The Photon Yield Study Of HERD Transition Radiation Detector Radiator

The High Energy cosmic-Radiation Detection(HERD)facility,a new generation of space high-energy particle experiments proposed and led by China,is scheduled to be installed on China's Space Station in 2027 to search for dark matter particles with higher sensitivity and detect high-energy cosmic rays with higher accuracy.The energy of cosmic ray particles detected by HERD ranges from 30 Ge V to several Pe V,but the energy above TeV cannot be calibrated by traditional calibration methods.The transition radiation detector(TRD)is one of the payloads of HERD.The absolute energy in the TeV energy region of the calorimeter is calibrated in orbit by using the transition radiation(TR)principle.The transition radiator with high photon yield is the basis for calibrating the calorimeter precisely with TRD.To study the TR photon yields of different radiators,a new current ratio method that uses two identical ionization chambers as detectors and collects the ratio of the current signals in the two detectors is proposed in this paper.This method can intuitively compare the relative TR photon yield between radiators without separating the ionization energy loss background.Various types of regular polypropylene radiators and irregular foam and sponge radiators have been tested at Beijing Test Beam Facility(BTBF)E2line.It was found that the TR photon yield of the regular radiators was significantly better than that of the irregular radiators.According to the beam experimental conditions and detector structure,a Monte Carlo simulation program using the GEANT4 framework for the photon yield measurement of transition radiators is constructed in this paper,which is used to evaluate the experimental results and verify the accuracy of the TR-related model in GEANT4.With the aid of the detection efficiency obtained by the simulation,the absolute TR photon yield of each radiator is obtained by calculating and processing the two experimental current values.For regular radiators,there is a high agreement between the simulated and experimental ?values,with an error of less than 8%.The regular GXU0.5 × 300 radiator demonstrates an excellent absolute photon yield of about 4.05±0.97 photons per electron.Irregular radiators show a lower photon yield,which may be due to their inherent low yields or higher self-absorption of the radiator materials.In addition,due to the inapplicability of the TR generation model of the irregular radiators in GEANT4,there is a great difference between the simulated and experimental results.Considering the beam test results and the consistency between simulation and experiment,regular radiators will be selected for HERD eventually.The current ratio method and absolute TR photon yield proposed in this paper can provide references for the experimental design and optimization of TRD radiators in the future.