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An important element of the state system for guaranteeing the unity of neutron measurements performed on nuclearphysics setups is the reference neutron field. By definition [1, 2] this field consists of a region of the neutron field of the nuclear-physics setup that is fixed in space and is certified with respect to its constant spectral characteristics.The basic principle of supporting neutron measurements on nuclear-physics setups, based on the requirements of economy and taking into account the complexity and labor intensiveness of metrological work, is decentralized by unified (regulated) reproduction of the units of quantities under conditions which approach as close as possible the working measurements with one-step transfer of the dimensions of the units directly to the means of measurement [2].It is obvious that the requirement of guaranteeing unity with the decentralized approach to the creation of the reference fields is directly associated with unification of both the means of measurements and the methods for determining the spectral characteristics from the experimental data. The latter procedure is especially important for reference fields of neutrons from pulsed reference nuclear reactors, for which the method of integral detectors (a general name for methods employing the integral form of the response of the detectors: neutron-activational, different methods with fission detectors, and others) is, with respect to all nuclear-physical factors, almost the only method of investigation and reproduction of spectral characteristics. The problem of determining the neutron spectrum from data obtained from integral detectors is an improperly posed problem, and the stability of the results of solving the problem depends, to a large degree, on the choice of the a priori (initial) approximation.Using the approach, proposed in [3], for forming an a priori spectrum and the results of the successful application of this approach for the description of the neutron spectrum for the standard field at the center of the BIR-2 core [4], we attempted to work out a unified representation of the neutron spectrum in the intracore regions of reactors with a predominately metal core. Pulsed research reactors with a metal core are employed by many scientific laboratories (SPR II, III at the Sandia National Laboratory in the USA, BIR-2 and BR-1 at the All-Union Scientific-Research Institute of Electrophysical Apparatus (VNIIt~F), BARS-2 and -5 at All-Union Scientific-Research Institute of Technophysical Apparatus (VNIITF), Russia; Caliban in France; YAYOI in Japan; CFBR II in China; etc. [5]). Because of the good screening by the fissioning materials, the neutron spectrum in the intracore cavities of such reactors is, as a rule, not influenced by the scattered neutrons of the reactor enclosure (scattering by objects and equipment surrounding the core, in the walls of the containment shell, and so on) and when a unified representation of the spectrum is possible, the spectrum can be used as a specialized standard for fast neutr...

The solution of scientific and technical problems in nuclear physics, biology, solid-state physics, and nuclear technology depends on the accuracy of measuring neutron fluxes and the energy spectrum of radiation.A description is now given of a metrological scheme for the reproducibility of units and it is shown that it is preferable to use master (reference) neutron sources based on nuclear reactors and neutron generators when measuring flux densities of fast neutrons in the range 1 The primary State standard with its checking scheme is mainly used for the purposes of dosimetry and radiation safety. The inventory of service measuring instruments includes a wide spectrum of radionuclide sources and radiometers with different sensitivities, in a broad interval of neutron energies. The main load falls on the master measuring instruments, and this makes it necessary when performing successive transfer to maintain high-quality metrological characteristics of the primary and working standards. A high accuracy of the primary standard makes it possible to certify working measuring instruments with an accuracy of 12-30%.The special State standard is mainly directed at metrological support of neutron measurements in steady-state, quasisteady-state, and pulsed radiation fields of nuclear reactors, accelerators, and other nuclear physics devices which are sources of neutrons. The radiation fields of nuclear physics devices are characterized by a neutron flux density in the range from 105 to 2 • 1019 s -1 "cm -2, a spectral variety in the range from thermal energies to 20 MeV, and the presence of background radiation.Working measurements made on nuclear physics devices include determining the flux (fluence), flux density, and spectral characteristics of the neutron radiation field at the investigated points. A feature of the measurements is that the solution of many scientific and technical problems requires an accuracy close to the maximum attainable with the present-day state of development of science in measurement technique. There is almost no accuracy margin between the standard and working measuring instruments. This approach makes it impossible to implement metrological support based on the principle of the successive transfer of unit sizes. Metrological support of neutron measurements in the radiation fields of nuclear physics devices is therefore based on the principle of directly creating working standards and master