101 research outputs found
Molecular Beams
Contains report on one research project.Joint Services Electronics Program (Contract DA36-039-AMC-03200(E
Molecular Beams
Contains a report on a research project.Lincoln Laboratory (Purchase Order DDL BB-107)United States Air Force (Contract AF19(628)-500
Microwave Spectroscophy
Contains reports on four research projects.U. S. Army Signal Corps under Contract DA36-039-sc-87376Lincoln Laboratory, Purchase Order DDL B-00337U. S. ArmyU. S. NavyU. S. Air Force under Air Force Contract AF19(604)-740
Molecular Beams
Contains reports on four research projects.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E
Molecular Beams
Contains research objectives and reports on two research projects.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 36-039-AMC-03200(E)Sloan Fund for Basic Research (M. I. T. Grant 99
Molecular Beams
Contains reports on four research projects.Lincoln Laboratory, Purchase Order DDL BB-107U. S. Air Force under Contract AF 19(628)-50
The "0.4 eV" Shape Resonance of Electron Scattering from Mercury in a Franck-Hertz Tube
The alternative version of the Franck-Hertz experiment with mercury, in which
a two-grid tube is used as a combination of electron gun, equipotential
collision space, and detection cell, was analyzed recently in considerable
detail. In particular, it was inferred that, at optimal pressure, the formation
of peaks in the anode current at inelastic thresholds is mediated inside the
detection cell by the large variation, a maximum at 0.4 eV, in the cross
section for elastic scattering. This variation is due to a shape resonance in
the electron-mercury system and is observable persuasively at the onset of
anode current as a sharp peak followed by a clear minimum. In the present
paper, the passage of electrons through the second grid to anode region is
analyzed in terms of kinetic theory. The discussion is based on a simplified
expression for the electron current derivable from an approximate form of the
Boltzmann transport equation that maintains the spatial density gradient but
omits elastic energy losses. The estimated range of pressure underlying this
kind of idealization is in good agreement with experiment. An explicit solution
is obtained by constructing an analytic expression for the momentum transfer
cross section of mercury using a recent theory of generalized Fano profiles for
overlapping resonances. This solution is used in order to model successfully
the formation of peaks at the threshold of anode current and at excitation
potentials, and to explain the dependence of the observed profiles on the
pressure and on the sign and magnitude of the potential across the detection
cell
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