6 MeV storage ring dedicated to hard X-ray imaging and far-infrared spectroscopy

The tabletop storage ring, 6 MeV MIRRORCLE, is dedicated to hard X-ray imaging as well as far-infrared (FIR) spectroscopy. In spite of low electron energy, the 6 MeV MIRRORCLE generates hard X-rays ranging from 10 keV up to its electron energy and milliwatt order sub-millimetre range FIR rays. Bremsstrahlung is the mechanism for the hard X-ray generation. Images produced with 11× geometrical magnification display a sharply enhanced edge effect when generated using a 25 mm rod electron target. Bright far-infrared is generated in the same way using a conventional synchrotron light source, but with MIRRORCLE the spectral flux is found to be ∼1000 times greater than that of a standard thermal source. Partially coherent enhancement is observed in the case of FIR output.     

Undulators for the PSI Light Sources

The Swiss Light Source (SLS) at the Paul Scherrer Institut (PSI) started user operation in 2001. It has been the first medium energy light source to rely on undulators for the production of X-rays up to 20 keV. For soft X-rays, APPLE II-type undulators, providing full polarization control and quasiperiodic electromagnetic undulators, have been installed. The hard X-ray range has been accessed by the newly developed small-gap, short-period, in-vacuum undulators operated on high harmonics. Based on this, FEMTO, the first hard X-ray undulator source for femtosecond (fs) experiments, started operation in 2006.     

整体X光透镜性能实验研究

利用高计数率探测器和低功率光源,在大的能量范围内,同时测量了整体X光透镜的传输效率和焦斑直径与能量的关系。实验结果表明：透镜的焦斑直径随着能量的升高而减小;对04-5-10-5透镜而言,在高于5．8keV的能量范围内,透镜的传输效率随着能量的升高而降低,在低于5．8keV的能量范围内,透镜的传输效率随着能量的升高而增加。通过测量不同能量的X射线在透镜会聚光束中的空间分布,研究了短出口焦距透镜的光晕现象,光晕会导致透镜焦斑直径增大和传输效率测量值的增加。利用轴向扫描法研究了整体X光透镜出口焦距和能量的关系,实验结果表明：会聚透镜的出口焦距随着X射线能量的升高而增加。     

Investigation of roughness cross correlation in a Ni/C multilayer mirror by X-ray diffuse scattering method

The possibility of applying X-ray diffuse scattering for studying roughness in multilayer X-ray mirrors, including the correlation of roughnesses of neighboring interfaces (roughness cross-correlation) is considered. It is shown that the reliability and informativeness of this method can be improved by rejecting the classical experimental schemes and using alternative schemes in which not only the intensity of diffuse scattering itself, but also its dependence on certain experimental parameters (conditions), vary. Such parameters can be the spatial coherence of incident radiation, the direction of the momentum transfer relative to the specular diffraction plane, or the X-ray wavelength. In the framework of this approach, the results of comparative measurements of diffuse scattering from a Ni/C multilayer X-ray mirror prepared by laser ablation are considered for two close values of photon energy: below (8.325 keV) and above (8.350 keV) the K absorption edge for nickel. It is shown that, in view of effective screening of deep layers in the hard photoabsorption mode, this method provides more reliable (as compared to the standard diffuse scattering method) information on the evolution of interfaces between the layers. It is found that the smoothing of roughness in the experimental sample occurs over large spatial scales such as the micrometer scale. Only large-scale defects with a size exceeding 10 µm are replicated well from layer to layer. Possible physical reasons for the observed effect are considered. It is shown that effective smoothing on the micrometer and submicrometer spatial scales is of fundamental importance for preparing multilayer X-ray mirrors with high reflectances.     

Absolute measurement of photon flux using ionization chamber in (6~20) keV synchrotron radiation X-rays

Absolute measurement of photon flux under high-fluence rate X-rays was required in photon diagnostics for X-ray lasers. A free-air ionization chamber used for the reproducibility of air-kerma in high-fluence rate X-ray was designed, and the monoenergetic X-rays flux of (6–20) keV were absolutely measured on Beijing Synchrotron Radiation Facility. The energy spectrum of the monoenergetic X-rays was measured using a silicon drift detector, and the proportion of higher harmonics was determined. The saturation curve, air attenuation correction factor, and composite loss correction factor of the free-air ionization chamber were obtained experimentally. The air-kerma rate for the (6~20) keV monoenergetic X-ray was measured accurately, and the relative combined standard uncertainty of the air-kerma is 0.61%.     

