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Unformatted text preview: 30. Radioactivity and radiation protection 1 30. RADIOACTIVITY AND RADIATION PROTECTION Revised September 2009 by S. Roesler and M. Silari (CERN). 30.1. Definitions [1,2] 30.1.1. Physical quantities : Fluence, (unit: 1/m 2 ): The uence is the quotient of dN by da , where dN is the number of particles incident upon a small sphere of cross-sectional area da = dN/da . (30 . 1) In dosimetric calculations, uence is frequently expressed in terms of the lengths of the particle trajectories. It can be shown that the uence, , is given by = dl/dV, where d l is the sum of the particle trajectory lengths in the volume d V . Absorbed dose, D (unit: gray, 1 Gy=1 J/kg=100 rad): The absorbed dose is the energy imparted by ionizing radiation in a volume element of a specified material divided by the mass of this volume element. Kerma, K (unit: gray): Kerma is the sum of the initial kinetic energies of all charged particles liberated by indirectly ionizing radiation in a volume element of the specified material divided by the mass of this volume element. Linear energy transfer, L or LET (unit: J/m, often given in keV/ m): The linear energy transfer is the mean energy, d E , lost by a charged particle owing to collisions with electrons in traversing a distance d l in matter. Low-LET radiation: X-rays and gamma rays (accompanied by charged particles due to interactions with the surrounding medium) or light charged particles such as electrons that produce sparse ionizing events far apart at a molecular scale ( L < 10 keV/ m). High-LET radiation: neutrons and heavy charged particles that produce ionizing events densely spaced at a molecular scale ( L > 10 keV/ m). Activity, A (unit: becquerel, 1 Bq=1/s=27 picocurie): Activity is the expectation value of the number of nuclear decays occurring in a given quantity of material per unit time. 30.1.2. Protection quantities : Protection quantities are dose quantities developed for radiological protection that allow quantification of the extent of exposure of the human body to ionizing radiation from both whole and partial body external irradiation and from intakes of radionuclides. Organ absorbed dose, D T (unit: gray): The mean absorbed dose in an organ or tissue T of mass m T is defined as D T = 1 m T Z m T Ddm . Equivalent dose, H T (unit: sievert, 1 Sv=100 rem): The equivalent dose H T in an organ or tissue T is equal to the sum of the absorbed doses D T,R in the organ or tissue K. Nakamura et al. , JPG 37 , 075021 (2010) (http://pdg.lbl.gov) July 30, 2010 14:36 2 30. Radioactivity and radiation protection caused by different radiation types R weighted with so-called radiation weighting factors w R : H T = X R w R D T,R . (30 . 2) It expresses long-term risks (primarily cancer and leukemia) from low-level chronic exposure. The values for w R recommended by ICRP  are given in Table 30.1....
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This note was uploaded on 06/07/2011 for the course PHYS 4132 taught by Professor Kutter during the Spring '11 term at University of Florida.
- Spring '11