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The article reviews thermal neutron detector developments in the Department of the IBR-2 Spectrometer Complex of the Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research (FLNP JINR). A variety of detector types are considered: neutron monitors, ring detectors, position-sensitive detectors (PSD), and scintillation detectors. The experience of exploitation of these detectors at the research facilities of the FLNP JINR is presented.

Three neutron instruments at the Neutron Physics Laboratory (NPL) in Řež near Prague — small-angle scattering (SANS) MAUD, strain scanner SPN-100 and strain diffractometer TKSN-400 — have been modernized recently with new 2D position-sensitive detectors (PSDs) from JINR, Dubna. Here we report on the progress made in relation to the possibilities of the diffractometers due to the improved performance of the detectors. The first part of the paper is dedicated to a detailed description of the hardware and software of the PSDs, as well as its integration with the in-house experimental control software. Then practical examples of neutron scattering experiments for each of the upgraded facilities are presented.

A prototype of a neutron spectrometer based on a gas proportional counter with recoil-proton registration is created at the Frank Laboratory of Neutron Physics at the Joint Institute for Nuclear Research (FLNP JINR) in Dubna. The spectrometer is developed to measure the kinetic energy of protons scattered elastically at small angles that are produced by (n, p) reaction in an environment containing hydrogen. The elaborated prototype consists of two cylindrical proportional counters used as cathodes. They are placed in a gas environment with a common centrally situated anode wire. Studies on the characteristics of the neutron spectrometer were conducted using 252Cf and 239Pu-Be radioisotope neutron sources. Measurements were made with monoenergetic neutrons produced by the 7Li(p, n)7Be reaction when a thin lithium target was bombarded with a proton beam from an EG-5 electrostatic accelerator, as well as with neutrons from the reaction D(d, n) 3He with a gas deuterium target.

The Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research is one of the leading centers of neutron research in Russia. Within the works on the modernization of detector systems, researchers of the laboratory have designed and fabricated linear and area gas-filled position-sensitive detectors of thermal neutrons and the area monitor detector with a low attenuation of the incoming beam. These devices and their main characteristics have been described.

A one-dimensional position-sensitive detector of thermal neutrons has been developed to equip high-efficiency neutron spectrometers at the ИБР-2 research reactor. The detector is based on a multiwire proportional chamber filled with a mixture of 3He + CF4 and has an active area of 200 × 80 mm and a spatial resolution of 2 mm. The detector has been used to good effect in the REFLEX and HRFD spectrometers of the ИБР-2 reactor, as well as in the diffraction facility of the ИВВ-2M research reactor (Zarechnyi, Russia).

For the investigation of neutron induced fission of heavy nuclei in the resonance energy range the fast multilayer ionization fission chamber with a 239Pu content of 1.6 g was constructed. The chamber is compact and a minimum of material has been used for its construction. The chamber is divided into 19 sections containing no more than 100 mg of 239Pu in a section whose intrinsic capacity is less than 100 pF. By using fast preamplifiers and constant fraction discriminators together with the combined method of amplitude and pulse length discrimination the background due to α-particles is suppressed and a less perturbed pulse height distribution is obtained. The absolute fission fragments detection efficiency of the chamber is (60±8)%. Its time resolution does not exceed 2.6 ns.

Gamma-ray spectra from239Pu(n,f) reaction were measured with the gamma spectrometer on the pulsed reactor IBR-30. The fast 19-section ionization chamber with 1.6 g of239Pu targets was used. The fission gamma-rays within the 32 ns time window were measured using a Ge(Li) detector. Based on the measured gamma-ray spectrum in the (0.1–1.8) MeV interval, the total number of emittedγ-quanta-multiplicity 〈N γ tot 〉 and total energy of γ-quanta per fission event, 〈E γ tot 〉, were calculated. The results were 7.0±0.6γ/fission and 6.8±0.5 MeV/fission respectively.

A new gas multi-section ring-shaped detector (MSRD) for thermal neutrons has been developed at the Frank Laboratory of Neutron Physics (FLNP) of the Joint Institute for Nuclear Research (JINR) for ...

Gamma-ray spectra from resonance neutron induced fission of 239 Pu at 0.2 eV to 230 eV were measured with the high resolution gamma-spectrometer at the pulsed reactor IBR — 30 as a resonance neutron source. The fast 19-section ionization chamber with the 239 Pu targets was used for detecting fission gamma-rays in coincidence with fission fragments pulse inside the time window of 290 ns.On the ground of the observed gamma-peaks in the (0.1 – 1.6)MeV interval the fragment identification was made and the independent yields of some fragments were obtained in both the full interval energy and individual resonances. The results are compared with the thermal neutron data.