Activation analysis irradiation procedures

Trace amounts of Tc are also determined in filter paper and vegetable samples by neutron activation analysis The procedure consists of the following major steps separation of technetium from the sample, thermal neutron irradiation of the Tc fraction to produce °°Tc, post-irradiation separation and purification of °°Tc from other activated nuclides, and counting of the 16 s Tc in a low-background P counter. The estimated detection limits for Tc in this procedure are 5 x 10 g in filter paper and 9 x 10 g in vegetable samples. 

Imagine you wish to detect ppm levels of A1 in a matrix containing iron, calcium, and silicon. Assume you have access to a modern nuclear reactor. Describe an activation analysis procedure to do this analysis. Be sure to describe the irradiation conditions, any pre- or postirradiation chemistry, and the counting strategy. Indicate how you would deal with any interferences in the analysis. 

Analysis of Particles by Neutron Activation Analysis. The analytical neutron activation procedure used for the collected particles involved two irradiations of each filter (short-and long-term) using the standard procedures. The standards for neutron activation analysis were made with aliquots of known standards (1.000 ppt Fisher Scientific Standards) in sealed tubes. These standards were always counted with the samples. The following were the standards used in this study Na and Cl Cu and Mn Al, V, and Ti K and Br Zn and Hg Co and Cr As and Ag Se, Sc, Sb, and La and Fe, Mg, and I. 

Modern bulk analysis methods make possible non-destructive chemical identification, which means that the sample remains intact after the analysis. Such a procedure is provided by electron microprobe or X-ray fluorescence analyses, in which the sample is irradiated by electron beams or X-rays and the elemental composition is determined on the basis of induced characteristic X-ray emissions. These methods have been successfully employed to study both stratospheric (Junge, 1963) and tropospheric (Gillette and Blifford, 1971) aerosol particles. Neutron activation analysis is also widely used to identify the chemical composition of atmospheric particulate matter (e.g. Duceef ai, 1966 Rahn etal., 1971) this is also a non-destructive procedure. 

After the cooling period, the sample is either counted directly or some chemical manipulation is performed before counting. The first procedure is known as instrumental neutron activation analysis (INAA), whereas the latter is referred to as radiochemical neutron activation analysis (RNAA). In RNAA a stable carrier for the element to be determined may be added to the sample after irradiation. The carrier is equilibrated with the element in the sample (often by fusing it with Na202, or treating it with strong acid). Then the element of interest is separated along with the carrier. The chemical yield of the separation is determined from the amount of carrier recovered, and this correction is applied to the measured activity. 

Glover et al. (1998, 2001) developed an ultra-sensitive method for the analysis of Th in bioassay and environmental samples and pre-concentration radiochemical neutron activation analysis (PC-RNAA) was applied. In the pre-irradiation procedure, Th was concentrated using... 

In order to resolve the present inconsistencies in serum and blood vanadium determination, Byrne and Versieck [81] reported a totally postirradiation radiochemical neutron activation analysis method. Their procedure was as follows After irradiating the sample for up to 12 min at a nuclear reactor neutron flux of 4 x 10 n/cm -sec the sample was transferred to a 100-mL, long-necked, silica Kjeldahl flask containing 3 mL 18 M H2SO4, 20 ji,g V carrier, and a weighed aliquot of... 

In particular, the neutron activation analyst, to whom efficiency curves may be an irrelevance, is not weU served by most spectrum analysis packages. As far as activation analysis is concerned, there is much evidence to show that absolute analysis, calculating concentrations from first principles, is much less accurate than comparative analysis. Apart from aU of the problems which derive from having to use efficiency calibration curves, there are specific problems associated with defining and measuring neutron fluxes and cross-sections which make absolute analysis not worthwhile, in my opinion (although there are those who have devoted a considerable amount of effort into developing absolute neutron activation analysis procedures who would dispute that). For that reason, almost every activation analysis involves irradiation of samples and standards. A direct comparison between them is the simplest solution. 

Neutron activation analysis is a useful technique for measurement of rare earths particularly at low concentration. All rare earths except Dy and Er activate to nuclides with sufficiently long half-lives that a nuclear reactor on site is not required. In many samples, the rare earths can be determined by INAA which lends itself well to automated procedures and has the additional advantages that many elements can be determined simultaneously and that it is non-destructive. It is inherently free from blanks (assuming pre-irradiation concentration is not required) and is usually free of interferences or matrix effects. The disadvantages are that one may have to work with high levels of radioactivity if maximum sensitivity is required and analyses based on long-lived elements may require several weeks before results are available. 

Routine irradiation approvals Routine operations, such as isotope production or irradiation of samples for activation analysis, should have a practical procedure for control such as a simple irradiation form containing only the most important information. They should be approved within the reactor facility. Non-routine irradiations should be treated as a new experiment (see para. 5.54). 

The software is the heart of the pneumatic transfer system (PTS) for neutron activation analysis. The system not only controls the irradiation procedure but also manages the... 

These techniques are designed to minimize both the actual working time, required and the analytical uncertainties in sample analysis. Sample preparation and neutron activation procedures are based on proved analytical and microanalytical techniques. The unusually high sensitivity, reliability, and accuracy are achieved through a choice of optimum irradiation and counting times for the y-ray detection systems. 

The low concentration level of I in brain samples requires sensitive analytical methods. At the Jozef Stefan Institute, Ljubljana, several techniques have been developed for the determination of in different biospheric samples using a short irradiation to induce 1 (Dermelj et al, 1990). One RNAA method was applied for human brain analysis in NAAL-Berhn (BER II Reactor). The method consists of burning the activated samples in an oxygen atmos-ph ere and separating I using oxidation—reduction and extraction cycles, while chemical yield was determined by spectrophotometry for each sample, using recovery of the elemental iodine carrier. Details of the procedure have been pubhshed 2004 (Andrasi et al., 2004). 

---