Alpha particle quantitative

SIMS analysis of electrodeposited Th alpha-particle sources gives rise to higher signals for the ThO and ThO/ than for Th. This leads to difficulties in quantitation as the oxide to atomic ion ratios will be sensitive to local oxygen concentrations. Isobaric... 

Much of the work reported here considers the bare nuclei C6+, N7+, Os+, F9+, and Ne10+ as the incident radiations. However, the results so obtained can be applied to protons, deuterons, and alpha-particles on one hand and fission fragments on the other without serious difficulty— i.e., with only some quantitative differences. 

The yield for a low-mass sample, e.g., 1 mg or less for alpha-particle measurement, can be determined with nonisotopic carrier in an aliquot taken before preparing the counting source. The analytical technique can be instrumental, such as colorimetry or atomic absorption spectrometry. Subsequent source preparation, by precipitation, evaporation, or electrodeposition, must be quantitative or highly reproducible so that a reliable yield value for this final step can be included in the total yield. 

General environmental survey instruments (e.g., alpha particle meters) are available, but they are not specific for plutonium. The predominant analytical method for measuring plutonium present at or near background concentrations in both biological and environmental media requires radiochemical separation and purification in conjunction with a quantitative measurement technique (e.g., alpha spectrometry, liquid scintillation, or mass spectrometry). 

Moore and Arnold (1996) married the delayed coincidence system of Giffin et at. (1963) with a gas flow system described by Rama et al. (1987) for the measurement of Ra and Ra in seawater. In this procedure Ra is quantitatively extracted from a known volume of seawater onto a column of Mn-fibre. The meeisurement is based on the observation that Rn produced by Ra decay is quantitatively ejected from the Mn-fibre (Butts et al., 1988 Rama et al., 1987). The partially dried Mn-fibre is placed in an air circulation system and helium is circulated over the Mn-fibre and through a scintillation cell where alpha particles from the decay of Rn and daughters are recorded. Fig. 13-6 is a schematic diagramme of the gas flow system. 

RBS can provide absolute quantitative analysis of elemental composition with an accuracy of about 5%. It can provide depth-profile information from surface layers and thin films to a thickness of about 1 pm. In some cases, however, the high-energy beam can damage the surface. This is particularly a problem with insulating materials, such as polymers, alkali halides, and oxides. The Mars Pathfinder mission in 1997 contained an alpha proton X-ray spectrometer (APXS). In its RBS mode, the spectrometer bombarded samples with alpha particles and determined elemental composition via energy analysis of the backscattered particles. In addition to RBS, the APXS instrument was designed to carry out proton emission and particle-induced X-ray emission (PIXE) experiments. Soil and rock compositions were measured and compared to those from the earlier Viking mission. 

Nondenaturing two-dimensional electrophoresis and subsequent anti-apoA-I im-munoblotting of normal plasma helps to discriminate a bulk of HDL, which has electrophoretic alpha mobility (a-HDL), from a quantitatively minor proportion, which has electrophoretic pre-jS-mobility (pre/fi-HDL). In plasma from Tangier patients the latter particle is the only apoA-I containing lipoprotein [4, 26]. 

On the other hand, the low concentration of a radionuclide provides opportunities for use as tracer in chemical and physical studies. In radioanalytical chemistry, one benefit is that the addition of a stable-element carrier permits analysis without the requirement of quantitative analyte recovery. Another benefit is the opportunity to deposit very thin sources that minimize self-absorption in a source of alpha-and beta-particle radiation. 

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