Radiochemical techniques using radiation detection

The first paper on X-ray emission spectroscopy with quantitative analysis in the title was Heading s paper of 1922. In 1923, Coster and Hevesy discovered the element hafnium by this technique. However, owing to the experimental difficulties it was not widely used until improvements in radiation detection from radiochemical studies became available. With the development of scintillation covmters it became a relatively simple and effective analytical technique, now known as X-ray fluorescence spec-trometric analysis. 

Chemistry used in the recovery of plutonium from irradiated fuel must provide a separation from all these elements, other fission and activation products, and the actinides (including a large amount of unburned uranium), and still provide a complete recovery of plutonium. The same issues apply to the recovery of uranium from spent thorium fuel. Most of the processes must be performed remotely due to the intense radiation field associated with the spent fuel. As in the enrichment of uranium, the batch size in the later steps of the reprocessing procedure, where the fissile product has become more concentrated, is limited by the constraints of criticality safety. There is a balance between maximizing the yield of the precious fissile product and minimizing the concentrations of contaminant species left in the final product These residual contaminants, which can be detected at very small concentrations using standard radiochemical techniques, provide a fingerprint of the industrial process used to recover the material. 

The luminescence produced when radiation strikes a phosphor is one of the oldest methods of detecting radioactivity and X-rays, and it is still used widely for certain types of measurements. In its earliest application, the technique involved the manual counting of flashes that resulted when individual photons or radiochemical particles struck a zinc sulfide screen. The tedium of counting individual flashes by eye led Geiger to develop gas-filled transducers, which were not only more convenient and reliable but more responsive to radiation. The advent of the photomultiplier tube (Section 7E-2) and better phosphors, however, has given new life to the technique, and scintillation counting has again become one of the important methods for radiation detection. 

What are the advantages of the radiochemical method compared with other in situ techniques It offers a direct relationship between surface radiation (N ) and surface concentration, which allows a direct measurement of the amount of adsorbed molecules on the electrode, a condition difficult to determine with other in situ techniques. The main limitation of the technique is the availability of radioactive forms of the compound the experimenter wants to study. In this respect, the type of radiation preferred is of the P-type, mainly because of the ease of detection and minimal safety hazards. Typical P-emitters used are H, C, S, Cl, and P, which as constituents of molecules, open a great variability of compounds for study. Figure 6.21 shows some experimental results obtained for the measurement of adsorption on single crystals using this radiochemical method. 

The experimental technique devised in this work is based on a NAA method. Neutron irradiation of solid waste forms of simulated HLW (see Table II) produces activation of the elements in the sample. The activation products can be readily measured before and after leaching by radiochemical and/or instrumental techniques. In order to be useful for these purposes, the activation product must have a sufficiently energetic and abundant radiation (either 6 or y) to be easily detected, as well as a sufficiently long half-life several days or more) to be useful for relatively... 

Among the advantages of using radiotracers we can list the following (a) radiotracers are easy to detect and measure with high precision to sensitivities of to 10" g (b) the radioactivity is independent of pressure, temperature, chemical and physical state (c) radiotracers do not affect the system and can be used in nondestructive techniques (d) if the tracer is radiochemically pure, interference from other elements is of no concern (common in ordinary chemical analyses) (e) for most radioisotopes the radiation can be measured independently of the matrix, eliminating the need for calibration curves. 

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