The continuous absorption of light in alkali-metal vapours

1953 ◽  
Vol 219 (1136) ◽  
pp. 89-101 ◽  
Keyword(s):  
Cross Section ◽  
Alkali Metals ◽  
Theoretical Calculations ◽  
Wave Length ◽  
Energy Difference ◽  
Continuous Absorption ◽  
Absorption Of Light ◽  
Sodium Vapour ◽  
Good Agreement ◽  
Dipole Length

The first section of this paper is an account of some experiments on the absorption of light in sodium vapour from the series limit at 2412 Å to about 1600 Å (an energy difference of 2·6 eV). The absorption cross-section at the limit is 11·6 ± 1·2 x 10 -20 cm 2 . The cross-section decreases giving a minimum of 1·3 ± 0·6 x 10 -20 cm 2 at 1900 Å and then increases to 1600 Å. A theoretical calculation by Seaton based on the dipole-length formula gives good agreement with the experiments at the series limit and also correctly predicts the wave-length for the minimum, but it predicts a significantly lower absorption at the minimum. The experiments described in the first section of the paper conclude a series on the absorption of light in the alkali metals. The second section consists of a general discussion of the results of these experiments and of their relation to theoretical calculations. There is good agreement between theory and experiment except in regard to the magnitude of the absorption at the minimum.

scholarly journals The continuous absorption of light in potassium vapour

1928 ◽  
Vol 117 (777) ◽  
pp. 486-508 ◽  
Keyword(s):  
Vapour Pressure ◽  
Alkali Metals ◽  
Wave Length ◽  
Experimental Conditions ◽  
General Application ◽  
Continuous Absorption ◽  
Wide Range ◽  
Absorption Of Light ◽  
Relative Absorption ◽  
Band Absorption

While considerable attention has been paid to the line and band absorption of the alkali metals, very little work has been done on the continuous absorption. R. W. Wood and Holtzmark have observed the existence of this absorption, and Harrison has made some measurements on the continuous absorption of sodium in the region 2500 Å. U. - 2150 Å. U. In the present paper, results are given for potassium over a wide range of wave-length (4000 Å. U. - 2200 Å. U.) and under widely different experimental conditions. The ordinary methods of spectrophotometry have usually been designed to measure the absorption of solutions, etc., and are not suitable for measuring the absorption in a vapour unless the vapour pressure can be kept absolutely constant. A method of spectrophotometry has been developed by which it is possible to obtain measurements of the relative absorption coefficients for different wave-lengths correct to about 2 per cent, without keeping the vapour pressure absolutely constant. While the method is specially suitable for the measurement of an absorption which is not quite steady, it is really of quite general application.

scholarly journals On the absorption of light by crystals

1938 ◽  
Vol 167 (930) ◽  
pp. 384-391 ◽  
Keyword(s):  
Absorption Spectrum ◽  
Wave Length ◽  
Short Wave ◽  
Point Of View ◽  
Theoretical Point ◽  
Lattice Vibrations ◽  
Short Wave Length ◽  
Continuous Absorption ◽  
Absorption Of Light ◽  
Positive Hole

The purpose of this paper is to discuss the absorption of light by non-metallic solids, and in particular the mechanism by which the energy of the light absorbed is converted into heat. If one considers from the theoretical point of view the absorption spectrum of an insulation crystal, one finds that it consists of a series of sharp lines leading up to a series limit, to the short wave-length side of which true continuous absorption sets in (Peierls 1932; Mott 1938). In practice the lattice vibrations will broaden the lines to a greater of less extent. When a quantum of radiation is absorbed in the region of true continuous absorption, a free electron in the conduction band and a "positive hole" are formed with enough energy to move away from one another and to take part in a photocurrent within the crystal. When, however, a quantum is absorbed in one of the absorption lines , the positive hole and electron formed do not have enough energy to separate, but move in one another's field in a quantized state. An electron in a crystal moving in the field of a positive hole has been termed by Frenkel (1936) an "exciton".

