High-energy radiation from old pulsars

In this paper, we study nonthermal high energy radiation from old rotation-powered pulsars with ages greater than 10⁶ yr based on the revised outer gap model. In this model, the inclination angle and geometry of the magnetic field have been taken into account, and the fractional size f of the outer gap is determined by the electron/positron pair production process. The cascade process caused by the back-flowing particles moving from the outer gap to the star will produce the observed nonthermal X-ray emission, and the relativistic particles accelerated in the outer gap will produce gamma-rays via curvature radiation. For nine old pulsars which have been detected to have nonthermal X-rays, we first use the observed nonthermal X-ray emission to estimate reasonable inclination angles, and then estimate their gamma-ray emissions. We also study the possibilities of gamma-ray emissions from other old rotation-powered pulsars. We compare our predicted gamma-ray flux with the sensitivities of AGILE and Fermi.

     

Refractive Lenses for Microscopy and Nanoanalysis

X-rays offer indispensable opportunities for science, medicine, and technology due to a large variety of exceptional properties. The large penetration depth of X-rays in matter allows one to investigate the inner structures of an object without destructive sample preparation, or inside special sample environments, such as chemical reactors or pressure cells. In this way, X-rays are ideally suited to study physical and chemical processes in situ and operando. In addition, X-ray analytical techniques, such as X-ray diffraction, fluorescence, and absorption, provide atomic-scale structure information, elemental concentrations, and the chemical state of a given elemental species inside the sample. With the advent of highly brilliant synchrotron radiation sources of the third generation, it became possible to combine X-ray analytics with microscopy, triggering the rapid development of new types of optics for X-rays, amongst which refractive X-ray lenses have progressed at a spectacular pace.     

Experiment of X-ray Generations Using Laser-Compton Scattering at LINAC of SINAP

Laser Compton scattering(LCS) can generate X-rays or y-rays with high brightness and easy controlled polarization by applying high-peak-power laser pulses to relativistic electron bunches.One of the most promising approaches to short pulsed X-ray sources is the laser synchrotron source.It is based on LCS between picoseconds relativistic electron bunches and picoseconds laser pulses.A project of Shanghai laser electron gamma source with LCS method has been proposed on Shanghai synchrotron radiation facility.Before that,a prototype has been developed in the beamline of the linear accelerator at the Shanghai Institute of Applied Physics,Chinese Academy of Sciences.The LCS experiment was carried out by using the 107 MeV,5 Hz,1 ns,0.1 nC electron bunches from the linear accelerator and the 18 ns,10 MW peak power,Nd:YAG laser pulses.In this communication,we describe the details and report the first results of this experiment.     

高能电子在强激光场中的同步辐射获得超短X射线脉冲

 研究了逆流相对论高能电子与强激光脉冲相互作用的同步辐射过程,当电子具有合适的初速度且传播方向与激光的传播方向相反时,电子在激光脉冲中心作圆周运动。由于电子的运动半径比传统同步辐射环中电子的运动半径小几个数量级,因此电子的辐射能量大大增加。研究发现此过程可以获得阿秒和泽秒X射线脉冲;同时发现随着入射电子初能量的增加和激光能量的增强,获得X射线脉冲脉宽越来越短,强度越来越大。这使得激光同步辐射可以成为一种强大的短波长短脉宽的辐射光源。     

New high-power source of directional electromagnetic radiation

A new source of electromagnetic radiation in a wide spectral range can be based on multiple contactless deflection of the beams of charged particles in a circular channel. The radiation with wavelengths ranging from submillimeter to radio ranges can be generated using nonrelativistic electrons. Directional radiation is obtained at relativistic energies. The IR, optical, and UV radiation can be generated. The X-ray and gamma-radiation can be obtained at relatively high energies. The new source is compared with the source of synchrotron radiation. The radiation intensity at energies of 1–2 GeV is relatively high, since strong currents are possible in the ring channel. The channeling and synchrotron emission are simultaneously obtained at relatively small (several tens of nanometers) internal diameters of the ring.     

