<p>A neutron spectrometer is described. The spectrometer includes a first conversion screen (8) comprising a neutron absorbing material and a phosphor material, a first wavelength-shifting light-guide (14) arranged to receive photons from the phosphor material of the first conversion screen and generate wavelength-shifted photons therefrom and a first photodetector (22)optically coupled to the first wavelength-shifting light-guide and arranged to detect the wave- length-shifted photons. The spectrometer further includes a second conversion screen (12) comprising a neutron absorbing material and a phosphor material, a second wavelength-shifting light-guide (16) arranged to receive photons from the phosphor material of the second conversion screen and generate wavelength-shifted photons there- from, and a second photodetector (24) optically coupled to the second wavelength-shifting light-guide and arranged to detect the wave- length-shifted photons. A neutron moderator material is arranged between the first and second conversion screens to moderate neutrons.</p>
