Calibration of a 6Li diamond-sandwich spectrometer with quasi-monoenergetic neutrons

In the present article we describe calibration measurements of the compact neutron spectrometer at the PTB quasi-monoenergetic neutron reference fields. The spectrometer is based on two diamond detectors enclosing a 6Li neutron converter. The conversion occurs through the 6Li(n,t)4He reaction, featuring the Q-value of 4.8 MeV. The incident neutron energy is measured through the sum of energies of the two conversion reaction products: t and α. The prototype used in this work was based on two 4 × 4 mm2 100μm thick single crystal CVD commercial diamond plates. The measurements were performed in the fission spectrum domain at five different neutron energies varying from 0.3 up to 2 MeV. The obtained data showed a very good neutron energy reconstruction, i.e. in agreement with its reference values within statistical uncertainties or with absolute deviations below 11 keV. The energy resolution of the spectrometer was found to be about 100 keV (RMS) with a small (about 9 keV/MeV) rising trend towards higher energies. The measured detection efficiency was found to be compatible with predictions based on analytical calculations and on Geant4 simulations within 3% statistical and 4% systematic uncertainty.