Spectrometric multisphere system with thermoluminescent detectors

In this work the development of a neutron spectrometric system based on a set of moderating spheres with thermoluminescent detectors (TLD) is shown. >From the radiation protection point of view, the system allow us to do measurements of neutron spectrum at pulsating fields originated at medical accelerators, investigation accelerators and neutron fields of up to 100 MeV such as that present during the assessment of air transport doses. As result of experience with multisphere system based on 3 He detectors we know that these ones are not capable of doing measurements of pulsating fields spectra because of the time dependence of the pulses. After that, it arose the necessity of having a passive measurement system. At the same time the measurements during commercial flights with radiation dose rates very low show the need of an integrator system. he system consisted of 12 spheres made of high-density polyethylene with diameters between 2 and 12 inches, and TL detectors sensitive to thermal, epithermal and gamma radiation (TLD-600). The gamma component is subtracted using the data from the TLD-700 that are sensitive mainly to gamma radiation. Both couple of detectors are located in the centre of the spheres. The spectrum is obtained using the different moderation degree from the set of spheres. The system with the smallest sphere diameter is more sensitive to the lower energy range and by contrary the larger is more sensitive to the highest energy range. The energy neutron response matrix for a Bonner Sphere spectrometric system was calculated using the MCNP4B Monte Carlo code for the energy range between thermal and 100 MeV with the cross sections obtained from the ENDF/B-VI. This matrix was used as input for the LOUHI82 unfolding programme, which uses the spheres.The system calibration results with an americium beryllium 1.14 107 n/s source are shown. (author)