X-ray Production Efficiency Research Articles

Theoretical Calculation and Experimental Determination of X-ray Production Efficiencies for Copper, Zirconium, and Tungsten.

Theoretical Calculation and Experimental Determination of X-ray Production Efficiencies for Copper, Zirconium, and Tungsten.

Population III X-ray binaries and their impact on the early universe

ABSTRACT The first population of X-ray binaries (XRBs) is expected to affect the thermal and ionization states of the gas in the early Universe. Although these X-ray sources are predicted to have important implications for high-redshift observable signals, such as the hydrogen 21-cm signal from cosmic dawn and the cosmic X-ray background, their properties are poorly explored, leaving theoretical models largely uninformed. In this paper we model a population of X-ray binaries arising from zero metallicity stars. We explore how their properties depend on the adopted initial mass function (IMF) of primordial stars, finding a strong effect on their number and X-ray production efficiency. We also present scaling relations between XRBs and their X-ray emission with the local star formation rate, which can be used in sub-grid models in numerical simulations to improve the X-ray feedback prescriptions. Specifically, we find that the uniformity and strength of the X-ray feedback in the intergalactic medium is strongly dependant on the IMF. Bottom-heavy IMFs result in a smoother distribution of XRBs, but have a luminosity orders of magnitude lower than more top-heavy IMFs. Top-heavy IMFs lead to more spatially uneven, albeit strong, X-ray emission. An intermediate IMF has a strong X-ray feedback while sustaining an even emission across the intergalactic medium. These differences in X-ray feedback could be probed in the future with measurements of the cosmic dawn 21-cm line of neutral hydrogen, which offers us a new way of constraining population III IMF.

Measurement and Calculation of X-Ray Production Efficiencies for Copper, Zirconium, and Tungsten.

Electron probe microanalysis (EPMA) is based on physical relations between measured X-ray intensities of characteristic lines and their X-ray production efficiency, which depends on the specimen composition. The quality of the analysis results relies on how realistically the physical relations describe the generation and emission of X-rays. Special experiments are necessary to measure X-ray production efficiencies. A challenge in these experiments is the determination of the detection efficiency of the spectrometer as a function of the photon energy. An energy-dispersive spectrometer was used in this work, for which the efficiency was determined at metrological synchrotron beamlines with an accuracy of ±2%. X-ray production efficiencies for the L series and the Kα series of copper and zirconium and for the M and L series of tungsten were determined at energies up to 30 keV in a scanning electron microscope. These experimental values were compared with calculated X-ray production efficiencies using physical relations and material constants applied in EPMA. The objective of the comparison is the further improvement of EPMA algorithms as well as extending the available database for X-ray production efficiencies. Experimental data for the X-ray production efficiency are also useful for the assessment of spectrum simulation software.

The impact of spin-temperature fluctuations on the 21-cm moments

This paper considers the impact of Lyman-alpha coupling and X-ray heating on the 21-cm brightness-temperature one-point statistics (as predicted by semi-numerical simulations). The X-ray production efficiency is varied over four orders of magnitude and the hardness of the X-ray spectrum is varied from that predicted for high-mass X-ray binaries, to the softer spectrum expected from the hot inter-stellar medium. We find peaks in the redshift evolution of both the variance and skewness associated with the efficiency of X-ray production. The amplitude of the variance is also sensitive to the hardness of the X-ray SED. We find that the relative timing of the coupling and heating phases can be inferred from the redshift extent of a plateau that connects a peak in the variance's evolution associated with Lyman-alpha coupling to the heating peak. Importantly, we find that late X-ray heating would seriously hamper our ability to constrain reionization with the variance. Late X-ray heating also qualitatively alters the evolution of the skewness, providing a clean way to constrain such models. If foregrounds can be removed, we find that LOFAR, MWA and PAPER could constrain reionization and late X-ray heating models with the variance. We find that HERA and SKA (phase 1) will be able to constrain both reionization and heating by measuring the variance using foreground-avoidance techniques. If foregrounds can be removed they will also be able to constrain the nature of Lyman-alpha coupling.

