X-ray Polarization Measurements Research Articles

Simple filters enable x-ray polarization measurements

Measurements of the degree and angle of polarization of emission from astronomical sources enable physical characterization of the objects and environmental conditions fromwhich the photons originate. However, a lack of suitable instrumentation in the x-ray and gamma-ray regimes has been frustrating astronomers for over three decades. To date, only one unambiguous astrophysical x-ray polarization measurement has been obtained: the Crab Nebula was observed to exhibit 19% linear polarization at 2.6keV.1 Conventional x-ray polarimetry relies on Bragg reflection or Thomson scattering, but instruments operating on the basis of either effect tend to suffer from low sensitivity. The next generation of large x-ray observatories currently under study—such as the International X-ray Observatory2 (IXO) and Astro-H3— have triggered renewed interest in practical x-ray polarization measurements. Device efficiency improvements have been facilitated by the development of novel gaseous detectors that can operate in the x-ray regime.4, 5 We have been pursuing an alternative approach to achieve x-ray polarimetry by developing dichroic filters that work in an analogous way to standard optical Polaroid R © film.6–8 These low-mass devices could add a polarimetry capability to the existing focal-plane microcalorimeter instruments proposed for these new observatories, while avoiding the cost and complexity of developing and operating additional detectors solely dedicated to x-ray polarimetry.6 At visible wavelengths, polarization can be detected using highly ordered materials such as H-sheet Polaroid, a polyvinyl alcohol polymer impregnated with iodine. Polarization of 33.17keV x-rays using ordinary H-sheet material was successfully analyzed for the first time in 1997.9 However, the Figure 1. Energy spectra for an inclusion compound of 1-bromoadamantane in a thiourea host. The red and black curves are for χ = 90 and 0◦, respectively, where χ is the angle between the crystal’s dichroic axis and the polarization direction of the photons. Such measurements were first reported by Chao and collaborators.10

X-ray polarization measurement for fast electrons in intense-laser-produced plasma under oblique incidence

Study on x-ray polarization spectroscopy was performed for intense-laser-produced plasma under laser-oblique incidence. The laser pulse was focused onto a polyvinylchloride target at angles of 67 degrees and 7 degrees to the target normal at average intensities of 1017-18 W/cm2. There were differences in the spectra for shifted Kα lines of C1 atoms between the oblique and nearly normal incidence, indicating the low laser-energy absorption in the oblique incidence. A difference in polarization degrees of C1 Heα lines was also observed, and this means the polarization of incident laser pulse affect velocity distribution functions of fast electrons in intense-laser-produced plasma.

Ｘ線分光の現在 ＩＶ．Ｘ線吸収微細構造分光法

XAFS (X-ray Absorption Fine Structure) is a powerful technique, which provides element-specific information on atomic and electronic structures even for samples without long-range periodic structure. Owing to the recent developments of synchrotron radiation facilities, it has become possible also for non-expert researchers to obtain such information using XAFS. In this lecture, the basic concept and analytic procedures are presented including the utilization of X-ray polarization and time-resolved measurements.

Measuring energy dependent polarization in soft γ-rays using Compton scattering in PoGOLite

Linear polarization in X- and γ-rays is an important diagnostic of many astrophysical sources, foremost giving information about their geometry, magnetic fields, and radiation mechanisms. However, very few X-ray polarization measurements have been made, and then only mono-energetic detections, whilst several objects are assumed to have energy dependent polarization signatures. In this paper, we investigate whether detection of energy dependent polarization from cosmic sources is possible using the Compton technique, in particular with the proposed PoGOLite balloon-experiment, in the 25–100 keV range. We use Geant4 simulations of a PoGOLite model and input photon spectra based on Cygnus X-1 and accreting magnetic pulsars (100 mCrab). Effective observing times of 6 and 35 h were simulated, corresponding to a standard and a long duration flight, respectively. Both smooth and sharp energy variations of the polarization are investigated and compared to constant polarization signals using chi-square statistics. We can reject constant polarization, with energy, for the Cygnus X-1 spectrum (in the hard state), if the reflected component is assumed to be completely polarized, whereas the distinction cannot be made for weaker polarization. For the accreting pulsar, constant polarization can be rejected in the case of polarization in a narrow energy band with at least 50% polarization, and similarly for a negative step distribution from 30% to 0% polarization.