Development of In-Situ/Operando Sample Cells for Soft X-ray Transmission Spectromicroscopy at UVSOR-III Synchrotron

In-situ/operando techniques have been developed for spectromicroscopic studies of heavy elements using hard X-rays with high transmittance in samples and long focal length of optical elements (i.e., long working distance) at photon energies >4 keV. On the other hand, in-situ measurements in the soft X-ray region for spectromicroscopic studies of light elements at deep inner shells and heavy elements at shallow inner shells face significant technical challenges due to several difficulties, including low transmittance and short focal lengths of optical elements. Scanning transmission X-ray microscopy (STXM) in the soft X-ray region is a promising technique for in-situ observation in comparison with other microscopic techniques using electrons and ions, considering its characteristics, such as high resolving power in energy and in space, low radiation damage, and two-dimensional (and three-dimensional) chemical state analysis using near-edge X-ray absorption fine structure.     

Detection of low energy scattered X-rays using charged spheres

To detect low energy scattered X-ray dose below 9.5 keV simply, we have designed a low energy X-ray detector that uses multiple electrically charged conductive spheres floated by static electricity repulsion force. This detector detects the dose with the following steps (principles): (1) positive and negative ions are generated by ionization function of low energy X-rays projected in the detector; (2) those ions neutralize the electrically charged conductive spheres floated; (3) accordingly, the spheres fall; and (4) the detector detects low energy X-ray dose from the number of the conductive spheres fallen. This paper verified performance of this detector.     

Cosmological evolution of supermassive black holes in galactic centers unveiled by hard X-ray observations

We review the current understanding of the cosmological evolution of supermassive black holes in galactic centers elucidated by X-ray surveys of active galactic nuclei (AGNs). Hard X-ray observations at energies above 2 keV are the most efficient and complete tools to find “obscured” AGNs, which are dominant populations among all AGNs. Combinations of surveys with various flux limits and survey area have enabled us to determine the space number density and obscuration properties of AGNs as a function of luminosity and redshift. The results have essentially solved the origin of the X-ray background in the energy band below ∼10 keV. The downsizing (or anti-hierarchical) evolution that more luminous AGNs have the space-density peak at higher redshifts has been discovered, challenging theories of galaxy and black hole formation. Finally, we summarize unresolved issues on AGN evolution and prospects for future X-ray missions.     

Molecular-orbital X-rays from 1 GeV 208Pb + 208Pb and 209Bi + 209Bi collisions

We have measured the spectra of continuum X-rays above the characteristic K lines for 4.5 to 4.8 MeV/N ²⁰⁸₈₂Pb → ²⁰⁸₈₂Pb, Pb → Bi, Bi → Pb and Bi → Bi collisions. Above ≈400 keV X-ray energy the spectral shape and intensity agree roughly with calculations of Kirsch et al. for the 1sσ molecular-orbital (MO) X-ray spectrum from Pb-Pb. Deviations from the theory below ≈400 keV suggest transitions to other MO's.     

A black hole spectral signature

An accreting black hole is, by definition, characterized by the drain. Namely, the matter falls into a black hole much the same way as water disappears down a drain — matter goes in and nothing comes out. As this can only happen in a black hole, it provides a way to see “a black hole”, an unique observational signature. The accretion proceeds almost in a free-fall manner close to the black hole horizon, where the strong gravitational field dominates the pressure forces. In this paper we present analytical calculations and Monte-Carlo simulations of the specific features of X-ray spectra formed as a result of upscattering of the soft (disk) photons in the converging inflow (CI) into the black hole. The full relativistic treatment has been implemented to reproduce these spectra. We show that spectra in the soft state of black hole systems (BHS) can be described as the sum of a thermal (disk) component and the convolution of some fraction of this component with the CI upscattering spread (Greens) function. The latter boosted photon component is seen as an extended power-law at energies much higher than the characteristic energy of the soft photons. We demonstrate the stability of the power spectral index over a wide range of the plasma temperature 0 – 10 keV and mass accretion rates (higher than 2 in Eddington units). We also demonstrate that the sharp high energy cutoff occurs at energies of 200–400 keV which are related to the average energy of electrons m_ec² impinging upon the event horizon. The spectrum is practically identical to the standard thermal Comptonization spectrum when the CI plasma temperature is getting of order of 50 keV (the typical ones for the hard state of BHS). In this case one can see the effect of the bulk motion only at high energies where there is an excess in the CI spectrum with respect to the pure thermal one. Furthermore we demonstrate that the change of spectral shapes from the soft X-ray state to the hard X-ray state is clearly to be related with the temperature of the bulk flow. In other words the effect of the bulk Comptonization compared to the thermal one is getting stronger when the plasma temperature drops below 10 keV. We clearly demonstrate that these spectra emerging from the converging inflow are a inevitable stamp of the BHS where the strong gravitational field dominates the pressure forces.     