Reionization and beyond: detecting the peaks of the cosmological 21 cm signal

[ABRIDGED] The cosmological 21cm signal is set to become the most powerful probe of the early Universe, with first generation interferometers aiming to make statistical detections of reionization. There is increasing interest also in the pre-reionization epoch when the intergalactic medium was heated by an early X-ray background. Here we perform parameter studies varying the halo masses hosting galaxies, and their X-ray production efficiencies. We also relate these to popular models of Warm Dark Matter cosmologies. For each parameter combination we compute the signal-to-noise (S/N) of the large-scale (k~0.1/Mpc) 21cm power for both reionization and X-ray heating for a 2000h observation with several instruments: 128 tile Murchison Wide Field Array (MWA128T), a 256 tile extension (MWA256T), the Low Frequency Array (LOFAR), the 128 element Precision Array for Probing the Epoch of Reionization (PAPER), and the second generation Square Kilometre Array (SKA). We show that X-ray heating and reionization in many cases are of comparable detectability. For fiducial astrophysical parameters, MWA128T might detect X-ray heating thanks to its extended bandpass. When it comes to reionization, both MWA128T and PAPER will also only achieve marginal detections, unless foregrounds on larger scales can be mitigated. On the other hand, LOFAR should detect plausible models of reionization at S/N > 10. The SKA will easily detect both X-ray heating and reionization.

EXTRA-NUCLEAR STARBURSTS: YOUNG LUMINOUS HINGE CLUMPS IN INTERACTING GALAXIES

Hinge clumps are luminous knots of star formation near the base of tidal features in some interacting galaxies. We use archival Hubble Space Telescope UV/optical/IR images and Chandra X-ray maps along with GALEX UV, Spitzer IR, and ground-based optical/near-IR images to investigate the star forming properties in a sample of 12 hinge clumps in five interacting galaxies. The most extreme of these hinge clumps have star formation rates of 1 - 9 M(sun)/yr, comparable to or larger than the `overlap' region of intense star formation between the two disks of the colliding galaxy system the Antennae. In the HST images, we have found remarkably large (~70 pc) and luminous (M(I) ~ 12.2 to -16.5) sources at the centers of these hinge clumps, sometimes embedded in a linear ridge of fainter star clusters. We have found strong X-ray emission from several of these hinge clumps. In most cases, this emission is well-resolved with Chandra and has a thermal X-ray spectrum, thus it is likely due to hot gas associated with the star formation. The ratio of the extinction-corrected diffuse X-ray luminosity to the mechanical energy rate (the X-ray production efficiency) for the hinge clumps is similar to that in the Antennae galaxies, but higher than those for regions in the normal spiral galaxy NGC 2403. Two of the hinge clumps have point-like X-ray emission much brighter than expected for hot gas; these sources are likely `ultra-luminous X-ray sources' (ULXs) due to accretion disks around black holes. The most extreme of these sources, in Arp 240, has a hard X-ray spectrum and an absorbed X-ray luminosity of ~2 X 10^41 erg/s; more than expected by single high mass X-ray binaries (HMXBs), thus it may be either a collection of HMXBs or an intermediate-mass black hole (>=80 M(sun)). [ abridged ]

Measuring the X-ray background in the reionization era with first generation 21 cm experiments

The X-ray background during the epoch of reionization is currently poorly constrained. We demonstrate that it is possible to use first generation 21 cm experiments to calibrate it. Using the semi-numerical simulation, 21cmFAST, we calculate the dependence of the 21 cm power spectrum on the X-ray background flux. Comparing the signal to the sensitivity of the Murchison Widefield Array (MWA) we find that in the redshift interval z =8-14 the 21 cm signal is detectable for certain values of the X-ray background. We show that there is no degeneracy between the X-ray production efficiency and the Lyα production efficiency and that the degeneracy with the ionization fraction of the intergalactic medium can be broken.

