Rıdvan Ünal

Comparison of level density models in (γ, n) reactions of some lanthanide nuclei

Level densities are required at excitation energies where discrete level information is not available or incomplete to get a reliable theoretical analysis of cross sections, spectra, and angular distributions. The total reaction cross sections of some lanthanides (141Pr, 142Nd, 144Sm, 153Eu, 160Gd, 159Tb, 165Ho, 175Lu) were calculated using TALYS 1.2 code for gamma-induced reactions through the five level density models in the incident gamma energy range from 5 to 30 MeV. All calculations from the present study were compared with each other and with the experimental data obtained from EXFOR library. The total photo-neutron reaction cross-section values obtained from the model calculations and experimental measurements taken from EXFOR confirm the presence of systematical disagreements reported in the literature, except 165Ho case where one can see a satisfactory agreement.

Mean grain size evaluation of tungsten- and boron-carbide composites sintered at various temperatures by ultrasonic methods

In this study, the mean grain size of different ceramic-metal composites made from tungsten carbide and boron carbide have been determined with the ultrasonic velocity technique. In addition, the electroless coating method was used to coat the tungsten carbide samples. The prepared samples were sintered at different temperatures ranging from 1200°C to 1400°C in an argon atmosphere. Powders were placed in a 30 mm diameter mold and pressed using a hydraulic press at a pressure of 200 bar. The results were compared to the mean grain size obtained from Scanning Electron Microscopy (SEM). This study shows a clear dependence of ultrasonic velocity on grain size in composites of boron carbide and tungsten carbide. Especially the temperature dependence of mean grain size for tungsten carbide composites can be seen very clearly.