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.

Gamma-ray emission from massive young stellar objects

Abstract: Context. Massive stars form in dense and massive molecular cores. The exact formation mechanism is unclear, but it is possible that some massive stars are formed by processes similar to those that produce the low-mass stars, with accretion/ejection phenomena occurring at some point of the evolution of the protostar. This picture seems to be supported by the detection of a collimated stellar wind emanating from the massive protostar IRAS 16547 4247. A triple radio source is associated with the protostar: a compact core and two radio lobes. The emission of the southern lobe is clearly non-thermal. Such emission is interpreted as synchrotron radiation produced by relativistic electrons locally accelerated at the termination point of a thermal jet. Since the ambient medium is determined by the properties of the molecular cloud in which the whole system is embedded, we can expect high densities of particles and infrared photons. Because of the confirmed presence of relativistic electrons, inverse Compton and relativistic Bremsstrahlung interactions are unavoidable. Aims. We aim at making quantitative predictions of the spectral energy distribution of the non-thermal spots generated by massive young stellar objects, with emphasis on the particular case of IRAS 16547 4247. Methods. We study the high-energy emission generated by the relativistic electrons that produce the non-thermal radio source in IRAS 16547 4247. We also study the result of proton acceleration at the terminal shock of the thermal jet and make estimates of the secondary gamma-rays and electron-positron pairs produced by pion decay. Results. We present spectral energy distributions for the southern lobe of IRAS 16547 4247, for a variety of conditions. We show that high-energy emission might be detectable from this object in the gamma-ray domain. The source may also be detectable at X-rays through long exposures with current X-ray instruments. Conclusions. Gamma-ray telescopes like GLAST, and even ground-based Cherenkov arrays of new generation can be used to study non-thermal processes occurring during the formation of massive stars.

Characterization of a synthetic single crystal diamond detector for dosimetry in spatially fractionated synchrotron x-ray fields.

Abstract: Purpose: Modern radiotherapy modalities often use small or nonstandard fields to ensure highly localized and precise dose delivery, challenging conventional clinical dosimetry protocols. The emergence of preclinical spatially fractionated synchrotron radiotherapies with high dose-rate, sub-millimetric parallel kilovoltage x-ray beams, has pushed clinical dosimetry to its limit. A commercially available synthetic single crystal diamond detector designed for small field dosimetry has been characterized to assess its potential as a dosimeter for synchrotron microbeam and minibeam radiotherapy. Methods: Experiments were carried out using a synthetic diamond detector on the imaging and medical beamline (IMBL) at the Australian Synchrotron. The energy dependence of the detector was characterized by cross-referencing with a calibrated ionization chamber in monoenergetic beams in the energy range 30–120 keV. The dose-rate dependence was measured in the range 1–700 Gy/s. Dosimetric quantities were measured in filtered white beams, with a weighted mean energy of 95 keV, in broadbeam and spatially fractionated geometries, and compared to reference dosimeters. Results: The detector exhibits an energy dependence; however, beam quality correction factors (kQ) have been measured for energies in the range 30–120 keV. The kQ factor for the weighted mean energy of the IMBL radiotherapy spectrum, 95 keV, is 1.05 ± 0.09. The detector response is independent of dose-rate in the range 1–700 Gy/s. The percentage depth dose curves measured by the diamond detector were compared to ionization chambers and agreed to within 2%. Profile measurements of microbeam and minibeam arrays were performed. The beams are well resolved and the full width at halfmaximum agrees with the nominal width of the beams. The peak to valley dose ratio (PVDR) calculated from the profiles at various depths in water agrees within experimental error with PVDR calculations from Gafchromic film data. Conclusions: The synthetic diamond detector is now well characterized and will be used to develop an experimental dosimetry protocol for spatially fractionated synchrotron radiotherapy.

The Spectral Properties of Shocked Two-Component Accretion Flows in the Presence of Synchrotron Emission

Abstract: Two-component advective flows have Keplerian accretion disks on the equatorial plane that is surrounded by sub-Keplerian transonic flows. In this Letter, we study the spectral properties of these flows when the shocks are present. The shock acceleration produces nonthermal electrons in the postshock region that in turn produce power-law synchrotron radiation. The soft photons generated by the bremsstrahlung and synchrotron processes in the sub-Keplerian flow, as well as the multicolor blackbody emission from the Keplerian disk, are Comptonized by the thermal and nonthermal electrons. By varying Keplerian and sub-Keplerian rates, we are able to reproduce the observed soft and hard states as far as the X-ray region is concerned and "low γ-ray intensity" and "high γ-ray intensity" states as far as the soft γ-ray region is concerned. We also find two pivotal points where the spectra intersect, as is observed in, e.g., Cyg X-1.

Recent applications and current trends in analytical chemistry using synchrotron-based Fourier-transform infrared microspectroscopy

Abstract: Synchrotron radiation based Fourier-transform infrared (SR-FTIR) microspectroscopy is an emerging technique, which is increasingly employed in analytical sciences. This technique combines FTIR spectroscopy (namely specific identification of molecular groups within a variety of environments: organic/inorganic, crystallized/amorphous, solid/liquid/gas) with high brightness, and therefore small spot size and faster acquisition of high-quality spectral imaging data from a synchrotron light source. In this article, we review several recent applications of SR-FTIR that have led to much of the improved analytical capabilities. Performing analytical science at large-scale facilities allows one to access state-of-the-art equipment and capabilities, receive expert assistance from the facility staff, and have the possibility of combining SR-FTIR microscopy with other synchrotron-based X-ray microimaging techniques.