Intense Superradiant X Rays from a Compact Source Using a Nanocathode Array and Emittance Exchange

A novel method of producing intense short wavelength radiation from relativistic electrons is described. The electrons are periodically bunched at the wavelength of interest enabling in-phase superradiant emission that is far more intense than from unbunched electrons. The periodic bunching is achieved in steps beginning with an array of beamlets emitted from a nanoengineered field emission array. The beamlets are then manipulated and converted to a longitudinal density modulation via a transverse-to-longitudinal emittance exchange. Periodic bunching at short wavelength is shown to be possible, and the partially coherent x-ray properties produced by inverse Compton scattering from an intense laser are estimated. The proposed method increases the efficiency of x-ray production by several orders of magnitude, potentially enabling compact x-ray sources to produce brilliance and flux similar to major synchrotron facilities.

Characterization and optimization of pyroelectric X-ray sources using Monte Carlo spectral models

Pyroelectric X-ray sources produce emission through bulk heating of a ferroelectric crystal. In this study, a least-square based systematic curve fitting of X-ray emission to predicted models is used to generate an equivalent monoenergetic incident electron energy to simplify further X-ray source optimization. The measured X-ray spectrum of a 1cm3 lithium tantalite crystal cycled over 140K are shown to be approximated by those of an 85keV monoenergetic electron beam. Using monoenergetic electron sources, common configurations for transmission and directional X-ray sources are simulated using electron targets comprised of gold, silver, copper, molybdenum and tungsten. X-ray production efficiency depends on target material selection, incident electron energy, and target thickness for both transmission and reflection geometries. At 20keV, silver produced 69.7% more flux was in comparison to copper, the least efficient target material at this energy. Conversely, at 85keV copper outperformed silver, the least efficient target material at this energy, by 21.6%. Pyroelectric X-ray sources can be improved for flux and energy tuning through the use of modeling and target design. Continued development of pyroelectric X-ray sources can lead to wide scale implementation for industrial X-ray fluorescence and medical therapeutic applications.

인버터방식의 고전압 발생장치를 이용한 의료용 X선 기기의 특성평가

Medical X-ray has been brought many changes according to the rapid development of high technology. Especially, for high-voltage generator which is the most important in X-ray generation the traditional way is to use high-voltage electric transformers primarily. However, since it is large and heavy and the ripple rate of DC high-voltage applied to X-ray tube is too big, it has a disadvantage of low X-ray production efficiency. To solve these problems, the studies about high-voltage power supply are now proceeding. At present, the high-voltage generator that generates high-voltage by making high frequency using inverter control circuit consisting of semiconductor device is mainly used. High-voltage generator using inverter has advantages in the diagnosis using X-ray including high performance with short-term use, miniaturization of power supply and ripple reduction. In this study, the X-ray high-voltage device with inverter type using pulse width modulation scheme to the control of tube voltage and tube current was designed and produced. For performance evaluation of produced device, the control signal analysis, irradiation dose change and beam quality depending on the load variation of tube voltage and tube current were evaluated.

3D polymer gel dosimetry and Geant4 Monte Carlo characterization of novel needle based X-ray source

In the recent years, there have been a few attempts to develop a low energy x-ray radiation sources alternative to conventional radioisotopes used in brachytherapy. So far, all efforts have been centered around the intent to design an interstitial miniaturized x-ray tube. Though direct irradiation of tumors looks very promising, the known insertable miniature x-ray tubes have many limitations: (a) difficulties with focusing and steering the electron beam to the target; (b)necessity to cool the target to increase x-ray production efficiency; (c)impracticability to reduce the diameter of the miniaturized x-ray tube below 4mm (the requirement to decrease the diameter of the x-ray tube and the need to have a cooling system for the target have are mutually exclusive); (c) significant limitations in changing shape and energy of the emitted radiation. The specific aim of this study is to demonstrate the feasibility of a new concept for an insertable low-energy needle x-ray device based on simulation with Geant4 Monte Carlo code and to measure the dose rate distribution for low energy (17.5 keV) x-ray radiation with the 3D polymer gel dosimetry.

A New Look at Optical and X-ray Emission in SDSS/XMM-Newton Quasars

AbstractWe develop a new approach to the well-studied anti-correlation between the optical-to-X-ray spectral index, αox, and the monochromatic optical luminosity, lopt. By cross-correlating the SDSS DR5 quasar catalog with the XMM-Newton archive, we create a sample of 327 quasars with both optical and X-ray spectra, allowing αox to be defined at arbitrary frequencies, rather than the standard 2500 Å and 2 keV. We find that while the choice of optical wavelength does not strongly influence the αox−lopt relation, the slope of the relation flattens significantly with X-ray energy. This result suggests a change in the efficiency of X-ray photon production, where the efficiency of low energy X-ray production depends more strongly on the seed (optical/UV) photon supply. We discuss implications for line-driven wind models.

