Systematic behavior of mass-yield curves in low-energy fission of actinides

Mass yield curves of spontaneous fissions, thermal-neutron induced fissions, monochromatic-neutron and proton induced fissions of actinides are reviewed. Mean masses of light and heavy asymmetric mass yield peaks are listed. The subtle change of the shape of the asymmetric heavy peak is expressed in terms of the parameters of two Gaussians that fit the observed data well. One Gaussian is narrow in width and always peaks at A=133–136 while the other is broader and peaks at A=140–144. The FWHM of the heavy asymmetric peak becomes minimum for the fissioning mass A=240–245. An analysis of the projectile energy dependence of mass yield curves indicated, at least, two distinctively different behaviors, one for asymmetric products and the other for symmetric products. From the energy dependence of the peak-to-valley rations, the extra-energy required for symmetric mass division, or the difference in the fission barrier heights, in the nomeuclature of the two-mode hypothesis, is deduced for a wide range of fission nuclides.     

Isomeric yield ratios of fission products in proton-induced fission of232Th

Isomeric yield ratios of 11 fission products were measured in the system of 13 MeV proton-induced fission of²³²Th by an on-line ion-guide isotope separator. It was found that the closed shell structures of primary fragments and their complementary fragments affect the isomeric yield ratios. Isomeric yield ratios of¹²¹Cd (11/2⁻, 3/2⁺) and¹³⁵Xe (11/2⁻, 3/2⁺) were measured precisely in the proton energy range of 13 to 26 MeV to investigate their energy dependence. It was found that the isomeric yield ratios increased slightly with proton energy. The results were discussed in connection with the deformation of fission fragments and fission modes.     

The intensities of low-energy electronic absorption transitions of some carbonyls and thiocarbonyls

The intensities of low-energy electronic transitions for some carbonyls and thiocarbonyls have been calculated from CNDO wavefunctions.Quite good agreement with experimental results has been obtained, where the latter are available. A satisfactory approximation for calculating intensities employs only one-center integrals. From the calculated trends in oscillator strengths, the absorption of thiophosgene at 4.46 eV can be identified as the π→π* ¹A₁←X?¹A₁ system. Another, very weak, system of thiophosgene at ≈ 3.9 eV is tentatively assigned to an n→π* ¹A₁ ← X?¹ A₁ transition, with the n orbital localized on the chlorine atoms.     

Applications of pressurized cation exchange chromatography for fission yield determination

In order to determine the fission yields of lanthanides precisely, lanthanides with carriers of 1–2 mg per element are separated from each other by means of pressurized cation exchange chromatography-HIBA concentration gradient elution: The effects of initial loading technique, concentration gradient, flow rate, and temperature on separation were investigated in detail. Under the optimum conditions adopted according to the results given in this work, all the lanthanides can be completely separated within about 90 minutes with a recovery of more than 95% and purity higher than 99%.     

Spectral locations of low-energy electronic transitions in some fluorene derivatives

The low energy singlet—singlet (S-S) and triplet—triplet (TT) absorption spectra of fluorene and 2-amino fluorene were measured. Also, the spectral locations of low-energy SS and TT intensity maxima of 2-methoxy, 2-hydroxy, 2,7-diamino, and 2-dimethylamino fluorene were recorded.When expressed in wavenumbers (energy) and within measurement accuracy, the following holds for the 2-position substituted fluorene: (a) the red shift caused by a certain substituent is about the same in both (singlet and triplet) manifolds; (b) the energy difference between SS and TT absorption maxima in fluorene as well as in all the substituted compounds is about the same and (c) the spectral red shifts observed in fluorene in the singlet and triplet manifold due to substitution by auxochromic groups can probably be used in fair approximation to estimate anticipated red shifts in other chromophores.For 2,7-diamino fluorene; p-terphenyl, p,p′-diamino, p,p′-diethylamino terphenyl, p-quaterphenyl; p,p′-diamino, p,p−diethylamino quaterphenyl, spectral relations (a) to (c) also hold rather well.     

Uptake studies of some fission products using ceramic materials

The uptake of Eu(III) and Zr(IV) was studied on ceramic materials of TiO₂, SiO₂ and Al₂O₃, prepared by the hydrolysis process. The uptake behavior of Eu(III) and Zr(IV) was investigated under different experimental conditions such as contact time, pH-value in the presence and in absence of complexing agent. X-ray fluorescence, powder morphology, specific surface area, X-ray diffraction analysis in addition to the DTA and TG were applied on the tested ceramic samples. The present study showed that the ceramic materials, prepared by an advanced technique are not only efficient for uptake of Eu(III) and Zr(IV), but also permitted the separation of these radioisotopes.     

Cluster expansion of the wavefunction: Ionizations and some low-energy excitations of naphthalene

Ionizations and some lower singlet valence and Rydberg excitations of naphthalene are studied by the SAC/SAC CI method with 100 (44 π + 56 σ) active MOs. A systematic assignment of the ionization spectra is given. In particular, assignments are given for the peaks in the 13–20 eV region. A large σ-electron correlation effect is found for the valence excited B_1u state, together with a large effect of the d_π polarization function. The controversy concerning the assignment of the Rydberg nd_π orbitals is resolved: Robin's assignment of the 3d_π orbital at 6.73 eV above the ground state is supported.     

Contamination of some important kinds of plants by fission products

Quantitative data for some of the radionuclides, most important because of their intensity and radiotoxicity, present in the biosphere after the Chernobyl accident are given for a selected number among numerous plant and food samples analyzed before and after the accident.     

