Radioactivity measurement, natural

Fisenne, I.M. and N.H. Harley, Lung Dose Estimates from Natural Radioactivity Measured in Urban Air, USAEC Report HASL-TM-74-7 New York, NY (1974). 

Natural Radioactivity Measurement. The naturally occurring radionuclides U(226Ra), Th(232Th), and K(40K) can also be determined on 100-g samples by direct counting of unirradiated samples using anticoincidence shielded multidimensional y-ray spectrometers (29, 30). These spectrometers use large (12 in. diameter X 8 in thick) principal Nal(Tl)... 

Fisenne, I.M., Harley, N.H. (1973). Lung dose estimates from natural radioactivity measured in urban air. USAEC Report HASL-TM-74-7, New Yo-k. 

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. 

The most reliable methods for establishing the age of a long-lasting object (such as a mountain) depend upon the presence of natural radioactivity. The decay of the radioactive elements can be likened to a clock that is partially unwound. By studying the extent to which the clock has unwound, we cannot tell the age of the clock but we can measure how long ago it was wound. 

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. 

Aerodynamic Size Distributions of Naturally-Radioactive Aerosols. Measurements of radionuclide distributions using cascade impactors indicate that Be-7 and Pb-210 are associated with larger aerosols than Pb-212 and Pb-214 (Robig et al., 1980 Papastefanou and Bondietti, 1986). Measurements of Pb-210 associations over oceans indicated activity median aerodynamic diameters (AMAD) near 0.6 pm (Sanak et al., 1981). The impactor measurements of Moore et al. (1980) on Pb-210, Bi-210, and Sr-90 sizes in continental air indicated that about 80% of the activity from all three nuclides was associated with aerosols below 0.3 pm. That work also determined that the mean age of aerosol Pb-210 was about a week. Knuth et al. (1983) compared Pb-210 and stable Pb sizes at a continental location and found that 78% of the Pb-210 found below 1.73 pm was smaller than 0.58 pm. Young (1974) reported that the most of the Be-7 in the atmosphere was associated with submicron aerosols. 

We were quite elated, and it appeared that it was a rich field. Now, fifty years later, I must say that it wasn t as rich as we thought. But we have over the years discovered half a dozen natural radioactive elements, and two of these, the samarium-147 with its decay to neodymium-143 and rhenium-187 with its decay to osmium-187, prove to be of use in Nuclear Dating. The importance of rhenium is that it is iron soluble while the other radioactivities are insoluble in metallic iron. In fact, the best half life we have for rhenium-187 was obtained by measuring the osmium-187 to rhenium-187 ratio in iron meteorites which had been dated by other methods. This work was started many years ago by Dr. Herr and others in Germany. The half life is 43,000,000,000 years. 

Nuclear dating has been most helpful in establishing the history of the earth and of the moon and of the meteorites. The fact is, there is no other way of measuring their ages. Prior to the discovery of natural radioactivity in the late 19th century, indirect methods were used to estimate the age of the earth, but there were no real answers until the radioactivity of thorium, uranium, and potassium were discovered and we began to understand atomic structure and to realize that nuclear transformation was essentially independent of the chemical form. 

The measurement of natural radioactivity with a y-ray detector determined the activity coefficient (the quantity of y-rays emitted), whieh is a specific characteristic of each type of sediment or rock. Specifically, a high y-ray count indicates the unmistakable presence of a elay matrix and thus constitutes useful information for the synthesized, integrated interpretation of this and other measurements performed. 

Krey P, Fiseene I, Perry P, et al. n.d. Natural radioactivity in the biosphere. Environmental Measurements Laboratory, New York, NY. 

Archaeologists have long sought methods for obsidian characterization that were rapid, reliable, non-destructive, and low-cost. Among the various methods investigated were visual techniques (79), density measurements (20), magnetic properties (27), thermoluminescence (22), fission-track analysis (25), Mossbauer spectroscopy (24), and natural radioactivity (25). Although some of the methods occasionally identified differences between sources, the overlap between sources was such that their overall reliability was unsatisfactory. The most successful method of characterization for obsidian provenance research has been compositional analysis (26). 

These heavy elements, which are naturally radioactive, are less interesting in chemical kinetics than the light elements which are involved in the majority of chemical reactions. The use of light elements has been made possible through the production of artificial radioactivity and through the finding of practical means of concentrating isotopes to such an extent that their concentrations can be determined by means of density measurements. Extraordinary refinements in these measurements have been a necessary part of these developments. 

Several methods that do not require chemical separation are available for measuring uranium in urine (in units of total mass or total activity). These methods include spectrophotometric (total mass), fluorometric (total mass), kinetic phosphorescence analysis (KPA) (total mass), and gross alpha (total activity) analyses (Wessman 1984). The most widely used methods for routine uranium analysis are a-spectrometry and liquid scintillation spectrometry. These methods utilize the natural radioactivity of uranium and are sensitive and require little sample preparation. Photometric techniques such as fluorometry and phosphorometry are less widely used, but kinetic phosphorescence analysis is becoming more widely used. Measurements of total uranium do not provide the relative isotopic abundance of the uranium isotopes, but this may only be important when converting between activity and mass when the isotopic ratios are uncertain. 

The measurement of the natural radioactivity of or of is also used for dating. However, interferences have to be taken into account due to the production of these radionuclides in nuclear reactors and by nuclear explosions. 

For the investigation of meteorites various experimental methods are applied, in particular mass spectrometry, neutron activation analysis, measurement of natural radioactivity by low-level coimting and track analysis. The tracks can be caused by heavy ions in cosmic radiation, by fission products from spontaneous or neutron-induced fission and by recoil due to a decay. Etching techniques and measurement of the tracks give information about the time during which the meteorites have been in interstellar space as individual particles (irradiation age). 

The activity of naturally radioactive elements is a measure of their mass. Prerequisites of application of the correlation between mass and activity according to eq. (17.1) are that the isotopic composition of the element to be determined is constant and that interfering radioactive impurities are absent. If the daughter nuelides are also radioactive, radioactive equilibrium must be established or the daughter nuclides must be separated off quantitatively. Interference of radioactive impurities may be avoided by measuring the a or y spectrum of the radionuclide considered. 

Martinez-Aguirre et al. (1994) have performed an extensive study of the presence of natural radioactivity around a phosphate fertilizer factory complex situated in an estuarine area of southwest Spain. The study has concluded that the wastes from such industries are the cause of the enhancement of natural radioactivity in the immediate environment. Thus, significantly high levels of U and Th-isotopes and Ra are detected in water and sediment samples collected in this area. These conclusions, based on the enhanced isotopic concentrations, are further supported by the measured U, Th and Ra isotopic activity ratios being quite different from any observed elsewhere in undisturbed estuaries. These isotope activity ratios appear to be very sensitive indicators of waste disposal practices in such environments. 

High-purity detection systems having a very low background are suitable tools for the direct measurement of low-level radioactivity in environmental samples. The background features of the detection system are of considerable importance because they have to be known for one to obtain an estimate of the detection limit and of the minimum detectable activity (Curie, 1968). The natural radioactivity background originates from the uranium and the thorium series from K and from cosmic rays. Natural radioactivity is found in most materials, and it is necessary to shield the... 

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