A compact soft X-ray microscope using an electrode-less Z-pinch source

Soft X-rays (< 1Kev) are of medical interest both for imaging and microdosimetry applications. X-ray sources at this low energy present a technological challenge. Synchrotrons, while very powerful and flexible, are enormously expensive national research facilities. Conventional X-ray sources based on electron bombardment can be compact and inexpensive, but low x-ray production efficiencies at low electron energies restrict this approach to very low power applications. Laser-based sources tend to be expensive and unreliable. Energetiq Technology, Inc. (Woburn, MA, USA) markets a 92 eV, 10W(2pi sr) electrode-less Z-pinch source developed for advanced semiconductor lithography. A modified version of this commercial product has produced 400 mW at 430 eV (2pi sr), appropriate for water window soft X-ray microscopy. The US NIH has funded Energetiq to design and construct a demonstration microscope using this source, coupled to a condenser optic, as the illumination system. The design of the condenser optic matches the unique characteristics of the source to the illumination requirements of the microscope, which is otherwise a conventional design. A separate program is underway to develop a microbeam system, in conjunction with the RARAF facility at Columbia University, NY, USA. The objective is to develop a focused, sub-micron beam capable of delivering > 1 Gy/second to the nucleus of a living cell. While most facilities of this type are coupled to a large and expensive particle accelerator, the Z-pinch X-ray source enables a compact, stand-alone design suitable to a small laboratory. The major technical issues in this system involve development of suitable focusing X-ray optics. Current status of these programs will be reported. (Supported by NIH grants 5R44RR022488-03 and 5R44RR023753-03)

X-ray emission from the extended discs of spiral galaxies

We present a study of the X-ray properties of a sample of six nearby late-type spiral galaxies based on XMM-Newton observations. Since our primary focus is on the linkage between X-ray emission and star formation in extended, extranuclear galactic disks, we have selected galaxies with near face-on aspect and sufficient angular extent so as to be readily amenable to investigation with the moderate spatial resolution afforded by XMM-Newton. After excluding regions in each galaxy dominated by bright point sources, we study both the morphology and spectral properties of the residual X-ray emission, comprised of both diffuse emission and the integrated signal of the fainter discrete source populations. The soft X-ray morphology generally traces the inner spiral arms and shows a strong correlation with the distribution of UV light, indicative of a close connection between the X-ray emission and recent star formation. The soft (0.3-2 keV) X-ray luminosity to star formation rate (SFR) ratio varies from 1-5 x 10^39 erg/s(/Msun/yr), with an indication that the lower range of this ratio relates to regions of lower SFR density. The X-ray spectra are well matched by a two-temperature thermal model with derived temperatures of typically ~0.2 keV and ~0.65 keV, in line with published results for other normal and star-forming galaxies. The hot component contributes a higher fraction of the soft luminosity in the galaxies with highest X-ray/SFR ratio, suggesting a link between plasma temperature and X-ray production efficiency. The physical properties of the gas present in the galactic disks are consistent with a clumpy thin-disk distribution, presumably composed of diffuse structures such as superbubbles together with the integrated emission of unresolved discrete sources including young supernova remnants.

Chandra spectroscopy of the hot star β Crucis and the discovery of a pre-main-sequence companion