Enhanced betatron radiation by a modulating laser pulse in laser wakefield acceleration

We propose a new idea to enhance and control the betatron radiation by using a modulating laser pulse in laser wakefield acceleration. In this scheme, a high-power laser pulse is used for self-trapping and acceleration of the plasma electrons and the accelerated electron beam is modulated by a separately-propagating laser pulse for large amplitude betatron oscillations and microbunching. In this way, the relatively low power modulating laser pulse can enhance the X-ray photon flux and energy significantly. We performed two-dimensional particle-in-cell simulations to demonstrate the idea and the results show that a sub-TW laser pulse is enough for electron beam modulation and it can generate easily-controllable fs X-ray pulses with a wide range of photon energies from soft X-rays to hard X-rays.     

ZnO:Ga晶体对硬X射线的时间及能量响应

 介绍了ZnO:Ga晶体对重复频率快脉冲硬X 射线的时间响应,利用X射线荧光分析仪测量了ZnO:Ga晶体对10～100 keV硬X射线的能量响应。结果表明:ZnO:Ga晶体对硬X射线响应的上升时间为316 ps,半高宽为440 ps;对40 keV以上的X射线的能量响应很平坦。该晶体可以作为一种新颖的硬X射线探测元件。     

Laser acceleration in novel media

With newly available compact laser technology [1] we are capable of producing 100?PW-class laser pulses with a single-cycle duration on the femtosecond timescale. With this fs intense laser we can produce a coherent X-ray pulse that is also compressed, well into the hard X-ray regime (～10?keV) and with a power up to as much as 10 Exawatts. We suggest utilizing these coherent X-rays to drive the acceleration of particles. Such X-rays are focusable far beyond the diffraction limit of the original laser wavelength and when injected into a crystal it forms a metallic-density electron plasma ideally suited for laser wakefield acceleration. If the X-ray field is limited by the Schwinger field at the focal size of ～100?nm, the achievable energy is 1?PeV over 50?m. (If the X-rays are focused further, much higher energies beyond this are possible). These processes are not limited to only electron acceleration, and if ions are pre-accelerated to beyond GeV they are capable of being further accelerated using a LWFA scheme [2] to similar energies as electrons over the same distance-scales. Such high energy proton (and ion) beams can induce copious neutrons, which can also give rise to intense compact muon beams and neutrino beams that may be portable. High-energy gamma rays can also be efficiently emitted with a bril- liance many orders of magnitude above the brightest X-ray sources by this accelerating process, from both the betatron radiation as well as the dominant radiative-damping dynamics. With the exceptional conditions enabled by this technology we envision a whole scope of new physical phenomena, including: the possibility of laser self-focus in the vacuum, neutron manipulation by the beat of such lasers, zeptosecond spectroscopy of nuclei, etc. Further, we now introduce along with the idea of vacuum as a nonlinear medium, the Schwinger Fiber Accelerator. This is a self-organized vacuum fiber acceleration concept, in which the repeated process of self-focusing and defocusing for the X-ray pulse in vacuum forms a modulated fiber that guides the intense X-rays.     

微型X射线管出射谱特征研究及Be窗厚度确定

微型X射线管已广泛应用于现场元素分析、放射性医疗等领域,对于微型X射线管铍窗,普遍认为除保证管内真空外,应越薄越好。采用蒙特卡洛方法,模拟了从50～500 μm范围内共13个Be窗厚度的微型X射线管出射X射线谱。按照在应用中的作用,将出射X射线划分为不同能量段进行分析。通过分析谱线特征,发现Be窗厚度应依据其应用要求合理选择。因此,提出了K系特征X射线与轫致辐射强度的比值和低能射线与激发射线计数比值等参量作为评价Be窗厚度最优化的判断依据。除上述评判指标外,铍窗的厚度最优化选择还应考虑Be窗对不同能量X射线的屏蔽效果。依据模拟结果分析,原位(现场)X射线能量色散荧光分析应用中,Be窗厚度约250 μm的微型X射线管最为合适。与50 μm铍窗厚度出射射线相比,71.66%低能原级X射线被屏蔽,5~50 keV能量原级X射线仅有21.31%被屏蔽,低能射线强度占总X射线比值小于10%,且K系X射线占激发射线的比例仍保持较高的水平。因此,采用250 μm铍窗厚度的微型X射线管作为能量色散激发源,能保证探测器探测的有效信号比值较高,低能X射线对探测器的能量分辨率的影响最小,而且能量色散分析谱线的散射本底相对强度处于较低的水平,从而保证元素分析结果精准度。对于放射性治疗的应用中,则铍窗厚度越薄越好,此时,低能X射线具有较高的通量,能保证辐射剂量在治疗组织中剂量的集中。     

EUV and fast ion emission from cryogenic liquid jet target laser-generated plasma

