Spectrometers for mixed neutron and gamma radiation with liquid and crystal organic scintillators have found application in low-intensity fields of radionuclide sources and neutron generators for measuring the main characteristics of the radiation [1,2]. Neutrons with energy 14 MeV, emanating from tritium targets, interacting with the material of the target blocks (iron, copper, molybdenum) in turn generate prompt and gamma radiation according to the reactions (n, n′), (n, n′γ), and (n, 2n′γ). In addition, the gamma radiation arises in target blocks as result of interaction with 14-MeV neutrons in the reactions (n, α) and (n, p). Background gamma radiation, resulting from the interaction of 14-MeV neutrons with the material of the objects surrounding the target blocks (walls, ceilings, floors, structural components of generators, and so forth) is present in the experimental rooms. It follows that when generators are certified it is necessary to determine the characteristics of not only the neutron but also the gamma radiation, including the energy spectra and the absolute fluxes of gamma radiation at the measurement point. The objectives of the present work are to investigate a single-crystal scintillation neutron spectrometer with stilbene for precision measurement of the energy spectra and absolute flux of 14-MeV neutrons and photons emitted together with the neutrons and to establish the possibility of using such a spectrometer for certifying reference neutron fields produced by radionuclide sources and generators [2].Two experimental facilities were used in this work. Each one consisted of a source of 14-MeV neutrons (S) and a spectrometer (D) (Fig. 1). The generators NG-160 (All-Russia Research Institute of Physicotechnical and Radio Measurements, VNIIFTRI) and NG-200 (Moscow Engineering Physics Institute) were used as sources. The neutrons were obtained from the reaction 3 H(d, n) 4 He. The neutron fluxes from the targets of the generators were monitored with radiometers, and the ~3 MeV α particles accompanying the neutrons were also monitored with an error not exceeding 3% with confidence probability 0.95 [3,4]. To determine the characteristics of the neutrons and photons reliably, the measurements were performed predominantly on a standard neutron source from the VNIIFTRI; this source was part of the State National Standard GÉT 51-80 for units of flux density and fluence of neutrons for nuclear-physical facilities [4]. The neutrons were generated in tritium-titanium targets of the generators by accelerated beams of atomic deuterons with energy ~150 and 200 keV. Thick (target activity with respect to tritium 1.1·10 11 Bq) and specially prepared thin (activity 1.5·10 9 Bq) tritium-titanium targets with diameter 14.3 and 45 mm, respectively, were used in the measurements.The spectrometer included a detector of neutrons and gamma rays (probe), which consisted of a scintillation block -a stilbene crystal combined with a FÉU-93 photomultiplier, an electronic circuit for separating pulses according to their form...
