Yu. M. Burmistrov

Orienting reaction in invertebrates

Changes in motor and vegetative indices in freshwater crayfish during sudden changes in the environmental situation are described. The results suggest that freshwater crayfish characterized by a sedentary lifestyle nevertheless constantly control the milieu in which they find themselves, by recording diverse changes in its parameters. Apparently the physiological nature of the reactions to “neutral” stimuli issuing from the milieu, is, in representatives of the higher invertebrates, very similar to that of the higher mammals, and may be described using the concepts of the orienting reflex and activity of an investigatory character which follows it. The question is posed in this context of the possibility of the appearance in this situation of emotional reaction of the animals investigated.

Determination of the 1S0 neutron-neutron scattering length in the nd breakup reaction at energies in the range En = 40−60 MeV

The first results are obtained in a kinematically complete experiment devoted to measuring the n + d → p + n + n reaction yield at energies in the range En = 40−60 MeV and various angles of divergence of two neutrons (Δθ = 4°, 6°, and 8°) in the geometry of neutron-neutron final-state interaction. The 1S0 neutron-neutron scattering length ann is determined by comparing the experimental energy dependence of the reaction yield with the results of a simulation in the Watson-Migdal approximation, which depend on ann. For En = 40 MeV and Δθ = 6° (the best statistics in the experiment), the value ann = −17.9 ± 1.0 fm was obtained. A further improvement of the experimental accuracy will make it possible to remove the existing disagreement of the results from different experiments.

Bioelectric field potentials of the ventilatory muscles in the crayfish.

This study investigated the pattern of the electrical field potentials recorded near the prebranchial chamber of the native crayfish Astacus leptodactylus. Inside the prebranchial chamber, the electrical waves had maximal amplitude and showed 2-4 peaks per cycle. Potentials with the same frequency but smaller amplitude and simpler shape were also recorded outside the chamber, near the edge of the carapace, and at some distance towards the caudal direction. Correlation of these electrical potentials with movements of the scaphognathite in intact Procambarus cubensis with a transparent external wall of the prebranchial chamber has shown a high coincidence both in rate and phase of the two processes. The electrical activity picked up by an electrode located in the prebranchial chamber or near it represents the cumulative electrical field generated by the muscles moving the scaphognathite, and may be termed as the electroscaphognathitegram (ESG). The correlation of the mechanoscaphognatitegram determined optically from the magnified image of the scaphognathite and the ESG allowed us to suggest that the ascending phase of single electrical wave corresponds to the activation of the muscles responsible for downward movement of the scaphognathite, whereas its descending phase reflects its upwards movement.

Possibility of determining microimpurities in materials using a activation measuring complex based on a photoneutron source

An activation measuring complex containing a W–Be photoneutron source of neutrons and a lowbackground gamma spectrometer is designed at the Russian Academy of Sciences Institute for Nuclear Research. The photoneutron source is mounted on the beam of a LUE-8 industrial electron linear accelerator with an electron energy of 7–8 MeV and contains a tungsten bremsstrahlung target, a photoneutron beryllium target, and a fast neutron moderator. The measuring component of the complex includes a detector made from high purity germanium, positioned inside a low-background chamber with active-passive protection. Neutron-activation analysis (NAA) is used to determine the content of microimpurities in a substance. A procedure for measuring ultralow contents of elements in aerosol filters is developed. Contents of Au, As, Sb, Mn, Fe, W, and other elements are measured in a variety of samples. The limits of detecting microimpurities in materials are estimated.

An experimental setup for studying neutron-neutron final state interaction on the neutron channel of the Moscow Meson Factory

A setup for measuring the singlet nn-scattering length in the n + d → p + n + n reaction is described. It is composed of a neutron hodoscope with an angular aperture of 12° and a scintillation detector for protons escaping at an angle of 90° with the beam direction. The exit angles and the energies of a proton and both neutrons are measured. The neutron energies are measured using the time-of-flight method. At a time resolution of ∼0.6 ns and a flight base of ∼5.5 m, the accuracy in measuring the neutron energy is ∼1% at an energy of ∼15 MeV. The dependence of the reaction yield on the relative energy of two neutrons is investigated. The neutron-neutron final-state interaction manifests itself as a peak in this distribution.

