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Determination of h e by a New Method

Determination of h e by a New Method A new method for the direct determination of h e has been developed which does not involve the short wavelength limit of the continuous x-ray spectrum. The excitation potential V e of helium from the ground state to the 2 p P 1 1 ∘ state is measured as the energy, in electron volts, lost by electrons causing this excitation. Experimentally, this energy is determined as the difference between two voltages. The value of h e is calculated from the basic equation h ν ̃ c = V e e ; here ν ̃ is the wave number of the radiation from helium in the 2 p P 1 1 ∘ state. Four factors make possible an order-of-magnitude increase in precision over other earlier work dependent on excitation or ionization potentials: (1) the difference method of obtaining the excitation potential; (2) a gold evaporation technique which essentially eliminates contact potentials and makes possible a great reduction in surface charges; (3) the high precision in both the slit system and in the uniformity of the magnetic field; and (4) the fact that the absolute magnitudes of the electron beam energy, the magnetic field, and the work function of the cathode do not need to be known. A total of 156 determinations of h e were made under varying experimental conditions. A multiple correlation analysis of these data shows no significant variation of h e with experimental conditions. The value obtained with its standard error is h e = ( 1.3790 ± 0 . 0 0 0 2 ) × 10 - 17 erg·sec/esu. This value is in fairly good agreement with the values found from the short wavelength limit of the continuous x-ray spectrum and with the indirect value computed from all significant work on atomic constants. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical Review American Physical Society (APS)

Determination of h e by a New Method

Dunnington, F. G; Hemenway, C. L; Rough, J. D
Physical Review , Volume 94 (3) – May 1, 1954
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Publisher
American Physical Society (APS)
Copyright
Copyright © 1954 The American Physical Society
ISSN
1536-6065
DOI
10.1103/PhysRev.94.592
Publisher site
See Article on Publisher Site

Abstract

A new method for the direct determination of h e has been developed which does not involve the short wavelength limit of the continuous x-ray spectrum. The excitation potential V e of helium from the ground state to the 2 p P 1 1 ∘ state is measured as the energy, in electron volts, lost by electrons causing this excitation. Experimentally, this energy is determined as the difference between two voltages. The value of h e is calculated from the basic equation h ν ̃ c = V e e ; here ν ̃ is the wave number of the radiation from helium in the 2 p P 1 1 ∘ state. Four factors make possible an order-of-magnitude increase in precision over other earlier work dependent on excitation or ionization potentials: (1) the difference method of obtaining the excitation potential; (2) a gold evaporation technique which essentially eliminates contact potentials and makes possible a great reduction in surface charges; (3) the high precision in both the slit system and in the uniformity of the magnetic field; and (4) the fact that the absolute magnitudes of the electron beam energy, the magnetic field, and the work function of the cathode do not need to be known. A total of 156 determinations of h e were made under varying experimental conditions. A multiple correlation analysis of these data shows no significant variation of h e with experimental conditions. The value obtained with its standard error is h e = ( 1.3790 ± 0 . 0 0 0 2 ) × 10 - 17 erg·sec/esu. This value is in fairly good agreement with the values found from the short wavelength limit of the continuous x-ray spectrum and with the indirect value computed from all significant work on atomic constants.

Journal

Physical Review – American Physical Society (APS)

Published: May 1, 1954

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