Detector Response Characterization at LANSCE for Spectrum Unfolding*

Direct characterization of fast neutron spectra (> 1 MeV) is complicated due to the physics of neutron interactions and often relies on simulation or time-of-flight (TOF) techniques.  Spectrum unfolding allows fast neutron detectors, such as organic scintillators, to be used for characterizing spectra in fields where TOF techniques are not feasible.  Examples include nonproliferation/safeguards, nuclear emergency response, warhead verification, background characterization, and cross section measurements.

Spectrum unfolding requires the response of the detector to mono-energetic neutrons be well characterized.  Typically TOF measurements using a ²⁵²Cf source or an accelerator are used for characterization.  Recent work has shown characterization of several detector materials (deuterated and non-deuterated), sizes, and photomultipliers (PMT, SiPM) to be feasible with the neutron beam of LANSCE at LANL.  This work will be presented and compared to existing methods.  The beam at LANSCE allows detectors to be characterized in much less time and with better statistics, particularly at higher energies (> 10 MeV), than existing methods.  Future work will focus on characterizing additional materials, temperature dependence, and creating data sets for simulation validation.