A novel design of survey instrument for neutrons

*A survey instrument has been designed and developed for measuring neutrons with energies in the range from thermal to 20 MeV. The device is spherically symmetric, and features a polyethylene moderator and Borotron ® attenuating layer to facilitate accurate detection of fast and intermediate energy neutrons, combined with air-filled guides to channel low-energy neutrons to the single, central proportional counter. Response characteristics in monoenergetic neutron fields have been calculated using Monte Carlo techniques, and are supported by preliminary measured data; the likely performance in workplace fields has also been assessed. Overall, the design offers significant advantages over the alternatives currently available, being acceptably sensitive with an H*(10) response characteristic that is relatively energy- and angle-independent, whilst being comparatively light. A simple ‘upgrade’ that may reliably extend the scope of the device up to the GeV energy scale has also been explored.