Reaction radiochemical study

Finally the ESR spectrum of Nb(7r-allyl)4/alumina was unaffected by the addition of ethylene gas to the ESR sample tube. It is assumed that polyethylene is produced in this process since polymer can be isolated from larger scale reactions under similar conditions. The accepted mechanism for the ethylene growth reaction postulates a steady-state concentration of a a-bonded transition metal-hydrocarbon species which would be expected to modify the ESR spectrum of the supported complex. A possible explanation for the failure to detect a change in the ESR spectrum may be that only a small number of the niobium sites are active for polymerization. Although further experiments are needed to verify this proposition, it is consistent with IR data and radiochemical studies of similar catalyst systems (41, 42, 43). 

A radiochemical study [104] of the element distribution in the 238U+238U reaction at the unilac revealed the expected broad distribution of reaction products. Below uranium, where losses by sequential fission of transfer products are not significant, the observed yields decreased exponentially from Z=92 down to Z= 73. This trend was well reproduced [105] by a theoretical model treating nucleon transfer in the intermediate collision complex as a diffusion process. By extrapolation of the model to Z=70 nuclei about 100 microbam total production cross section resulted, associated with broad distributions of neutron numbers and excitation energies. 

S. M. Qaim, Radiochemical Studies of Complex Particle Emission in Low and Intermediate Energy Reactions, Radiochim. Acta 70/71,163 (1995)... 

R. Bock (Ed.), Heavy Ion Collisions, 3 Vols., North-Holland, Amsterdam, 1979-1981 D. A. Bromley (Ed.), Treatise on Heavy Ion Science, Vol. 4, Plenum Press, New York, 1985 R. Bock, G. Herrmaim, G. Siegbert, Schwetionenforschung, Wiss. Buchges., Darmstadt, 1993 J. V. Kratz, Radiochemical Studies of Complex Nuclear Reactions, Radiochim. Acta 70/71, 147 (1995)... 

The behavior of iodine at trace levels is often anomalous compared with that at macro concentrations. Because of these anomalies, in radiochemical investigations of iodine, either trace analysis or synthesis of labeled compounds, care must be taken to develop proper procedures to deal with potential problems. At the beginning of this review, it is necessary to briefly discuss the major chemical reactions of iodine, which are of importance to radiochemical studies and may be involved in chemical analysis and isotope production. Also included in this discussion are... 

The relevance of iodine chemistry to radiochemical studies has been briefly reviewed, including major iodine reactions in aqueous solutions, isotopic reactions and radiation effects in aqueous solutions. 

The thermodynamic treatment has been applied mainly to understanding stars in photographic emulsions. The end products are also the radioactive nuclei observed in radiochemical studies. The appUcation of evaporation theory to prediction of the yields of radioisotopes is rather hmited (see Morrison [2]). The form that a more general application might take may be indicated by Hal-pern s treatment of the yield of radioisotopes from photo-nuclear reactions (see Sect. 47). 

Gas-Phase Reactions of Free Methyl Cations with Amines and Their Organosilicon Analogues A Radiochemical Study... 

Berkeley cyclotron for several months prior to shipping the plate to Segre s group in Italy in late December, 1936. Perrier and Segre began their radiochemical studies in late January, more than 6 weeks after the end of bombardment. On the surface exposed to the deuterons, they found strong activity, chiefly due to very slow electrons ascribed to more than one substance of a half-value period of some months in addition to (which they could not explain, but did not attribute to reactions with molybdenum). 

Darmstadtium (Z = 110) has been produced only indirectly in " Ca-induced reactions, though neutron-deficient isotopes could arise in irradiations of thorium targets. A single atom of Ds has been reported in the decay chain of F1, with a decay interval of 8 ms [353]. The 13-s SF isotope Ds is the terminal member (see Hs, above) of the F1 decay chain, produced in the " Pu(" Ca,3n) reaction [331, 349, 358-361]. It is the only known Ds isotope that is appropriate for radiochemical studies. The 0.2-s isotope Ds is a member of the F1 decay chain, best produced in the " PuC Ca,3n) reaction [316]. 

Eichler, B., Zude, F., Fan, W., Trautmann, N., Herrmann, G. Complex transport reactions in a temperature gradient tube—radiochemical study of volatilization and deposition of irridium oxides and hydroxides. Radiochim. Acta 61, 81-90 (1993)... 