POLAR: A compact detector for GRB polarization measurements

Through polarization measurements of X-rays can provide essential information for identifying processes responsible of their emission by astrophysical objects, almost no experimental data exist yet. We propose here a novel wide field compact detector for hard X-ray polarization measurements based on Compton scattering process and made of low-Z fast scintillators.

Measurement of X-ray polarization using optical imaging detector with capillary plate

The performance of the optical imaging capillary gas proportional counter (CGPC) was investigated using polarized X-rays with an energy of 15 keV at SPring-8. The CGPC with a fill gas of Ar+8% CH 4+2% TMA at 1 atm was operated at a gas gain of 15 000. The CGPC was irradiated by a polarized X-ray beam in the center region using a slit of 300 μm×300 μm. Images of single photoelectron tracks were obtained by an image-intensified CCD camera combined with the CGPC through a lens system. The average distance between the starting point and the barycenter for single photoelectron tracks was 1.1 mm. The angular distribution is obtained from the directions of the lines connected between the starting point and the barycenter for each image of the photoelectron tracks. From a least-squares fitting, the modulation factor was 25.1±2.0% for the X-rays with a polarization degree of 99%.

Interfacial Layer - A New Mechanism for Electromechanical Response

ABSTRACTElectric field induced phase transition has been used to explain the high strain response in some PVDF-based EAP. However, it is hard to understand some features (such as the relationship between the strain and the preload) of elastomers - an important type of EAPs. In this paper, we reported the study of recrystallization on high-energy-electron irradiated P(VDF-TrFE) copolymer. The morphology and structure as well as the structural transformation in the recrystallized copolymers were studied by means of X-ray diffraction, DSC, FTIR, and polarization measurements. The effect of crosslinking induced by the irradiation is discussed. The results suggest that a new interface layer existed in the recrystallized polymers. The partially ordered interfacial layer is a novel micro-origin of a high polarization obtained in an EAP. Based on this concept, the effect of preload on the E-M performance of the elastomers can be well explained. A new method to develop high performance electroactive polymer is outlined by using the interface state.

Application of x-ray polarization measurements to study plasma anisotropy in plasma focus machines

This paper presents recent space resolved experimental study of polarization of He-like argon spectra in plasma focus. Consideration is made on dominant anisotropy mechanisms responsible for preferential orientation of different excited states at the moment of de-excitation in dense hot plasmas. Essential attention is given to alignment along the resulting electromagnetic field created as by exciting electron and also by the local electromagnetic field existing inside the plasma. Such study would provide the tool to diagnose distribution of electromagnetic fields and to count for anisotropy effects when calculating plasma parameters.

High-resolution x-ray crystal spectrometer/polarimeter at torus experiment for technology oriented research-94

A high-resolution x-ray polarimeter has been installed at the torus experiment for technology oriented research (TEXTOR-94). The instrument consists of two spectrometers in Johann geometry, utilizing the dependence of Bragg reflection on the polarization. The dispersion plane of the so-called horizontal spectrometer coincides with the midplane of the tokamak, whereas the dispersion plane of the so-called vertical spectrometer lies perpendicular to the midplane of the tokamak. Both spectrometers operate with cylindrically bent quartz crystals of dimensions 153 mm×38 mm×0.7 mm with a 2d spacing of 4.9130 Å. The radii of curvature of the horizontal and vertical spectrometer crystals are 3820 mm and 4630 mm, respectively. The detectors are multiwire proportional counters having a large entrance window of 180 mm×90 mm, with a high count rate capability of up to 2.5×105 photons/s, and a spatial resolution of 0.4–0.65 mm, depending on the count rate. The unique data acquisition system makes it possible to record up to 8192 spectra per TEXTOR-94 discharge to study fast events and impurity transport. The instruments are sensitive to spurious amounts of argon in hydrogen or deuterium discharges and aim for x-ray polarization measurements and other core plasma diagnostics like electron temperature, ion temperature, plasma rotation, impurity transport, and relative abundance of Ar15+/Ar16+. The first measurements of toroidal rotation speed, ion and electron temperatures show a very good agreement with charge exchange recombination spectroscopy (XRS) and electron cyclotron emission (ECE) diagnostics available at TEXTOR-94. The measured values of the ratio Ar15+/Ar16+ are higher than that predicted from coronal equilibrium. The ratio depends strongly upon the electron density both for ohmic and neutral beam injection cases. This suggests that the charge state distribution is also dependent on diffusion and charge exchange processes in the plasmas.