Generation of X-rays at bubble cavitation in a fast liquid jet in dielectric channels

The paper presents the results of studying the combined shock-wave radiation-emission processes associated with cavitation phenomena that occur at fast directional motion of a liquid jet into a closed working chamber through narrow dielectric channels. These processes induce high-power tunable X-ray radiation outside the chamber. At a relatively small liquid pressure, cavitation has been shown to generate shock waves in the chamber walls, which excites surface atoms and leads to the emission of X-rays from the outer surface of the chamber. At a high liquid pressure, the liquid jet does not touch the chamber walls and the cavitational shock waves lead to the excitation of the surface atoms of the jet itself accompanied by the generation of optical and X-ray radiation in the jet, which has been also observed in experiments.     

Theoretical and experimental study of the electronic structure of tin dioxide

The electronic structure of tin dioxide has been theoretically studied within the linearized augmented plane wave method using the Wien2k program package. The total and local partial electron densities of states have been calculated. The X-ray emission K-spectrum of oxygen has been calculated. The X-ray absorption spectra of the tin M _4,5-edge and oxygen K-edge have been calculated by simulating the supercell and core hole. The calculated results have been compared with the experimental data obtained using synchrotron radiation.     

Anomalous scattering,transport, and spatial distribution of X-ray fluorescence at the exit of polycapillary structures

The angular distribution of the X-ray intensity at the exit of microchannel plates at grazing incidence of monochromatic radiation on the walls of microcapillaries has been investigated. The angles and energies of the primary radiation quanta at which the synchrotron beam excites X-ray fluorescence propagating inside polycapillary structures have been determined. The angular dependences of the intensity distribution of X-rays transmitted through the microcapillaries have been studied theoretically and experimentally for energies corresponding to the region of anomalous dispersion near the L _2,3 absorption edges of silicon. The propagation of waves in hollow polycapillary waveguides, the excitation of X-ray fluorescence, and the X-ray diffraction at the exit of microchannel plates have been modeled mathematically. The mathematical model takes into account the presence of a transition layer on the microchannel surface.     

Radiation damage in soft X-ray microscopy

The rates of chemical transformation by radiation damage of polystyrene (PS), poly(methyl methacrylate) (PMMA), and fibrinogen (Fg) in a X-ray photoemission electron microscope (X-PEEM) and in a scanning transmission X-ray microscope (STXM) have been measured quantitatively using synchrotron radiation. As part of the method of dose evaluation in X-PEEM, the characteristic (1/e) sampling depth of X-PEEM for polystyrene in the C 1s region was measured to be 4 ± 1 nm. Critical doses for chemical change as monitored by changes in the X-ray absorption spectra are 80 (12), 280 (40) and 1230 (180) MGy (1 MGy = 6.242*ρ eV/nm³, where ρ is the polymer density in g/cm³) at 300 eV photon energy for PMMA, Fg and PS, respectively. The critical dose for each material is comparable in X-PEEM and STXM and the values cited are thus the mean of the values determined by X-PEEM and STXM. C 1s, N 1s and O 1s spectroscopy of the damaged materials is used to gain insight into the chemical changes that soft X-rays induce in these materials.     

Generation of femtosecond X-ray pulses via laser–electron beam interaction

The generation of femtosecond X-ray pulses will have important scientific applications by enabling the direct measurement of atomic motion and structural dynamics in condensed matter on the fundamental time scale of a vibrational period. Interaction of femtosecond laser pulses with relativistic electron beams is an effective approach to generating femtosecond pulses of X-rays. In this paper we present recent results from proof-of-principle experiments in which 300 fs pulses are generated from a synchrotron storage ring by using an ultrashort optical pulse to create femtosecond time structure on the stored electron bunch. A previously demonstrated approach for generating femtosecond X-rays via Thomson scattering between terawatt laser pulses and relativistic electrons is reviewed and compared with storage-ring based schemes.     

