Contamination radionuclides

Hutchins DA, Teyssie J-L, Boisson F, et al. 1996b. Temperature effects on uptake and retention of contaminant radionuclides and trace metals by the brittle star Ophiothrix fragilis. Mar Environ Res 41(4) 363-378. 

Lengemann, F. W., Wentworth, R. A. and Comar, C. L. 1974. Physiological and biochemical aspects of the accumulation of contaminant radionuclides in milk. In Lactation A Comprehensive Treatise, Vol 3. B. L. Larson and V. R. Smith (Editors). Academic Press, New York. 

Radiochemical Purity. A sample is radiochemically pure at the time of counting if no other radionuclide is detected in it. As a general rule, the radiochemical procedure is chosen to separate from the radioanalyte all other radionuclides that are in the sample. Purification steps must be added to the usual procedure if the level of contaminant radionuclides is very high relative to the concentration of the radioanalyte. 

Re-analysis with better purification should be considered if the count rate is unexpectedly high or the observed half life and radiation energies are not those of the radioanalyte. Contaminant radionuclides may be tolerated if they do not interfere with counting the radioanalyte, or can be subtracted from the count rate with only a minor increase in detection uncertainty. In spectral analysis of alpha particles and gamma rays, for example, contaminant radionuclides are tolerated in the sample if they do not interfere with counting the characteristic spectral peaks of the analyte. 

Chemical separation of a radionuclide from other radionuclides is intended to recover most of the radionuclide while removing most of the accompanying contaminants. Purification specifications usually can be relaxed by selecting a radiation detector that measures the radionuclide of interest without detecting some of the contaminant radionuclides, either by discrimination against certain types of radiations or by spectral energy analysis. 

The separation method generally is selected from available methods that are described as purifying the radionuclide of interest from the identified contaminant radionuclides. Scavenging steps can be inserted that separate the major contaminant radionuclides from the radionuclide of interest. The selected method must be tested to determine all DF values for the contaminant radionuclides or at least to demonstrate for the sample under consideration that none interfere with the radiation measurement. A separation step will have to be repeated or additional separation steps will have to be added when a single step does not achieve the required DF. 

Chemical separation and radiation detection can work together in discriminating against interfering radiation. Chemical separation may not be necessary if the radiation from contaminant radionuclides is not detected by the selected detection instrument or does not interfere with the measurement, e.g., by spectral analysis. 

The sample—typically about 20 ml water—is distilled for purification. Reagents and holdback carriers may be added to the distilling flask to prevent volatile forms of contaminant radionuclides from being distilled. Initial distillation may be... 

Sources conventionally are prepared by precipitation to permit gravimetric measurement of stable isotopic carrier yield, as discussed in Section 6.3. The isotopic carrier must be in the same chemical state as the radionuclide of interest, or the sample must be processed to achieve this requirement when carrier is added. The precipitating agent is selected to obtain a pure precipitate of the radioelement with a large, but not necessarily quantitative, yield and reproducible weight. If this precipitate does not completely purify the sample, as is often the case, then previous separation steps should have done so. The various purification steps must eliminate extraneous solids that will add to the carrier yield and contaminant radionuclides that will add to the count rate. The purification steps must reduce such contaminants to a small fraction of the amount to be weighed and counted. Occurrence in nature of significant amounts of the isotopic carrier in the sample must be determined in control samples to correct the yield value. 

The spectrometer permits confirmation of the observed radionuclide by its spectrum, within the limitations of spectral distortion by energy losses and the radiation background associated with the measurement. It also permits setting the lower and upper energy discriminators for optimum values for each radionuclide of interest. The energy ranges beyond the region of interest usually are measured at the same time to confirm the absence of contaminant radionuclides. Two or three radionuclides may be detected simultaneously by such discriminator control... 

A purification procedure can be considered appropriate if separation from other radionuclides is so effective that, in the absence of the radioelement of interest, no radioactivity is detected in the purified sample. That is, the measured radioactivity is zero within the measurement uncertainty. If the radioelement of interest is present, then contaminants should not observably increase its measured activity. To plan the procedure, the amount of each contaminant radionuclide that remains after applying the separation methods is calculated in terms of its decontamination factor (DF) (see Section 3.1). Meeting the stated criteria depends on the initial concentrations of the radioelement of interest and of each contaminant radionuclide in the sample, and on the achieved DF. Because these values generally are not known initially, reasonable concentrations must be assumed and subsequently revised when initial measurement results become available. 

The traditional way to express mobility, e.g. in contaminant/radionuclide transport models, is by means of the solid/liquid distribution coefficient or Kd (L/kg) ... 

Environmental Problems—This section describes N Reactor operational activities that affected the environment. The affected environs are groundwater contamination (radionuclides, volatile organics, polychlorinated biphenyls (PCB), metals, and other Inorganics) soil contamination (surface and vadose zone contamination from radionuclides and organic compounds) biota contamination (flora [vegetation] and fauna [animals] from radionuclide uptake by plants or Ingestion by animals) and evaluated radiation at the Columbia River (unshielded sediments In the 1301-N Liquid Waste Disposal Facility). 

Monitoring of solid waste. Stored solid waste should be checked for external radiation and for possible surface contamination. In the event of the detection of external contamination, appropriate identification of the contaminating radionuclides should be performed. An appropriate record keeping system should be established and maintained to provide accountability for and traceability of solid waste. 

Levels of gamma radiation in most of the Arctic do not exceed natural background and are 2-3 microrem/hour. Average density of surface contamination is less than half in middle latitudes [Arctic, p. 25]. Nevertheless there are places of local contamination. Radionuclides are collected in moss and lichen and throng the food-chain moss-reindeer-human get into human organisms. Accumulation of Sr in bones of reindeer farmers in some cases is 60 times higher than that in bones of residents of middle latitudes [Arctic, p. 62]. 

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