| Activity |
The number of radiochemical transformations that take place in a sample during a specified period of time. |
| Alpha (a) emission |
Particulate radiation consisting of fast moving helium nuclei (2 protons, 2 neutrons) produced by the disintegration of heavy nuclei of atomic number 52. |
| Autoradiography |
The method of producing a viewable image of radioactive areas using photographic (X-ray) film. |
| Background |
Naturally occurring low-level radioactivity that can be detected by a scintillation counter. It must be subtracted from the total count to obtain net counts of the sample. |
| Becquerel (Bq) |
A Standard International Unit of radioactivity, which is equal to 1 disintegration per second and equal to 2.7 x10-11Ci. |
| Beta (b) emission |
An electron ejected from a nucleus during radioactive transformation. Beta particles produced by a given nuclei have a range of initial energies from a maximum, which is characteristic of the nuclide. |
| Bremsstrahlung |
Electromagnetic radiation produced when an electrically charged particle, such as an electron, is slowed down by the electric field of an atomic nucleus.
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| Carrier-free |
A preparation of a radioisotope to which no carrier isotope has been added, and for which precautions have been taken to minimize contamination with other isotopes. Material of high specific activity is often loosely referred to as carrier-free, but more correctly this should be termed material of high isotopic abundance. |
| Curie |
A unit of radioactivity which is equal to 3.7 x 1010 Bq. |
| Efficiency |
Refers to a detector. It is the ratio of the number of radiations actually detected by the detector to the number of radiations emitted by the source. |
| Electron capture |
Radioactive transformation in which the nucleus absorbs an electron from an inner orbital. The remaining orbital electrons rearrange to fill the empty electron shell and in so doing energy is released as electromagnetic radiation at X-ray wavelengths and/or as electrons.
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| Electron volt (eV) |
A unit of energy equal to the kinetic energy acquired by an electron when accelerated through a potential difference of 1 volt.
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| Enantiomorph |
Either of two forms of a substance that are mirror images of each other.
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| Gamma (g) emission |
Electromagnetic radiation emitted by atomic nuclei, the wavelength is generally in the range 1 W 10-10 to 2 W 10-13 m.
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| Half-life |
The period of time in which the activity of a radionuclide decays to half of its initial value. |
| Isotopes |
Nuclides having the same atomic number but different mass numbers. |
| Isotope effect |
A phenomenon that can occur when two isotopes of the same atomic number (or their compounds) may have a detectable difference in their chemical and physical behavior. |
| Isotopic abundance |
The number of atoms of a particular isotope in a mixture of the isotopes of an element, expressed as a fraction of all the atoms of the element.
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| Labeled compound |
A compound in which an isotope is incorporated into the molecule. Go to Nomenclature of isotope labeling for more details.
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| Liquid Scintillation Counting |
A technique used for measuring radioactivity of carbon 14 and tritium compounds, as well as other isotopes. The compound is dissolved in a scintillation fluid (or cocktail) which allows the energy from the particles to be transferred to the cocktail and then emitted as light photons (scintillations) which can be detected on a scintillation counter. |
| Milliatom |
The atomic weight of an element in milligrams. |
| Millimole (mmol) |
The molecular weight of a compound in mg. |
| Nuclide |
A species of atom characterized by its mass number, atomic number, and energy state, provided that the mean life in the state is long enough to observe. |
| Positron |
The antiparticle of the electron, having the same mass but an equal and opposite charge. It is produced in certain decay processes. |
| Radioactive concentration |
The activity per unit volume, normally expressed in mCi/mL. Not the same as the specific activity. |
| Radioactivity |
The property of certain nuclides of emitting radiation by the spontaneous transformation of their nuclei. |
| Radiochemical |
A compound in which one or more of the atoms of the compound are present in a radioactive form. |
| Radiochemical purity |
Purity of a radioactive material--the proportion of the total radioactivity that is present in the stated isotopic form. |
| Radiolabelled compound |
A compound in which one or more of the atoms of a proportion of the molecules is replaced by a detectable radioactive isotope. |
| Radionuclide (radioisotopic) purity |
Of a radioactive isotope, the proportion of the total radioactivity that is present in the stated isotopic form. |
| Scintillation |
The term used to describe light flashes emitted by luminescent substances when excited by high energy radiation. |
| Scintillation counter |
An instrument used to measure the scintillations emitted by a radioactive substance. Used to determine such things as radioactive concentration or specific activity. |
| Specific activity |
The radioactivity per unit mass of an element or compound containing a radioactive nuclei. Normally expressed as millicuries per milligram, millicuries per millimole, or as curies per millimole. |