ELECTRIC FIELD INDUCED ANTIFERROELECTRIC TO FERROELECTRIC PHASE TRANSITION OF Pb (Zr,Sn,Ti)O3 CERAMICS AND TAILORING OF PROPERTIES THROUGH COMPOSITION MODIFICATION

In order to obtain a new kind of antiferroelectric (AFEt) ceramics wi th lower AFEt-Ferroelectric (FER) switching field Ef and less hysterisis loss ΔE for application of large displacement actuato r, Ba2+ ionics was employed to control the relative stability between AFEt, FER, and parroelelctrics (PEc) phases in (Pb097-xBaxLa002)(Zr055Sn035Ti01)O3 (0≤x≤02) system. Structural chan ges and electric properties as a function of Barium content x have been investig ated by X-Ray diffraction, dielectric properties, polarization and longitudinal strain measurement. It is observed that AFEt changes to FER, and finally to ferroelectric relaxors(RFE) as Ba content x increases from zer o to 02. Based upon these expermental result, we are able to tailor the AFE-FE switching parameters such as Ef, ΔE and AFEt operating t emperature range ΔT through modifying the Ti/Sn ratio near AFEt/FER phase boundary in the (Pb087Ba01La00 2)(Zr06TiySn04-y)O3 (004 ≤y≤009) system. Finally, a new kind of AFEt ceramics with Ef =16kV/mm，ΔE=085kK/mm， and longitudinal strain x=01%—02% which is appropriate for application of digital actuators has been obtained. Phase dia gram with composition located near AFEt/FER boundary of t he studied system has been determined.

Polarization from magnetized accretion discs in active galactic nuclei

Polarization of radiation emerging from magnetized, electron-scattering-dominated accretion discs in active galactic nuclei (AGN) may be strongly affected by Faraday rotation. We present fully self-consistent Monte Carlo calculations of the resulting polarization in plane-parallel electron-scattering atmospheres for magnetic fields of constant strength and both vertical and random topology. We provide analytic fits to our results and apply them to simple accretion disc models. We find that Faraday rotation by an equipartition magnetic field may be of major importance in determining the polarization at optical and ultraviolet wavelengths in AGN. It may also be important for future X-ray polarization measurements of black hole candidate X-ray binaries.

Experimental evidence for a spontaneous relaxor to ferroelectric phase transition in [formula omitted] - 10% Ti

From X-ray diffraction, polarization and dielectric measurements, it is shown that a 0.9 Pb(Mg 1 3 Nb 2 3 )O 3 - 0.1 PbTiO 3 ceramic undergoes a zero-field rhombohedral phase transition. This material transforms spontaneously from a relaxor into a normal ferroelectric upon cooling. On such an observation, the influence of titanium on Pb(Mg 1 3 Nb 2 3 )O 3 based ceramics is discussed.

Soft X-ray polarization and magnetic circular dichroism measurement system

We report an apparatus for measuring polarization and magnetic circular dichroism (MCD) in the soft x-ray region of synchrotron radiation. It consists of a polarimeter and a magnetic circuit of 2.1 Tesla at the sample. The polarimeter consists of a phase shifter and an analyzer, each using V/C multilayer mirrors. We made full-polarization measurement of soft x-rays at 84.7 Å from the bending magnet. Based on this evaluation of polarization, we obtained MCD spectra of novel nitride Fe 16N 2(100) film on GaAs substrate.

SXRP: an X-ray polarimeter for the SPECTRUM-X-Gamma Mission

TheStellar X-ray Polarimeter (SXRP) is a focal plane instrument which will be flown on the SPECTRUM-X-Gamma mission in 1993. The polarimeter is composed of two separate instruments: the first exploits the dependence on the polarization of the Bragg reflection from a graphite crystal, and of the Thomson scattering from a metallic lithium target. The second instrument makes use of the recently discovered polarization dependence of X-ray photoemission from CsI. The SXRP will permit sensitive measurements of several hundreds of known X-ray sources. X-ray polarization measurements will allow us to constrain the physical mechanisms and the geometries of several classes of galactic X-ray sources, such as X-ray pulsars, black-hole candidates and supernova remnants. Moreover, and for the first time, SXRP will be able to perform highly sensitive measurements of the brightest extragalactic sources.

