard • Stopped by paper and dead layer of skin • Uranium, Thorium, Radon and radon daughters

  9. Beta Decay • Energetic electron – singly ionized • External hazard to skin and eyes • Internal hazard via ingestion or inhalation of beta emitter • Produces bremsstrahlung radiation • A 1 MeV beta can travel up to 12 feet in air and 1 cm in plastic • Phosphorus, Tritium, Carbon, Sulfur

  10. Gamma Decay • X-rays and gamma rays are photons – no charge • External radiation hazard to deep organs and tissues • Internal hazard via ingestion or inhalation of gamma emitter • Lead (high electron density) is good for shielding x and gamma rays • Iodine 125 gammas (30 keV) can be easily stopped with 1/8 inch of lead

  11. Neutron shielding material depends on the energy of the neutrons

  12. x-ray e- Bremsstrahlung X-Rays plastic electrons • Bremsstrahlung x-ray intensity increases with increasing atomic number of absorber, and the average x-ray energy increases with increasing electron energy. (activity of the source is also a factor) lead

  13. Shielding for beta emitting material plastic lead 90Sr

  14. Shielding for gamma emitting material Low energy gamma or x-ray High energy gamma or x-ray

  15. Typical background is 0.03 mR/hr or 100 cpm GM pancake probe NaI probe Battery check Range selector

  16. Background Radiation360 millirem per year Source: BEIR V Report, 1990

  17. Annual Occupational Dose Limits * Declared Pregnant Woman

  18. Biological Effects • Many groups exposed to ionizing radiation at high levels resulted in adverse effects. • Somatic effects • Prompt - skin burns and cataracts • Delayed - cancer • Genetic effects • Teratogenetic effects

  19. X-Ray Burns 500+ rad 5,000+ rad P-32 - 6.5 rad/hr/uCi S-35 - 2.5 rad/hr/uCi

  20. Cancer • Radiation can damage cells through two methods; • Production of free radicals and • Direct damage to the DNA. • Risk factor for radiation dose: • 4% increase in risk of dying of cancer for every 100 rem of dose. • Normal cancer risk is 20%.

  21. 0.03 r e c n a c m 0.02 o r f h t a e d f o k s i R 0.01 0.00 0 10 20 30 40 50 60 70 Committed Lifetime Dose (rem) Dose Response Relationship Effect is Detrimental risk level is uncertain Predictable Effects Risk Is not Predictable below 20 rem Occupational dose – above background

  22. ALARA • ALARA - As Low As Reasonably Achievable • Time • Distance (inverse square law) • Shielding • Contamination Control

  23. 2 x 1 . D D 2 1 x 2 Inverse Square Law 45 mrem/hr @ 3.3 cm D - Dose x - distance 5 mrem/hr @ 10 cm 50,000 mrem/hr @ 0.1 cm

  24. Radioactive Sealed Sources • Sealed sources used as a source of radiation • Alpha particles • Beta particles • Gamma ray • Bremsstrahlung • Neutron sources • Permanently enclosed in either a capsule or another suitable container designed to prevent leakage or escape of the radioactive material • Inventory and Use records are required

  25. Radioactive Sealed Sources • Tested for surface contamination and leakage • Sources may leak radioactive material • Tested usually once every 6 months for beta & gamma emitters that are > 100 uCi • Tested every 3 months for alpha emitters > 10 uCi • Allowable limit is less than 0.005 uCi • A leaking source shall immediately be removed from use • Action to be taken to prevent contamination • Source to be repaired or disposed of • RPP has a shielded storage facility for sources that are not in use.

  26. Security and Transportation • All radiation sources must be kept locked up when not in use. • Experiments left unattended should be labeled “Experiment in Progress.” • An up-to-date use log of all sources must be kept at the storage location. • All radiation laboratories will be locked when unattended for extended periods. • When you are the means for security, you must challenge unknown persons entering the lab.

  27. General Radiation Safety • No food or beverages in the lab • Keep a survey meter conveniently close by • ALARA - time, distance, and shielding • Label radioactive materials and equipment • Never remove sources from the Jr Physics Lab

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