ABSTRACT
A typical gas-filled detector* has a capacitance of about 50 pF, and the charge will be collected in a time of the order of 1 μs. If all the charge created by the 3-MeV particle is collected, the voltage and current expected are of the order of
V Q C
i Q t
= ≈ × ×
× ≈ × ≈
= ≈ ×
10 1 6 10 50 10
0 5 10 0 5
. . .C/el F
V mV
1 6 10 10
1 6 10 19
6 8. .× ∼ ×
−A A
with both values well within our measuring ability with standard instruments. In an ionized gas without an electric field, electrons and positive ions will move at ran-
dom with an average kinetic energy equal to (3/2) kT, where k = Boltzmann constant and T = temperature of the gas (kelvin). When an electric field is present, both electrons and positive ions acquire a net velocity component along the lines of the electric field. Electrons move toward the positive electrode; positive ions toward the negative one. e force on either charge carrier is the same and is equal to F = Ee, where E = electric field intensity, but the acceleration is quite different. e acceleration a is equal to F/M, where M is the mass of the ion or electron. erefore, the acceleration of an electron will be thousands of times larger than the acceleration of an ion. e time it takes the electrons to reach the positive electrode of a typical detector is about 1 μs. e corresponding time for the positive ions is about 1 ms, a thousand times longer.
