Next-to-next-leading order correction to 3-jet rate and event-shape distribution

The hadronic events from the e ⁺ e ⁻ annihilation data at the centre-of-mass energies ranging from 60 to 197 GeV were studied. The AMY and OPAL Collaborations offered a unique opportunity to test QCD by measuring the energy dependence of different observables. The coupling constant, α _s, was measured by two different methods: first by employing the three-jet observables. Combining all the data, the value of as at next-to-next leading order (NNLO) was determined to be 0.117 ± 0.004(hard) ± 0.006(theo). Secondly, from the event-shape distributions, the strong coupling constant, α _s, was extracted at NNLO and it’s evaluation was tested with the energy scale. The results were consistent with the running of α _s, expected from QCD predictions. Averaging over different observables, α _s was determined to be 0.115 ± 0.007(hard) ± 0.003(theo).     

Induced photonuclear interaction by Rhodotron-TT200 10 MeV electron beam

In this paper the photonuclear interaction induced by 10 MeV electron beam generating high-intensity neutrons is studied. Since the results depend on the target material, the calculations are performed for Pb, Ta and W targets which have high Z, in a simple geometry. MCNPX code has been used to simulate the whole process. Also, the results of photon generation has been compared with the experimental results to evaluate the reliability of the calculation. The results show that the obtained neutron flux can reach up to 10¹² n/cm²/s with average energies of 0.9 MeV, 0.4 MeV and 0.9 MeV for these three elements respectively with the maximum heat deposited as 3000 W/c³, 4500 W/c³ and 6000 W/c³.     

Shift and broadening of emission lines in Nd<Superscript>3+</Superscript>:YAG laser crystal influenced by input energy

Spectroscopic properties of the flashlamp-pumped Nd ³⁺:YAG laser as a function of input energy were studied over the range of 18–75 J. The spectral widths and shifts of quasi-three-level and four-level inter-Stark emissions within the respective intermanifold transitions of \(^{\mathrm {4}}\mathrm {F}_{\mathrm {3/2}}\to ^{\mathrm {4}}{\kern -2.7pt}\mathrm {I}_{\mathrm {9/2}}\) and \(^{\mathrm {4}}\mathrm {F}_{\mathrm {3/2}}\to ^{\mathrm {4}}{\kern -2.7pt}\mathrm {I}_{\mathrm {11/2}}\) were investigated. The emission lines of \(^{\mathrm {4}}\mathrm {F}_{\mathrm {3/2}}\to ^{\mathrm {4}}{\kern -2.7pt}\mathrm {I}_{\mathrm {9/2}}\) shifted towards longer wavelength (red shift) and broadened, while the positions and linewidths of the \(^{\mathrm {4}}\mathrm {F}_{\mathrm {3/2}}\to ^{\mathrm {4}}{\kern -3.5pt}\mathrm {I}_{\mathrm {11/2}}\) transition lines remained constant by increasing the pumping energy. This is attributed to the thermal population as well as one-phonon and multiphonon emission processes in the ground state. This phenomenon degrades the output performance of the lasers.     

The measurements of thermal neutron flux distribution in a paraffin phantom

The term ‘thermal flux’ implies a Maxwellian distribution of velocity and energy corresponding to the most probable velocity of 2200 m s^???1 at 293.4 K. In order to measure the thermal neutron flux density, the foil activation method was used. Thermal neutron flux determination in paraffin phantom by counting the emitted rays of indium foils with two different detectors (Geiger–Muller counter and NaI(Tl)) was the aim of this project. The relative differences of the outcome of the experiments were between 2.5% and 5%. The final results were compared with MCNP4C outputs and the best agreement was generated using NaI(Tl) by a minimum discrepancy of about 0.6% for the foil placed 8.5 cm from the neutron source.     