The photo-ionization cross-section of neon

1953 ◽  
Vol 220 (1140) ◽  
pp. 71-76 ◽  
Keyword(s):  
Cross Section ◽  
Ionization Cross Section ◽  
Wave Length ◽  
Grazing Incidence ◽  
Absorption Coefficients ◽  
Ionization Cross ◽  
Ionization Limit ◽  
Resonance Transitions ◽  
Photo Ionization ◽  
Dipole Length

The absorption of radiation of wave-length between 230 and 800 Å in neon was measured photometrically in a grazing incidence vacuum spectrograph. For wave-lengths longer than that corresponding to the first ionization limit the absorption coefficients were found to be zero except for photo-excitation of resonance transitions. Two sharp absorption edges were observed at 575 and 256 Å corresponding to the L 3 - and L 1 -edges respectively with a flat maximum between them. The photo-ionization cross-section at the first ionization limit was found to be 5⋅4 x 10 -18 cm 2 independent of the pressure between 50 and 500 μ ; this should be compared with the theoretical value of 5⋅8 x 10 -18 cm 2 obtained by Seaton using a dipole-length approximation. Between 575 and 400 Å the calculated and experimental curves agreed closely within the limits of measurement.

RADIAL SENSITIVITY OF THE ELASTIC SCATTERING AROUND THE COULOMB BARRIER ENERGIES FOR WEAKLY-BOUND AND HALO NUCLEI

2012 ◽  
Vol 27 (21) ◽  
pp. 1250118
Author(s):  
Y. SERT ◽  
T. CANER ◽  
O. BAYRAK ◽  
I. BOZTOSUN
Keyword(s):  
Elastic Scattering ◽  
Cross Section ◽  
Coulomb Barrier ◽  
Optical Potential ◽  
Theoretical Calculations ◽  
Fusion Cross Section ◽  
Halo Nuclei ◽  
Weakly Bound ◽  
Medium Mass ◽  
Good Agreement

The radial sensitivity of the elastic scattering of the weakly-bound 6 Li and halo 6 He nuclei on medium-mass 64 Zn target and heavy target 208 Pb is examined around the Coulomb barrier energies. We present that very good agreement between theoretical and experimental results have been obtained with small χ2/N values. The fusion cross-section and volume integrals of the potentials have been deduced from the theoretical calculations for all studied systems at relevant energies. We have also analyzed the elastic scattering of the 6 He +208 Pb system at E lab = 14, 16, 18, 22, 27 MeV in order to investigate whether there is a dispersion relation between the real and imaginary parts of the optical potential.

scholarly journals Continuous absorption of light in cæsium vapour

1934 ◽  
Vol 143 (849) ◽  
pp. 472-481 ◽  
Keyword(s):  
Wave Length ◽  
Principal Series ◽  
Short Wave ◽  
Main Difficulty ◽  
Absorption Cell ◽  
Absorption Tube ◽  
Short Wave Length ◽  
Continuous Absorption ◽  
Absorption Of Light ◽  
Photo Ionization

A region of continuous absorption lying on the short wave-length side of the limit of the principal series and corresponding to the photo-ionization of the atom is to be expected in the alkali metal vapours. The currents due to photo-ionization have been measured and several attempts have been made to observe the absorption. The main difficulty is in the action of the vapour on the windows of the absorption cell. This has usually been overcome by keeping the ends of the absorption tube cool and checking the diffusion of the vapour from the centre of the tube by means of a foreign gas. This gas produces a large and complicated effect on the absorption (Harrison). In the present experiments it has been found possible to avoid the use of a foreign gas by employing a long absorption tube and a low vapour pressure. Cæsium was used because it gives a sufficient pressure at a moderate temperature and because its series limit lies in the most convenient region of the spectrum.

Deviation from Stoichiometry and Lattice Properties of Semiconducting SnTe Phase

1995 ◽  
Vol 378 ◽  
Author(s):  
E. I. Rogacheva ◽  
G. V. Gorne ◽  
O. N. Nashchekina
Keyword(s):  
Thermal Resistance ◽  
Cross Section ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Theoretical Calculations ◽  
Linear Change ◽  
Deviation From Stoichiometry ◽  
Temperature Dependences ◽  
Thermal Conductivity Λ ◽  
Good Agreement

AbstractThe temperature dependences of lattice thermal conductivity λp in the range of 300-650 K were obtained for SnTe1+x semiconducting phase with x =0-0.04. It is established that the nonstoichiometric vacancies are centers of effective scattering of phonons. The scattering cross-section calculated from experimental data is in a good agreement with the theoretical calculations based on the Klemens theory. The linear change of thermal resistance with temperature is observed, which evidences the prevalence of three-phonon scattering processes. The additional thermal resistance grows as the concentration of cation vacancies increases.

