S. I. Potashev

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.

Neutron-deuteron breakup reaction as a tool for studying neutron-neutron interactions

An analysis of the most recent data on the reaction nd → pnn revealed a serious discrepancy between theoretical predictions and cross sections measured for this reaction in various configurations where the role of neutron-neutron interactions is important. In view of this, it seems necessary both to develop theoretical approaches and to obtain new experimental data. For this purpose, a setup for studying the neutron-deuteron breakup reaction was created at the Institute for Nuclear Research on the basis of the neutron beam in the RADEX channel and deuterium targets. This facility makes it possible to perform experiments over a broad region of primary-neutron energies (10–60 MeV) and in various (final-state interaction, quasifree scattering, and spatial-star) configurations. Preliminary results of the respective experiment were obtained for configurations of final-state neutron-neutron interaction and quasifree neutron-neutron scattering.

A neutron beam spectrometer based on a scintillation detector with n-γ pulse shape discrimination

A scintillation spectrometer with pulse shape separation of signals from neutrons and gamma quanta, installed on the RADEX neutron beam channel at the Institute for Nuclear Research is described. The need for n-γ separation is due to the presence of a substantial gamma background at the location of the spectrometer. To optimize n-γ separation, new parameters of the pulse shape separation and methods for calculating them are proposed. Significant improvement in the n-γ separation is obtained. Applying new parameters allows us to use information about only part of the scintillation pulse, enabling the operation of the spectrometer at high count rates and pulse pileup. Such a spectrometer can be used to monitor the RADEX neutron beam channel and determine the energy distribution of neutrons in the beam.

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.

Analysis of Data Measured with a Neutron Detector Based on a Boron-10 and Helium-3 Counter on a Source of Photoneutrons

Data obtained on the IN-LUE photoneutron source at the Russian Academy of Sciences’ Institute for Nuclear Research are analyzed. The data are acquired using a position-sensitive neutron detector with an active 10B layer and a 3He SNM-18 counter. The efficiency of the 10B detector relative to the 3He counter ranges from 2 to 4% for different modes of accelerator operation. Waveforms of the 3He counter’s pulses are recorded using a built-in L-CARD L-783 multifunctional high speed signal processor with sampling frequencies of up to 3 MHz. The amplitude and time spectra of thermal neutrons are obtained from the waveforms using induced electromagnetic signals from the accelerator dump and neutron pulses. Using a cadmium mask with slits and a position-sensitive detector with a low (<10−7) sensitivity to electromagnetic interference and the gamma-ray background allows the spatial resolution of the10B detector to be determined and the contribution from neutrons with different energies to b estimated.

Accuracy of Determining Coordinates by Means of Charge Division in a Position-Sensitive Thermal Neutron Detector Based on Boron-10

A charge division algorithm is proposed for determining coordinates in a positional sensitive neutron detector based on a layer of 10B and an ion chamber. Experimental impedances of the input resistances of amplifiers and their gain factors are considered in order to improve spatial resolution. The best spatial resolution of ~2 mm with respect to the horizontal X-coordinate and ~4 mm with respect to the vertical Y-coordinate is achieved at a power supply voltage of 700 V. The efficiency of thermal neutron registration is ~3%. A helium-3 counter of known efficiency is used to monitor thermal neutrons.

Two-dimensional solid state gaseous detector based on 10B layer for thermal and cold neutrons

Two-dimensional solid state gaseous detector for thermal and cold neutrons is created. The detector has active area of 128 x 128

Setup for studying quasi-free neutron-neutron scattering in the energy range of 20–60 MeV

mm^2

Particles of liquid-crystalline dispersions formed by (nucleic acid-rare earth element) complexes as a potential platform for neutron capture therapy

,

A thin-walled air-ionization chamber for proton therapy

^{10}B