Measurement of the neutron energy response curve of 4H-SiC detector based fission target detection system at the CSNS Back-n white neutron source

The fission target detection system, which is based on U-235(or U-238)fission target and large area 4H-SiC detector, has been developed for pulsed neutron detection. However, calibration of its neutron energy response curve is challenging due to its very low detection efficiency to fast neutrons. In the past, the calibration of the neutron sensitivity for the fission target detection system was limited to using -14 MeV neutrons generated by the Cockcroft-Walton accelerator. To obtain the response function for the complete range of neutron energies, extrapolation based on neutron fission cross sections was required. In this paper, we present the calibration of its energy response at the China Spallation Neutron Source (CSNS) Back-n beam line using the time of flight method, both with double-bunch and single-bunch mode in end-station 1(with a flight path of -55 m). The SiC detector with a thin sensitive thickness of 30 mu m has lower scattering background than the traditional Si-PIN detector . As a result, the energy response curve of the fission target detection system above 0.26 MeV has been successfully acquired. The spectrum of the double-bunch mode was unfolded using the Bayesian algorithm, and the results indicate that, under conditions of sufficient counts, this method can yield results similar to those obtained from the single-bunch mode. The issue of pulse height defect of SiC detector to fission fragments is discussed. This experiment confirms that our detection system of SiC+fission target has a strong signal-to-noise ratio and anti-interference capability. At the same time, it demonstrates that this device has its own advantages in measuring the energy response of low sensitivity detectors.