HW15-1-2a2b - 2. What effect does each of the following...

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PROBLEMS 1. Should the quenching gas in a GM tube have a higher or lower ionization potential than the major tube gas? Why? Solution: The quench gas should have a lower ionization potential than that of the major tube gas (hereafter, simply called the tube gas). As the positive tube-gas ions drift toward the cathode wall, they collide with quench gas molecules and, because of their lower ionization potential, there is a tendency to transfer an electron from the quench gas molecule to the tube-gas ion thereby neutralizing it. The resulting positively charged quench-gas molecule then drifts to the cathode where the energy liberated in the neutralization of the molecule causes the molecule to dissociate rather than to free an electron from the cathode surface (and thus start another avalanche).
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Unformatted text preview: 2. What effect does each of the following changes have on the performance of a proportional counter? (a) The diameter of the anode wire is increased. (b) The pressure of the fill gas is increased. (c) The atomic number of the wall material is increased. Solution: (a) By increaging the diameter of the central anode wire, the electric field is decreaged near the wire surface. This reduces the multiplication factor of the avalanche mechanism and thus reduces the magnitude of the output pulses from the detector. (b) Increaging the gag pressure increages the density of gag atoms in the cham-ber. Consequently, more atoms are near the anode so that there is a slight increage in the avalanche multiplication effect. Also increaged gag pressure 8-1 July 24. 2002...
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This note was uploaded on 02/01/2010 for the course ECE 4130 taught by Professor Cady during the Spring '06 term at Cornell University (Engineering School).

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