Synchrotron radiation

About: Synchrotron radiation is a research topic. Over the lifetime, 14639 publications have been published within this topic receiving 244775 citations. The topic is also known as: magnetobremsstrahlung radiation & Synchrotron Radiation.

A Fast X-Ray Absorption Spectrometer for Use with Synchrotron Radiation

Abstract: A quasi-parallel and polychromatic beam of synchrotron radiation is focused and dispersed by a curved crystal, so that the energy of each ray of the focused beam varies as a function of convergence angle through the focus. The specimen is placed at the focus. By measuring the X-ray intensity distribution across the beam behind the focus, in the presence and absence of the specimen, the absorption spectra of Cu and Ni metal foils were obtained. Using an X-ray film as the detector, a spectrum from a Cu foil was obtained in 0.1 seconds when the SPEAR storage ring at Stanford was operated at 3.1 GeV and 80 mA. The energy resolution is approximately 2.0 eV and the energy range of the spectrum is approximately 1 keV.

Time-resolved x-ray imaging of aluminum alloy solidification processes

Abstract: Time-resolved direct-beam X-ray imaging, with intense, coherent, and monochromatic third-generation synchrotron radiation, and a high-resolution fast-readout detector system have been used for in-situ studies of dendritic and eutectic growth processes in Al-Cu alloys. Temporal and spatial resolutions down to 0.25 seconds and 2.5 μm, respectively, were obtained with a field of view up to 1.4×1.4 mm2. Solid-liquid interfaces and various phase-specific segregates could be observed, and their dynamics could be traced in a sequence of temporally resolved images formed by phase and amplitude contrast from the sample. This article does not present any detailed analysis of a specific solidification phenomenon; instead, it presents to the scientific community an innovative technique for in-situ monitoring of such a phenomenon in real metallic systems.

Will reduced radiation damage occur with very small crystals

Abstract: The primary event which occurs when an X-ray photon of energy less than 30 keV is absorbed in a protein crystal (or other organic material) is the production of a photoelectron with a similar energy to that of the absorbed photon. The electron then scatters inelastically off the surrounding material losing energy in the process. This reduction in energy takes place over track lengths of a few µm for 20 keV electrons. The vector distances between the initial and final positions of the photoelectrons are less than the track lengths owing to the non-linear tracks followed by the electrons. For crystals with smaller dimensions than the vector distances, a significant proportion of the energy could leave the crystal with the high-energy electrons. This could provide an advantage in terms of reduced radiation damage. In order to estimate the possible benefits, calculations of the electron tracks are given, initially using the continuous slowing-down approximation. A Monte Carlo approach is then used to provide more accurate values of the vector distance travelled by electrons inside a protein crystal. The calculations indicate that significant reductions in radiation damage could occur for crystals of a few µm in size. The benefits would be greater when operating at higher energies. In addition, a scheme for realising the possible benefits in a practical situation is described. This could then form the basis of trial experiments.

High-Energy Emission from Millisecond Pulsars

Abstract: The X-ray and gamma-ray spectrum of rotation-powered millisecond pulsars is investigated in a model for acceleration and pair cascades on open field lines above the polar caps. Although these pulsars have low surface magnetic fields, their short periods allow them to have large magnetospheric potential drops, but the majority do not produce sufficient pairs to completely screen the accelerating electric field. In these sources, the primary and secondary electrons continue to accelerate to high altitude and their Lorentz factors are limited by curvature and synchrotron radiation reaction. The accelerating particles maintain high Lorentz factors and undergo cyclotron resonant absorption of radio emission, that produces and maintains a large pitch angle, resulting in a strong synchrotron component. The resulting spectra consist of several distinct components: curvature radiation from primary electrons dominating from 1 - 100 GeV, synchrotron radiation from primary and secondary electrons dominating up to about 100 MeV, and much weaker inverse-Compton radiation from primary electrons a t 0.1 - 1 TeV. We find that the relative size of these components depends on pulsar period, period derivative, and neutron star mass and radius with the level of the synchrotron component also depending sensitively on the radio emission properties. This model is successful in describing the observed X-ray and gamma-ray spectrum of PSR J0218+4232 as synchrotron radiation, peaking around 100 MeV and extending up to a turnover around several GeV. The predicted curvature radiation components from a number of millisecond pulsars, as well as the collective emission from the millisecond pulsars in globular clusters, should be detectable with AGILE and GLAST. We also discuss a hidden population of X-ray-quiet and radio-quiet millisecond pulsars which have evolved below the pair death line, some of which may be detectable by telescopes sensitive above 1 GeV. Subject headings: pulsars: general - radiation mechanisms: nonthermal - stars: neutron - gamma rays: theory