The critical ionization potentials of uranium hexafluoride and hydrogen fluoride

MDDC 874


UNITED STATES ATOMIC ENERGY COMMISSION


THE CRITICAL IONIZATION POTENTIALS OF URANIUM HEXAFLUORIDE
AND HYDROGEN FLUORIDE


by
J. R. White
A. E. Cameron

Tennessee Eastman Corporation






This document consists of 1 page.
Date Declassified: April 21, 1947

This document is for official use.
Its issuance does not constitute authority
for declassification of classified copies
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Technical Information Division, Oak Ridge Directed Operations
Oak Ridge, Tennessee


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THE CRITICAL IONIZATION POTENTIALS OF URANIUM HEXAFLUORIDE


AND HYDROGEN FLUORIDE


By J. R. White and A. E. Cameron


The critical ionization potentials of uranium hexalluoride and of hydrogen fluoride were deter-
mined by using a VGIA ion gauge. Filament emission was held constant at such a value that the grid
current was in a plateau region and the grid to filament potential varied. The onset of ionization was
determined by plotting ion current as a function of applied voltage. Ions were collected on the plate
by application of a small fixed potential, and secondary emission and space charge effects evaluated
by measuring the ionization potential of mercury. The correction was determined, using the value of
10.4* volts for the first ionization potential of mercury, and was subtracted from the potential ob-
served for uranium hexafluoride. Measurements were made with hydrogen fluoride to eliminate the
possibility that the potential observed with uranium hexafluoride was due to hydrolysis products.
The measurements upon uranium hexalluoride were repeated in a 60 mass spectrometer of the
Nier type, so that ions other than the UFs, could be identified and measured. The ionizing case and
the electron trap were operated at the same potential, so that the voltage drop from the filament to
these elements was a measure of the ionization potential. The effect of space charge, thermal exci-
tation and secondary emission in the ionizing region were evaluated by using mercury as reference
gas. Filament emission was held constant at 1.4 ma, and no potentials except that between filament
and Ionizing case were varied after measurements upon mercury. Potentials were measured with a
voltmeter which had been calibrated carefully against a laboratory potentiometer. The critical po-
tential was determined by the intersection of the plots of ion current against voltage, before and
after reaching the critical potential.

The mean value for several determinations upon the mercury standard was 15.1 volts. A cor-
rection of -4.7 volts was accordingly applied to the observed critical ionization potentials for the
individual uranium fluoride ions. The critical ionization potentials are shown in the table:

Critical Ionization Potential
Ion Spectrometer Triode
UF5 15.5 v 15.9 v
UF.4 20.1 v ---
UFa* 23.5 v --
UF/ 29.9 v ----
UF1/ 37.9 v ---
U* 50.3 v ---
HF ----- 5.4
These data may be regarded as giving a correct representation of the order of magnitude, but a
probable error range of from 5% for the UF5+ ion to 15% for the U' appears likely because of the
wide departure of potentials from that of the reference gas.
This paper is based on the results of research performed under Contract W-704-eng-23, with
the Manhattan Project, Oak Ridge, Tennessee.

Bleakney, W., Phys. Rev. 35:139 (1930).


MDDC 874




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