Development and experimental validation of a fast neutron spectrometry system based on Superheated Drop Detectors (SDDs) operating under different external pressures

Abstract

In this paper, the spectrum of 241Am-Be neutron source was measured by developing and using a neutron spectrometer system based on Superheated Drop Detectors (SDDs) operating under various external pressures. The system consisted of a set of SDDs fabricated by in situ polymerization method. The external pressures were controlled by the amount of Freon-12 added onto the surface of detectors. Also, this system includes a Geant4 simulation application capable of calculating the response of SDDs made from various materials at various temperatures and pressures. Ultimately, the system contained a customized program to design and train the Adaptive Network-based Fuzzy Inference System (ANFIS) for fast neutron spectrum unfolding. This program has the capability of designing the ANFIS with different rule structures and various parameters of the fuzzy inference system.In the present study, the simulation application was used to calculate the response matrix of five SDDs under external pressures of 0.86, 1.93, 2.72, 3.48, and 3.85 atm in 20 energy bins from 0.5 MeV to 514 MeV at 28 °C. Furthermore, the customized program was utilized to design a FIS structure using the FCM method with six membership functions for each input.Neutron spectra published in the IAEA technical reports series no. 403 and 318 were utilized as the Target data. The response matrix was used to obtain the input data of ANFIS by multiplying the target data by the response matrix. 99% of data (373 out of 377) was considered as the train data and the rest as the test data.After fabrication of SDDs, they were exposed to an 241Am-Be neutron source. The average numbers of the formed bubbles in SDDs with different external pressures were introduced to the trained ANFIS, and finally, the unfolded spectrum was the output of the ANFIS. The RMSE for the measured neutron spectrum was the acceptable value of 0.016. The reasonable agreement between the unfolded and reference 241Am-Be neutron spectra shows that the developed neutron spectrometry system can be a suitable candidate for fast neutron spectrometry.