scholarly journals Diffusive transport of energetic electrons in the solar corona: X-ray and radio diagnostics

2018 ◽  
Vol 610 ◽  
pp. A6 ◽  
Author(s):  
S. Musset ◽  
E. P. Kontar ◽  
N. Vilmer
Keyword(s):  
Solar Corona ◽  
Free Path ◽  
Electron Distribution ◽  
Transport Model ◽  
Imaging Spectroscopy ◽  
Mean Free Path ◽  
Diffusive Transport ◽  
X Rays ◽  
Energetic Electrons ◽  
X Ray

Context. Imaging spectroscopy in X-rays with RHESSI provides the possibility to investigate the spatial evolution of X-ray emitting electron distribution and therefore, to study transport effects on energetic electrons during solar flares. Aims. We study the energy dependence of the scattering mean free path of energetic electrons in the solar corona. Methods. We used imaging spectroscopy with RHESSI to study the evolution of energetic electrons distribution in various parts of the magnetic loop during the 2004 May 21 flare. We compared these observations with the radio observations of the gyrosynchrotron radiation of the same flare and with the predictions of a diffusive transport model. Results. X-ray analysis shows a trapping of energetic electrons in the corona and a spectral hardening of the energetic electron distribution between the top of the loop and the footpoints. Coronal trapping of electrons is stronger for radio-emitting electrons than for X-ray-emitting electrons. These observations can be explained by a diffusive transport model. Conclusions. We show that the combination of X-ray and radio diagnostics is a powerful tool to study electron transport in the solar corona in different energy domains. We show that the diffusive transport model can explain our observations, and in the range 25–500 keV, the scattering mean free path of electrons decreases with electron energy. We can estimate for the first time the scattering mean free path dependence on energy in the corona.

A Universal Equation for the Emission Range of X Rays from Bulk Specimens

2007 ◽  
Vol 13 (5) ◽  
pp. 354-357 ◽  
Author(s):  
Raynald Gauvin
Keyword(s):  
Electron Beam ◽  
Free Path ◽  
Beam Energy ◽  
Mean Free Path ◽  
Electron Beam Energy ◽  
X Rays ◽  
Bulk Materials ◽  
Universal Equation ◽  
Electron Trajectories ◽  
X Ray

The derivation of a universal equation to compute the range of emitted X rays is presented for homogeneous bulk materials. This equation is based on two fundamental assumptions: the φ(ρz) curve of X-ray generation is constant and the ratio of the emitted to the generated X-ray range is equal to the ratio of the emitted to the generated X-ray intensity. An excellent agreement is observed with data obtained from Monte Carlo simulations of 200,000 electron trajectories in C, Al, Cu, Ag, Au, and an Fe–B alloy with boron weight fractions equal to 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 0.99, performed with the electron beam energy varied from 1 to 30 keV in 1-keV steps. When the ratio of the generated X-ray range to the photon mean free path is much smaller than one, the emission X-ray range is equal to the generated X-ray range, but when this ratio is much greater than one, the emission X-ray range is constant and is given by the product of the effective photon mean free path multiplied by the sine of the take-off angle.

scholarly journals Recent Observations of Energetic Electrons in Solar Flares

1980 ◽  
Vol 91 ◽  
pp. 227-230
Author(s):  
S. R. Kane
Keyword(s):  
Spatial Resolution ◽  
Solar Flares ◽  
Electron Distribution ◽  
Energetic Electron ◽  
Low Energy ◽  
Thermal Source ◽  
X Rays ◽  
Energetic Electrons ◽  
X Ray ◽  
Wide Range

SummaryIt has been apparent for the last few years that a large fraction of the total energy released during a solar flare appears initially in the form of energetic electrons accelerated during the impulsive phase. An estimate of the energy of these electrons is based on the observed hard x-ray spectra as well as the assumed form (thermal or non-thermal) of the electron distribution. Even after the basic form of the electron distribution is assumed, additional assumptions, such as the low energy cut-off in the case of the power law energy spectrum or existence of a multi-thermal source in the case of the thermal spectrum, are usually required. In order to test these assumptions, measurements of the hard x-ray spectrum with spatial resolution and covering a wide range of x-ray energy are essential. In absence of good spatial resolution, as is the case with most of the presently available hard x-ray observations, the impulsive x-ray emission at energies hv ≲ 10 keV is often unobservable because of the presence of a large background of relatively intense gradual emission associated with most flares. Observations made in the past suffered either because of the lack of a clearly identifiable impulsive x-ray emission at low energies (Peterson et al, 1973) or an adequate spectral resolution (Kahler, 1973). Thus so far it has not been possible to measure unambiguously the spectrum of impulsive x-rays ≲ 10 keV and hence to deduce a possible low energy cut-off in the energetic electron spectrum. Here we report briefly such an observation made with the ISEE-3 x-ray spectrometer experiment and its implications with regard to the characteristics of energetic electrons in solar flares.

