Radioactive decay correction

When a given nucKde is used to trace the yield of its element in a chemical reaction, the fundamental assumption is that the chemical state of all isotopes of the same element is identical this is ensured through mixing and performing isotopic-exchange reactions. In tracer chemistry, it is important that there be no isotopic fractionation. If a signiftcant period of time has elapsed between the characterization of the concentration of the tracer nuclide and the measurement of its concentration in the final sample, then an appropriate radioactive decay correction must be appKed. 

The C content of a sample is described in a similar manner. The basis for Rq is an oxalic acid standard of the US National Bureau of Standards normalized for C fractionation and corrected for radioactive decay since a reference date January 1, 1950 (Stuiver and Polach, 1977). The absolute value of Rq is 1.176-10 (Stuiver et al, 1981). 

Analyses of this type are correct only if all of the product nuclide comes from radioactive decay. This is not known with certainty, but when age estimates using different pairs of nuclides give the same age and samples from different locations also agree, the age estimate is likely to be accurate. Note also that 3.8 X 10 years agrees with the qualitative limits derived from naturally occurring radioactive nuclides. 

Measured concentrations of Th and Pa in marine sediments consist of three components that scavenged from seawater that supported by U contained within lithogenic minerals and that produced by radioactive decay of authigenic U. Most of the proxies described in this paper make use of only the scavenged component. Measured °Th and Pa must therefore first be corrected for the presence of the other two... 

If we choose a much larger than 1 (thin samples d<0.5L) or h pL (thick samples d>>L), the final steady-state exhalation deviates very little from the free exhalation rate and we do not need to know the reshaping time or use Equation 2 for corrections. An air grab sample taken at any time (and corrected for radioactive decay if necessary) after closure, will yield the free exhalation rate to a good approximation, provided that the can is perfectly radon-tight. 

Pulmonary retention functions are given as fractions of the initial pulmonary burden and are not corrected for radioactive decay of lMCe Ti/> = 285 d). 

Since radiopharmaceuticals are prepared in advance prior to the actual administration, calculations must take into account corrections for loss of radioactivity by radioactive decay. Using the expression, A, = A0 x e KI, one can calculate the radioactivity of an isotope remaining at any time t after the initial assay. This is explained in the following examples. 

Mass-spectroscopic technique has also been used with non-fissile targets after pile or cyclotron bombardment to determine the mass-numbers of radioactive nuclides. In one case, the branching ratios of certain isotopes for and electron capture decay (where different elements are produced by the two routes) were determined from the amount of the stable end-products of radioactive decay, using the mass-spectrometer to identify the isotopes concerned and to correct for any stable impurities of the elements concerned (98). For some purposes, mass-spectroscopic separations could be very valuable technically such as the... 

A/-[3-(2-[ F]fluoropyridin-3-yloxy)-propyl]-2-bromoacetamide (p F]FPyBrA) was recently prepared by nucleophilic / eferoaromatic radiofluorination using a three-step radiochemical pathway and obtained in 20% overall non-decay-corrected yield in less than 85 min. In this reagent, the pyridinyl moiety carries the radioactive fluorine and the 2-bromoacetamide function ensures the alkylation of phosphorothioate monoester groups at the 3 - or 5 -end of a single-stranded oligonucleotide [18],... 

Note that the reaction rate coefficients are not divided by R, because radioactive decay will occur whether or not the elements are adsorbed to the sediments. With the exception of the source/sink terms, these equations look like that provided in Example 2.2. The solution will be simply given here with the reader required to apply a technique similar to Example 2.2 that shows that the solution is correct. 

Table 2.8. Relative activities in air filters (corrected for radioactive decay to 26.4.86)... 

Figure 3.2 shows results of the experiment in which the initial concentration of stable I2 was 0.013 /ug m-3. The scrubber was not in operation. All results are corrected for radioactive decay of 132I. The airborne concentration rose initially as the source was mixed in the air within the containment shell. The activity on the charcoal-loaded papers was due mainly to inorganic iodine, and this declined with a half-life of about 30 min, as 132I was adsorbed on surfaces. Plaques of various materials were exposed periodically to monitor the deposition. In other experiments with more iodine carrier, loss by deposition was more rapid. 

Begemann Libby (1957) estimated that 1.1 kg of T was released to atmosphere for each megatonne (MT) thermonuclear explosion. The tests between 1954 and 1963 had a fusion yield of 320 MT. Allowing for radioactive decay, the global inventory in 1963, including tritium in the atmosphere, groundwater and oceans, was about 330 kg. French and Chinese thermonuclear tests between 1968 and 1977 may have added another 20-30 kg. In 1972, by which time most of the pre-1963 tritium had returned to the earth s surface, a world-wide survey of oceanic waters gave a total of 164 kg (Ostlund Fine, 1979). Corrected for radioactive decay, this is equivalent to an inventory of 270 kg in 1963. 

Beta decay is a general term applied to radioactive decay processes that result in the mass number A remaining constant while the atomic number Z changes. There are three types of beta decay beta-minus (/3 ) decay, positron (/3+) decay, and electron capture decay. It should be mentioned that (3 decay is often referred to as just beta decay, which is not strictly correct, because it is only one type of beta decay. 

In this experiment, the Ge detector with spectrometer is calibrated for its efficiency, s, with a standard that emits a set of gamma rays at energies that span the range of interest, usually from a few keV to 1.5 MeV. The counting efficiency is calculated from the ratio of the net count rate to the reported disintegration rate at each full-energy peak in the spectrum. A correction for radioactive decay is needed. 

Correct the beta-particle count rate for radioactive decay by dividing by e-o.693t/to.5wjiere t js tjie tjme 0f decay between separation and counting for 234Th and t0 5 is the half life of 234Th. 

In the ceruloplasmin experiments appropriate aliquots of specimens were placed in small test tubes and assayed for Cu64 activity in a well-type scintillation counter. Analyses were made with reference to a Cu64 standard prepared and assayed at the outset and whenever other samples were assayed. This permitted correction for radioactivity decay of this 12.8-hour half-life isotope. 

H, C, P, and l. The word isotope comes from Greek, meaning at the same place , a useful way to remember that all isotopes of an element are in the same place in the Periodic Table of elements. While not quite correct, often the words isotope and nuclide are used interchangeably. Thus, radioisotopes may be termed radionuclides. The later refers to an atom with an unstable nucleus that undergoes radioactive decay, and these may be naturally occurring or artificially produced. 

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