A liquid jet of either nitrogen or argon of 20 μm diameter was exposed to intense laser fields with pulse durations between 70 fs and 250 ps, leading to intensities of 10¹⁶ W cm^-2 and 10¹³ W cm^-2, respectively. The emission of extreme UV light and soft X-rays shows the characteristic lines of hydrogen-like nitrogen and carbon-like argon. For nitrogen the emitted photon flux at 250 ps was about two orders of magnitude higher than for 70 fs pulses. A weak dependence on the laser polarization with respect to the liquid jet axis was found. The kinetic energy of the emitted ions easily exceeded 100 keV for nitrogen and 200 keV for argon for a pulse duration close to 2 ps. Received: 21 August 2000 / Revised version: 20 December 2000 / Published online: 22 March 2001     

Increase in the superconducting transition temperature in Zr-Hf alloys due to <Emphasis Type="Italic">s-d</Emphasis> electron transfer under pressure

Correlation between the roughness of neighboring interfaces (roughness cross correlation) in a Ni/C X-ray multilayer mirror (XMM) prepared by laser ablation was studied by measuring X-ray diffuse scattering (XDS). The XDS intensities in the vicinity of the first Bragg reflection were measured at different photon energies: slightly below (8.325 keV) and slightly above (8.350 keV) the nickel photoabsorption K edge. The effective screening of the contribution from the deep layers to the XDS cross section due to the strong damping of the wave field at a photon energy higher than the photoabsorption edge allowed information on the character of the in-depth roughness cross correlation in the sample to be obtained. In particular, the characteristic lateral correlation length of the roughness was 0.35 µm at a photon energy of 8.325 keV (the contribution to the XDS cross section of the entire XMM volume), and it increased to 0.4 µm at a photon energy of 8.350 keV (predominantly the contribution from the upper layers). These data give direct evidence for the mechanism of smoothing of the interfacial roughness in the process of Ni/C XMM growth on anomalously large (up to micron) spatial scales. It was found that only rough large-scale defects with sizes of ≥10 µm are reproduced reasonably well from layer to layer. The processes of viscous flow and (or) reevaporation of high-energy target ions during deposition, which is characteristic of the laser method of XMM preparation, may serve as a possible explanation of the observed phenomenon.     

Soft X-ray radiation due to a nanosecond diffuse discharge in atmospheric-pressure air

A source of soft X-rays with an effective photon energy of 9 keV and a subnanosecond pulse width is built around a gas diode filled with atmospheric-pressure air and a UAEB-150 generator. A collector placed behind a grounded mesh electrode detects an electron beam and a pulse with positive polarity, the latter being due to an electric field surrounding the mesh. It is shown that the intensity of soft X-rays from the gas-diode-based source depends on the material of a massive potential anode; namely, it grows with an increase in the atomic number of the cathode material. In the case of a tantalum anode, X-ray photons with an effective energy of 9 and 17 keV contribute to the exposure dose.     

X-ray fluorescence in some rare earth and high Z elements excited by 661.6 keV γ-rays

The K-shell X-ray fluorescence cross sections are determined experimentally for 10 elements such as Pb, Hg, Ir, W, Lu, Tm, Dy, Tb, Gd and Nd at excitation energy of 661.6 keV associated with γ-rays of ¹³⁷Cs radioisotope. The technique employed involves the measurement of total intensity of fluorescent K X-rays that follow the photoeffect absorption of a known flux of γ-rays using a well type Nal(Tl) detector. The obtained results are compared with the available theoretical values and other measured values.     

X射线探测器的脉冲标定技术

利用强流电子束技术产生通量密度为10¹⁸—10¹⁹X-ray photon/sr·s的脉冲CuKX射线源,标定PIN型硅二极管半导体探测器对X光子的脉冲灵敏度。用绝对X射线监测器——P10气体脉冲电离室作为脉冲X射线通量密度的标准。脉冲电荷自动测量仪由微处理机进行程序控制,并予以实时校准。该电离室测量通量密度的精度为±5％,适用的能通量率范围可达4×10^-9—2×10²W/cm²,适用的光子能量范围为1.5—10keV,标定探测器的精度为±7.0％,并发现PIN型硅二极管的脉冲灵敏度比稳态X射线束标定的灵敏度高30％左右。 关键词：     

聚龙一号丝阵负载Z箍缩硬X射线能谱测量

为获取聚龙一号实验装置负载放电产生硬X射线的能谱分布,设计了一套7通道硬X射线能谱仪。介绍了这套多通道硬X射线能谱仪的测谱原理、主要参数及根据测量结果回推光源辐射能谱的解谱算法。在聚龙一号装置丝阵负载物理实验中对测量系统进行考核,获得了信噪比较高的测量波形。利用最大熵方法进行解谱,获得了丝阵负载产生的硬X射线能谱分布,辐射能段主要集中在200~500 keV附近,且1 MeV以上光子份额较低。