scholarly journals Study the effect of addition Rockwool fibers on the Shielding Radiation  for the X-ray of Low Density Polyethylene (LDPE): دراسة تأثير إضافة ألياف الصوف الصخري على الحجب الإشعاعي للأشعة السينية للبولي اثيلين واطىئ الكثافة

2020 ◽  
Vol 4 (2) ◽  
Author(s):  
Shaymaa H. Jasim, Wisam A. Radhi, Riyadh M. Ramadhan, Raed M
Keyword(s):  
Free Path ◽  
Attenuation Coefficient ◽  
Mean Free Path ◽  
Weight Percent ◽  
Linear Attenuation Coefficient ◽  
X Rays ◽  
X Ray ◽  
Minimum Value ◽  
Maximum Value ◽  
The Mean

The extinction of X-rays (radiation attenuation) was studied using the low-density samples of polyethylene polymer to which the rockwool fibers powder is added as filled filler. This latter was blended with (weight percent) and with a micro-filler (filler particle) the sizes equal to or less than<212 μm. Furthermore, the free path average and linear attenuation coefficient were calculated.  Experimental results showed that the rockwool fibers powder act to reduce the spaces between polymer chains particularly when the weight percent is more than (10%), which implies the capability of the polymer/filler to make, the X-rays applied to the samples; disappear at these rates used in this study. The experimental work was conducted by applying a radiation beam having an energy of 30 kV based on the use of the X-ray unit with two tubes which are; X-ray generating tube and G-M detector with an energy of VG.M =600. The magnitudes of the mean free path are inversely proportional to the weight percent of the compound material whereas the proportionality of these percentages which are particularly the high ones which occur at experimental values of the linear attenuation coefficient. The value of the mean free path of 1.28 cm is the maximum value obtained at a weight percent of 1 %, whereas the minimum value of the mean path was 0.877 cm at a weight percent of 10 %. In addition, the maximum value of the attenuation coefficient obtained is 4.754 cm-1 at a weight percent of 10% and its minimum value at a weight percent of 1% was 0.7 cm-1. The maximum value of transmittance and the minimum value of absorbance were obtained at a weight percent of 10%, are (31.8) and (68.2) respectively. Through the practical results that we obtained that are better suited to high percentages more additive proportions can be used than the percentages used in this research to shielding X-rays more.

Study the Effect of Weight Fractions of Different Powders on the Attenuation Performances of the Epoxy Composite

2021 ◽  
Vol 19 (9) ◽  
pp. 142-151
Author(s):  
Khaled W. Yahya ◽  
Edrees E. Khadeer
Keyword(s):  
Free Path ◽  
Attenuation Coefficient ◽  
Lead Oxide ◽  
High Weight ◽  
Weight Fraction ◽  
Mean Free Path ◽  
X Rays ◽  
X Ray ◽  
Industry Research ◽  
Medical Facilities

Among all types of radiation, X-ray has always garnered the most interest, owing to the growing availability of X-ray tubes in industry, research institutions, and medical facilities. In this research, the linear (μl) and mass (μm) attenuation coefficient, half value layer (HVL) and mean free path (λ) of the epoxy polymer-based composites which includes both lead oxide (Pb3O4), mixture of (Fe2O3 + Pb3O4) and barium sulfate (BaSO4) with different weight percentages were determined experimentally for the incident photon energies of (29-35 kV) emitted from (X-rays) source. The dispersion of the filler was also investigated using a scanning electron microscope to examine the composites morphology. The obtained results showed that adding these powders to epoxy has an effect on the X-ray shielding abilities of the prepared composites, meaning that there is a direct relationship between the weight ratios of the composite material with the linear (μl) and mass (μm) attenuation coefficient, and an inverse relationship with the half value layer (HVL) and free path rate (λ). While changing the X-ray shield with applied voltages showed a behavior opposite to what was mentioned above. The result also shows that the lead oxide (Pb3O4) composites yield better attenuation performance than the pure epoxy and the other two composites, especially at high weight fraction (50 Wt.%) of this filler, which due to the high density of these fillers and fine dispensability in the polymer matrix.

scholarly journals 1/4 Ke V Diffuse Background and the Local Interstellar Medium

1989 ◽  
Vol 120 ◽  
pp. 536-536
Author(s):  
S.L. Snowden
Keyword(s):  
Interstellar Medium ◽  
Filling Factor ◽  
Thermal Emission ◽  
Mean Free Path ◽  
Physical Parameters ◽  
X Rays ◽  
Local Interstellar Medium ◽  
X Ray ◽  
Diffuse Background ◽  
X Ray Background

