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Radiation Biology

Radiation Biology. Particles lose energy in matter. Eventually energy loss is due to ionization. Energy transferred describes the kinetic energy gained by charged particles. Energy imparted is the energy lost by charged particles. Energy Transfer. 1.1. 2.8. 4.2. 5.4. 10 MeV.

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Radiation Biology

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  1. Radiation Biology

  2. Particles lose energy in matter. Eventually energy loss is due to ionization. Energy transferred describes the kinetic energy gained by charged particles. Energy imparted is the energy lost by charged particles. Energy Transfer 1.1 2.8 4.2 5.4 10 MeV particle energy 3.6 2.0 0.1 9.0 energy transferred 2.8 3.3 2.8 1.1 energy imparted

  3. Kerma is the energy transferred per unit mass. Kinetic Energy Released per unit MAss Radiative kerma is due to bremmstrahlung and annihilation. Collision kerma subtracts the reradiated photons. Net energy transferred per mass Kerma

  4. Absorbed dose or dose is the energy imparted per unit mass. Like kerma dose is based on mean changes in energy. Two units are used. 1 gray (Gy) = 1 J / kg 1 rad = 100 erg / g (older) Absorbed Dose

  5. Dose can be compared to physical effects. Lethality refers to the likelihood that a dose will be fatal. Cell death Whole body death (see graph at right) Lethality Lethality % Dose (cGy) Federation of American Scientists

  6. Exposure is defined by the ionization produced by photons. Gammas and X-rays Charge per unit mass in air The unit of exposure is the Roentgen (R). 1 R = 2.58 x 10-4 C / kg Useful Conversion Show that the original roentgen is equivalent to the modern one. Look up constants: Density of air at STP is 0.001293 g / cm-3 1 esu = 3.34 x 10-10 C 3.34 x 10-10 C / 1.293 x 10-6 kg = 2.58 x 10-4 C / kg Exposure

  7. The effect of radiation on tissue depends on the linear energy transfer (LET). Higher LET is more damaging Radiation has a weighting factor based on particle. Factor WR or Q In terms of LET LET L (keV / mm in water) < 10; WR = 1 10 – 100; WR = 0.32L – 2.2 > 100; In terms of particle e, g, m; WR = 1 n; WR = 5 – 20 p; WR = 5 a; WR = 20 Radiation Factor

  8. The equivalent dose is a measure that combines the type of radiation and dose. Unit is Sievert (Sv) 1 Gy equivalent Older unit is rem Roentgen equivalent man 1 rad equivalent 100 rem = 1 Sv Natural doses Cosmics: 0.3 mSv / yr Soil: 0.2 mSv / yr Radon: 2 mSv / yr Total natural: 3 mSv / yr Environmental hazards Flying at 12 km: 7 mSv / hr Chest x-ray: 0.1 mSv Mammogram: 1 mSv CT scan: 20 mSv Equivalent Dose

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