Next-to-next-to-leading order calculation of the strong coupling constant α s by using moments of event-shape variables

The next-to-next-to-leading order (NN’LO) quantum chromodynamics (QCD) correction to the first three moments of the four event-shape variables in electron–positron annihilation, the thrust, heavy jet mass, wide, and total jet broadening, is computed. It is observed that the NNLO correction gives a better agreement between the theory and the experimental data. Also, by using the above observables, the strong coupling constant (α _s) is determined and how much its value is affected by the NNLO correction is demonstrated. By combining the results for all variables at different centre-of-mass energies $\alpha_{\rm s} ({M_{Z^0}})=0.1248\pm 0.0009\left( {\exp\!.} \right)_{-0.0144}^{+0.0283} \left({\mbox{theo}.} \right)$ is obtained.     

Neutronic simulation of a research reactor core of (232Th, 235U)O 2 fuel using MCNPX2.6 code

The small reactor design for the remote and less developed areas of the user countries should have simple features in view of the lack of infra-structure and resources. Many researchers consider long core life with no on-site refuelling activity as a primary feature for the small reactor design. Long core life can be achieved by enhancing internal conversion rate of fertile to fissile materials. For that purpose, thorium cycle can be adopted because a high fissile production rate of ²³³U converted from ²³²Th can be expected in the thermal energy region. A simple nuclear reactor core arranged 19 assemblies in hexagonal structure, using thorium-based fuel and heavy water as coolant and moderator was simulated using MCNPX2.6 code, aiming an optimized critical assembly. Optimized reflector thickness and gap between assemblies were determined to achieve minimum neutron leakage and void reactivity. The result was a more compact core, where assemblies were designed having 19-fuel pins in 1.25 pitch-to-diameter ratio. Optimum reflector thickness of 15 cm resulted in minimal neutron leakage in view of economic limitations. A 0.5 cm gap between assembles achieved more safety and 2.2% enrichment requirements. The present feasibility study suggests a thermal core of acceptable neutronic parameters to achieve a simple and safe core.     

A benchmark study on uncertainty of ALICE ASH 1.0, TALYS 1.0 and MCNPX 2.6 codes to estimate production yield of accelerator-based radioisotopes

Radioisotopes find very important applications in various sectors of economic significance and their production is an important activity of many national programmes. Some deterministic codes such as ALICE ASH 1.0 and TALYS 1.0 are extensively used to calculate the yield of a radioisotope via numerical integral over the calculated cross-sections. MCNPX 2.6 stochastic code is more interesting among the other Monte Carlo-based computational codes for accessibility of different intranuclear cascade physical models to calculate the yield using experiment-based cross-sections. A benchmark study has been proposed to determine the codes’ uncertainty in such calculations. ¹⁰⁹Cd, ⁸⁶Y and ⁸⁵Sr production yields by proton irradiation of silver, rubidium chloride and strontium carbonate targets are studied. ¹⁰⁹Cd, ⁸⁶Y and ⁸⁵Sr cross-sections are calculated using ALICE ASH 1.0 and TALYS 1.0 codes. The evaluated yields are compared with the experimental yields. The targets are modelled using MCNPX 2.6 code. The production yields are calculated using the available physical models of the code. The study shows acceptable relative discrepancies between theoretical and experimental results. Minimum relative discrepancy between experimental and theoretical yields is achievable using ISABEL intranuclear model in most of the targets simulated by MCNPX 2.6. The stochastic code utilization can be suggested for calculating ¹⁰⁹Cd, ⁸⁶Y and ⁸⁵Sr production yields. It results in more valid data than TALYS 1.0 and ALICE ASH 1.0 in noticeably less average relative discrepancies.     

Influence of the laser-diode temperature on crystal absorption and output power in an end-pumped Nd:YVO<Subscript>4</Subscript> laser

In this work, we studied the influence of heat loaded into the laser crystal in an end-pumped solid-state Nd:YVO₄ high power laser. We have shown experimentally that the optimum value of the laser-diode temperature for the maximum pump power absorption by the Nd:YVO₄ crystal and the maximum Nd:YVO₄ laser output power are approximately similar to that of a system of the low power type, but by increasing the pump power, different values can be obtained.