电子磁矩对同步辐射频谱的修正

本文从偶极子辐射场的Heaviside-Feynman表达式出发, 用经典的电动力学方法推导了考虑内禀磁矩影响后的相对论电子辐射频谱分布的表达式, 并对做匀速圆周运动的极端相对论性电子的同步辐射, 计算了两个偏振方向上的考虑磁矩修正后的辐射谱. 计算结果表明对于特征频率为ω_c的同步辐射, 如果ħω_c≥10 keV, 内禀磁矩对辐射的修正是可观的. 通过同步辐射的内禀磁矩修正, 本文讨论了电子束极化度与辐射场偏振度的依赖关系, 并基于此关系提出一种测量电子束极化度的新方法. 关键词： 同步辐射 电子内禀磁矩 同步辐射偏振度 束流极化度     

ESRF 11th users' meeting and workshops

More than 90 participants from Europe, the US and Japan gathered from April 27 to 29, 2005, in Zeuthen, near Berlin, to hold a lively international meeting on time-resolved soft X-ray science. The meeting continued the series of preceding workshops held in 2002 in Napa (California, USA) and in 2003 in Montreux (Switzerland). It was organized by the three synchrotron radiation sources BESSY (Berlin, Germany), the Swiss Light Source SLS (Villigen) and the French synchrotron radiation source SOLEIL (Orsay).

The aim of the workshop was to bring together the existing ultrafast laser community and the emerging ultrafast X-ray community in order to discuss recent scientific highlights from both fields and to outline new directions for the application of ultrafast X-rays.     

Active galactic nuclei at gamma-ray energies

Active Galactic Nuclei can be copious extragalactic emitters of MeV–GeV–TeV γ rays, a phenomenon linked to the presence of relativistic jets powered by a super-massive black hole in the center of the host galaxy. Most of γ-ray emitting active galactic nuclei, with more than 1500 known at GeV energies, and more than 60 at TeV energies, are called “blazars”. The standard blazar paradigm features a jet of relativistic magnetized plasma ejected from the neighborhood of a spinning and accreting super-massive black hole, close to the observer direction. Two classes of blazars are distinguished from observations: the flat-spectrum radio-quasar class (FSRQ) is characterized by strong external radiation fields, emission of broad optical lines, and dust tori. The BL Lac class (from the name of one of its members, BL Lacertae) corresponds to weaker advection-dominated flows with γ-ray spectra dominated by the inverse Compton effect on synchrotron photons. This paradigm has been very successful for modeling the broadband spectral energy distributions of blazars. However, many fundamental issues remain, including the role of hadronic processes and the rapid variability of a few FSRQs and several BL Lac objects whose synchrotron spectrum peaks at UV or X-ray frequencies. A class of γ-ray-emitting radio galaxies, which are thought to be the misaligned counterparts of blazars, has emerged from the results of the Fermi-Large Area Telescope and of ground-based Cherenkov telescopes. Soft γ-ray emission has been detected from a few nearby Seyfert galaxies, though it is not clear whether those γ rays originate from the nucleus. Blazars and their misaligned counterparts make up most of the ≳100 MeV extragalactic γ-ray background (EGB), and are suspected of being the sources of ultra-high energy cosmic rays. The future “Cherenkov Telescope Array”, in synergy with the Fermi-Large Area Telescope and a wide range of telescopes in space and on the ground, will write the next chapter of blazar physics.     

