Neutron spectrometry at various altitudes in atmosphere by passive detector technique

Abstract

A new experimental system, constituted by passive detectors, has been developed to measure neutron spectra at various altitudes in the atmosphere. The knowledge of the neutron spectrum is required to evaluate with a good accuracy the neutron contribution to the total dose, due to the cosmic ray exposure, in fact the flux-to-dose conversion factors strongly depend on neutron energy. Moreover, in many dosimetric applications, as the dose evaluation to the aircrew in service on intercontinental flights, the passive system is not only the most convenient but it is often the unique technique. The experimental system is constituted by the passive bubble detector BD100R, polycarbonate foils, polycarbonate bottles, sensitive in low and intermediate neutron energy range, and the bismuth stack, sensitive in the high energy range. Experimental data were obtained in high mountain measurements at Matterhorn (3600 m altitude, 46 N ) and Chacaltaya (5230 m altitude, 16 S), during flights at 12000 m and on board of stratospheric balloons at 38000 m. All the spectra obtained show, as expected, the evaporation peak around 1 MeV and the second direct bump around 100 MeV; the results, different in the neutron flux intensity, confirm the satisfactory sensitivity of this experimental technique.