The Absorption of Ultra-Short X-Rays by Elements of High Atomic Number

1936 ◽  
Vol 50 (2) ◽  
pp. 110-114 ◽  
Author(s):  
Matthew T. Jones
Keyword(s):  
Atomic Number ◽  
X Rays ◽  
High Atomic Number

Tomodensitométrie axiale: relation entre l'intensité tomographique et la densité de la matière

1994 ◽  
Vol 31 (2) ◽  
pp. 426-434 ◽  
Author(s):  
X. Boespflug ◽  
N. Ross ◽  
B. Long ◽  
J. F. Dumais
Keyword(s):  
Compton Scattering ◽  
Atomic Number ◽  
Computer Tomography ◽  
Empirical Model ◽  
Linear Correlation ◽  
X Rays ◽  
Photoelectric Absorption ◽  
High Atomic Number ◽  
Liquid Samples

The calibration of an axial tomodensitometer, used in sedimentology, was carried out on minerals and liquid samples. This study, taking into consideration the interactions between X rays and matter, revealed (i) a good correlation between the density of samples containing elements with low atomic number, which undergo only Compton scattering, and the intensity readings obtained by computer tomography and (ii) readings higher than predicted by linear correlation for samples containing elements with high atomic number, which undergo both Compton scattering and photoelectric absorption. An empirical model is used to correct the readings and correlate them with the density.

scholarly journals The Auger effect in xenon and krypton

1937 ◽  
Vol 158 (893) ◽  
pp. 46-54 ◽  
Keyword(s):  
Atomic Number ◽  
Wave Length ◽  
Short Wave ◽  
X Rays ◽  
Expansion Chamber ◽  
High Atomic Number ◽  
Short Wave Length ◽  
Relativistic Treatment ◽  
Number Curve ◽  
Auger Effect

In an earlier paper an account was given of a determination of the efficiency of emission of K series radiations from argon atoms ionized in the K shell. This efficiency, usually termed the K yield, was calculated from a statistical count of ordinary K photoelectron tracks and Auger pair tracks observed in a Wilson expansion chamber. These experiments have been extended to xenon and krypton, and the present paper describes the measurement of the K yields of these two gases. Determinations of the K yields for elements of high atomic number with the cloud expansion chamber should be of especial value, as other methods which depend on the measurement of X-ray energy by ionization currents encounter considerable difficulties owing to the increasing importance of scattering with short wave-length X-rays. The need for new measurements for the heavier elements has been emphasized recently by the striking divergence between the results of two extensive series of measurements, one due to Berkey and the other to Arends, both of whom used an ionization method. Berkey found a well-defined maximum in the K yield-atomic number curve in the neighbourhood of atomic number 44 after which the K yield suddenly decreased with increasing atomic number, an effect which is in direct contradiction with the experiments of Arends and existing theory. In connexion with the latter, too, measurements of the K yields for elements of high atomic number are of importance as calculations made recently by Massey and Burhop show that a relativistic treatment of the Auger effect yields rather lower values of the K yield for the higher atomic numbers than was expected by Burhop from his non-relativistic treatment.

X-Ray Fluorescence of Intermediate- to High-Atomic-Number Elements Using Polarized X Rays

1981 ◽  
Vol 25 ◽  
pp. 75-79 ◽  
Author(s):  
R. B. Strittmatter
Keyword(s):  
Atomic Number ◽  
Matrix Effects ◽  
Low Energy ◽  
Detection Sensitivity ◽  
Excitation Source ◽  
X Rays ◽  
X Ray ◽  
High Atomic Number ◽  
Increase In Accuracy

The use of polarized x rays as the excitation source for x-ray fluorescence (XRF) measurements has been shown to significantly improve signal-to-background ratios. However, previous studies on polarized x rays applied to XRF techniques have concentrated on low-energy fluoresced x rays (<30 keV). In many cases strong matrix effects exist or the analyte is encased by a material that strongly attenuates low-energy x rays. These situations may preclude accurate assays based on L x-ray detection, and techniques based on the detection of higher energy K x rays may be more suitable because of the increased penetrability of higher energy x rays. The measurements and calculations reported in this work were made to assess the improvement in signal-to-background ratios and the increase in accuracy and detection sensitivity achievable by using polarized x rays as the excitation source for fluoresced x rays having energies between 25 and 110 keV.

