553,016 research outputs found
Extended range X-ray telescope
An X-ray telescope system is described which is comprised of a tubular mount having a collecting region remote from the one axial end. A soft X-ray/XUV subsystem associated with the collecting region directs only relatively soft, near on-axis X-rays/XUV radiation incident on a first portion of the collecting region into a first detector sensitive to relatively soft X-rays/XUV radiation. A hard X-ray subsystem associated with the collecting region directs only relatively hard near on-axis X-rays incident on a second portion of the collecting region into a second detector sensitive to relatively hard X-rays
Comparison of X-ray and gamma-ray dose-response curves for pink somatic mutations in Tradescantia clone 02
Microdosimetric data indicate that the mean specific energy,zeta, produced by individual charged particles from X rays and gamma rays is different for the two radiation qualities by nearly a factor of two. In order to test whether this influences the initial, linear component in the dose-effect relations, a comparison was made between dose-response curves for pink somatic mutations inTradescantia clone 02 stamen hairs following X and gamma irradiations. Absorbed doses ranged from 2.66 to 300 rad. The results are in agreement with predictions made on the basis of microdosimetric data. At low doses gamma rays are substantially less effective than X rays. The RBE of gamma rays vs. X rays at low doses was approximately 0.6, a value lower than those usually reported in other experimental systems
Absorption of high-energy gamma rays in Cygnus X-3
The microquasar Cygnus X-3 was detected at high energies by the gamma-ray
space telescopes AGILE and Fermi. The gamma-ray emission is transient,
modulated with the orbital period and seems related to major radio flares, i.e.
to the relativistic jet. The GeV gamma-ray flux can be substantially attenuated
by internal absorption with the ambient X-rays. In this study, we examine
quantitatively the effect of pair production in Cygnus X-3 and put constraints
on the location of the gamma-ray source. Cygnus X-3 exhibits complex temporal
and spectral patterns in X-rays. During gamma-ray flares, the X-ray emission
can be approximated by a bright disk black body component and a non-thermal
tail extending in hard X-rays, possibly related to a corona above the disk. We
calculate numerically the exact optical depth for gamma rays above a standard
accretion disk. Emission and absorption in the corona are also investigated.
GeV gamma rays are significantly absorbed by soft X-rays emitted from the inner
parts of the accretion disk. The absorption pattern is complex and anisotropic.
Isotropization of X-rays due to Thomson scattering in the companion star wind
tends to increase the gamma-ray opacity. Gamma rays from the corona suffer from
strong absorption by photons from the disk and cannot explain the observed
high-energy emission, unless the corona is unrealistically extended. The lack
of absorption feature in the GeV emission indicates that high-energy gamma rays
should be located at a minimum distance ~10^8-10^10 cm from the compact object.
The gamma-ray emission is unlikely to have a coronal origin.Comment: 11 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
X-ray source uses interchangeable target anodes to vary X-ray wavelength
Compact laboratory X ray tube generates X rays of various wavelengths by using interchangeable target anodes. The wavelength of the X rays depends on the metal from which the anode is made
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.Comment: Final version accepted by ApJ. 32 pages, 3 figure
X-Ray Emission from Jupiter, Saturn, and Earth: A Short Review
Jupiter, Saturn, and Earth - the three planets having dense atmosphere and a
well developed magnetosphere - are known to emit X-rays. Recently, Chandra
X-ray Observatory has observed X-rays from these planets, and XMM-Newton has
observed them from Jupiter and Saturn. These observations have provided
improved morphological, temporal, and spectral characteristics of X-rays from
these planets. Both auroral and non-auroral (low-latitude) 'disk' X-ray
emissions have been observed on Earth and Jupiter. X-rays have been detected
from Saturn's disk, but no convincing evidence for X-ray aurora on Saturn has
been observed. The non-auroral disk X-ray emissions from Jupiter, Saturn, and
Earth, are mostly produced due to scattering of solar X-rays. X-ray aurora on
Earth is mainly generated via bremsstrahlung from precipitating electrons and
on Jupiter via charge exchange of highlyionized energetic heavy ions
precipitating into the polar atmosphere. Recent unpublished work suggests that
at higher (>2 keV) energies electron bremsstrahlung also plays a role in
Jupiter's X-ray aurora. This paper summarizes the recent results of X-ray
observations on Jupiter, Saturn, and Earth mainly in the soft energy (~0.1-2.0
keV) band and provides a comparative overview.Comment: 17 pages, 12 figure
Solar X-ray spectrum reproduced in vacuum
Desired low energy X rays are produced by modifying commercial ion tubes and combining them with standard power supplies and control circuitry. These X rays have less deviation from the solar X ray spectrum in energy and intensity
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