[en] Full text: Measurements of neutron fluxes play a vital part in modern physics. Such investigation fields as nuclear physics, physics of elementary particles, physics of cosmic rays and astrophysics use the neutron measurements as instruments to gain information about the structure of the matter on the scales from one fermi up to hundreds of kiloparsecs. The neutrons are also widely used in such important applications as nuclear energetics, medicine, defectoscopy and others. Usually, neutron detection is based on proportional counters. The gas filling used in these counters is either expensive (³He) or dangerous because of its toxicity (¹⁰BF₃) to be dealt with. Moreover, these counters have a bad, not better than 2-3 mcs temporal resolution, which results in a limitation of the maximum trustworthy counting rate due to a pile up neutron pulses: the highest registered intensity cannot exceed a value of about 2x10⁵ s ^-1, whereas measurement of neutron fluxes up to 10⁷-10⁸ is necessary for many experiments. Depending on the energy of the investigated neutrons, various methods are used for their registration. Detection of neutrons with the energy E>10 MeV succeeds via interactions with C nuclei in carbon-reach substances. Detection of neutrons having energies E<0.1 MeV is accomplished through the scattering of neutrons in a hydrogen-containing medium with the subsequent registration of knocked out protons. In the energy range below 0.1 MeV, neutrons may be slowed down to energies E∼0.5 keV with subsequent registration of the products of n(p,d)γ reaction. Further neutrons deceleration until the thermal energies (E∼10^-2 eV) could even be done if necessary. Plastic scintillators enriched by ⁶Li or ¹⁰B may be used as an active medium for the detection of decelerated neutrons. Inside a boron-containing plastic scintillator, the registration of charged products of the reaction ¹⁰B(n,α)⁷Li takes place. In 6% of the events this reaction produces a ground state ⁷Li nucleus along with a 1.78 MeV α-particle. In 94% of the events the lithium nucleus is created in an excited state ⁷Li*, which is accompanied by emission of a 1.47 MeV α-particle and a 0.478 MeV γ-quantum. In contrast to lithium, the use of more inexpensive boron in plastic scintillators is preferable, because the percentage of the necessary ¹⁰B isotope in natural boron is high enough (19.9%), permitting one to avoid the expensive procedure of its enrichment. Cross-sections σ of 1 eV neutrons on ⁶Li and ¹⁰B are 149 b and 609 b, respectively; with the energy increase they change as σ∼E^-0.5 . It is seen that the use of ¹⁰B for the neutron registration is four times more effective than that of '⁶Li (but for the case of lithium, the energy release of the ⁶Li(n,α)t reaction is 4.8 MeV and no γ-radiation is emitted). We used a boron-containing molded polystyrene scintillator SC-331 which is manufactured in the Institute of High Energy Physics. The light output of the scintillator is about 56-60% of that for anthracene, luminescence maximum wavelength is about 420 nm and it contains 2-3% by weight of natural boron. It is known, that the light output of α-particle-induced scintillations is considerably lower than that from β-particles of corresponding energy. Our measurements have shown that the SC-331 scintillator light output for the reaction ¹⁰B(n, α)⁷Li is equivalent to the β-particle of an energy of about 110-130 keV. At the same time, the SC-331 scintillator light output for a minimum ionizing particle is equivalent to that from a β-particle depositing an energy of about 2000 keV per 1 cm of the thickness of the boron-containing scintillator. As opposed to boron ionization counters, the boron containing plastic scintillators do not have the defects spoken above. Indeed, the radiation decay times for scintillators being only about a few nanoseconds, the temporal resolution of scintillation neutron counters is of the same order, which permi ts to study neutron fluxes three orders more intensive than the gas counters do. At the same time, their amplitude resolution in the range of neutron peak corresponds to the best (helium) gas counters. (author)