The absorption of light by thallium vapour on the short wave-length side of the series limit

1954 ◽  
Vol 224 (1156) ◽  
pp. 83-90 ◽  
Keyword(s):  
Cross Section ◽  
Wave Length ◽  
Theoretical Work ◽  
Short Wave ◽  
Broad Line ◽  
Absorption Cross ◽  
Sharp Line ◽  
Short Wave Length ◽  
Absorption Of Light ◽  
The Continuum

Measurements of the absorption of light in thallium vapour from the series limit at 2030 to 1450Å are described. The absorption cross-section at the series limit is 4∙5 ± 0∙8 × 10 -18 cm 2 and the f -number for the continuum over the range of the experiment is 0∙025 ± 0∙005. Auto-ionization lines are observed at 2007, 1610 and 1490Å in agreement with those reported by Beutler & Demeter (1934 b ). The moderately sharp line at 2007Å ( 2 P 0 ½ → 4 P 3/2 ) has an f -number of 0∙005 ± 0∙001 and a lifetime of 18 ± 5 × 10 -15 s, while the broad line at 1610Å ( 2 P 0 ½ → 2 D 3/2 ) has an f -number of 0∙52 ± 0∙09 and a lifetime of 2∙2 ± 0∙1 × 10 -15 s. The 1490Å line ( 2 P 0 ½ → 2 P ½ ) is sharp and the f -number is estimated to be of the same order as that of the line 2007Å. These results are discussed in relation to the auto-ionization selection rules and previous experimental and theoretical work is reviewed.

Continuous Absorption of Light in Sodium Vapour

Nature ◽  
1950 ◽  
Vol 165 (4201) ◽  
pp. 723-724 ◽  
Author(s):  
R. W. DITCHBURN ◽  
P. J. JUTSUM
Keyword(s):  
Continuous Absorption ◽  
Absorption Of Light ◽  
Sodium Vapour

Longitudinal Thermal Movement of Polymer Concrete Irrigation Aqueducts

2015 ◽  
Vol 1129 ◽  
pp. 586-592
Author(s):  
Kyu Seok Yeon ◽  
Jin Yong Hwang ◽  
Chul Young Kim ◽  
Jung Heum Yeon
Keyword(s):  
Cross Section ◽  
Theoretical Calculations ◽  
Field Measurements ◽  
Polymer Concrete ◽  
Span Length ◽  
Water Leakage ◽  
Joint System ◽  
Expansion Joints ◽  
Thermal Movement ◽  
Good Agreement

This study evaluates the longitudinal thermal movements of precast polymer concrete aqueducts made with MMA modified UP polymer concrete. The aqueduct investigated in this study had a total span length of 30 m, which is composed of three 10 m span flumes with an inner cross-section of 700 x 600 mm. To accomplish this objective, temperature and corresponding longitudinal movements of transverse expansion joints were continuously monitored in the field for 23 months. The maximum seasonal variation of joint displacement was found to be approximately 13 to 14 mm, which is relatively high. Also, the field measurements were compared with theoretical calculations to validate the experimental data, and the results showed a good agreement with each other. Finally, in this study, an adjustable expansion joint system for aqueducts was devised in order to prevent water leakage and joint deterioration resulting from successive thermal movements of joints.

Absorption cross-sections in the vacuum ultra-violet III. Methane

1955 ◽  
Vol 229 (1176) ◽  
pp. 44-62 ◽  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Wave Length ◽  
Ultra Violet ◽  
Photoionization Cross Section ◽  
Absorption Cross ◽  
Continuous Absorption ◽  
Length Range ◽  
Photo Ionization ◽  
Vacuum Ultra Violet

Cross-sections for the continuous absorption of radiation by methane in the wave-length range 1600 to 350A have been measured. The absorption is analyzed so as to distinguish between absorption leading to photo-dissociation processes and absorption due to photoionization. The main photo-ionization process is CH 4 +hv->CH 4 + -e - , and the photoionization cross-section is measured for free electron energies from 0 to about 20 eV. Little evidence is found for processes such as CH 4 + hv-> CH 2 + H+e - The results are compared with calculations by Dalgamo. The paper includes an account of the technique of photographic spectrophotometry in the region 1100 to 200A.

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