A Thin-Walled Multichannel Air Ionization Chamber

A high-sensitivity air ionization chamber with extremely thin walls and a narrow gap has been designed for monitoring therapeutic beams of protons and other particles. The new components of the chamber are 1.5-μm-thick polyimide films created using special technology on quartz and stainless-steel rings. These films are coated with nanolayers of copper and gold and serve as the chamber electrodes. The chamber has high transparency and is hence able to detect protons and α particles with energies of >200 and >500 keV, respectively. The signal-to-noise ratio is high owing to a reduced leakage current (<40 pA). The beam profiles and the two-dimensional dose distributions are detected in 60 cathode strips grown up on thin films in a sensitive area of 8 × 8 cm2. The chamber is also suitable for the detection of low-energy nuclei.

Estimation of the possibilities of a neutron generator-based source of thermalized neutrons for activation analysis

Characteristics of a source of thermal neutrons based on an evacuated NG-400 neutron generator with the maximum flux (Φf) 2 × 1011 neutron/s for 14 MeV neutrons and 2 × 109 neutrons/s for 3 meV neutrons have been investigated. The possibilities of its application for neutron activation analysis have been estimated. The distribution, composition, and density (φT) values of the thermal neutron flux have been measured in the inner cavity of the moderator using activation detectors. φT was 2 × 108 and 2 × 106 neutrons/cm2 s for thermalized neutrons with energies of 14 and 3 MeV, respectively. The possibilities of the apparatus have been estimated theoretically and experimentally for the cases of thermalized neutrons of 14 MeV and 3 MeV.

Studies of final-state neutron-neutron interaction in the nd breakup reaction at energies 40–140 MeV

An experiment is proposed for determining the nn-scattering length with necessary accuracy from the dependence of the nd breakup reaction yield on the energy of relative motion of two neutrons in the kinematic region where the final-state nn interaction is best manifested. Reaction events are simulated under actual experimental conditions. The test experiment carried out at the neutron channel of the Moscow Meson Factory (INP) gives grounds to believe that statistically grounded data can be obtained in the experiment on determination of the nn-scattering length.

Investigation of a Two-Coordinate Gas-Discharge Detector of Slow Neutrons with a 10B Solid Converter

A two-coordinate detector based on a 10B layer and a gas-discharge chamber with a sensitive area of 128 mm2 and 3-mm-thick input and output windows intended for recording slow neutrons are investigated. The recording efficiency is more than 3% at a wavelength of 1.82 Å. The recording efficiency is estimated to be ~8% at a wavelength of 8 Å. The measured background contribution is less than 0.0001% of the thermal neutron one. For the Ar + 25%CO2 + 0.3%CF3Br gas mixture, the spatial resolution is about 2 mm along one of the coordinates under standard conditions. The neutron position is determined by the charge division method.

Studying the Neutron Yield from a Target of a Compact Neutron Source on the LUE-8 Accelerator Using Helium-3 and Boron-10 Detectors

The neutron yield from a target of a photoneutron source on the beam of the LUE-8 accelerator is studied to optimize the mode of accelerator operation for research in nuclear and solid state physics. Neutrons are detected using a helium-3 counter with an efficiency of 80% for thermal neutrons and a position-sensitive detector with a 10B layer working in the counting mode. These detectors ensure stable operation under conditions of a high gamma-ray background and electromagnetic interference. The desired signals are identified by processing the spectra recorded by a pulse height analyzer. The technique is tested using a constant neutron source under conditions of a minimal gamma-ray background and electromagnetic array. The pulse rise time is 3 μs and the pulse decay time is approximately 15 μs. In an experiment on the accelerator, data from the 10B detector are acquired as a event-by-event sequence of the pulse height and absolute time. At the same time, data from the 3He detector are transformed into a pulse height spectrum. These two detectors show satisfactory agreement in measuring the neutron yield normalized to the current of the accelerator beam.