In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74 ks observation of the nearby early B giant, beta Cru (B0.5 III), with the Chandra HETGS. We find that the X-ray spectrum is quite soft, with a dominant thermal component near 3 million K, and that the emission lines are resolved but quite narrow, with half-widths of 150 km/s. The forbidden-to-intercombination line ratios of Ne IX and Mg XI indicate that the hot plasma is distributed in the wind, rather than confined near the photosphere. It is difficult to understand the X-ray data in the context of the standard wind-shock paradigm for OB stars, primarily because of the narrow lines, but also because of the high X-ray production efficiency. A scenario in which the bulk of the outer wind is shock heated is broadly consistent with the data, but not very well motivated theoretically. It is possible that magnetic channeling could explain the X-ray properties, although no field has been detected on beta Cru. We detected periodic variability in the hard (hnu > 1 keV) X-rays, modulated on the known optical period of 4.58 hours, which is the period of the primary beta Cep pulsation mode for this star. We also have detected, for the first time, an apparent companion to beta Cru at a projected separation of 4 arcsec. This companion was likely never seen in optical images because of the presumed very high contrast between it and beta Cru in the optical. However, the brightness contrast in the X-ray is only 3:1, which is consistent with the companion being an X-ray active low-mass pre-main-sequence star. The companion's X-ray spectrum is relatively hard and variable, as would be expected from a post T Tauri star.

A low energy tunable pulsed X-ray source based on the pseudospark electron beam

A low energy pulsed X-ray source with 17 J electrical input energy has been constructed based on the vacuum spark configuration triggered by the pseudospark electron beam. With such a low input electrical energy, the frequently studied X-ray emitting vacuum spark plasma is not obtained. Instead, this configuration gives rise to a point-like electron beam-target pulsed X-ray source at the tip of the anode. Emission of X-ray is observed during the pre-breakdown phase. The X-ray spectrum is dominated by the characteristic line emission of the anode material. The total X-ray energy emission from the source can be estimated by assuming it to be a monochromatic point source. It is found to have an X-ray production efficiency of 0.1%, giving an average X-ray dosage of 18 mGy per pulse. X-ray radiography of small biological sample is demonstrated to illustrate a potential application of the present X-ray source.

ChandraX-Ray Imaging of the Interacting Starburst Galaxy System NGC 7714/7715: Tidal Ultraluminous X-Ray Sources, Emergent Wind, and Resolved HiiRegions

We present high spatial resolution X-ray imaging data for the interacting galaxy pair NGC 7714/7715 (Arp 284) from the Chandra X-ray telescope. In addition to the unresolved starburst nucleus, a variable point source with LX ≈ 1040 ergs s-1 was detected 15 (270 pc) to the northwest of the nucleus, coincident with a blue, extremely optically luminous (MV ≈ -14.1) point source on Hubble Space Telescope images. Eleven other candidate pointlike ultraluminous X-ray sources (ULXs) were also detected in the vicinity of NGC 7714/7715, two of which exceed 1040 ergs s-1. Ten of these appear to be associated with interaction-induced features, but only two are associated with star formation regions. We also found diffuse emission with LX ≈ 3 × 1040 ergs s-1 extending 11'' (1.9 kpc) to the north of the nucleus. Its spectrum can be fitted with either a two-temperature MEKAL function (kT = 0.59 and 8 keV) or a 0.6 keV MEKAL function plus a power law (Γ = 1.8 ± 0.2). The hard component may be due to high-mass X-ray binaries (HMXBs) with possible contributions from inverse Compton radiation, while the soft component is likely from a superwind. Superbubble models imply an expansion age of ≈15 Myr, supporting previous assertions of an intermediate-age nuclear stellar population in addition to a 5 Myr starburst. We also detected extended X-ray emission associated with four extranuclear H II region complexes. The emission from these H II regions and the nuclear starburst could be due to either an enhanced population of HMXBs relative to Local Group galactic averages or to diffuse gas heated by winds from supernovae, if the X-ray production efficiency LX/Lmech is high (≈5%). To estimate LX/Lmech, we collected published data for well-studied H II regions and superbubbles in nearby galaxies. For H II regions with ages less than 3.5 Myr, the median LX/Lmech ≈ 0.02%, while for older star formation regions, LX/Lmech ≈ 0.2%–7%. Thus, it is possible that gas heating by supernovae may be sufficient to account for the observed X-rays from these H II regions. In galaxies much more distant than NGC 7714, for example, the Cartwheel galaxy, H II region complexes similar to those in NGC 7714 will be unresolved by Chandra and will mimic ULXs. No X-ray emission was detected from the Type Ib supernova SN 1999dn, with an upper limit of ≈2 × 1038 ergs s-1.

