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Radiation

Radiation. Samar El-Sayed. Radiation. Radiation is an energy in the form of electro-magnetic waves or particulate matter, traveling in the air. The structure of the atom. ELECTRON negative, mass nearly nothing. PROTON positive mass (“1”). NEUTRON neutral mass (“1”).

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Radiation

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  1. Radiation Samar El-Sayed

  2. Radiation • Radiation is an energy in the form of electro-magnetic waves or particulate matter, traveling in the air.

  3. The structure of the atom ELECTRON negative, mass nearly nothing PROTON positive mass (“1”) NEUTRON neutral mass (“1”)

  4. The structure of the atom MASS NUMBER = number of protons + number of neutrons 4 He SYMBOL 2 ATOMIC NUMBER = number of protons

  5. Isotopes Notice that the mass number is different. 16 O 17 18 O O 8 8 8 Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more. An isotope is an atom with a different number of neutrons

  6. Radioactivity Spontaneous emission of particles and/or electromagnetic radiation from an unstable nucleus. Radiation The nucleus is more stable after emitting some radiation – this is called “radioactice decay”.

  7. Half life = radioisotope = new atom formed The time required for radioactive matter to decrease by one half (lose 50% of its activity). The decay of radioisotopes can be used to measure the material’s age. … After 2 half lives, another half have decayed (that’s 12) At start there are 16 radioisotopes After 1 half life, half have decayed (that’s 8)

  8. Physical half life Time required for the radioactive substance to lose 50% of its activity by radioactive decay • Biological half life Time required by the body to eliminate 50% of internally deposited quantity of radioactive substance • Effective half life Time required for radionuclide in body to decrease by 50% as a result of biological elimination & radioactive decay

  9. Linear energy transfer (LET) • linear collision stopping power • The ionization density (e.g., ion pairs/cm of tissue) along the path of the radiation. • The energy a charged particle imparts to matter per unit length as it traverses the matter • Depends on: • Charge • Velocity • High LET : alpha • Low LET: beta particles, x-ray, gamma ray

  10. Types of Radiation Ionizing Radiation Radiation that has sufficient energy to dislodge orbital electrons Non-Ionizing Radiation Radiation that does not have the ability to dislodge electrons, but can still cause biological damage by causing chemical changes or by heating (vibrating) molecules. Examples are ultraviolet light, microwaves.

  11. Ionizing radiation

  12. Ionization Radiation is dangerous because it “ionises” atoms – in other words, it turns them into ions by “knocking off” electrons.

  13. particulate Ionizing radiation Types of ionizing radiation Short wave electromagnetic uncharged Charged x-ray +ve -ve gamma rays neutrons alpha beta

  14. X and gamma radiation are penetrating radiation and an EXTERNAL HAZARD. found in medical uses stopped by lead naturally present in soil and cosmic radiation

  15. Alpha Radiation can’t penetrate skin internal hazard stopped by paper found in soil, radon and other radioactive materials It is only a hazard when inside body (internal hazard)

  16. Beta Radiation is a Skin, Eye and Internal Hazard skin, eye and internal hazard stopped by plastic found in natural food, air and water

  17. Alpha Beta Gamma/ X-ray The Penetrating Power of Radiation

  18. Dangers of radioactivity Alpha Beta Gamma OUTSIDE the body  and  are more dangerous as  radiation is blocked by the skin. INSIDE the body an  source causes the most damage because it is the most ionising.

  19. Measurement units Exposure in air Air Radioactivity Absorbed dose in tissue (Dose equivalent) Absorbed dose in matter

  20. Radioactivity • Number of disintegration nuclei / unit time (sec). • Disintegration : spontaneous transformation in number or internal arrangement of protons, neutrons in the nucleus. • Units: Becquerel (Bq) = 1 disintegration/second (dps) Curie (Ci) 1 Ci = 3.7 X 1010 Bq

  21. Exposure • A measure of what is emitted • Charge (number of ions) produced in air from ionization by gamma and x-rays • Units: • coulomb/ Kg air • Roentgen (R)

  22. Absorbed Dose • The amount of energy absorbed by a given mass (e.g. water or tissue ) • Units: Gray (Gy) Rad (Roentgen Absorbed Dose) 1 Gy = 100 rad

  23. Dose Equivalent • Risk adjusted absorbed dose. • The absorbed dose is weighted by the radiation type and tissue susceptibility to biological damage • Takes into account the biological effect of the various types of radiation = absorbed dose X Radiation Weighting Factor • Units Sievert (Sv) 1 Sv = 100 rem rem

  24. The Radiation Weighting Factor (RWF) • Reflects differences in the amount of each type of radiation necessary to produce the same biologic effect

  25. What is an individual's dose equivalent from 10 mrad of gamma rays, 5 mrads of Beta particles and 10 mrads of neutrons? (m = milli = 1/1000) Dose Equivalent = mrads X RWF = mrems Gamma dose equivalent = 10 x 1 = 10 Beta dose equivalent = 5 x 1 = 5 Neutron dose equiv. = 10 x 10 = 100 Total 115 mrems

  26. An exposure to 1 mrad of gamma, 10 mrad of Beta particles, and 5 mrad of fast neutron radiations would give an individual a dose equivalent of: • 16 mrem • 16 µ Ci • 61 mrem • 61 mrads

  27. What dose of X-ray would produce the same biologic effect as 50 mrad of gamma or beta radiation? The RWF for X-ray is also one; therefore, a dose of 50 mrads of X-ray radiation would produce the same biologic effect as 50 mrads of gamma or beta radiation.

  28. If the radioactive material in the case study had been an alpha-emitter instead of a beta and gamma emitter, would the biologic effects be greater? Explain. if the radioactive material was emitting alpha particles the biologic effectiveness would be greater. The RWF for alpha particles is 20, which indicates a given dose of alpha radiation is twenty times more biologically effective than the same dose of beta or gamma radiation.

  29. If a physiciancalculates that a young boy at the scene of an accident received a maximum beta or gamma radiation radiation dose of 50 millirads (mrad). Express this dose in millirems (mrem) and Sieverts (Sv). The RWF for beta or gamma radiation is one; therefore, a dose of 50 mrads of beta or gamma radiation is equivalent to 50 mrem or 0.05 rem. One Sievert = 100 rem; therefore, 0.05 rem = 0.0005 (5×10−4) Sv

  30. Natural Sources Artificial sources Sources of radiation

  31. Internal contamination (i.e., radionuclide deposited within the body) External contamination (i.e., radionuclide deposited on the body surface) External exposure (Irradiation by an external source. Internal Contamination External Contamination External Exposure Exposure to ionizing radiation

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