Appendix A Units and Constants Energy 1 electron volt (eV) = 1.602 × 10−12 erg 1 kiloelectron volt (keV) = 1.602 × 10−9 erg 1 million electron volts (MeV) = 1.602 × 10−6 erg 1 joule (J) = 107 ergs 1 watt (W) = 107 ergs/s = 1 J/s 1 rad = 1 × 10−2 J/kg = 100 ergs/g 1 gray (Gy) = 100 rad = 1 J/kg 1 sievert (Sv) = 100 rem = 1 J/kg 1 horsepower (HP) = 746 W 1 calorie (cal) = 4.184 J Charge 1 electronic charge = 4.8 × 10−10 electrostatic unit = 1.6 × 10−19 C 1 coulomb (C) = 6.28 × 1018 charges 1 ampere (A) = 1 C/s Mass and Energy 1 atomic mass unit (amu) = 1.66 × 10−24 g = 1/12 the atomic weight of 12 C = 931 MeV 1 electron rest mass = 0.511 MeV 1 proton rest mass = 938.78 MeV 1 neutron rest mass = 939.07 MeV 1 pound = 453.6 g G. B. Saha, Physics and Radiobiology of Nuclear Medicine, 335 DOI 10.1007/978-1-4614-4012-3, © Springer Science+Business Media New York 2013 336 Appendix A. Units and Constants Length 1 micrometer, or micron (μm) = 10−6 m = 104 Å 1 nanometer (nm) = 10−9 m 1 angstrom (Å) = 10−8 cm 1 fermi (F) = 10−13 cm 1 inch = 2.54 cm Activity 1 curie (Ci) = 3.7 × 1010 disintegrations per second (dps) = 2.22 × 1012 disintegrations per minute (dpm) 1 millicurie (mCi) = 3.7 × 107 dps = 2.22 × 109 dpm 1 microcurie (μCi) = 3.7 × 104 dps = 2.22 × 106 dpm 1 becquerel (Bq) = 1 dps = 2.703 × 10−11 Ci 1 kilobecquerel (kBq) = 103 dps = 2.703 × 10−8 Ci 1 megabecquerel (MBq) = 106 dps = 2.703 × 10−5 Ci 1 gigabecquerel (GBq) = 109 dps = 2.703 × 10−2 Ci 1 terabecquerel (TBq) = 1012 dps = 27.03 Ci Constants Avogadro’s number = 6.02 × 1023 atoms/g · atom = 6.02 × 1023 molecules/g · mole Planck’s constant ( h) = 6.625 × 10−27 erg · s/cycle Velocity of light = 3 × 1010 cm/sec π = 3.1416 e = 2.7183 Appendix B Terms Used in Text Absorption A process by which the total energy of a radiation is removed by an absorber through which it passes. Accelerator A machine to accelerate charged particles linearly or in circular paths by means of an electromagnetic field. The accelerated particles such as α-particles, protons, deuterons, and heavy ions possess high energies and can cause nuclear reactions in target atoms by irradiation. Accuracy A term used to indicate how close a measurement of a quantity is to its true value. Annihilation radiation γ-Radiations of 511 keV energy emitted at 180° after a β+-particle is annihilated by combining with an electron in matter. Apoptosis A process of cell death in which a programmed sequence of events leads to the elimination of cells making room for new cells. 12 Atomic mass unit (amu) By definition, one twelfth of the mass of 6C, equal to 1.66 × 10−24 g or 931 MeV. Atomic number ( Z) The number of protons in the nucleus of an atom. Attenuation A process by which the intensity of radiation is reduced by absorp- tion and/or scattering during its passage through matter. Attenuation coefficient The fraction of γ-ray energy attenuated (absorbed plus scattered) per unit length of an absorber (linear attenuation coefficient, μ) or per gram of an absorber (mass attenuation coefficient, μm). Auger electron An electron ejected from an energy shell, instead of a character- istic x-ray emission, carrying the energy equal to that of the x-ray minus its binding energy. Average life (τ) See Mean life. Avogadro’s number The number of molecules in 1 g mole of any substance or the number of atoms in 1 g atom of any element. It is equal to 6.02 × 1023. Becquerel (Bq) A unit of radioactivity. One becquerel is equal to 1 disintegration per second. Binding energy The energy to bind two entities together. In a nucleus, it is the energy needed to separate a nucleon completely from other nucleons in the nucleus. In a chemical bond, it is the energy necessary to separate two binding partners an infinite distance. G. B. Saha, Physics and Radiobiology of Nuclear Medicine, 337 DOI 10.1007/978-1-4614-4012-3, © Springer Science+Business Media New York 2013 338 Appendix B. Terms Used in Text Biological half-life ( Tb) The time by which one half of an administered dosage of a substance is eliminated by biological processes such as urinary and fecal excretions. Bremsstrahlung γ-Ray photons produced by deceleration of charged particles near the nucleus of an absorber atom. Carrier A stable element that is added in detectable quantities to a radionuclide of the same element, usually to facilitate chemical processing of the radionu- clide. Carrier-free A term used to indicate the absence of any stable atoms in a radio- nuclide