Characterization of 8 MeV Cherenkov Thresholding of Carbon Dioxide Gas

The energy thresholding characteristic of carbon dioxide (CO
₂
) Cherenkov gas is significant for the detection of fusion
$\gamma $
-rays. In this article, the energy thresholding characteristic of CO
₂
(at 300 K and 4.02 atm.) gas is experimentally calibrated by a pulse electron beam with picosecond duration time and adjustable energies. Three mirrors with the ultraviolet reflectivity are used to make an off-axis light collection system. For electron energy of 10 MeV (above the Cherenkov threshold energy), the collected pulse photon spectrum has good agreement with the theoretical spectrum of Cherenkov radiation, confirming that Cherenkov radiation dominates collected photons than non-Cherenkov sources. The threshold energy resolution (12/7.5 MeV) is improved to ~10
⁴
, an order higher than the reported value of ~10
³
. The improvement on the threshold energy resolution of CO
₂
gas is mainly attributed to the ultraviolet mirrors, suppressing lights with a wavelength higher than 280 nm. This work can provide significant support for the further application of the Cherenkov detector in the fusion
$\gamma $
-ray diagnosis.