Radioactive counting techniques

An alternative method i to incorporate a fluorescent indicator into the thin layer when non-fluorescing materials show as dark spots on a fluorescent background. Radioactive counting techniques can be used for the detection oflabelled compounds. 

Following the pioneer work of Aston and Dempster, there were rather limited advances made in the field of isotopic abundance measurements until 1935 when A. 0. Nier (85) introduced a number of improvements to mass spectrometer design. Since then, many more refinements have been made, particularly with regard to more efficient ion sources and to more sensitive ion detectors, so much so, that the mass spectrometer has become an extremely sensitive instrument for the detection of practically all of the elements, and its sensitivity remains second only to that of radioactive counting techniques. 

In addition to the 4 stable isotopes sulfur has at least 9 radioactive isotopes, the one with the longest half-life being which decays by activity (Kmax 0.167 MeV, 87.5 d). can be prepared by Cl(n,p), S(n,> ) or S(d,p) and is commercially available as SeicmcQt H2S, SOCb and KSCN. The radiation has a similar energy to that of C ( mav 0.155 MeV) and similar counting techniques can be used (p. 276). The maximum range is 300 min in air and 0.28 mm in water, and effective shielding is provided by a perspex screen 3-10 mm thick. The preparation of many - S-containii compounds has been... 

In the carbon-14 expts, HMX/RDX product was isolated qualitatively, separated Into its components, and each component assayed for carbon-14 beta radioactivity using a liquid scintillation counting technique (Ref 11). DPT-l4C was isolated as an intermediate product from the reaction mixt and similarly radioassayed. For the nitrogen-15 tagged AN expts, HMX and RDX were assayed mass spectrometrically for i5N/i4N ratios from which atom %1SN contents were calcd. In die course of these expts, each tagged species was added initially and also at subsequent stages of the reaction process. The important observations and results are summarized as ... 

Soon after this discovery the harnessing of the technique to the measurement of all the U isotopes and all the Th isotopes with great precision immediately opened up the entire field of uranium and thorium decay chain studies. This area of study was formerly the poaching ground for radioactive measurements alone but now became part of the wonderful world of mass spectrometric measurements. (The same transformation took place for radiocarbon from the various radioactive counting schemes to accelerator mass spectrometry.)... 

One common characteristic of many advanced scientific techniques, as indicated in Table 2, is that they are applied at the measurement frontier, where the net signal (S) is comparable to the residual background or blank (B) effect. The problem is compounded because (a) one or a few measurements are generally relied upon to estimate the blank—especially when samples are costly or difficult to obtain, and (b) the uncertainty associated with the observed blank is assumed normal and random and calculated either from counting statistics or replication with just a few degrees of freedom. (The disastrous consequences which may follow such naive faith in the stability of the blank are nowhere better illustrated than in trace chemical analysis, where S B is often the rule [10].) For radioactivity (or mass spectrometric) counting techniques it can be shown that the smallest detectable non-Poisson random error component is approximately 6, where ... 

The counting techniques described in this paper are also readily applicable to studies of "hot radioactive waste (z.e.j radioactive waste from reprocessed nuclear fuel). With this type of material, the cesium can be analyzed as 30-y (662-keV y), the RE as 13-y Eu (964-keV and 1408-keV y), strontium as 28-y Sr (after chemical separation and beta counting), and the actinides by group separation and alpha counting. 

The chemical yields were determined by gamma-counting techniques. The sample contained a number of radioactive isotopes of gadolinium prior to isotope separation. 

The use of such techniques for radiochemical work has been discussed In detail (203,250,251). In these studies a platinum electrode of large surface area (52 mesh, 30 mm high, 10 mm i.d.) coated with silver chloride is placed in contact with 10 ml of solution containing a very low concentration of radioactive silver. The solution Is stirred magnetically. The electrode is then removed from the solution, washed with nitric acid, rinsed with acetone, and the radioactivity counted. 

Let us briefly discuss again the limitations of radioactive decay measurement. The observation of the radioactive decay of a single atom is possible, consequently, with efficient apparatus for the detection of the decay particles and a radioactive species with a half-life of seconds and minutes, it is possible to detect all or nearly all of a small number of radioactive atoms in the presence of a large number of nonradioactive atoms with radiation detection techniques. However, as the half-life increases, the time taken to carry out an experiment with a small number of radioactive atoms naturally increase, for half-lives, of say, 10 years efficient detection of the radioactive decay products becomes impossible unless the measurement can be continued for 10 years. Therefore, studies of long-lived radioactive isotopes invariably use very large numbers of atoms and the apparatus detects the decay of only a small fraction of the total during the experiment. In this situation the mass spectrometric detection sensitivity surpasses by far the sensitivity of radioactive counting methods. 

Emanation thermal analysis is usually carried out in conjunction with other TA techniques, most notably DTA and EGA. In this context, ETA can be considered as a coupled TA technique. Carrier gas at a constant flow rate is used to carry the released gas from the sample to appropriate detectors—usually radioactive counting devices. In the case of desorbed radon, a scintillation counter is used, whereas Geiger counters are used for krypton, xenon, and argon. 

T3. Taplin, G. V., Meredith, O. M., and Kade, H., The radioactive ( I-tagged) rose bengal uptake excretion test for liver function, using external gamma ray scintillation counting techniques. J. Lab. Clin. Med. 46, 656-678 (1955). 

Radioactive Strontium. Exposures to radioactive strontium can be determined readily by measuring levels of radioactivity in blood or urine by liquid scintillation counting techniques. In addition, whole body counters can determine the level of radiostrontium retained in the skeleton. There appears to be no need for additional biomarkers of exposure to radioactive strontium. 

The quantity of radioactive strontium is typically determined by gas-flow proportional, liquid scintillation, and Cerenkov counting techniques (Scarpitta et al. 1999). The standard EPA analytical... 

Radiochemical Standards. The most widely used method for obtaining standards for calibrating IR analysis consists of copolymerizing 14C-labelled monomers (generally ethylene1) so that the copolymer composition is determined by radioactive counting, by either a solution or a microcombustion technique (20,26, 29, 57, 59, 73). 

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