APPENDIX E Glossary


Accelerator

A machine designed to accelerate charged particles (typically electrons, protons, deuterons, or ions) to energy levels suitable for bombarding a target and studying the resulting nuclear reactions. Among the types of accelerators are Van de Graff electrostatic accelerators, linear accelerators, cyclotrons, and synchrotrons.

Alpha particle

A positively charged particle consisting of two protons and two neutrons, identical to the nucleus of the helium atom, emitted by several radioactive substances.

Alpha radiation

Some radioactive elements, particularly those with a high atomic number, decay by emitting a positively charged particle, the alpha particle, which is identical to the nucleus of a helium atom. Alpha radiation has very little penetrating power, but it may present a serious hazard if alpha emitters are inhaled, ingested, or taken in through the skin.

Atom

The smallest particle of an element that retains the characteristics of that element. The atom consists of a small positively charged nucleus surrounded by a cloud of negatively charged electrons. An atom is characterized by its mass number (A) and its atomic number (Z).

Atomic number (Z)

The number of protons in an atomic nucleus.


Background radiation

The radiation produced by naturally occurring radioactive isotopes in the surroundings and biological tissue. Cosmic rays also contribute to the background radiation.

Beta decay

Radioactive transformation of a nuclide in which the atomic number increases or decreases by unity with no change in the mass number; the nucleus emits a beta particle during beta decay.



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APPENDIX E Glossary Accelerator A machine designed to accelerate charged particles (typically electrons, protons, deuterons, or ions) to energy levels suitable for bombarding a target and studying the resulting nuclear reactions. Among the types of accelerators are Van de Graff electrostatic accelerators, linear accelerators, cyclotrons, and synchrotrons. Alpha particle A positively charged particle consisting of two protons and two neutrons, identical to the nucleus of the helium atom, emitted by several radioactive substances. Alpha radiation Some radioactive elements, particularly those with a high atomic number, decay by emitting a positively charged particle, the alpha particle, which is identical to the nucleus of a helium atom. Alpha radiation has very little penetrating power, but it may present a serious hazard if alpha emitters are inhaled, ingested, or taken in through the skin. Atom The smallest particle of an element that retains the characteristics of that element. The atom consists of a small positively charged nucleus surrounded by a cloud of negatively charged electrons. An atom is characterized by its mass number (A) and its atomic number (Z). Atomic number (Z) The number of protons in an atomic nucleus. Background radiation The radiation produced by naturally occurring radioactive isotopes in the surroundings and biological tissue. Cosmic rays also contribute to the background radiation. Beta decay Radioactive transformation of a nuclide in which the atomic number increases or decreases by unity with no change in the mass number; the nucleus emits a beta particle during beta decay.

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Beta particle A synonym for an electron or a positron when it is emitted in the process of beta decay. Beta radiation Some radioactive elements emit from the nucleus charged particles of low mass called beta particles. Positive beta particles are positrons, and negative beta particles are identical to the electrons in the atom. Such beta radiation has a penetrating power intermediate between that of alpha and gamma radiation. Charged particle A particle whose net charge is not zero; protons and electrons are examples of charged particles; neutrons, by contrast, are uncharged. Curie (Ci) A unit of measurement describing the radioactive disintegration rate of a substance; 1 curie = 3.700 × 1010 disintegrations per second. Cyclotron A machine capable of accelerating a beam of charged subatomic particles in an outward spiral pathway to high energies and speeds by the application of electromagnetic forces. Cyclotron vault The massive concrete structure that completely surrounds the cyclotron, beam tubes, and target stations and that acts as a biological shield against the neutron and gamma radiation emitted by the cyclotron when it is in operation. Decay product The substance formed by the radioactive decay of a radioactive nuclide. Some radionuclides decay through a sequence of steps with many successive decay products. Detector Any device that can detect the presence of a particle or nuclear fragment produced in a nuclear reaction and measure one or more of its physical properties. Deuterium A naturally occurring isotope of hydrogen. A deuteron, the nucleus of the deuterium atom, consists of one proton and one neutron; hence, it is approximately twice as heavy as ordinary hydrogen. Diagnostic medicine Identification of disease by means of the patient's symptoms and other objective measurements. Dose The amount of energy delivered to a mass of material by ionizing radiation passing through it. Electron A particle that has unit negative charge and 1/1,840 the mass of a proton. Atoms consists of a cloud electrons around a nucleus. Electron volt, (eV) The amount of energy acquired by any particle with a unit electric charge when it is accelerated through a potential difference of 1 volt; 1 keV = 1 thousand electron volts; and 1 MeV = 1 million electron volts. Element A substance that cannot be divided into simpler substances by chemical means, being made up of a collection of atoms that have the same number of protons in their nuclei, and therefore the same atomic number. Epithermal neutron A neutron with kinetic energy typically in the range of between 1 keV and 1 MeV.