Contribution of x-ray total reflection to the background intensity in EPMA

1990 ◽  
Vol 48 (2) ◽  
pp. 202-203
Author(s):  
Werner P. Rehbach ◽  
Peter Karduck
Keyword(s):  
Atomic Number ◽  
Target Material ◽  
Total Reflection ◽  
Background Intensity ◽  
X Rays ◽  
Characteristic Radiation ◽  
X Ray

In the EPMA of soft x rays anomalies in the background are found for several elements. In the literature extremely high backgrounds in the region of the OKα line are reported for C, Al, Si, Mo, and Zr. We found the same effect also for Boron (Fig. 1). For small glancing angles θ, the background measured using a LdSte crystal is significantly higher for B compared with BN and C, although the latter are of higher atomic number. It would be expected, that , characteristic radiation missing, the background IB (bremsstrahlung) is proportional Zn by variation of the atomic number of the target material. According to Kramers n has the value of unity, whereas Rao-Sahib and Wittry proposed values between 1.12 and 1.38 , depending on Z, E and Eo. In all cases IB should increase with increasing atomic number Z. The measured values are in discrepancy with the expected ones.

scholarly journals The sensitivity of atomic analysis by X-rays

1932 ◽  
Vol 135 (828) ◽  
pp. 637-656 ◽  
Keyword(s):  
Atomic Number ◽  
Target Material ◽  
High Sensitivity ◽  
Major Constituent ◽  
X Rays ◽  
Depth Of Penetration ◽  
X Ray ◽  
Constituent Element ◽  
The Difference ◽  
Atomic Analysis

In a previous paper it was shown that 0·0007 per cent, of 29 Cu and 0·0003 per cent, of 26 Fe could be detected in 30 Zn by atomic analysis by X-ray spectroscopy. This sensitivity is greater than that which was claimed by Noddack, Tacke, and Berg, who set the limit at about 0·1 per cent, for non-metals, and by Hevesy, who stated it to be about 0·01 per cent, for an element present in an alloy. It was later suggested by Hevesy that the high value of the sensitivity which we found might result from the fact that some of the alloys we had used were composed of elements of almost equal atomic number, and that the sensitivity would be smaller for a constituent of low atomic number mixed with a major constituent of high atomic number. To elucidate these disagreements we have made further observations of the sensitivity with elements of different atomic number and have investigated the conditions which can influence the sensitivity. The Factors Determining Sensitivity . The detection of one element in a mixture of elements depends upon the identification of its K or L lines in the general spectrum emitted by the mixture under examination. The intensity with which these lines are excited in the target (“excited intensity”) is proportional to the number of atoms of the constituent element excited, i. e ., to its concentration and to the volume of the target in which the cathode ray energy is absorbed. The depth of penetration of the cathode rays is determined by the density of the target material and by their velocity ( i. e ., by the voltage applied to the X-ray tube). Schonland has shown that the range of homogeneous cathode rays in different elements, expressed as a mass per unit area, is approximately constant and is independent of the atomic number of the absorbing element. When their velocity is increased, the cathode rays will penetrate to a greater depth, and therefore a greater number of atoms of all constituents will be ionised. This will increase the “excited intensity” of the lines due to the particular constituent sought equally with those lines of the other elements present. The intensity of a line further depends upon the difference between the voltage applied to the X-ray tube and that necessary to excite the series. For these reasons, a high applied voltage is required for a high sensitivity.

Backscatter dose effects for high atomic number materials being irradiated in the presence of a magnetic field: A Monte Carlo study for the MRI linac

2016 ◽  
Vol 43 (8Part1) ◽  
pp. 4665-4673 ◽  
Author(s):  
Syed Bilal Ahmad ◽  
Arman Sarfehnia ◽  
Anthony Kim ◽  
Matt Wronski ◽  
Arjun Sahgal ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Monte Carlo ◽  
Atomic Number ◽  
Monte Carlo Study ◽  
High Atomic Number ◽  
Dose Effects

Light Element Analysis

1969 ◽  
Vol 13 ◽  
pp. 26-48
Author(s):  
A. K. Baird
Keyword(s):  
Atomic Number ◽  
Matrix Effects ◽  
Light Element ◽  
Electron Excitation ◽  
Electron Gun ◽  
X Rays ◽  
Element Analysis ◽  
X Ray ◽  
High Emission ◽  
Quantitative Analyses

Qualitative and quantitative analyses of elements below atomic number 20, and extending to atomic number 4, have been made practical and reasonably routine only in the past five to ten years by advances in: 1) excitation sources; 2) dispersive spectrometers; 3) detection devices; and 4) reductions of optic path absorption. At present agreement is lacking on the best combination of parameters for light element analysis. The principal contrasts in opinion concern excitation.Direct electron excitation, particularly as employed in microprobe analysis (but not limited to such instruments), provides relatively high emission intensities of all soft X-rays, but also generates a high continuum, requires the sample to be at essentially electron gun vacuum, and introduces practical calibration problems (“matrix effects“). X-ray excitation of soft X-rays overcomes some of the latter three disadvantages, and has its own limitations. Sealed X-ray sources of conventional or semi-conventional design can provide useful (if not optimum) light element emission intensities down to atomic number 9, hut with serious loss of efficiency in many applications below atomic number 15 largely because of window-thinness limitations under electron bombardment.

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