Neutron spectrum unfolding for the development of a novel neutron detector for fusion

Highlights: • This paper details the results from an initial experiment performed at the FNG with prototype detector capsules, comprising of a graphite capsule containing a selection of dosimetry foils, irradiated under a 14 MeV neutron field as part of the Novel Neutron Detector for Fusion project implemented under the EUROFusion Enabling Research 2017 program. • Measured activities of each capsule are compared with activities derived from simulations performed using MCNP. • The experimental results have been applied to neutron spectrum unfolding methodologies: MAXED based on the maximum entropy method, and GRAVEL an iterative non-linear least squares algorithm. • Reaction rates calculated from unfolded neutron spectra are compared with measured reaction rates. • Simulations used in this work provide an accurate calculation for the neutron field in this experiment and the unfolding algorithms do not introduce any unphysical results. Furthermore, neither the enclosure type nor material used in this work affect the neutron activation results. -- Abstract: In future fusion power plants, such as DEMO, the D-T neutron emission rate is predicted to exceed 1 × 10²¹ n s⁻¹. Accurately monitoring neutron energies and intensities will be the primary method for estimating fusion power, and calculating key nuclear parameters, including the tritium breeding ratio and nuclear heating. The noVel nEutRon Detector for fusIon (VERDI) project, implemented under the EUROFusion Enabling Research 2017 program, aims to develop a detector capable of withstanding the harsh environment of a future fusion power plant. The VERDI detector is based on the foil activation technique, which relies on neutron spectrum unfolding methods to process the convolution of gamma-ray measurement and detector response function to infer the neutron energy spectrum. This paper details the experimental method and results collected using six prototype VERDI detectors during an initial experiment performed in July 2017 at the ENEA Frascati Neutron Generator (FNG) under D-T neutrons (14 MeV). The measured activities of product isotopes are compared with equivalent data calculated using the FISPACT-II code to provide an average C/E_act agreement of 1.05±0.13. Experimental results from the FNG have been applied to neutron spectrum unfolding techniques using established unfolding codes, MAXED and GRAVEL.