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Fast neutron A neutron with kinetic energy typically of 1 MeV. Fission The process whereby the nucleus of a heavy element, for example, uranium or plutonium, splits into two nuclei of lighter elements(fission products) accompanied by the release of substantial amounts of energy and particles, usually neutrons. Fission products The complex mixture of substances produced in the process of fission. The primary fragments produced in fission are themselves radioactive and decay through succession of radioactive isotopes until a stable form is reached. Gamma radiation Most radioactive elements emit from the nucleus electromagnetic radiation called gamma rays. Gamma radiation is penetrating and can cause radiation exposure many tens of meters from external sources. It is also the radiation that is most readily measured by monitoring equipment such as film badges and dosimeters. Gamma ray An extremely energetic photon emitted in many nuclear reactions and in the decay of many radioactive nuclides. Half-life The time in which the activity of a radioactive species will decline to half of its initial activity value by radioactive decay. The half-life of a radioactive species is a characteristic property of that species and is independent of its amount or physical condition. Hot cell An enclosure for the safe handling of radioactive substances; it protects the operator against both internal and external radiation. Isotopes Forms of the same element whose nuclei contain different numbers of neutrons and therefore have different mass numbers. Isotopes of an element have nearly identical chemical properties but differ in their nuclear properties. For instance, some isotopes of an element, but not others, may be radioactive. An example is hydrogen, which has three isotopes with relative masses of 1, 2, and 3. The two lighter isotopes, hydrogen (relative mass of 1) and deuterium (relative mass of 2), are stable but the third, tritium (relative mass of 3), is radioactive. Mass number (A) The total number of protons and neutrons contained in the nucleus of an atom. The mass number is used to characterize isotopes, for example, uranium-235 is the isotope of uranium that has a mass number of 235. The nuclei of different elements can have the same mass number. Metabolism All of the physical and chemical processes by which the living body is maintained and also those by which energy is made available for various forms of work. Monoclonal antibody A protein produced in an animal or human by a single family of cells response to stimulation by an antigen and capable of reacting specifically with that antigen.

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Neutron A nuclear particle having no charge and a mass approximately equal to that of a proton. Neutrons are present in all atoms except those of the lightest isotope of hydrogen. Neutrons are released in large numbers in nuclear explosions and are very penetrating. Neutron number (N) The number of neutrons in an atomic nucleus. Nuclear medicine A branch of medicine in which radioisotopes are used principally to diagnose or treat disease. Nuclear physics The study of the characteristics, behavior, and internal structure of the atomic nucleus. Nuclear reaction Any change brought about in the states of one or more nuclei as a collision or spontaneous decay. Nucleus The small, dense, positively charged core of the atom, consisting of neutrons and protons held together by strong nuclear forces. Nuclide An atomic nucleus characterized by the number of protons, the number of neutrons, and energy content. Photon The unit of energy associated with the element with the electromagnetic wave; the unit of the electromagnetic field, which carries energy and momentum. Positron A fundamental particle of matter having the same mass and the same magnitude of charge as those of an electron, but with a positive charge. Positron emission tomography (PET) Often known by the acronym PET. A technique in nuclear medicine in which the physiological and pathological processes occurring in the tissues of a patient may be visualized and quantified through the application of positron-emitting radioisotopes. Proton A positively charged particle found in all atoms. The nucleus of the lightest isotope of hydrogen consists of one proton. Radiography The technique of generating radiographs or pictures produced on a sensitized surface or film by a form of radiation, typically X-ray radiography or neutron radiography. Radioisotope, radionuclide The name given to a substance in which the number of neutrons in the atom's nucleus have been increased or reduced to bring about nuclear instability, which is manifested by the emission of radiation. Scattering When two particles collide, they are said to scatter off each other during the collision. Spallation A nuclear reaction in which nuclei, on being bombarded by high-energy particles, liberate a number of other particles (protons, neutrons, and alpha and heavier particles). Also known as fragmentation. Spectroscopy The branch of physics concerned with the production, measurement, and interpretation of the electromagnetic spectra arising from either the emission or absorption of radiant energy by various substances.

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Target The substance bombarded with neutrons or other particles to produce radioisotopes. Therapeutic medicine Treatment of disease to secure a cure or a reduction or palliation of symptoms. Thermal neutron A neutron with kinetic energy typically in the range of less than 1 kiloelectron volt (keV). Transmutation A process in which a nuclide of one chemical element is transformed into a nuclide of a different chemical element. A common transmutation process is neutron capture followed by beta decay. Tritium A radioactive isotope of hydrogen (3H or T). The nucleus of the tritium atom consists of one proton and two neutrons; hence, it is approximately three times as heavy as ordinary hydrogen. X-ray Highly penetrating radiation emanating from atomic transitions of an element; X-rays are produced, for example, by electron bombardment of a metallic target.