Isotopic source

Gammagraphic weld inspection in the lower range of steel thicknesses has been done with Iridium and Ytterbium isotope sources throughout the past. The large majority of applications has been using Iridium due to the unfavourable economical parameters of Ytterbium, obviously with non-optimal results at thin wall inspections. 

Radiation. Protection against high voltage and fixed isotope sources of radiation is usually a matter of shielding and the observance of strict... 

The isotopic purity of the product is usually about 48-62%, the rest of the material being mainly undeuterated. (An alternate preparation of a-mono-deuterio ketones of high configurational and isotopic purity is the mild oxidation of cis- or tra 5-deuterated alcohols under Jones conditions, see sections V-D and VII-A.) Treatment with zinc in acetic acid-OD has also been applied to the deiodination of 2a-iodoandrost-4-ene-3,17-dione. In a slightly modified version the iodine in 19-iodocholesterol acetate has been replaced with tritium by using tritium oxide as the isotope source/... 

Some of the intended categories of use of radioisotopic reference material have been reviewed recently by Fajgelj et al. (1999). They include assignment of property values, establishing the traceability of a measurement result, determining the uncertainty of a measurement result, calibration of an apparatus, assessment of a measurement method, use for recovery studies and use for quality control purposes. It should be noted however that, in general, natural matrix reference materials are not recommended for calibration purposes. This should preferably be done with pure chemical forms of the element labelled with the isotope of interest. Calibrated isotopic sources of this kind are available from a number of commercial suppliers and are not the subject of this review. 

The effect of ionising radiation is described in Section 4.2. Most often, accelerated tests are carried out using gamma radiation from an isotope source or an electron beam from an accelerator. Radiation from nuclear reactors can also be used but will be a mixed radiation which may or may not be suitable for the simulation. The penetration of an electron beam is inherently limited which means that only relatively thin samples can be treated. Hence, gamma irradiation is the more versatile technique. With thin samples, such that penetration limits are not a problem, there are conversion factors to approximately equate the various radiations and energies to an equivalent gamma dose. 

The uniform isotopic composition of dissolved Mo in the oceans is readily understood in terms of the 10 -10 year Mo ocean residence time. For example, given an ocean mixing time of 10 years, and assuming that the 5 Mo contrast of different Mo isotope sources is <5%o (consistent with the range of values measured to date). Mo isotope variations between ocean basins or with depth should be <5%o/(10V10 ) = 0.05%o. Such variations are smaller than present analytical uncertainties. 

It appears as if one of the level K electrons of the atom disappears into the nucleus. The void created induces X-ray fluorescence from the nucleus Y. There are several known radionucleides of this type, which have sufficiently long periods that they can be used as different energy sources (see Table I3.l). These are typically used in portable instruments. The activity of these isotopic sources is generally in the order of a few mCi and they can yield a flux of 106 to 108 photons/s/steradian. Because these sources require a permit for use as well as permanent protection because they emit continuously, their use is rapidly diminishing. 

Isocratic mode, 47 Isotope ratio, 318 Isotopic abundance, 317 Isotopic dilution, 330 Isotopic source, 241... 

An important reaction used quite widely for this purpose is irradiation by neutrons and measurement of die energies of radiations emitted. The source of the neutrons may be a nuclear reactor, a particle accelerator, or an isotopic source, that is, a sealed container in which neutrons are produced by alpha rays emitted by a source such as radium, sodium-24(24Na), yttrium-88f8sY), etc., and arranged so that the alpha rays react-with a substance such as beryllium which in turn emits neutrons. The neutrons react with stable nuclides in the sample to produce radioactive ones. Thus... 

Table II. Results of Oxygen Isotope Sourcing for Historic and Prehistoric Delta Beads Based on Modern Shell Data...

Because of the wide range of densities of interest, an additional isotope source was needed... 

