Definitions and units 263 Definitions and units The following glossary is intended as a conveniently accessible source of technical terms used in context with ion tracks. It is compiled mainly on the basis of the references [1], [2], [3], [4], [5], [6]. [1] D.H. Menzel (editor): "Fundamental Formulas of Physics." Dover Publications, New York, 1960 [2] "Glossary of Terms used in Nuclear Science." British Standards Institution, B.S. 3455, 1962 [3] "The Radiochemical Manual." Amersham, the Radiochemical Centre, 1966 [4] Cohen, E., P. Giacomo: "Symbols, Units, Nomenclature and Fundamental Constants in Physics." International Union of Pure and Applied Physics (IUPAP), Revision 1987,67 pp. (1987). [5] Alan Isaacs (editor): "Concise Dictionary of Physics." Oxford University Press, pp. 1-295, 1985. [6] Hansen, J.W.: "Experimental Investigation of the Suitability of the Track Structure Theory in Describing the Relative Effectiveness of High-LET Irradiation of Physical Radiation Detectors." RiSl/l National Laboratory, DK-4000 Roskilde, Denmark; RiSl/l-R-507, (1984). absorbed dose, absorbed energy per unit mass. SI atoms of the element. The atomic number de­ unit is the Gray (Gy). I Gy = 1 J / fines the chemical properties of the element. kg = 104 erg / g = 6.25-1015 eV/g. atomic radius of hydrogen, ao = h2 / 4n2 m e2 = actuator, a device for inducing an action. 0.5292-10-8 cm. alpha particle, (a), the nucleus of a 4He atom con­ atomic weight (W), for a given specimen of an sisting of two protons and two neutrons. element, the mean weight of its atoms, ex­ pressed in either atomic mass units (physical areal density of targets, (Ps)' thickness-equivalent scale) or atomic weight units (chemical scale). of targets, Ps ;;; P d, where p is the mass density and d the target thickness, usually given in atomic weight unit (awu), one-twelfth of the mean mg / cm2. mass of the neutral atoms of naturally occurring carbon. areal dose (fluence), number of accumulated (recorded) particle tracks per unit surface area. A vogadro number, N A = 6.0220-1023 / mole, number of molecules per mole. asp~ct ratio, ratio between length and width of an ion track. bar, unit of pressure. 1 bar = lOS Pa = 750.19 torr. atom, a unit of matter consisting of a single nu­ barn, a unit of cross-section. 1 bam = 10-24 cm. cleus surrounded by one or more orbital elec­ Becquerel (Bq), unit of radioactivity, 1 Bq = trons. The number of electrons corresponds to 1 decay event / s. Official unit before 1986: the number of protons in the nucleus. 1 Curie (Ci) = 3.7-1010 decay events / s. atomic mass (A • u), mass of a nuclide measured beta particle, electron. in atomic mass units, where A = atomic mass Bohr magneton, JlB = e h / (4n me c) = number, and u = atomic mass unit. 9.2741 - 10-24 Joule pro Tesla. atomic mass number (A), mass number of a nu­ Bohr radius, ao = a / 4 n R~ = 0.529177-10-8 cm. clide, nucleon number, number of protons and a = fine structure constant, n = 3.1415, R~ = neutrons in the nuclide. A is the nearest integer Rydberg constant. to its atomic mass. Bohr velocity, Vo = 2n e 2 / h = a c = atomic mass unit (u), one-twelfth of the mass of a 2.1847-108 cm / s, where e electron charge, 27 = neutral atom of 12C, u = 1.6606-10- kg. h = Planck constant, a = fine structure con­ atomic number (2) of an element, nuclear charge stant, C = velocity of light. number, number of protons in the nucleus of the Boltzmann constant, k = R / N A = 1.3806-10-23 J 264 Defmitions and units fK = 1.3806.10-16 erg / K. R = molar gas con­ number, u = atomic mass unit, NA = Avogadro stant, N A = Avogadro constant. number, V rn = molar volume. Bragg peak: region of maximum energy loss of a density, number - (N), number of atoms per vol­ high energy ion traversing matter. ume element, N = P / (A u), where p = mass bremsstrahlung, the electromagnetic radiation re­ density, A = atomic mass number, u = atomic sulting from the retardation of charged particles. mass unit. calorie, unit of thermal energy, 1 calorie = dose, energy -, absorbed energy per unit mass. SI 4.18400 Joules. unit is the Gray (Gy). 1 Gy = 1 J / kg = 104 erg / g = 6.25.1015 eV / g. Radiation en­ capacitance, unit of capacitance is the Farad (F). 