MEASUREMENT OF WEAK ION CURRENTS IN A MASS-SPECTROGRAPH USING AN IONIZATION CHAMBER (in Russian)
A system is described for the mensurement of weak ion currents in a mass spectrograph. The system uses gas multiplication. The ion current is transformed at a nickel target into an electron current and is then amplified in an ionization chamber. Ions having an energy of 2 kev are admitted through a collecting slit, accelerated between two electrodes up to 20 kev, and then impinged on a nickel plate. The coefficient of secondary emission is practically independent of energy above 7 kev and is equal to 4.3 for H/sub 2/O/sup +/ ions. The secondary electrons are accelerated by an electric field into the ionization chamber which is at ground potential. A cylindrical ionization chamber is used. Measurements have shown that when the chamber is filled to a pressure of 44 mm of Hg and at ion currents of the order of 10/sup -12/ amp the curve of the current through the ionization chamber as a function of the potential difference between the electrodes has a plateau beginning at 5 v. The coefficient of amplification of the system as a function of the energy of the electrons at various pressures is shown. The stability of the amplification coefficient was faund to be plus or minus 2%. It is believed that when the electrons pass through the chamber windows they are strongly scattered nnd therefore enter the chamber at an angle to the central collecting electrode. For this reason, it is suggested that higher amplification coefficients would be obtained if the diameter of the chamber were increased. By using a Geiger tube instead of an ionization chamber, the system cnn be used to count individual ions. (J.S.R.)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-12-010787
- OSTI ID:
- 4323810
- Journal Information:
- Pribory i Tekh. Ekspt., Vol. Vol: No. 5; Other Information: Orig. Receipt Date: 31-DEC-58
- Country of Publication:
- Country unknown/Code not available
- Language:
- Russian
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