Further advances in the study of the mechanisms of redox reactions. A. G. Sykes, Adv. Inorg. Chem. Radiochem., 1967,10,153-245 (425). 

The study of the radiochemical reactions of arsenic atoms in benzene solution was carried further by comparing the product spectra of neutron irradiated ASCI3 solutions and GeC solutions which have undergone beta decay. The product spectra were found to be remarkably similar, especially when considered only as to the number of As-0... 

A series of papers by Merz and Riedel describe work designed to compare radiochemical behaviour following n,y n,p E.C. and p decay. Gallium isotopes are produced in most of the cases studied, but isotopes of Sn, Pb, Ge and Sb were also involved. Unfortunately, the various chromatography fractions were not well identified, so that it is not easy to draw definite conclusions from this work. Nevertheless, several things do appear to be clear. Some interesting data are presented in Table 5, comparing the effects of electron capture, neutron capture, and the (n,p) reaction. 

A detailed study of the radiochemical reactions of phenylarsenic compounds has been published by Grossmann. Once again unable to effect isolation of all compounds, he was able, however, to get evidently reliable values for the sums of all compounds with one, two and three phenyl-arsenic bonds, respectively, as well as ionic arsenic and a further organic-soluble fraction which appeared to be a group of polymeric phenylarsenic compounds. Selected data from this work are given in Table 6. 

Throughout the studies discussed in this review there persist a number of questions of so fundamental a nature as to preclude much further progress in the field before additional insight is available. These involve areas in which decisive experiments have not yet been done, and in which such experiments appear to be either very difficult or totally impossible. These questions arise What is the nature of the starting species What effects result from reactions extraneous to the radiochemical phenomenon— adsorption, exchange, etc. At what stage following the nuclear event do the observed chemical reactions occur ... 

The radiochemistry of ruthenocene has been studied by Baumgartner and Reichold (9) and by Harbottle and Zahn (29). It is found that neutron irradiation of crystalline RuCp2 yields about 10% of the radioactive ruthenium as RuCp2- More specifically, an isotopic difference in the radiochemical yield is found Ru, 9.6 0.1% Ru, 10.7 0.2% and Ru, 9.9 0.2% (29). In liquid solution the isotopic effect is much more pronounced, although the yields are lower. This was suggested by Harbottle as a general principle the greatest isotope effects are associated with the lowest yields. While this principle has not yet been substantiated, it seems reasonable since any thermal reactions which may increase the yields would not likely show any isotope effect. 

The apphcations described here illustrate the wide range of uses for robotic systems. This chapter is not intended to he exhaustive there are many other examples of successful applications, some of which are referenced below. For instance, Brodach et al. [34] have described the use of a single robot to automate the production of several positron-emitting radiopharmaceuticals and TTiompson et al. [3S] have reported on a robotic sampler in operation in a radiochemical laboratory. Both of these apphcations have safety imphcations. CHnical apphcations are also important, and Castellani et al. [36] have described the use of robotic sample preparation for the immunochemical determination of cardiac isoenzymes. Lochmuller et al. [37], on the other hand, have used a robotic system to study reaction kinetics of esterification. 

Aromatic fluorine for halogen (F-X) exchange reactions (DMSO, 160°C, 20 min) in an [ F]fluoride-cryptand-oxalate system using 4 -halo-acetophe-nones (F, Cl, Br and I) has also been studied. The relative efficacy of the exchange is the following one F-F > F-Cl > F-Br > F-I, the radiochemical yield for the exchange F-F being similar to that of the commonly employed NO2 or +NMej displacements [113]. 

Bromo [ F]fluoride (Section 3.9.1) addition across a double bond was used in the synthesis of fluorine-18-labelled steroids of high specific radioactivity. After addition, the bromine is removed by reduction or by dehydrobromination. [ F]Fluoro-5a-dihydrotestosterone was obtained in about 3% radiochemical yield (Scheme 17) [64] and 6a-p F]fluoroprogesterone in only 0.3% [65]. The yields were quite low but sufficient to allow for animal studies. These reactions had been tested out successfully with simpler model alkenes [66]. 

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