高线密度X光透射光栅衍射效率

高线密度X光透射光栅是各种高分辨光栅摄谱仪的核心色散元件,为了获得较高的光谱分辨率,工作在2~5 keV能区的光谱仪需要使用5000 l/mm的X射线透射光栅。为了获得光栅的绝对衍射效率,采用同步辐射光在多个能点对5000 l/mm的X光透射光栅进行衍射效率实验标定,通过光栅相对衍射效率拟合获得了光栅结构参数,与光栅结构测量结果非常接近。然后,采用衍射效率的矩形栅线模型,计算得到了光栅的绝对衍射效率。     

Highlights of synchrotron radiation

The applications of the electromagnetic radiation generated by relativistic electrons circulating in synchrotrons and storage rings have rapidly extended into many scientific disciplines. This article first briefly reviews the history of synchrotron radiation, and recapitulates its properties. The available sources are listed, and some aspects of the facilities that are required to make use of the radiation are discussed, with particular emphasis on the optical elements. Several noteworthy examples of scientific research conducted with synchrotron radiation are described. These are drawn principally from the X-ray region, and comprise X-ray fluorescence, small-angle scattering, powder profile refinement, extended X-ray absorption fine structure, topography, time-resolved spectroscopy, and VUV and photoelectron spectroscopy of solids. In conclusion, a few topics are mentioned relating to the future expansion and application of synchrotron radiation research facilities.     

Adventures with Synchrotron Radiation at Harvard

In the late 1950s, a 6 GeV electron synchrotron (the CEA) was being built at Harvard/MIT. Ed Purcell, who generally trafficked in volts (or maybe kilovolts), but never gigavolts, was thinking about what one could do with all that synchrotron radiation that otherwise would uselessly warm up the walls of the beamline (I remember well his student Roger Tsien's nice drawing of radiation from kinks in the outgoing E-field lines of an electron in relativistic circular motion; see Figure 1).     

Ultra-short efficient laser-driven hard X-ray source operated at a kHz repetition rate

Ultra-short bursts of hard X-ray radiation are generated by interaction of high-contrast femtosecond laser pulses with a jet of liquid Ga. The X-ray emission shows a strong dependence on the angle of incidence and polarization of the laser beam, consistent with the processes of resonant absorption and vacuum heating. As much as 60% of the total X-ray emission consists of [_Ga]K radiation (9.22–9.25 keV) with a photon flux of 6×10⁹ photons/(ssrad). Using this novel X-ray source, static diffraction patterns from a GaAs(111) crystal were recorded with an acquisition time of 2 s. PACS 52.38.Ph; 52.59.Px; 52.50.Jm     

X-ray transition radiation of electrons with energy of 300 to 900 MeV in periodic multifoil radiators

Results of experiments conducted at the Tomsk synchrotron to study resonant X-ray transition radiation generated by relativistic electrons in periodic multifoil radiators are reviewed. Both the internal synchrotron beam and the external secondary electron beam from the pair magnetic γ-spectrometer with energies ranging from 300 to 900 MeV were used in the experiments. The radiators consisted of many thin amorphous foils of various materials. The generation of X-ray radiation in a compound radiator consisting of a multifoil radiator and a crystal is also studied. In this case, the resonant X-ray transition radiation generated in the multifoil radiator is diffracted in the crystal and emitted at Bragg angles, together with the parametric X-ray radiation generated in the crystal. Spectral and angular properties of the resonant X-ray transition radiation and diffracted resonant X-ray transition radiation are investigated. The ratio between the contributions from the diffracted resonant X-ray transition radiation and other types of radiation to the total coherent X-ray radiation flux generated by electrons in periodic structures and crystals is estimated.     

Method of kinematic projecting of pulsar-emission profiles

A method for constructing profiles of incoherent pulsar emission based on the instantaneous angular phase distribution function of radiant power emitted by a relativistic source that moves in the magnetosphere of a neutron star is suggested. In general, this phase function depends on the kinematic parameters of the radiation source (its velocity and acceleration) and on the direction of radiation emission with respect to the rotating neutron star (the observation direction). The method is illustrated by the example of calculated profiles of fan pulsar radiation with the use of the phase function of synchrotron radiation. It is stated that his method can easily be generalized for other types of relativistic radiation. Tomsk State University; Tomsk State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 26–31, January, 2000.