Research on fusion neutron energy spectrum measurement using a Bonner sphere spectrometer based on a 4H-SiC detector

BackgroundMeasurements of neutron energy spectra and doses during discharges of fusion devices are crucial for radiation monitoring and protection, and Bonner sphere spectrometers are generally used to measure neutron energy spectra and doses.PurposeThis study aims to investigate the neutron energy spectrum and dose equivalent of an Experimental Advanced Superconducting Tokamak (EAST) under experimental neutral beam injection (NBI) heating conditions.MethodsFirst, a Bonner neutron sphere spectrometer consisting of a 6Li-coated 4H-SiC semiconductor detector and eight moderated spheres was developed, and measurements in NBI heating and discharge experiments were conducted. Subsequently, the experimental results were normalized with the neutron flux monitoring results of the fission ionization chamber (ZZ3) on the EAST device and combined with the neutron response functions obtained from the Monte Carlo simulation for each moderated sphere. Then, the maximum entropy program was used to calculate the neutron energy spectrum distribution of the experimental positions inside the hall. Finally, the neutron dose equivalent at this location was obtained using the fluence dose conversion coefficient and compared with the neutron energy spectrum and dose equivalent at the corresponding location in the main hall, simulated using an existing EAST Monte Carlo model.ResultsComparison results show that the overall agreement between the simulated and experimental energy spectrum distributions of the measurement position is good, and the neutron flux at the measurement position under the normalized fusion neutron source is 1.38×10-7 cm-2, with a ratio of 0.98 to the simulated value. The surrounding dose equivalent is about 2.27×10-11 μSv, with a ratio of 1.05 to the simulated value, which shows consistency.ConclusionsThe results of this study demonstrate that the multisphere spectrometer is reliable for measuring neutron spectra and dose equivalents in the EAST hall and providing data for radiation protection in fusion devices. It can also provide a reference for neutron spectrum measurements in high-power fusion devices.