Radioactive materials absorption

Acute Exposure, Radiation—The absorption of a relatively large amount of radiation (or intake of a radioactive material) over a short period of time. 

Treatment of Com. Ten microliters of an 80% acetone solution, containing 100 fig. of C14-gibberellin, was applied with a micropipet near the middle of the upper surface of the first leaf, followed by 10 fjl. of 0.1% Tween 20 and 50% ethyl alcohol in order to increase absorption of the radioactive material. The drop of solution was kept from running down by means of lanolin paste. Four normal and four dwarf com plants were thus treated, while untreated plants were kept as controls. The same number of dwarf plants was treated with 0.05 fic. of C14-5-aminotriazole in order to compare the pattern of translocation of gibberellin with that of a compound whose movement has been studied previously (4). The treated plants and controls were then placed in the growth chamber, and one or two specimens were harvested at the end of 1, 2, and 7 days, freeze-dried, and autoradiographed. 

Interesting chemical and structural phenomena can occur when radioactive materials are stored in the solid state Extensive studies have been made of both the chemical and physical status of progeny species that result from the a or 3" decay of actinide ions in several different compounds The samples have been both initially pure actinide compounds—halides, oxides, etc.—and actinides incorporated into other non-radioactive host materials, for example lanthanide halides. In general, the oxidation state of the actinide progeny is controlled by the oxidation state of its parent (a result of heredity). The structure of the progeny compound seems to be controlled by its host (a result of environment). These conclusions are drawn from solid state absorption spectral studies, and where possible, from x-ray diffraction studies of multi-microgram sized samples. 

Loss of radioactive material from the skin surface has been used to estimate in vivo percutaneous absorption. The difference in applied dose and residue on the skin is assumed to be absorbed. The characteristics of the radioisotope, penetrant, and vehicle may limit the usefulness of this procedure. Volatile materials may leave the surface without penetrating, and it is difficult to recover all material from the skin surface. In addition, skin may retain a reservoir of the penetrant that has not entered the circulation. 

As discussed already, radiopharmaceuticals are exposed to stability problems, particularly when radiolabeled compounds are involved. Decomposition of labeled compounds by radiolysis depends on the specific activity of the radioactive material, the energy of the emitted radiation, and the half-life of the radionuclide. Particles, such as a and p radiation, are more damaging than y rays, due to their short range and local absorption in matter. The stability of a compound is time dependent on exposure to light, change in temperature, and radiolysis. The longer a compound is exposed to these conditions, the more it will tend to break down. 

Expansion in water (%) y-ray absorption Fly ash and aggregates Fe203, UO2 0.358 Road-based applications [6] Encapsulation of radioactive materials... 

The test can be repeated, giving intrinsic factor orally together with the radioactive vitamin B12 - if the impaired absorption was because of a simple lack of intrinsic factor, and not to antiintrinsic factor antibodies in saliva or gastric juice, then a normal amount of the radioactive material should be absorbed and excreted. 

The methods range from simple, inexpensive absorption spectroscopy to sophisticated tunable-laser-excited fluorescence and ionization spectroscopies. AAS has been used routinely for uranium and thorium determinations (see for example Pollard et al., 1986). The technique is based on the measurement of absorption of light by the sample. The incident light is normally the emission spectrum of the element of interest, generated in a hollow-cathode lamp. For isotopes with a shorter half life than and Th, this requires construction of a hollow-cathode lamp with significant quantities of radioactive material. Measurement of technetium has been demonstrated in this way by Pollard et al. (1986). Lawrenz and Niemax (1989) have demonstrated that tunable lasers can be used to replace hollow-cathode lamps. This avoids the safety problems involved in the construction and use of active hollow-cathode lamps. Tunable semiconductor lasers were used as these are low-cost devices. They do not, however, provide complete coverage of the spectral range useful for AAS and the method has, so far, only been demonstrated for a few elements, none of which were radionuclides. 

The study of reaction rates presents difficulties not encountered in investigations concerned only with the original and final states of a chemical system. The progress of a reaction can be followed by (a) physical methods such as the observation of changes in electrical conductance, colour, volume, ultra-violet absorption or optical activity, or the measurement of the gas evolved, (b) chemical methods leading to the determination of reactants and products, (c) radiochemical methods in which the transfer of radioactive material is observed. 

Internal contamination Though inhalation, ingestion or transdermal absorption, radioactive material is deposited into body tissues... 

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