Induced radioactivity

A means of inducing radioactivity in a nonradioactive sample by bombarding the sample with neutrons. 

Radiochemical methods of analysis take advantage of the decay of radioactive isotopes. A direct measurement of the rate at which a radioactive isotope decays may be used to determine its concentration in a sample. For analytes that are not naturally radioactive, neutron activation often can be used to induce radioactivity. Isotope dilution, in which a radioactively labeled form of an analyte is spiked into the sample, can be used as an internal standard for quantitative work. 

Nernst equation an equation relating electrochemical potential to the concentrations of products and reactants, (p. 146) neutron activation a means of inducing radioactivity in a nonradioactive sample by bombarding the sample with neutrons, (p. 645)... 

Irradiation type Average energy, eV Coloration uniformity Induced radioactivity Locali2ed heating... 

With the exception of diamond coloring and the turning of topa2 blue, the source of the irradiation is immaterial. Gamma rays are the preferred source because of uniformity of coloration and the absence of heating and induced radioactivity. The most commonly seen gemstones enhanced by irradiation are summari2ed in Table 4. 

Activation Process of inducing radioactivity in a material by bombardment with other types of radiation, such as neutrons. 

Radioactive nuclei are used extensively in chemical analysis. One technique of particular importance is neutron activation analysis. This procedure depends on the phenomenon of induced radioactivity. A sample is bombarded by neutrons, bringing about such reactions as... 

In 1921, Irene Curie (1897-1956) began research at the Radium Institute. Five years later she married Frederic Joliot (1900-1958). a brilliant young physicist who was also an assistant at the Institute. In 1931, they began a research program in nuclear chemistry that led to several important discoveries and at least one near miss. The Joliot-Curies were the first to demonstrate induced radioactivity. They also discovered the positron, a particle that scientists had been seeking for many years. They narrowly missed finding another, more fundamental particle, the neutron. That honor went to James Chadwick in England. In 1935,... 

Radioactivity. Methods based on the measurement of radioactivity belong to the realm of radiochemistry and may involve measurement of the intensity of the radiation from a naturally radioactive material measurement of induced radioactivity arising from exposure of the sample under investigation to a neutron source (activation analysis) or the application of what is known as the isotope dilution technique. 

There is no induced radioactivity [30,44] with EB irradiation (unlike 7- or neutron irradiation) and hence EB-induced modification of materials is less hazardous compared to neutron or 7-ray-induced modifications. 

When a nucleus is placed in a flux of neutrons, it may capture another neutron. It thus is often unstable toward further decay by j3 -emission. The induced radioactivity is critical to the study of chemical consequences of neutron capture, since so few of these new nuclei are produced that generally they cannot be observed by any other means. This radioactivity is not, however, a part of the phenomenon which we wish to observe and, moreover, is occasionally a distraction. 

Radioactivity, Induced—Radioactivity produced in a substance after bombardment with neutrons or other particles. The resulting activity is "natural radioactivity" if formed by nuclear reactions occurring in nature and "artificial radioactivity" if the reactions are caused by man. 

Natural radioactivity derives from spontaneous nuclear disintegrations. Induced radioactivity derives from the bombardment of nuclei with accelerated subatomic particles or other nuclei. Both cause atoms of one nuclide to be converted to another nuclide. 

A sample was irradiated in a neutron flux and the induced radioactivity monitored after it was removed from the flux. The fully corrected results are presented below. 

As a result of slow (thermal) neutron irradiation, a sample composed of stable atoms of a variety of elements will produce several radioactive isotopes of these activated elements. For a nuclear reaction to be useful analytically in the delayed NAA mode the element of interest must be capable of undergoing a nuclear reaction of some sort, the product of which must be radioactively unstable. The daughter nucleus must have a half-life of the order of days or months (so that it can be conveniently measured), and it should emit a particle which has a characteristic energy and is free from interference from other particles which may be produced by other elements within the sample. The induced radioactivity is complex as it comprises a summation of all the active species present. Individual species are identified by computer-aided de-convolution of the data. Parry (1991 42-9) and Glascock (1998) summarize the relevant decay schemes, and Alfassi (1990 3) and Glascock (1991 Table 3) list y ray energy spectra and percentage abundances for a number of isotopes useful in NAA. 

Radium salts have the property of causing surrounding objects to become temporally radioactive. This "induced radioactivity," as it may be called, is found to be due to the... 

They do not induce radioactivity in foods or their packaging materials. 

In 1934 the Hungarian physicist Leo Szilard filed a patent with the British Patent Office. It was based on an idea, nothing more - an idea about how to harness nuclear energy. The Joliot-Curies had shown that bombarding nuclei with particles can induce radioactive decay artificially. And the work of Bothe and Chadwick had demonstrated that some radioactive nuclei emit neutrons. So what would happen if neutrons induced nuclear decay that led to more neutrons The result might be a chain reaction a self-sustaining release of nuclear energy. 

Gamma rays from cobalt-60 are also used to sterilize food, since they kill bacteria. The gamma rays are incapable of inducing radioactivity within the food, so the method is potentially clean . The rays do, however, produce some free radicals, which are potentially harmful substances. But the concentrations of these are very small, and they may well do less harm than the preservatives... 

There are three significant possible effects when radiation interacts with matter (5,6). First, the radiation can interact with the nucleus and induce radioactivity as in the case of neutrons. Second, displacement of atoms can occur. This has happened in a number of uranium- and thorium-containing minerals over geological periods. The outstanding example is zircon, which can contain over 10% Th and 2% U. The internal bombardment from these materials and their decay products over geological periods produces low or metamict zircon, where the disorder gives an amorphous state having a low density. 

Electro-magnetically Excited Fluorescence Raman spectro-photometry Induced radioactivity X-ray fluorescence... 

Induced radioactivity by bombardment of appropriate additives with high energy particles is in most cases impractical, costly and potentially harmful to personnel. Its use may conceivably be justifiably for very limited applications. In addition, extensive efforts would be required to demonstrate that such bombardment would have no deleterious effects on innocuous materials (eg, contents of a suitcase) in which expls may be hidden... 

Comprehensive research programs sponsored by the U. S. Atomic Energy Commission and the Army in this country have been under way for the past 14 years. These studies were concerned with ascertaining the physical and chemical changes in foods preserved by ionizing energy, with particular emphasis upon wholesomeness, nutritional adequacy, acceptability, and absence of induced radioactivity in foods intended for consumption by humans. 

Radiation beams induce radioactivity primarily by photonuclear reactions. In these reactions, the absorption of energy from the incident electron, x-ray, or 7-ray will produce an excited nucleus that will then emit a neutron, proton, triton, 7-ray, or other secondary radiation. The chart of the nuclides from carbon to sodium in Figure 1 demonstrates the type of nuclide resulting from the emission of a secondary radiation from a given parent nuclide (10). The threshold energies necessary for the incoming radiation to produce a secondary radiation are given for a few of the reactions most relevant to this report. 

A number of investigators have examined the production of radioactivity resulting from photoneutron reactions induced by high-energy electrons. Meyer (15) has reviewed these data and showed that the induced radioactivity, 72, in specific activity per unit dose (picocuries per gram of element times megarad) is reasonably well represented by Equation 1. 

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