Performance of THGEM as a Neutron Detector

Chapter One

Gas Quenching

Rewrite the first two sentences so quenching is more clearly described.

Gas quenching is a non-ionizing process occurs when a gas molecules with large cross sections for excitation and vibration states decrease a charged particle energy to create any ionization when the charged particle passes through. Usually, the gas mixture ,contains the ionization event, consists mostly of gas atoms as a main source of electrons and the quenching gas, when the free electrons are scattered after the ionization, their energy is decreased by quenching so the number of secondary electrons becomes less, Consequently, a higher voltage is required to get a gain from this mixture than a medium only has a non-quenching gas.<ref name="Sharma"> A.Sharma,F. Sauli, first Townsend coefficients measurements for argon gas european organization for nuclear research (1993) </ref >

Not only does the quenching process decreases the electron energy, but also decreases the positive ions energy (produced by ionization) when the ions collide with these gas molecules and emits a photon or more from these positive ions. These photons represent the energy loss in a form other than the ionization and also is called Argon escape peak in case of using Argon gas.

Gas quenching experimentally can be measured by evaluating Townsend first coefficients A,B for different gas mixtures. the following table represents the Townsend first coefficients' values for different ratio of Ar/CO2 gas mixtures:<ref name="Sharma"/>

Percentage of CO2	3.7	22.8	87.2	100
A [math] cm^{-1}Torr^{-1} [/math]	5.04	221.1	158.3	145.1
B [math] Vcm^{-1}Torr^{-1} [/math]	90.82	207.6	291.8	318.2
[math] \frac{E}{p} \,\,\, Vcm^{-1}Torr^{-1} [/math]	16.2	21.6	32.9	36.4

The electric field pressure ratio in the last row is the upper limit of the reduced electric field which Townsend's equation fits considering E as a uniform electric field.

References

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