Isotope yields

Iodine [7553-56-2] I, atomic number 53, atomic weight 126.9044, is a nonmetaUic element belonging to the halogen family in Group 17 (VIIA) of the Periodic Table. The only stable isotope has a mass number of 127. There are 22 other iodine isotopes having masses between 117 and 139 14 of these isotopes yield significant radiation. 

One disadvantage of the non-competitive method is the necessity to synthesize samples of isotopically pure (or at least highly enriched) reactants, and this can be tedious and expensive. Since light and heavy isotopomers are very often obtained using different synthetic pathways (in order to optimize isotopic yield), they may carry different impurities or different concentrations of the same impurity. Therefore it is necessary to meticulously purify both samples before running experiments. In this... 

Figure VIII-2 shows the principle of isotope enrichment by two-photon ioni/.ation of 233U atoms. The excitation wavelength is 4266.275 0.02 A. A band width of 0.1 cm 1 is much narrower than an isotope shift of 0.32cm 1. Since the preferentially excited 235U atoms decay in 10-7sec the second laser source to ionize the excited atoms must be pulsed within 10 - 7 sec. The wavelength of the second laser must be shorter than 3777 A, as the combined photon energy must exceed the ionization potential, 6.187 eV, of U atoms. If the first laser is set at 4266.325 A in coincidence with an absorption line of 238U atoms, an isotopic yield ratio of 3000 1 for 238U/23,U is obtained in comparison with 140 1 for the same ratio in the starting material.

Table II. Comparison of Calculated and Measured Isotope Yields for 13 HFIR Targets Processed During TRU Campaign 59.

In this case, and are the rate constants for molecules containing the light and heavy isotopes, respectively, and most reactions discriminate against the heavier isotope, yielding a>l. The inverse convention a = is also used... 

The yield of labelled acetylene is 90-100%. A variant, using labelled barium carbonate and excess of barium to make labelled BaC., then hydrolysis, has been used to prepare and . The isotopic yield is excellent if all traces of paraffin... 

Hydride reductions can be selective and produce products in high isotopic yields. 

The eflBciency of these methods of co-precipitation was studied for plutonium, only, by comparing the chemical recovery of the original yield monitor with that of a second (and different) plutonium isotope yield monitor added to the acid solution of the co-precipitated hydroxide or oxalate (6). This second monitor shows all losses following the coprecipitation step. The eflBciency of the hydroxide precipitation for plutonium extraction was in the range 70-80%. That for the oxalate coprecipitation was typically 75-85%. 

Investigations of the xenon isotope yields in the neutron-induced fission of U233 (81), U238 (118), Pu239 (82), and Pu241 (86) have also been carried out. In all cases, there is evidence of some increased yield in the xenon mass range. The sharpness of the peak at mass 134 varies considerably, however, and in the case of U233 + n fission, there is little evidence of fine structure... 

The reaction of hydrogen peroxide or alkyl hydroperoxides with alcohols labeled with the O isotope yields the corresponding organic peroxides containing oxygen of normal isotopic constitution, as shown in Table I (a = atoms per cent excess O over normal). 

Neutrons reacting with the other Li-isotope yield two He ... 

The chemical and isotopic yields, based on the conversion of sodium sulfate to sulfur, are 92%. Usually 2 to 3% of unreduced sulfate is recoverable. The remaining losses of about 5 % are mainly due to losses of colloidal sulfur and of hydrogen sulfide from the solid sodium sulfide. 

Chemical yield 95% or better. Isotopic yield 20% of the total (Fe + Fe ) activity is isolated as ferrocene. With a thermal-neutron flux of 1 X 10 neutrons cm." / sec.", six days irradiation produces a total of 140 juC./g. of Fe and 70 /iC./g. of Fe . (Higher neutron fluxes will yield proportionately higher specific activities.) The specific activity of the ferrocene is one-fifth of these values. 

Calculated and Experimental Isotope Yields for Various Beams on H2O Targets... 

Figure I. Calculated isotope yields from proton bombardments with incident beam energy. No is predicted.

FIGURE 8.39 Isotopic yield of the elements 98-101 in the reactions (crosses) [71]... 

The estimated isotopic yields of SH nuclei in the Th + Cf, and collisions at 800 MeV center-of-mass energy are shown in Fig-... 

The most uncertain quantity is the parameter v for the fission width distribution. The values one, two, and three have been recommended by different authors. Garrison (54) finds that a maximum likelihood test of the combined fission width distribution of four fissile isotopes yields V = 2.0, whereas Fischer 32) finds v = 2.2 for and v = 1.2 for... 

Interesting results were reported for the bombardments of Cm with the Ca, Ca, and projectiles. Production yields for elements through Fm are shown in Pig. 18.7a (Turler et al. 1992). Considerable difference is observed in the yields of the below-target elements with the highest yields observed for Ca, while for the above-target elements the lowest yields were observed for the Ca projectile. The most neutron-rich nuclides in the isotopic yield distribution were observed for the reactions with Ca (Hoffman et al. 1985). 

Unfortunately, the labeled 9Z,11E) CLA isomer was contaminated with (9 ,11 ) isomer and oveneduced fatty adds. Purification by C18 reversed-phase high-performance liquid chromatography (RP-HPLC) followed by silver resin chromatography furnished pure methyl (9Z,llfi)-[9,ll-2H]-octadecadienoate (isomeric purity >99% isotopic purity 82-88%) in 60-70% overall yields. In this paper, the author also noticed that increasing the ratio of quinoline to substrate and the volume of solvent resulted in improved chemical and isotopic yields, but the formation of overreduced by-products could uot be prevented. 

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