The 1/4 keV diffuse X-ray background (SXRB) is discussed in relation to the local interstellar medium (LISM). The most likely source for these soft X-rays is thermal emission from a hot diffuse plasma. The existence of a non-zero flux from all directions and the short ISM mean free path of these X-rays (1020HI cm-2), coupled with ISM pressure constraints, imply that the plasma has a local component and that it must, at least locally (nearest hundred parsecs), have a large filling factor. Our understanding of the geometry and physical parameters of the LISM is therefore directly tied to our understanding of the SXRB.

scholarly journals A potential lag between the open solar magnetic source flux and solar EUV and X-ray emissions as measured by the Earth's ionosphere during total solar eclipses

2009 ◽  
Vol 27 (6) ◽  
pp. 2449-2456 ◽  
Author(s):  
C. J. Davis ◽  
S. A. Bell ◽  
R. Stamper ◽  
A. W. V. Poole ◽  
L. A. McKinnell ◽  
...  
Keyword(s):  
Solar Corona ◽  
Relative Size ◽  
Unexpected Result ◽  
X Rays ◽  
X Ray ◽  
Magnetic Source ◽  
Flux Measurements ◽  
E Region ◽  
Solar Eclipses ◽  
Data Gap

Abstract. Measurements of the ionospheric E-region during total solar eclipses have been used to provide information about the evolution of the solar magnetic field and EUV and X-ray emissions from the solar corona and chromosphere. By measuring levels of ionisation during an eclipse and comparing these measurements with an estimate of the unperturbed ionisation levels (such as those made during a control day, where available) it is possible to estimate the percentage of ionising radiation being emitted by the solar corona and chromosphere. Previously unpublished data from the two eclipses presented here are particularly valuable as they provide information that supplements the data published to date. The eclipse of 23 October 1976 over Australia provides information in a data gap that would otherwise have spanned the years 1966 to 1991. The eclipse of 4 December 2002 over Southern Africa is important as it extends the published sequence of measurements. Comparing measurements from eclipses between 1932 and 2002 with the solar magnetic source flux reveals that changes in the solar EUV and X-ray flux lag the open source flux measurements by approximately 1.5 years. We suggest that this unexpected result comes about from changes to the relative size of the limb corona between eclipses, with the lag representing the time taken to populate the coronal field with plasma hot enough to emit the EUV and X-rays ionising our atmosphere.

scholarly journals On Special Features of Non-Thermal Solar X Radiation above 10 keV

1972 ◽  
Vol 14 ◽  
pp. 761-762
Author(s):  
G. Elwert ◽  
E. Haug
Keyword(s):  
Magnetic Field ◽  
Angular Distribution ◽  
Power Law ◽  
Impulsive Phase ◽  
X Rays ◽  
Energetic Electrons ◽  
X Ray ◽  
Preferred Direction ◽  
Field Lines ◽  
The Magnetic Field

The polarization and angular distribution of solar hard X radiation above 10 keV was calculated under the assumption that the X rays originate as bremsstrahlung from energetic electrons moving in a preferred direction. The source electrons are supposed to have a power-law spectrum. These conditions are to be expected in the impulsive phase of an X-ray burst. The spiral orbits of the electrons around the magnetic field lines are taken into account.

Imaging, Spectroscopy and Tomography of Frozen Hydrated Specimens With the Cryo Scanning Transmission X-Ray Microscope at The NSLS

1998 ◽  
Vol 4 (S2) ◽  
pp. 354-355
Author(s):  
J. Maser ◽  
C. Jacobsen ◽  
Y. Wang ◽  
A. Osanna ◽  
B. Winn ◽  
...  
Keyword(s):  
National Laboratory ◽  
Imaging Spectroscopy ◽  
Optical Resolution ◽  
Brookhaven National Laboratory ◽  
X Rays ◽  
X Ray ◽  
Measuring Techniques ◽  
Steady Improvement ◽  
Scanning Transmission ◽  
Synchrotron Light

With the steady improvement of x-ray optics with high resolution and efficiency, and continued development or adaptation of different imaging and measuring techniques, soft x-ray microscopy has emerged as a powerful method to image and analyze fully hydrated specimens of several micrometer thickness at sub-optical resolution (for a recent overview, see ref. 1). We report on experiments performed with the cryo scanning transmission x-ray microscope (cryo-STXM), which has recently come into operation at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory.Cryo-STXM uses x-rays with energies between the absorption edge of Carbon (E = 284 eV) and Oxygen (E = 543 eV) from the soft x-ray undulator at the NSLS. Fully hydrated specimens such as eucaryotic cells in water or ice layers of up to 10 micrometer thickness can be imaged without any additional need for contrast enhancing techniques.

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