Address of the President Sir Robert Robinson, at the Anniversary Meeting, 30 November 1949

1950 ◽  
Vol 201 (1064) ◽  
pp. 1-17
Keyword(s):  
Classical Tradition ◽  
Atomic Number ◽  
Atomic Weight ◽  
Optical Spectra ◽  
Radioactive Elements ◽  
X Ray ◽  
Close Analogue

The Copley Medal is awarded to Professor George Charles DE Hevesy, For. Mem. R. S., for his distinguished work on the chemistry of radioactive elements and especially for his use of isotopes as tracers in the study of biochemical problems. Hevesy was one of the last to join the distinguished company of discoverers of elements in the classical tradition. In 1923, in collaboration with Coster, he established the occurrence of the element with atomic number 72 in zirconia minerals, and called it hafnium. This was shown to be a close analogue and constant comparison of zirconium, but a method of separation by chemical means was devised. The atomic weight was found to be 178.6, and the X-ray and optical spectra were fully described.

Address of the President Sir Robert Robinson, at the Anniversary Meeting, 30 November 1949

1950 ◽  
Vol 137 (886) ◽  
pp. 1-17
Keyword(s):  
Classical Tradition ◽  
Atomic Number ◽  
Atomic Weight ◽  
Optical Spectra ◽  
Radioactive Elements ◽  
X Ray ◽  
Close Analogue

The Copley Medal is awarded to Professor Georg e Charles de Hevesy, For. Mem. R. S., for his distinguished work on the chemistry of radioactive elements and especially for his use of isotopes as tracers in the study of biochemical problems. Hevesy was one of the last to join the distinguished company of discoverers of elements in the classical tradition. In 1923, in collaboration with Coster, he established the occurrence of the element with atomic number 72 in zirconia minerals, and called it hafnium. This was shown to be a close analogue and constant comparison of zirconium, but a method of separation by chemical means was devised. The atomic weight was found to be 178·6, and the X-ray and optical spectra were fully described.

Henry Moseley, X-ray spectroscopy and the periodic table

2020 ◽  
Vol 378 (2180) ◽  
pp. 20190302 ◽  
Author(s):  
Russell G. Egdell ◽  
Elizabeth Bruton
Keyword(s):  
Periodic Table ◽  
Chemical Elements ◽  
Atomic Weight ◽  
X Rays ◽  
Radioactive Elements ◽  
Theme Issue ◽  
X Ray ◽  
Series Of Experiments ◽  
Radiological Characterization

Just over 100 years ago, Henry Moseley carried out a systematic series of experiments which showed that the frequencies of the X-rays emitted from an elemental target under bombardment by cathode rays were characteristic of that element and could be used to identify the charge on its atomic nucleus. This led to a reorganization of the periodic table, with chemical elements now arranged on the basis of atomic number Z rather than atomic weight A, as had been the case in previous tables, including those developed by Mendeleev. Moseley also showed that there were four ‘missing elements’ before gold. With further measurements up to uranium Z = 92, the Swedish physicist Manne Siegbahn identified two more missing elements. This paper provides an introduction to Moseley and his experiments and then traces attempts to ‘discover’ missing elements by X-ray spectroscopy. There were two successes with hafnium (Z = 72) and rhenium (Z = 75), but many blind alleys and episodes of self-deception when dealing with elements 43, 61, 85 and 87. These all turned out to be radioactive, with extremely small natural abundances: all required synthesis by a nuclear reaction, with radiological characterization in the first instance. Finally, the paper moves on to consider the role of X-ray spectroscopy in exploring the periodic table beyond uranium. Although the discovery of artificial radioactive elements with Z > 92 again depended on nucleosynthesis and radiological characterization, measurement of the frequencies or energies of characteristic X-rays remains the ultimate goal in proving the existence of an element. This article is part of the theme issue ‘Mendeleev and the periodic table’.

Thickness and composition determinations from T.E.M. specimens using both x-ray and backscattered electron data

1984 ◽  
Vol 42 ◽  
pp. 576-577
Author(s):  
M.D. Ball ◽  
H. Lagace ◽  
M.C. Thornton
Keyword(s):  
Electron Microscope ◽  
Atomic Number ◽  
Transmission Electron Microscope ◽  
Convenient Method ◽  
Flow Chart ◽  
X Ray ◽  
Intensity Measurements ◽  
Transmission Electron ◽  
Electron Intensity ◽  
Backscattered Electron

The backscattered electron coefficient η for transmission electron microscope specimens depends on both the atomic number Z and the thickness t. Hence for specimens of known atomic number, the thickness can be determined from backscattered electron coefficient measurements. This work describes a simple and convenient method of estimating the thickness and the corrected composition of areas of uncertain atomic number by combining x-ray microanalysis and backscattered electron intensity measurements.The method is best described in terms of the flow chart shown In Figure 1. Having selected a feature of interest, x-ray microanalysis data is recorded and used to estimate the composition. At this stage thickness corrections for absorption and fluorescence are not performed.

Is there a “universal” MAC equation?

1990 ◽  
Vol 48 (2) ◽  
pp. 228-229
Author(s):  
Robert E. Ogilvie
Keyword(s):  
Absorption Coefficient ◽  
Atomic Absorption ◽  
Atomic Number ◽  
X Ray ◽  
Time Period ◽  
Image Position

The search for an empirical absorption equation begins with the work of Siegbahn (1) in 1914. At that time Siegbahn showed that the value of (μ/ρ) for a given element could be expressed as a function of the wavelength (λ) of the x-ray photon by the following equationwhere C is a constant for a given material, which will have sudden jumps in value at critial absorption limits. Siegbahn found that n varied from 2.66 to 2.71 for various solids, and from 2.66 to 2.94 for various gases.Bragg and Pierce (2) , at this same time period, showed that their results on materials ranging from Al(13) to Au(79) could be represented by the followingwhere μa is the atomic absorption coefficient, Z the atomic number. Today equation (2) is known as the “Bragg-Pierce” Law. The exponent of 5/2(n) was questioned by many investigators, and that n should be closer to 3. The work of Wingardh (3) showed that the exponent of Z should be much lower, p = 2.95, however, this is much lower than that found by most investigators.