Zero-dimensional energetics scaling models for z-pinch-driven hohlraums

Wire array z pinches on the Z accelerator provide the most intense laboratory source of soft X rays in the world. The unique combination of a near-Planckian radiation source with high X-ray production efficiency (10 to 15% wall plug), large X-ray powers and energies (&gt;100 TW, ≥0.8 MJ in 6 ns to 7 ns), large characteristic hohlraum volumes (0.5 to &gt;10 cm3), long pulse lengths (5 to 20 ns), and low capital cost (&lt;100/radiated Joule) may make z pinches a good match to the requirements for driving high-yield scale (&gt;200 MJ yield) ICF capsules with adequate radiation symmetry and margin. The z-pinch-driven hohlraum approach of Hammer et al. (1999) may provide a conservative and robust solution to the requirements for high yield, and is currently being studied on the Z accelerator. This paper describes a multiple-region, 0-D hohlraum energetics model for z-pinch-driven hohlraums in four configurations. We observe consistency between the model and the measured X-ray powers and hohlraum wall temperatures to within ±20% in X-ray flux, for the four configurations. The scaling of pinch energy and radiation-driven anode-cathode gap closure with drive current are also examined.

Reionization by Hard Photons. I. X‐Rays from the First Star Clusters

Observations of the Ly-alpha forest at z~3 reveal an average metallicity Z~0.01 Z_solar. The high-redshift supernovae that polluted the IGM also accelerated relativistic electrons. Since the energy density of the CMB scales as (1+z)^4, at high redshift these electrons cool via inverse Compton scattering. Thus, the first star clusters emit X-rays. Unlike stellar UV ionizing photons, these X-rays can escape easily from their host galaxies. This has a number of important physical consequences: (i) Due to their large mean free path, these X-rays can quickly establish a universal ionizing background and partially reionize the universe in a gradual, homogeneous fashion. If X-rays formed the dominant ionizing background, the universe would have more closely resembled a single-phase medium, rather than a two-phase medium. (ii) X-rays can reheat the universe to higher temperatures than possible with UV radiation. (iii) X-rays counter the tendency of UV radiation to photo-dissociate H2, an important coolant in the early universe, by promoting gas phase H2 formation. The X-ray production efficiency is calibrated to local observations of starburst galaxies, which imply that ~10% of the supernova energy is converted to X-rays. While direct detection of sources in X-ray emission is difficult, the presence of relativistic electrons at high redshift and thus a minimal level of X-ray emission may be inferred by synchrotron emission observations with the Square Kilometer Array. These sources may constitute a significant fraction of the unresolved hard X-ray background, and can account for both the shape and amplitude of the gamma-ray background. This paper discusses the existence and observability of high-redshift X-ray sources, while a companion paper models the detailed reionization physics and chemistry.

Operational characteristics of a prototype x-ray needledevice

A prototype x-ray needle, which emits 62.5 kVp x-rays at the tip of a 20 cmlong, 4 mm diameter steel needle, has been developed by Titan Pulse SciencesIncorporated (PSI) (Albuquerque, NM) and was tested for its suitability inbrachytherapy applications in comparison with a similar device by thePhotoelectron Corporation. The depth dose profiles were also compared withthose of two common brachytherapy sources (125I and 192Ir). Thedepth dose characteristics of the radiation were comparable with the twobrachytherapy sources with a slightly reduced attenuation gradient. Thedose rate from the x-ray needle tip was relatively isotropic at the needletip and was continuously adjustable over the range of 0 cGy min-1 toupwards of 62 cGy min-1 at a reference distance of 1 cm in air. Wedetected a significant proportion of x-rays generated along the needleshaft, and not at the needle tip, as intended. The energy spectrum emittedfrom this device had a peak intensity at 21 keV and an average energy of28 keV. The beam was attenuated in both aluminium (the first half-valuelayer being less than 0.1 mm) and in water (50% dose at approximately2 mm). These studies confirm that although there is potential for a systemsimilar to this one for clinical applications, the simplistic electronguidance used in this particular prototype device limits it to researchapplications. Further optimization is required in focusing and steering theelectron beam to the target, improving x-ray production efficiency andusing x-ray target cooling to achieve higher dose rates.