sample. Collimator A device to confine a beam of radiation within a specific field of view. Collimators may be converging, pinhole, diverging, and parallel-hole types. Collimator efficiency The number of photons passing through the collimator for each unit of activity present in a source. Collimator resolution A component of spatial resolution of an imaging system contributed by the collimator. It is also called geometric resolution. Committed dose equivalent ( HT,50) The dose equivalent to organs or tissues of reference (T) that will be received from an intake of radioactive material by an individual during the 50-year period following intake. Compton scattering In this process, a γ-ray transfers only a partial amount of energy to an outer orbital electron of an absorber, and the photon itself is de- flected with less energy. Conversion electron (e−) See Internal conversion. Critical organ See Organ, critical. Cross section (σ) The probability of occurrence of a nuclear reaction or the for- mation of a radionuclide in a nuclear reaction. It is expressed in a unit termed barn; 1 barn = 10−24 cm2. Curie (Ci) A unit of activity. A curie is defined as 3.7 × 1010 disintegrations per second. Dead time The period of time that a counter remains insensitive to count the next after an event. Decay constant (λ) The fraction of atoms of a radioactive element decaying per unit time. It is expressed as λ = 0.693/t1/2, where t1/2 is the half-life of the ra- dionuclide. Deep-dose equivalent ( Hd) Dose equivalent at a tissue depth of 1 cm (1000 mg/ cm2) resulting from external whole-body exposure. Dose The energy of radiation absorbed by any matter. Dosimeter An instrument to measure the cumulative dose of radiation received during a period of radiation exposure. Dosimetry The calculation or measurement of radiation absorbed doses. Effective dose The sum of the products of the committed dose equivalent to each of the body organs and tissues and the weighting factor of the corresponding organ or tissue. (He = ΣWT × HT,50) Appendix B. Terms Used in Text 339 Effective half-life ( Te) Time required for an initial administered dose to be re- duced to one half as a result of both physical decay and biological elimina- tion of a radionuclide. It is given by Te = ( Tp × Tb)/( Tp + Tb), where Te is the effective half-life, and Tp and Tb are the physical and biological half-lives, respectively. Electron (e−) A negatively charged particle rotating around the atomic nucleus. It has a charge of 4.8 × 10−10 electrostatic units and a mass of 9.1 × 10−28 g, equivalent to 0.511 MeV, or equal to 1/1836 of the mass of a proton. Electron capture (EC) A mode of decay of a proton-rich radionuclide in which an orbital electron is captured by the nucleus, accompanied by emission of a neutrino and characteristic x-rays or Auger electrons. Electron volt (eV) The kinetic energy gained by an electron when accelerated through a potential difference of 1 V. Energy resolution Capability of a detecting system to separate two γ-ray peaks of different energies. It is given by the full width at half maximum (FWHM) of a given photopeak. Erg The unit of energy or work done by a force of 1 dyne through a distance of 1 cm. Fission (f) A nuclear process by which a nucleus divides into two nearly equal smaller nuclei, along with the emission of two to three neutrons. Free radical A highly reactive chemical species that has one or more unpaired electrons. Generator, radionuclide A device in which a short-lived daughter is separated chemically and periodically from a long-lived parent adsorbed on adsorbent material. For example, 99mTc is separated from 99Mo from the Moly generator with saline. Gray (Gy) The unit of absorbed radiation dose in SI units. One gray is equal to 100 rad. Half-life ( t1/2) A unique characteristic of a radionuclide, defined by the time dur- ing which an initial activity of a radionuclide is reduced to one half. It is re- lated to the decay constant λ by t1/2 = 0.693/λ. Half-value layer (HVL) The thickness of an absorbing material required to re- duce the intensity or exposure of a radiation beam to one half of the initial value when placed in the path of the beam. Internal conversion An alternative mode to γ-ray decay in which nuclear excita- tion energy is transferred to an orbital electron, which is then ejected from the orbit. Intrinsic efficiency The number of radiations detected divided by the number of radiations striking the detector.