Development of a transportable neutron spectrometer for operational dosimetry within the DONEUT project

Accurate neutron dose rate estimation demands precise measurement of both kinetic energy and neutron flux. This study introduces a multi-instrumented transportable neutron spectrometer/dose rate meter, developed as part of the DONEUT project. The prototype, optimized for 0–20 MeV neutron dose rates, is based on a polyethylene moderator with thermal neutron detectors at different depths to reconstruct energy spectra via unfolding algorithms. The initial DONEUT V1 design consists of a 25 cm diameter polyethylene cylinder with 32 embedded ZnS:LiF scintillators, coupled to a SiPM matrix via light guides and wavelength-shifting fibers. GEANT4 Monte-Carlo simulations guided detector configuration and design optimization. Unfolding methods (MAXED and GRAVEL) were applied to various moderator volumes and neutron energy spectra, including Am/Be and 252 Cf sources. This led to a “dome” prototype, DONEUT V1+, which improves vertical angles response uniformity and reduces weight. A sixth detection depth was added to enhance deconvolution robustness, particularly in the epithermal range, while the number of detectors was reduced from 32 to 24. A custom Python implementation of the GRAVEL algorithm was developed, replacing traditional codes, increasing flexibility and processing speed for energy spectra reconstruction. Experimental tests with moderated and unmoderated Am/Be sources were performed, benchmarked against NNS measurements, demonstrated dose equivalent rate (H*(10)) accuracy within 15%, even at low dose rates (~1 µSv/h) over a 10-minute measurement. The prototype reliably assesses dose rates from 1 to 100 µSv/h. A new version, DONEUTV2, insensitive to gamma background, is under development to extend the range to several mSv/h