Performance of THGEM as a Neutron Detector
Chapter One
Gas Quenching
Gas quenching is one of the most important factors that control the gaseous detectors.Usually, the gas mixture ,contains the ionization event, consists of gas atoms as a main source of electrons and gas molecules that has a large cross sections for excitation and vibration states to cool the electrons' energy to the non-ionizing mode modes, such a process is called gas quenching.Consequently, a higher electric fields required to get a higher gain.<ref name="Sharma"> A.Sharma,F. Sauli, first tawsend 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 | 5.04 | 221.1 | 158.3 | 145.1 |
| B | 90.82 | 207.6 | 291.8 | 318.2 |
| 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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