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Absolute calibration of a cold and thermal neutron detector using monochromatic neutron beam

— Time of ﬂight spectra for cold neutrons exiting the moderator volume of the LANSCE UCN source has been obtained using a commercial neutron scintillator, EJ-426, coupled to a Hamamatsu R1355. The absolute eﬃciency for this detector system was determined using a 37.4 meV (monochromatic) neutron beam from the Neutron Powder Diﬀrac-tion Facility (NPDF) at North Carolina State University’s PULSTAR reactor. We measured the absolute neutron ﬂux at the NPDF through thin foil activation and explored threshold eﬀects through analysis of the measured pulse height distribution for eﬀectively pure neutron signals from the NPDF beam. Non-uniformity of the ﬂux proﬁle across the detector and the detection eﬃciency as a function of the point of incidence of neutrons on the scintillator was explored using a X-Y translation system to perform scans using either ﬁxed or movable apertures. The results are generally consistent with our expectations for this system, and provide a quantitative assessment of the sensitivity of this system to cold and thermal neutrons.