Accelerator driven subcritical system neutron spectra determination issues

Accelerator Driven Subcritical Systems are reactors with very complex neutron spectra very much depending on primary accelerated particle induced neutron source reaction. The most powerful neutron source for ADSS applications is a spallation reaction of heavy target (Pb, Bi, U) and light ion beam (proton, deuteron, or light ion with energy of several hundreds MeV up to several GeV per nucleon). According to development of spallation neutron sources around the world (SNS, ESS, JSNS, CSNS) determination and simulation of total number of neutrons is quite well developed, however, very fast group of neutron spectra might be systematically underestimated, Nevertheless, cross-section data for this energy group have significant 'white spots', what together with incorrect group-wise spectral flux density determination might cause important reaction rates discrepancies. Conventional fast neutron detection methods, like ToF, Bonner spheres, or proton recoil, are very hard to use, or their utilization is limited just to experimental channels. Methodology of using special alloy as threshold activation detectors shielded with various spectral filters to provide as Inuch as possible information for signal deconvolution and final spectra unfolding. Method is standard enough and sufficiently robust to be use in synergy with other more challenging methods like delayed neutron fraction method or modern methods based on semiconductor pixel or strip detectors. Method can be used and validated on fusion devices, as well as cyclotron based neutron generators and powerful photoneutron sources based on microtron accelerators. (author)