Wiktionary
n. (context physics English) a radioactive nuclide
Wikipedia
A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is an atom that has excess nuclear energy, making it unstable. This excess energy can either create and emit, from the nucleus, new radiation ( gamma radiation) or a new particle ( alpha particle or beta particle), or transfer this excess energy to one of its electrons, causing it to be ejected ( conversion electron). During this process, the radionuclide is said to undergo radioactive decay. These emissions constitute ionizing radiation. The unstable nucleus is more stable following the emission, but will sometimes undergo further decay. Radioactive decay is a random process at the level of single atoms: it is impossible to predict when one particular atom will decay. However, for a collection of atoms of a single element the decay rate, and thus the half-life (t) for that collection can be calculated from their measured decay constants. The duration of the half-lives of radioactive atoms have no known limits; the time range is over 55 orders of magnitude.
Radionuclides both occur naturally and are artificially made using nuclear reactors, cyclotrons, particle accelerators or radionuclide generators. There are about 650 radionuclides with half-lives longer than 60 minutes (see list of nuclides). Of these, 34 are primordial radionuclides that existed before the creation of the solar system, and there are another 50 radionuclides detectable in nature as daughters of these, or produced naturally on Earth by cosmic radiation. More than 2400 radionuclides have half-lives less than 60 minutes. Most of these are only produced artificially, and have very short half-lives. For comparison, there are about 254 stable nuclides.
All chemical elements have radionuclides. Even the lightest element, hydrogen, has a well-known radionuclide, tritium. Elements heavier than lead, and the elements technetium and promethium, exist only as radionuclides.
Unplanned exposure to radionuclides generally has a harmful effect on living organisms including humans, although low levels of exposure occur naturally without harm. The degree of harm will depend on the nature and extent of the radiation produced, the amount and nature of exposure (close contact, inhalation or ingestion), and the biochemical properties of the element; with increased risk of cancer the most usual consequence. However, radionuclides with suitable properties are used in nuclear medicine for both diagnosis and treatment. An imaging tracer made with radionuclides is called a radioactive tracer. A pharmaceutical drug made with radionuclides is called a radiopharmaceutical.
Usage examples of "radionuclide".
The slightest kiss from a radionuclide and an object could be contaminated for centuries or hundreds of centuries.
HALF-LIFE: The time it takes for half the number of atoms in a radionuclide sample to disintegrate.
What mattered as much as the level or duration of exposure was the exact kinds of radionuclides nuclear fission products they had found.
A nasal smear for inhaled radionuclides was high but not alarmingly so.
Backtracking over all the samples he had processed so far, Garner saw that the abundance of the bacterium corresponded to the highest levels of radionuclides in solution.
Garner was gambling that both the bacteria and the radionuclides coincided within a single, dilute, and clearly heated water parcel.
They tinkered around with a natural culture of ferrooxidans until it acquired a taste for radionuclides in addition to naturally occurring isotopes.
It weaned itself on radionuclides and leached them out of the bedrock by bonding them in solution.
The three ships will then move along the length of the slick, several times if necessary, until the radionuclides are stripped from the water.
The thin crust of the basin floor that helped the explosives do their job so well is what allowed the seep of radionuclides in the first place.
Everyone working at the lake was being exposed to radionuclides equivalent to three hundred rem a year, sixty times the permitted exposure level for workers in the United States.
They have scavenged its ozone layer with chlorofluorocarbons, burdened it with acid aerosols, even laced it with radionuclides, but it is the warmup that has produced the most interesting effects.
We sample soil and groundwater, test which mushroom soaks up more radionuclides, check the DNA of mammals.