Determination of the fast fission yield of141Pr using neutron activation analysis

A method is described for the determination of the fission yield of¹⁴¹Pr. This method was developed to determine the fast fission yield of¹⁴¹Pr in the Mark III loading (enriched uranium with about 2% zirconium) of the fast fission breeder reactor, EBR-1. The burnup of the fuel sample was determined using the previously reported fission yield of¹³⁷Cs. Praseodymium was separated from uranium, plutonium and other fission products by a combination of precipitation and ion exchange stages. Thereafter,⁵⁵Mn was added to serve as an internal flux monitor and praseodymium determined by neutron activation analysis. A precision of ±2% was obtained. Presented at the 15th Annual Meeting of the American Chemical Society, Miami Beach, Florida (USA), April 1967.     

Absolute determination of the spontaneous fission yield of252Cf by radiochemical method

The distribution of mass in the spontaneous fission of²⁵²Cf has been investigated by the radiochemical determination of the absolute fission yields for 35 mass chains. A summation of the mass-yield curve gives a summed value of 199.4% which is in very good agreement with the value of 200% in fission. The mean masses of the light and heavy group are located at 106.39 and 141.82, respectively. The average number of neutron per fisson is 3.79±0.12. The peak-to-valley ratio is larger than 370. The width at one tenth of the maximum of the light and heavy group are 26.7 and 26.8 mass number, respectively. A comparison of previous investigators has resulted in recommended yields for 35 mass chains.     

Independent yield of88Y from thermal neutron induced fission of235U

The independent yield of⁸⁸Y from thermal neutron-induced fission of²³⁵U was determined relatively to the well-known yield of⁹¹Y. An upper limit obtained was 1.53×10^–8%.     

Extraction of americium,lanthanides and some fission product elements by bidentate phosphonates

The extraction of Am, Eu, Ce(III), Zr(IV), and Sr from aqueous nitric acid— nitrate media by dibutyl N,N-diethylcarbamylphosphonate and dibutyl N,N-diethylcar-bamylmethylenephosphonate dissolved in carbon tetrachloride was studied. The trivalent actinide and lanthanide elements may be separated in certain aqueous phase acidity regions from Fe(III), Zr(IV), and Sr, whereas the separation of actinide elements from the lanthanide elements is poor. The extractant to metal ratio in the extracted complexes of Am, Eu, and Ce(III) is 3. The interferences in the extraction due to acidic impurities in the extracting agent are discussed.     

High triplet yield from singlet fission in a thin film of 1,3-diphenylisobenzofuran

Direct observation of triplet absorption and ground-state depletion upon pulsed excitation of a polycrystalline thin solid film of 1,3-diphenylisobenzofuran at 77 K revealed a 200 ± 30% triplet yield, which was attributed to singlet fission.     

Measurement of uranium in human teeth and kidney stones with the fission track technique

The measurement of uranium in human teeth and kidney stones has been carried out by using the fission track activation technique. In this determination 2759 and 2205 absolute counts of tracks /for standard: 6940 and 1556/ for teeth samples and 1689 tracks /for standard: 1446/ for kidney stone samples have been made, respectively. The results obtained by this technique are the following: X_tooth/1/=/0.227±0.006/ ppm, X_tooth/2/=/0.143±0.007/ ppm and X_kidney=/0.568±0.020/ ppm. The experimental method is described and the results discussed.     

Isomeric yield ratio of146La and84Br in thermal neutron induced fission of235U

The independent isomeric yield ratio of¹⁴⁶La and⁸⁴Br in the thermal neutron fission of²³⁵U is reported for the first time with the values of 0.058±0.017 and 0.62±0.20, respectively. the yields have been determined using a fast radiochemical separation technique followed by -spectroscopy. The deduced rms angular momentum of⁸⁴Br is 5.9 from the statistical model analysis and the rms angular momentum of¹⁴⁶La is found too low to be determined.     

Singlet molecular oxygen quantum yield measurements of some porphyrins and metalloporphyrins

Hematoporphyrin IX dimethyl ester (HPDME), tetraphenylporphyrin (TPP), tetra(4-methoxyphenyl)porphyrin (TMPP), tetra(3,4-dimethoxyphenyl)porphyrin (TDMPP), tetra(3,4,5-trimethoxyphenyl)porphyrin (TTMPP), tetraanthrylporphyrin (TAP) and tetraacridylporphyrin (TACP), and their Zn²⁺, SnX ₂ ²⁺ , Pd²⁺ and Pt²⁺ complexes have been prepared and characterized. The singlet molecular oxygen quantum yield (ϕ_Δ) values of the above porphyrins and their metal derivatives in N,N-dimethyl formamide (DMF) have been measured in the presence of 1,3-diphenylisobenzofuran (DPBF) as¹O₂ acceptor using steady state technique after correcting for the intensity of light absorbed by the photosensitizers. The ϕ_Δ values for the free base porphyrins are usually around 0.60. Hematoporphyrin IX dimethyl ester and its metal derivatives follow the order: HPDME (ϕ_Δ = 0.60) > Zn HPDME (0.40) > PdHPDME (0.34) > Sn(OH)₂ HPDME (0.28) > PtHPDME (0.24). Zinc(II) complexes of tetraarylporphyrins show about 65% efficiency in ϕ_Δ values are compared to the ϕ_Δ values of their corresponding free base porphyrins. These results can be explained on the basis of catalyzed intersystem crossing to the ground state. The ϕ_λ values of the above free base porphyrins and their metal complexes in DMF in presence of DPBF using single-pulsed laser excitation technique follow similar trends.