Physics Procedia最新文献

Formation of channel optical waveguides due to the sequential point-to-point exposure of local stripe-like regions of Y-cut lithium niobate sample surface is experimentally investigated. The surface layer of the sample is thermally doped with Cu ions to increase its photorefractive sensitivity. The laser radiation with wavelength of 532 nm and optical power of 10 mW is used for the crystal exposure in experiments. The optical inhomogeneities formed during the sample exposure are studied with their probing by laser beams with wavelength of 633 nm.

A High Purity Germanium (HPGe) spectrometer has been designed and constructed for making precision measurements over extended time periods at the High Flux Isotope Reactor (HFIR) located at Oak Ridge National Lab (ORNL). Toward the effort of achieving long-term system stability and high spectral resolution, local environment control is utilized as part of the system design. Further, the remote operation of the spectrometer is aided by live-streaming system conditions and automatic out-of-range alert messaging. System performance over the 7-month Phase I period is presented.

Restrictions in CO₂-emissions have caused increased demands on decreased weight and increased use of lightweight materials in the automotive industry. Aluminium has shown to be of great interest due to its beneficial weight to strength ratio, and are suitable for hang-on parts such as roof, doors etc. However, the use of aluminium requires reliable joining techniques. This project has been focusing on laser welding of aluminium. It have been reported earlier that hot cracks and porosity are common defects while joining aluminium with laser welding. The aim with this project has been to produce crack free laser welds while joining thin aluminium sheets. Two different optics have been used in this project, oscillating- and triple-spot optics. The results from the experiments show that both the oscillating optics and the triple-spot optics can produce crack free welds. The amount of pores is shown to be low for both cases. The results do also show that the amount of pores in the welds increases with the weld length while the flange length is of minor impact. The mechanical properties are similar for the both optics. The oscillation specimens receive a higher tensile strength while the triple-spot specimens receive a larger elongation at break value.

Additive technologies, which obtained the wide spreading in the last decade, allow producing items of any shape from metal materials practically without additional mechanical treatment. This approach based on the layer by layer melting of powder material accordingly to the premade 3D-CAD model, provides the geometrical accuracy which mostly depends on the size of the used material. In the present study, as material a 410 L steel powder was chosen, for which the basic dependencies between the selective laser melting (SLM) parameters and the mechanical properties were determined. Trial batches of standard samples for uniaxial tension and impact strength tests (according to the ASTM A370 and ASTM E8 M standards) were produced. It was shown that in the as build (after SLM) the fracture appeared to be brittle with the impact strength 3-5 J/cm². The carried out heat treatment of quenching-tempering cycle and subsequent tests provide the viscous fracture and evaluation of impact strength up to 20-30 J/cm². Presumably, this is due to a refinement of the grain structure and the inner stresses reduction of the samples, which also acknowledges the execution EBSD analysis, which points to the presence of quenched and tempered martensite. The presence of high inner stresses can be attributed to two α-γ-α transformations that were revealed by dilatometry investigation. In the range of cooling or heating rates from 1 to 500 °C/s temperatures of phase transformation are shifted.

In order to specify influence of intermolecular interaction on IR spectrum of interacting species, an investigation of a process CCl₄ + Сr(АcacCl)₃ → CCl₄…Сr(АcacCl)₃ has been performed by means of Hartree–Fock–Roothaan method in MIDI basis set with p- and d- polarization functions. An estimation of intermolecular interaction in geometrical parameters, electron density function both between interacting particles and inside themselves, frequencies and intensities of normal modes has been carried out. Chemical bonds with the most significant shifts of characteristics under formation of nano-complex CCl₄…Сr(АcacCl)₃ have been noted.

The spectral lines broadening in femtosecond laser plasma generated by the 45 fs Ti:Sa laser pulses on the surface of the water solutions of Ba is investigated. Under the experimental conditions, determined the temperature of femtosecond laser plasma is 3000K.The contribution of the Doppler broadening for spectral lines width is minimal and amounts 0,0022 nm for Ba. The main mechanism of Ba spectral line broadening in experimental conditions is resonance. The resulting values of resonance broadening constitute a0,0349 nm for Ba I (413,24 nm), 0,0563 nm for Ba I (553,54 nm), 0,0241 nm for Ba II(455,41 nm), 0,0437 nm for Ba II (614,17 nm).

One of the main factors limiting the performance of conventional x-ray cargo inspection with material discrimination (MD) is the interlaced mode of system operation. Such systems use pulsed linac or betatron x-ray generators and produce alternate bremsstrahlung pulses with lower- and higher- end-point energies. Consequently, these systems provide about 50 mm lower penetration than a system operated in a non-interlaced mode, have a limited range of cargo areal densities with valid MD, and cannot perform MD of objects smaller than the pulse separation. Also, the limited pulse repetition rate of x-ray generators in interlaced mode limits the radiographic image quality at nominal commercial speeds of vehicles or trains.

Several new methods of cargo inspection with MD were recently introduced to address the above-mentioned limitations: dual-energy methods based on Scintillation-Cherenkov detectors [1]; multi-energy method based on intrapulse time-varying of spectral content of x-ray [1], [2]; multi-energy method utilized ramping-up energy packet of short x-ray pulses [3], [4]; and methods based on multi-energy betatron [5], [6]. All of these methods have electron accelerators as a core element. However, the accelerator requirements and, thus, their designs, are different for each system. In this paper, we will discuss the requirements for the accelerators, provide some details about their designs, and present several novel solutions for current and future projects.

A several hundred keV class compact proton microbeam system was developed as a prototype of a 1 MeV compact microbeam system to be used in micro-fabrication and micro-analyses. Optimization of an extraction condition was performed to increase demagnification and to achieve a beam diameter of approximately 1 μm. The beam diameter measurement showed that a diameter of 1.8 μm was obtained. This indicates that the compact microbeam system is a feasible alternative to a MeV class conventional large accelerator system.

It has previously been shown that the stability of the remote fusion cutting (RFC) process can be increased by modifying the intensity profile of the laser by means of a diffractive optical element (DOE). This paper investigates the quality of remote DOE cutting (RDC) conducted with a 3 kW single mode fiber laser in 0.5 mm stainless steel. An automatic measurement system is used to investigate how the travel speed, focus offset and angle of incidence effect the kerf width and kerf variance. The study shows that the RDC process has a very low kerf width variance, and that the kerf width decreases with cutting speed. Furthermore, selected etched samples show a significant increase in the perpendicularity of the cuts when compared to RFC. Also, on average, the depth of the layer of molten material for RFC is 83% deeper than for RDC.

The reliability of neutron resonance thermometry was discussed based on measurements of neutrons transmitted through tantalum (0.1 mm thick) and tungsten (1 mm thick) indicators at 26, 96, 189, and 285 degrees Celsius using the energy-resolved neutron imaging system, RADEN, at the Japan Proton Accelerator Complex (J-PARC). The intensity of transmitted neutrons at the sides of resonance dips were found to decrease with increasing temperature. Sensitivity coefficients to convert this decrease to temperature were derived, and two-dimensional distributions of the decreasing rates, being proportional to the temperature distribution, were obtained. The reliability of estimated temperature was calculated as a function of temporal and spatial resolution assuming that the dominant factor of the reliability was the uncertainty in the neutron counts. The authors set a target of neutron resonance thermometry for practical applications, and found a required efficiency of the neutron detector for resonance thermometry.