1 2 ergy deposited in a medium causes bond rupture, Farad = 1 Coulomb / Volt = 1 m- kg-I S4 N. radical formation, and physico- and chemical charge, electric -, given in units of Coulomb (C). changes, which are detectable in different ways. 9 1 C = 1 A s = 3.10 esu. dose equivalent, see Rem. A unit of biologically cross section of a nucleus, atom, or grain for a effective dose, defined as the absorbed dose in rad given radiation, that area perpendicular to the di­ multiplied by the quality factor - or relative bi­ rection of the radiation attributed geometrically ological effectiveness (RBE) -. For all x rays, for its interaction with the radiation; or, in other y rays, ~- rays and ~+ rays encountered from ra­ words, the number of interactions per unit time dioisotopes the RBE is 1. For a-particles and divided by the radiation flux and the number of heavier ions the RBE can be different from 1, scattering objects present. The cross section of a depending on the ion charge and its velocity. nucleus is roughly of the order of 10-24 cm, of an 16 Dose-response: relation between the deposited en­ atom roughly of the order of 10- cm. ergy per volume, in other words the dose, and Coulomb (C), the unit of electric charge. The the observed effect, which may for example be charge of 1 Coulomb corresponds to the charge optical absorption, survival of cells, etc .. For of an electrical current of 1 Ampere flowing dur­ many physical radiation recorders, irradiated by ing 1 second. 1 C = 1 A s. 1 Coulomb corre­ low-LET radiation, the dose-response function is sponds to the charge of 0.62414.1019 electrons. approximately linear at low doses and saturates Coulomb barrier of nuclear reactions, minimum exponentially at high doses and the response is a energy of projectile ions required for inducing single-valued function of dose within a large nuclear reactions. The coulomb barrier corre­ range of initial photon and electron energies. sponds to a specific energy in the range between dyne, unit of force, 1 dyne = 1 g cm S-2. 1 and 10 MeV/nucleon, depending on the projec­ electron, the negatively charged particle which tile/target combination. forms a constituent of all atoms. Electron charge Coulomb explosion, origin of the atomic collision e = - 1.60219.10-19 Coulomb = -4.8032.10-10 cascade.in solids, caused by the passage of a esu. Electron mass me = 9.1095.10-28 g. rapidly moving ion and leading to displaced Classical electron radius r e = e 2 / (me c2 ) = atoms and ultimately to a latent track. 2.8179.10-13 cm. Coulomb per kilogramm (C / kg), "unit" of ab­ electron volt (eV), a unit of energy equal to the ki­ sorbed dose, defined as total electron charge gen­ netic energy acquired by an electron when accel­ erated during - preferentially x or y - irradia­ erated through a potential difference of 1 volt. 1 tion. Official unit before 1986: 1 Roentgen = eV = 1.602.10-12 erg = 1.602.10-19 Joule. 4 2.58.10- C / kg. One Roentgen produces eV, electron volt. 1 eV = 1.602.10-12 erg. 3.7·1010 ion pairs in air at standard pressure and temperature. element, matter consisting of atoms having the same atomic number Z. Curie (Ci), old unit of activity. One curie corre­ sponds to 3.7.1010 nuclear transformations per energy, a measure of a system's ability to do work. second. 1 Ci = 3.7·1010 Bq. Potential energy is the energy stored in a body or system as a consequence of its position, shape, De Broglie wavelength of a particle, A = h / p , or state. Kinetic energy is energy of motion and where h = Planck constant, and p is the particle is usually defined as the work that will be done momentum. The magnitude of the associated by the body when it is brought to rest. For a wave vector is k == 21t / A = 21t P / h. body of mass m having a speed v, the kinetic delta ray: secondary and higher order electrons gen­ energy is m v2/2. The rotational kinetic energy erated by a primary radiation. This term is anal­ of a body with an angular velocity 0) is I 0)2/ 2, ogous to the terms alpha-ray and beta-ray. where I is its moment of inertia. density, electron - (Ne)' number of electrons per energy units, 1 erg = I g cm2 S-2. 1 J = 107 erg = volume element, Ne = Z P / (A u), where Z = 0.239 calories. 1 erg = 6.25.1011 eV. 1 eV = nuclear charge number, p = mass density, A = 1.6.10-12 erg. 1 kJ / mole = 1.038.10-2 eV / atomic mass number, u = atomic mass unit. molecule. density, mass - (p), mass per volume element, energy, free -, corresponds to the following two p = Au NA / V rn , where A = atomic mass thermodynamic functions. Gibbs free energy, Definitions and units 265 G=H-TS, is the energy liberated or absorbed in a ture T at which the energy is absorbed, reversible process at constant pressure and con­ t1S=t1Q/T.