The Stellar X-Ray Polarimeter for the Spectrum-X-Gamma Mission

AbstractWe describe an X-ray polarimeter which will be flown on the SPECTRUM-X-Gamma mission. The instrument exploits three distinct physical processes to measure polarization: Bragg reflection from a graphite crystal, Thomson scattering from a metallic lithium target, and photoemission from a Cesium Iodide photocathode. These three processes allow polarization measurements over an energy band of 0.3 keV to 12 keV. The polarimeter will make possible sensitive measurements of several hundred known X-ray sources. X-ray polarization measurements will allow us to constrain the geometry of gas flow in X-ray binaries, identify nonthermal emission in supernova remnants, test current models for X-ray emission in radio pulsars, determine the radiation mechanisms in active galactic nuclei, and search for inertial frame dragging (Lense-Thirring effect) around the putative black hole in Cygnus X-1.

Stellar X-Ray Polarimeter: a focal plane polarimeter for the Spectrum X-Gamma mission

This paper describes an X-ray polarimeter that will be flown on the Spectrum X-Gamma mission. The instrument exploits three distinct physical processes to measure polarization: Bragg reflection from a graphite crystal, Thomson scattering from a metallic lithium target, and photoemission from a cesium iodide photocathode. These three methods allow polarization measurements over an energy band from 0.3 to 12 keV. The polarimeter will make possible sensitive measurements of several hundred known X-ray sources. X-ray polarization measurements will make it possible to constrain the geometry of gas flow in X-ray binaries, identify nonthermal emission in supernova remnants, test current models for X-ray emission in radio pulsars, determine the radiation mechanisms in active galactic nuclei, and search for inertial frame dragging (Lense-Thirring effect) around the putative black hole in Cygnus X-1.

X-ray studies of electrocaloric lead-scandium tantalate ordered solid solutions

Abstract Precision x-ray studies, polarization and electrocaloric measurements have been made with PST-PSN solid solutions in the temperature range −180–+80°C. The large electrocaloric effect δT = 1.0–1.7°C is due to both particular features of structure rearrangement at the 1-order phase transition in the materials and a high ion ordering in sublattice B of the perovskite structure ABO3.

Solar flare hard X-ray observations

Recent hard X-ray observations of solar flares are reviewed with emphasis on results obtained with instruments on the Solar Maximum Mission satellite. Flares with three different sets of characteristics, designated as Type A, Type B, and Type C, are discussed and hard X-ray temporal, spatial, spectral, and polarization measurements are reviewed in this framework. Coincident observations are reviewed at other wavelengths including the UV, microwaves, and soft X-rays, with discussions of their interpretations. In conclusion, a brief outline is presented of the potential of future hard X-ray observations with sub-second time resolution, arcsecond spatial resolution, and keV energy resolution, and polarization measurements at the few percent level up to 100 keV.

The interpretation of hard X-ray polarization measurements in solar flares

We review recent observations of polarization of moderately hard X-rays in solar flares and compare them with the predictions of recent detailed modeling of hard X-ray bremsstrahlung production by non-thermal electrons. We find that the recent advances in the complexity of the modeling lead to substantially lower predicted polarizations than in earlier models and more fully highlight how various parameters play a role in determining the polarization of the radiation field. The new predicted polarizations are comparable to those predicted by thermal modeling of solar flare hard X-ray production, and both are in agreement with the observations. In the light of these results, we propose new polarization observations with current generation instruments which could be used to discriminate between non-thermal and thermal models of hard X-ray production in solar flares.

Use of Laue-geometry x-ray diffraction in the spectroscopy of laser plasmas

Laue x-ray crystal diffraction geometry offers a number of advantages for the spectroscopic diagnosis of laser plasmas. Applications of this diffraction configuration, such as absorption spectroscopy, time-resolved spectroscopy, and x-ray polarization measurements, are described.