Analysis of the application of the shadow cone technique for the determination of neutron spectrum with Bonner sphere spectrometer

• Bonner sphere spectrometer is used for neutron spectrum determination in a wide range of applications.
• The shadow cone technique is a method used with Bonner sphere spectrometer to evaluate the neutron scattered contribution.
• The response function matrix for the set of Bonner sphere spectrometer is calculated by Monte Carlo code.
• Different irradiation conditions with the considered shadow cones were investigated.

In this study, shadow cones were examined with Bonner sphere spectrometer (BSS) for the measurement of neutron spectrum of an 241Am–Be source. The BSS consists of a set of nine polyethylene spheres with a central 6LiI(Eu) scintillator sensitive to thermal neutrons. The energy response matrix of the BSS was determined by Monte Carlo simulations for the neutron energies from 10−8 to 100 MeV. A crucial problem in neutron measurements is determining the contribution of scattered neutrons coming from the structures and materials surrounding a source. For this purpose two shadow cones were manufactured and positioned between the source and the detector. Experiments were performed to select the optimal source-to-shadow cone distance. An unfolding code was used to obtain the neutron spectrum. The difference between the unfolded spectrum obtained by using the shadow cones and the ISO reference spectra was considered as a parameter to select the optimum condition in the shadow cone technique application.