The most widely used system in neutrons measurements related to radiological protection is the Bonner sphere spectrometer (BSS). It is based on a thermal detector, a set of polyethylene spheres, and the associated electronics in the case of an active detector like 10BF3 or 3He, or scintillators like 6LiI(Eu). The BSS is applied to characterise the neutron field from thermal to hundreds of MeV. One of the main advantages of the BSS system is its isotropic response to neutrons resulting from its spherical symmetric shape.
The BSS presents a good performance for radiation protection purposes, despite the fact of its low resolution, but a net limitation appears in the case of active detectors in pulsed or high intensity environmental radiation fields because of pile up effects or undesirable dead times. The best solution for this problem is using passive detectors (activation, track and thermoluminiscent), which have been applied in aircrew dosimetric determinations, pulsed fields from medical and research accelerators.
As various investigations have shown, a good knowledge of the response matrix of the BSS is crucial for obtaining reliable spectrometric results.