In this article, a review of the work on the low-yield products formed in the highly asymmetric binary fission (70A160) of heavy elements (HABF) is made. HABF may be viewed as an extension of the usual asymmetric fission process. A few interesting features of this mode of fission which are apparent from the data available in the literature are identified: The process (a) is rare, (b) seems to depend on the excitation energy of the fissioning system, (c) is highly influenced by shell effects. A closely related phenomenon, viz the recent discovery of spontaneous emission of heavy ions (A>4, Z>2) from heavy nuclei is also examined briefly. It is speculated that HABF may be an important decay mode for the very heavy and the yet-undiscovered superheavy elements. Suggestions for future experiments to further pin down this fission mode are also given in this article.
A transmission-corrected -ray counting method has been employed for the assay of uranium in crude Na2U2O7 cakes produced at the Uranium Conversion Facilities. A 3×3 NaI(TI) detector was used in conjunction with a 400-channel analyzer. The observed count rate of the 1 MeV -ray emitted by the238U in the sample was corrected for sample self-attenuation, measured with a65Zn (-energy 1115 keV) transmission source. A calibration factor determined by measuring a standard of known amount of radioactive material in the same form and geometry as the unknown sample was used to convert the transmission corrected count rate to the amount of uranium in the weighted sample. Another -spectrometric method is described for the assay of the U-content in the MgF2 slag produced during the magnesiothermic reduction of UF4 to U-metal ingots at the natural U-conversion plant.
The beneficiation of tailings from Kolar Gold Mines involves the flotation of sulphides. Appreciable amounts of arsenic and
antimony are expected to accompany gold in this process. The activation analysis of gold in these samples is facilitated by
a preseparation of gold from arsenic and antimony. The present paper describes a method for the rapid analysis of gold in
the concentration range 0.5 to 50 ppm using a simple pre-irradiation separation, with the recovery of gold being evaluated
by an isotope dilution technique using198Au tracer.
A potentiometric method has been developed for the determination of uranium in phosphate-perchlorate medium. A significant feature of this method is its applicability for the determination of uranium in uranium-bearing CaF2 slags and fused salt cakes generated at the natural uranium conversion and fabrication plants, respectively. These uraniumbearing slags and cakes contain large amounts of calcium and barium, respectively, where the conventional Davies-Gray and the related methods cannot be applied. A distinct advantage of the present method over coulometric determination of uranium in perchloric acid medium is that it can easily be adopted for routine analysis.
A simple and rapid method for spectrophotometric determination of palladium from highly acidic and highly radioactive nuclear waste using -benzoin oxime (ABO) as extractant and isobutyl methyl ketone (hexone) as diluent has been developed. The method can be employed over a wide range of nitric acid concentrations and for palladium concentrations in the range of 1·10–5M to 4·10–4M in the organic phase. The molar absorptivity was found to be 4·103l·mol–1·cm–1. Influence of various heavy metal ions, fission products and corrosion products was studied. The method was found to give a precision and accuracy better than 4% at 100 g of palladium.
Analysis of fissile materials in solution by fission track registration technique has been extended to plutonium in solution
of its alloys. In these estimations, the results agreed within 1–4% with the average of those obtained by other chemical and
instrumental methods like potentiometry, mass-spectrometry and X-ray fluorescence. Some special practical problems encountered
in the analysis of plutonium solutions are noted. Various factors affecting the results have been investigated and the necessary
precautions for reducing these errors have been indicated. The advantages of the method over some other conventional methods
have also been discussed. It is suggested that a source of about 10 μg of252Cf corresponding to a neutron flux of about 107 n·cm−2·sec−1 is ideal for these experiments.
A -spectrometric method has been developed for the assay of uranium in crude UF4, which is used as a secondary source of input material for producing nuclear grade U-metal at natural uranium conversion plants. The method makes use of a NaI (Tl) detector coupled with a multichannel analyzer. The 1 MeV -ray of238U is used for calibration. A method for the fabrication of uniform -assay calibration standards is also suggested, based on the results of this investigation. The calibration standards were prepared by soaking the matrix in uranium solution and then drying the whole material. The amount of238U in the crude UF4 sample was directly estimated by comparing the areas under the 1 MeV -ray peak of known calibration standards with the corresponding areas of the samples to be measured. 100 g each of the standard and the sample were counted. 5 crude UF4 samples were analyzed by this method. The uranium contents in these samples were found to be in the range of 12.2–28.7 g. To compare the -ray spectrometry results with a completely independent method, chemical analysis by potentiometry of all the samples was also done. The -spectrometric results were found to agree within ±18% with the chemical analysis results.
Sorption of Li+, Cs+ and Sr2+ on hydrous titanium oxide and magnetite as a function of pH in the presence and absence of -rays has been studied. pH-titrations of the irradiated hydrous oxides have also been carried out. It has been shown that the sorption characteristics of these oxides are not altered by -irradiation and the uptake of metal ions is governed by the equilibrium pH of the solution. Certain physical changes observed on irradiating of the hydrous oxide samples in water are discussed.
Quantitative determination of uranium in (U, Pu)O2 fuels is usually done by the DAVIES-GRAY method. High concentrations of phosphoric acid in the analytical waste generated by this method make the revocery of plutonium rather complex. Studies on the recovery of plutonium from nitric acid medium containing different concentrations of H3PO4 by conventional anion-exchange procedure reveal that more than 90% of the plutonium can be easily recovered when the phosphoric acid concentration is less than 0.5 M in the solution. A method was developed for the determination of uranium in the presence of plutonium, which involves the reduction of U(VI) to U(IV) by Fe(II) in a medium of 3.5M H3PO4 +4.5M H2SO4 instead of 10–11M H3PO4 so as to have the H3PO4 concentration 0.6M in the waste. A number of determinations of uranium in UO2(NO3)2 working standard solutions and (U, Pu) synthetic solutions with uranium at the 3–7 mg level were carried out by this method. The precision obtained was better than ±0.2% and the accuracy was also within the precision limits. The resulting analytical waste generated was directly subjected to anion exchange separation for the recovery of plutonium which was found to be more than 90%.
Mixtures of methanol and isopropanol in a ratio (v/v) varying from 91 to 19 have been gamma-irradiated at 77 K and relative yields of trapped electrons have been measured. The reactivity of the trapped electrons towards acetone and uranyl nitrate has been studied at various methanol isopropanol ratios. On the basis of the results, an attempt has been made to assess the relative importance of the reaction of the electron with the solute prior to trapping with respect to the tunnelling reaction of the trapped electron with the solute.