Most of the work performed on fruits and vegetables has been done with penetrating irradiation, generally from isotope sources such as cobalt-60 (2,13y 14). The objective of that work was to extend shelf life by postharvest treatment without using chemicals such as biphenyl, or o-phenyl-phenol (3, 5). Unfortunately, using x-rays or 7-rays affects the pulp of... 

T n 1962 the U. S. Army opened at its Natick Laboratories in Natick, Mass., the world s largest irradiation laboratory (2) for preserving foods by ionizing energy (Figure 1). This laboratory is unique in that, in addition to having two radiation sources, a 24-m.e.v., 18-kw. electron linear accelerator and a 1,250,000-curie cobalt-60 isotope source, it includes a food development-preparation laboratory and an experimental development kitchen (Figure 2). 

It should be noted that commercial neutron generators are also easily adopted to the generation of 2.8 MeV neutrons produced by the 2H(2H,w)3He reaction. In most cases it is merely necessary to replace the tritium target with one containing occluded deuterium. The neutron yield from this reaction is much less than for the D—T reaction and the useful flux is often not much greater than could be obtained by use of isotopic sources. About 35 elements have been found to possess reasonably high (n,n y) or (n,y) cross sections for 2.8 MeV neutrons 41>. Since the 8 most common elements in the earth s crust are not among those readily activated, there is some potential application of 2.8 MeV neutrons in analyses for certain elements in minerals and ores, where major element interferences via 14 MeV activation may be a problem. 

Wasik and Tsang [28,29] have described a method for the determination of traces of arene contaminants using isotope dilution gas chromatography. They used perdeuterated benzene as the isotope source and analysed solutions containing 10-20mg L 1 of benzene and toluene. This method is most effective when the isotope can be completely separated from the parent compound and other contaminant, otherwise the isotope ratio must be determined by mass spectrometry. 

Bollhofer, A., and Rosman, K. J. R. (2000). Isotopic source signatures for atmospheric lead The Southern Hemisphere. Geochim. Cosmochim. Acta 64, 3251-3262. 

Atomic absorption offers a more practical opportunity for determining isotopic composition than atomic emission. Useful reviews of the possibilities of the technique have appeared in two books [233, 234]. Isotopic analysis is in theory possible provided that highly enriched isotope sources are available, the absorption line width available is less than the isotopic displacement and for a given isotope the nuclear spin hyperfine components must be partially resolved from the other isotopic components of the absorption line. In the simplest possible case, for an element with two isotopes, the lamp is prepared from the first isotope and only this isotope in the atom cell will absorb the radiation. The procedure can then be repeated with a lamp prepared with the second isotope. Effectively this is an extension of the impressive selectivity of atomic absorption, because of the classic lock and key effect, treating the different isotopes as different analytes. 

Experiments done with naturally occurring isotope sources,... 

In science, one builds models based on experimental data and one then attempts to verify these models. Experiments using isotope sources provided data that were explained with microscopic models. However, these models could only be indirectly tested because entities that took part in these reactions were too short-lived to be directly observed. Photochemistry had the same problems and to solve it, the techniques of sector photolysis and flash photolysis were developed. The attempts to create sector radiolysis were only marginally successful. The analog of flash photolysis, pulse radiolysis, was developed in three laboratories almost simultaneously and the first publications appeared within a month of each other. ° ... 

This is an extension of the Allen and Svarovsky [13] x-ray gravitational sedimentometer. The x-rays are generated by an isotope source and, after passing through the suspension, they are detected by a scintillation counter. The signal from the counter passes to a pre-amplifier, and thence to a ratemeter, and a trace is recorded by a pen recorder. 

Meyers P. A. (1994) Preservation of elemental and isotopic source identification of sedimentary organic matter. Chem. Geol. 114, 289-302. 

Isotopic Source Apportionment ofPAHs in St. John s Harbor Am Example... 

As isotope sources are relatively cheap, the instrumentation is readily available, and the application simple, they find wide application in practically all fields of science and industry. It is not surprising that the importance of the use of these tools, in spite of the growth of other new methods, is steadily increasing. 

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