Multiparameter study of the long-range α-particles emitted in the thermal neutron induced fission of 235U

The correlations between the various parameters in the thermal neutron induced fission of ²³⁵U accompanied by long-range α-particles (LRA) have been measured employing a back-to-back gridded ionization chamber. Semiconductor detectors were placed symmetrically along the electric field direction of the chamber behind the thin windows of the collector plates for the measurement of the LRA energies. A distinguishing feature of the present method is that the angle between the fission fragments and the electric field direction (hence the direction of α-particle emission) is also determined electronically by the analysis of the coincident collector and grid pulses of the ionization chamber. About 5 × 10⁵ LRA-accompanied fission events and about 2 × 10⁶ binary fission events were recorded and analyzed to obtain a number of correlations of interest between the fragment mass, total kinetic energy, LRA energy and fragment-LRA angle. These experimental results are presented and discussed with regard to the emission mechanism of the LRA.     

Analysis of fission excitation functions and the determination of shell effects at the saddle point

A method is proposed to deduce the shell correction energy corresponding to the fission transition state shape of nuclei in the mass region around 200, from an analysis of the first chance fission values of the ratio of fission to neutron widths, (Γ _f /Γ _n )₁. The method is applied to the typical case of the fissioning nucleus²¹²Po, formed by alpha bombardment of²⁰⁸Pb. For the calculation of the neutron width, the level densities of the daughter nucleus after neutron emission were obtained from a numerical calculation starting from shell model single particle energy level scheme. It is shown that with the use of standard Fermi gas expression for the level densities of the fission transition state nucleus in the calculation of the fission width, an apparent energy dependence of the fission barrier height is required to fit the experimental data. This energy dependence, which arises from the excitation energy dependence of shell effects on level densities, can be used to deduce the shell correction energy at the fission transition state point. It is found that in the case of²¹²Po, the energy of the actual transition state point is higher than the energy of the liquid drop model (LDM) saddle point by (3 ± 1) MeV, implying significant positive shell correction energy at the fission transition state. Further, the liquid drop model value of level density parametera is found to be a few per cent smaller for the saddle point shape as compared to its spherical shape.     

Huang diffuse scattering from interstitials in an hcp lattice

Using the continuum theory of linear elasticity, the Huang diffuse scattering from interstitials in an hcp lattice has been calculated to distinguish between the possible interstitial configurations. The symmetry of the lattice permits four such configurations. In each case, the Huang diffuse scattering is averaged over all possible equivalent orientations (assumed to be equally populated) of the defect configuration. The limitations of Huang diffuse scattering in discriminating between defect configurations having the same long-range symmetry are discussed, considering the specia I cases of Mg and Zn.     

Hydrophobicity induced vapor-phase oxidation of propene over gold supported on titanium incorporated hybrid mesoporous silsesquioxane

Gold nanoparticles supported on highly hydrophobic ethane bridged Ti incorporated mesoporous organosilica are reported for enhanced vapor phase epoxidation of propene using H2 and O2.