Szilard-Chalmers

The study of Szilard-Chalmers reactions places considerable demands on the separation methods used. These molecular compounds are only weakly polar, if at all, and thus are not easily separable. Moreover, many of the compounds and especially the radicals and other intermediates formed are not very stable, often requiring the absence of air, moisture, and even light. Combining this with the fact that many of the product species are present in extremely small amounts, we have a nearly impossible situation. Nonetheless a good deal of reliable work has been done. 

In order to investigate chemical reaction mechanisms, it is useful to know the point at which the reaction starts. Regrettably, this is only rarely possible in Szilard-Chalmers studies, and is the object of one of the two most vigorous arguments in the field whether the bonds are all broken and there is a successive rebuilding of the molecules, or these is only a partial breakage of bonds, and little rebuilding is necessary. To illustrate with < 3 As, two possible sources of radioactive parent molecules are... 

Harbottle, G., Sutin, N. The Szilard-Chalmers Reaction in Solids. Advan. Inorg. Chem. Radiochem. /, 267—314 (1959). 

The earliest studies in this field were conducted largely to benefit from the Szilard-Chalmers effect—namely, the separation of radioactive atoms from the bulk material—in order either to make nuclear chemical study of radioactive nuclides or to effect an enrichment of radioisotopes. In Table II are listed some selected works of this type. 

Early Studies of Isotope Enrichment by the Szilard-Chalmers Effect... 

A sample of iodine-128 was produced in a Szilard-Chalmers reaction by irradiating a sample of ethyl iodide in a neutron source. The radio-iodine was extracted with sodium thiosulfate solution and then counted in a Geiger counter at various time Intervals. Use the tabulated data of t in minutes against C counts/min to find the rate equation and the half time. 

The main chemical methods of separation are 1. Solvent extraction 2. Ion exchange and chromatography 3. Distillation 4. Co-precipitation and adsorption. To these four should be added the less general methods such as leaching, crystallisation, the Szilard Chalmers and mass-spectro-tnetric methods. 

Intensity Slow Neutron Sources. I. The Szilard-Chalmers Enrichment of 35-9h. 82Br. J. Amer. chem. Soc. 74, 237 (1952). 

Williams, R. R. The Szilard-Chalmers Reaction in the Chain Reacting Pile. 

The Szilard-Chalmers Reaction in Solids Oarman Harbottle and Norman Sutin... 

Ela,stic-coIlision model, Szilard-Chalmers reaction and, 1 268-269... 

Elastic-inelastic collision model, Szilard-Chalmers reaction and, 1 269 Electrical conduction, in organic superconductors, 29 278-286 Electrical conductivity of chalcogenide halide compounds, 23 331 of Group IB, 23 337-339, 342, 346-349 photoelectric effects, 23 368, 410 semiconductors, 23 368, 390, 395-396, 400-402, 410-412 superconductors, 23 375-377 of graphite intercalation compounds, 23 290, 294, 309-310, 312, 317-318 Electric discharges arc type, 6 146-147 chemical reactions in, 6 189-191 chemical reactions in, 6 143-206... 

Szilard-Chalmers reaction, recrystallization and, 1 290-292 HoxN protein, 47 287 HoxW protein, 47 288 —HoxX protein, 47 290 hoxY gene product, 38 409-410 HjPOj-, 33 106... 

Ramsey theory, 22 201-204 Random-fragmentation model, Szilard-Chalmers reaction and, 1 270 Random-walk process, correlated pair recombination, post-recoil annealing effects and, 1 288-290 Rare-earth carbides, neutron diffraction studies on, 8 234-236 Rare-earth ions energy transfer, 35 383 hydration shell, 34 212-213 Rare gases... 

For several decades there has been research directed toward the attainment of enrichment, or separation of the product isotope of a nuclear reaction, as a direct result of the nuclear reaction itself. In principle this problem was solved in 1934 by the Szilard-Chalmers reaction. In this instance advantage is taken of the reaction product s recoil energy, which is sufficient to break a chemical bond. Thus, the product atom may be converted to a chemical state unlike that of the original, unreacted target atoms, and hence be chemically separated. 

In practice, the Szilard-Chalmers reaction has not been very successful for production of substantial quantities of any isotope although it often works well for tracer or low irradiation levels. When greater levels of neutron irradiation became feasible with development of nuclear reactors, it was found that both enrichment factors and product yields decreased as neutron exposures increased to the values required for significant isotope production. 

In the work reported here, which was directed toward the attainment of an isotopic enrichment of the trivalent actinide and lanthanide elements, the problem was compounded by the fact that these elements do not readily form appropriate compounds, like iodine in ethyl iodide. They do form some stable organic chelates, and, indeed, it is possible to obtain a Szilard-Chalmers reaction with such compounds. However, their radiation damage resistance does not appear adequate to permit useful production of an isotope like 247Cm, which requires a thermal neutron exposure ap-... 

Inorganic compounds may be more stable to radiation damage than organic compounds, and their decomposition products are less deleterious. Accordingly, a search was made for inorganic compounds which would contain these trivalent ions in a nonexchangeable state and, at the same time, allow recoil atoms ejected from their position in the structure to be separated. Szilard-Chalmers reactions have been reported for certain inorganic systems, for example clays ( ), but yields and enrichment factors were both low. 

In the classical Szilard-Chalmers reaction a specific bond or group of bonds is broken by the recoil energy. This reaction is analogous, but it is not clear whether such specific bonds are broken, or if physical factors related to pore trapping are involved. The mechanism of the interaction between the trivalent metals and zeolites is not completely understood. 

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