Fluctuation of ionization, scintillation and proportional scintillation yields due to alpha-particles in gaseous xenon under normal pressures

Fluctuation in ionization, scintillation and gas proportional scintillation (GPS) yields have been measured in gaseous xenon as a function of the reduced electric field strength E / N in Td (townsend), where E is the electric field strength in volts/cm and N the atomic number density of xenon. 1 Td is defined as 1×10 −17 V cm 2 . The measurements are made under the pressures of 0.1 and 0.2 MPa by a plane parallel ionization chamber (PPIC) equipped with a photo-multiplier tube (PMT) sensitive to VUV photons. It is found that the fluctuation in ionization is largely improved in PPIC if alpha-particles were almost vertically emitted to the plane of the electrode and their track lengths were nearly equal to the distance between the electrodes. The fluctuation in the scintillation is 33.5% (full-width at half-maximum (FWHM)) at the pressure of 0.1 MPa and 35.6% (FWHM) at the 0.2 MPa, respectively, including the fluctuation of 10% (FWHM) in the alpha-particle energy. The season may be attributed to the fluctuations in several parameters on PMT. In GPS, it is turned out that the proportional gain of about 17 photons/electron at 3.8 Td–45 photons/electron at 4.6 Td is easily achieved and its fluctuation is about a few percent. It is equal to twice of that value at the same reduced field in the case of 0.2 MPa. The fluctuation in the photon yields in GPS shows just equal to one of the ionization yields.