Design Of An Extended Range Multi-sphere Neutron Spectrometer

Neutron field investigation is one of the most important contents in acceleratorradiation protection. With the development of accelerator, accelerator types are variedand the accelerated ion energy is rising, so the highest energy of secondary neutronproduced from nuclear reaction is also rising. At present, Multi-sphere NeutronSpectrometer designed in us country are mainly used for neutron measurement under20MeV, so based on the existing Multi-sphere Neutron Spectrometer and thedevelopment of extended range neutron dosimeter, FLUKA code is used to calculate theneutron response of each neutron detector, which contains pure polyethylene andpolyethylene with auxiliary material (Cu, Pb, W). The moderator ball structure of eachneutron detector is determined based on calculated results, the thickness of purepolyethylene moderator ball are0,1.5,2.0,2.5,3.0,3.5,5.0,7.0,9.0,13.0and16.0(cm), and the combination of polyethylene moderator and auxiliary material are3C4-6,3P4-6,3P4.5-6.5and2P5-7. High energy neutron response are well modified for thedetectors contain auxiliary material in the moderator structure, which indicates that thespectrometer can be used to measure neutrons with high energy (GeV-level).The calculated results show that for the pure polyethylene moderator ball, as thepolyethylene thickness increasing, the peak value of the response curve appears athigher energy region, but the peak value decreased. For neutron with energy>20MeV,the response function of pure polyethylene moderator ball will decrease to a very low level. For neutron energies below10MeV, the response curve of moderator ball withauxiliary material behaves like that one of pure polyethylene moderator ball, but above10MeV the responses increase significantly due to the (n, xn) reaction of high energyneutron with auxiliary material.