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.

A Spectrum-Adaptive Decomposition Method for Effective Atomic Number Estimation Using Dual Energy CT

2020 ◽  
Vol 2020 (14) ◽  
pp. 293-1-293-7
Author(s):  
Ankit Manerikar ◽  
Fangda Li ◽  
Avinash C. Kak
Keyword(s):  
Atomic Number ◽  
Decomposition Method ◽  
Traditional Approach ◽  
Effective Atomic Number ◽  
Dual Energy ◽  
Performance Comparison ◽  
Estimation Methods ◽  
Dual Energy Ct ◽  
Projection Data ◽  
X Ray

Dual Energy Computed Tomography (DECT) is expected to become a significant tool for voxel-based detection of hazardous materials in airport baggage screening. The traditional approach to DECT imaging involves collecting the projection data using two different X-ray spectra and then decomposing the data thus collected into line integrals of two independent characterizations of the material properties. Typically, one of these characterizations involves the effective atomic number (Zeff) of the materials. However, with the X-ray spectral energies typically used for DECT imaging, the current best-practice approaches for dualenergy decomposition yield Zeff values whose accuracy range is limited to only a subset of the periodic-table elements, more specifically to (Z < 30). Although this estimation can be improved by using a system-independent ρe — Ze (SIRZ) space, the SIRZ transformation does not efficiently model the polychromatic nature of the X-ray spectra typically used in physical CT scanners. In this paper, we present a new decomposition method, AdaSIRZ, that corrects this shortcoming by adapting the SIRZ decomposition to the entire spectrum of an X-ray source. The method reformulates the X-ray attenuation equations as direct functions of (ρe, Ze) and solves for the coefficients using bounded nonlinear least-squares optimization. Performance comparison of AdaSIRZ with other Zeff estimation methods on different sets of real DECT images shows that AdaSIRZ provides a higher output accuracy for Zeff image reconstructions for a wider range of object materials.

A Calculation real abundance of gaseous elements of the comet PanSTARRS C/2011 S4

2020 ◽  
Vol 18 (45) ◽  
pp. 21-31
Author(s):  
Salman Zaidan Khalaf ◽  
Khaleel Abrahim ◽  
Imad Kassar Akeab
Keyword(s):  
Solar Wind ◽  
Physical Properties ◽  
Atomic Number ◽  
Mathematic Model ◽  
Emission Energy ◽  
X Ray ◽  
The Real

    X-ray emission contains some of the gaseous properties is produced when the particles of the solar wind strike the atmosphere of comet ISON and PanSTARRS Comets. The data collected with NASA Chandra X-ray Observatory of the two comets, C/2012 S1 (also known as Comet ISON) and C/2011 S4 (Comet PanSTARRS) are used in this study.    The real abundance of the observed X-ray spectrum elements has been extracted by a new simple mathematic model. The study found some physical properties of these elements in the comet’s gas such as a relationship between the abundance with emitted energy. The elements that have emission energy (2500-6800) eV, have abundance (0.1-0.15) %, while the elements that have emission energy (850-2500) eV and (6800-9250) eV have abundance (0.2-0.3) %.    The relation between interacted energy and atomic number is form two sets.  The interacted energy of each element is increased as the atomic number increased. This case has been seen in both comets

scholarly journals Review of the soft-X-ray laser research at CEL-V

1991 ◽  
Vol 9 (2) ◽  
pp. 493-499
Author(s):  
D. Naccache ◽  
J-L. Bourgade ◽  
P. Combis ◽  
C. J. Keane ◽  
J-P. Le Breton ◽  
...  
Keyword(s):  
Atomic Number ◽  
Collisional Excitation ◽  
X Ray ◽  
Order Of Magnitude ◽  
Laser Experiments ◽  
Magnitude Increase

We present some significant results of collisional excitation X-ray laser experiments in plasmas produced by a laser. We studied the amplification in Ne- and Ni-like ions by varying both the nature and the thickness of targets, the irradiation, and the wavelength of the driving laser. Some potentially interesting scalings as a function of the atomic number of the lasing element are demonstrated in the Ne-like system. An order-of-magnitude increase in gain in the Ni-like experiments was determined.

Recrystallization of metamict allanite

2011 ◽  
Vol 75 (4) ◽  
pp. 2393-2399 ◽  
Author(s):  
T. Beirau ◽  
C. Paulmann ◽  
U. Bismayer
Keyword(s):  
Crystal Structure ◽  
Igneous Rocks ◽  
Accessory Mineral ◽  
Recrystallization Process ◽  
Radioactive Elements ◽  
X Ray Diffraction ◽  
Geological Time ◽  
Α Decay ◽  
X Ray ◽  
Structural Recovery

AbstractAllanite is a common accessory mineral in igneous rocks. Allanite becomes metamict over geological time-scales as a result of the α-decay of radioactive elements in the crystal structure. This study focuses on the recrystallization of metamict allanite from Savvushka, Russia. The structural recovery produced by annealing was investigated by X-ray powder diffraction, single-crystal synchrotron X-ray diffraction and infrared spectroscopy. A kinetic analysis is presented that shows that the recrystallization process proceeds by at least two different mechanisms.

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