Specific activity of radionuclide

In this expression A(i) is the specific activity of radionuclide i, A(i) (r = 1) is the specific activity of nuclide i at r = 1, r is the radius of a debris particle, and mis a number between 0 and 1. A value of m = 0 implies that the activity is proportional to the volume of the particles. Such a volume dependence results for nuclides which combine with the matrix material in the cooling fireball and applies to the so-called refractory chains, such as the 95-, 11-, and 147-chains. A value of m = 1 or a surface-... 

The specific activities of radionuclides in debris from ground surface bursts are generally complicated functions of the particle size, in accordance with the composite nature of the debris. 

The specific activities of radionuclides in samples from surface burst debris are not necessarily unique functions of the particle size. The uniqueness is determined by the degree of mixing in the cloud, and is, therefore, expected to be a function of the time elapsed between the shot time and the sampling time. 

TABLE 3. Specific activity of radionuclides in bottom sediments and algae at Atomflof enterprise water area, 1998 (Bq/kg, dry weight)... 

In the absence of stable isotopes, the specific activity of radionuclides is given by... 

The introduction of NIREX GQs for packaging and disposal of ILW has resulted in the need to analyse or calculate the specific activities of radionuclides that had not been important historically. This paper identifies those nuclides that are likely to exceed the GQ in a range of Magnox waste streams and considers whether adequate procedures exist for all. For those... 

Assinder et al. (1985) reported that the behaviour of radionuclides in the Esk Estuary was determined by its physical characteristics and by its location close to the Sellafield discharge point. Relatively high specific activities of radionuclides in the dissolved phases of waters were encountered. They found that sediment reworked from earlier deposits within the estuary formed a major part of the sediment load of the tidal waters and therefore provided a significant part of the total activity of the particulate phase. The temporal and spatial variation of the total water activity for radionuclides such as Pu follows the pattern for suspended sediment concentration whereas, for conservative radionuclides (e.g. Cs), the... 

C8d = specific activity of radionuclide per gram at depth d in core C80 = specific activity of radionuclide at surface p = penetration coefficient... 

TABLE 1. Specific activity of radionuclides in Stereocaulon vesuvianum from slopes of Mt. Vesuvius (Bq kg 1 dry weight). 

Table II. 1 Half-life and specific activity of radionuclides. 259...

HALF-LIFE AND SPECIFIC ACTIVITY OF RADIONUCLIDES, DOSE AND DOSE RATE COEFFICIENTS OF RADIONUCLIDES AND SPECIFIC ACTIVITY... 

The specific activities of radionuclides contained in sediments collected in uncontaminated areas are listed in O Table 55.2. 

Carrier-free radiochemical is a radionuclide that is not contaminated with a stable or radioactive nuclide of the same element. The no carrier added (NCA) designation applies to most of the elements to which the term carrier free is indicated. The specific activity of a carrier-free radioisotope can be calculated by the following formula ... 

Table 1. Radionuclide specifications. (Amount of radionuclide is calculated on activity 10 times higher than average natural background which is 0.02 Bq/g DW) (DOEEM, 1998).

The distribution of the product radionuclides was studied as a function of irradiation periods of from 2-14 days (Table I). These data show that irradiation periods of greater than three or four days do not result in large increases in Os-191 yield but do lead to rapid increases in the Os-193, Ir-192, and Ir-194 impurities. As a result, a three day irradiation period has been chosen as a compromise between Os-191 yield and increasing levels of isotopic impurities. The rapid approach of Os-191 yield to a maximum value during a 14-day irradiation period suggests a maximum attainable specific activity of approximately 600 mCi/mg of enriched 0s-190 target. 

A knowledge of the size distribution function of the radioactive debris and the specific activity of individual fission product chains as a function of particle size suffice to define many important radiological properties of the land-surface nuclear explosion. If is the function of a radionuclide or fission mass chain distributed between particle sizes Di and D2, then... 

Radionuclides occur in the environment in such minute physical quantities that they are commonly referred to as being present at sub- or ultra-trace quantities. As an illustration of this Livens and Rimmer (1988) presented values relating the masses and specific activities of several artificial radionuclides and their typical concentrations in surface soils of the UK (see Table 7-1). This indicates the very small mass usually associated with one Becquerel of radioactivity, although as the half life of a radionuclide increases so does the mass per unit of radioactivity. The molarity concept is... 

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. 

As an example, data on specific activities of man-caused radionuclides in bottom sediments and algae taken at Atomflot water area in 1998 are demonstrated in Table 3. 

As follows from Table 3 data, specific activities of man-caused radionuclides vary within 1-2 orders of magnitude evidencing considerable heterogeneity of contamination levels in bottom sediments and algae. Table 3 also comprises specific activity data for " °K - natural-origin isotope. Comparisons show that in 1998 specific activity of man-caused radionuclides was by 1-2 orders of magnitude less as compared to that of " °K. 

Szilard-Chalmers reactions are characterized by the enrichment factor (i.e. the ratio of the specific activity of the radionuclide considered after separation to the average specific activity before separation), and by the yield (i.e. the ratio of the activity of the radionuclide obtained after separation to its total activity). Enrichment factors of up to about 1000 or more may be obtained, and yields of about 50 to 100% are of practical interest. 

From the previous sections it is evident that radionuclides of high specific activity often represent very small amounts (microamounts, non-weighable amounts < 1 pg) of matter, especially if the half-lives are short. Handling of such microamounts requires special precautions, because in the absence of measurable amounts of carriers the radionuclides are microcomponents and their chemical behaviom may be quite different from that observed for macrocomponents. This aspect is of special importance if the system contains liquid/solid, gas/solid or liquid/liquid interfaces. The percentage of radionuclides sorbed on the walls of a container depends on the chemical form (species) of the radionuclide, its concentration and specific activity, and on the properties of the container material. At high specific activity of a radionuclide in solution, the surface of a glass beaker generally offers an excess of surface sorption sites. 

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