A. A. Bogdzel

Development of gas-filled position-sensitive detectors of thermal neutrons at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research

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 multisectional annular thermal-neutron detector for the study of diffraction on microsamples in axial geometry

A new gaseous annular sectional thermal-neutron detector for the new neutron diffractometer at the IBR-2 reactor has been designed and manufactured at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research (JINR). The detector is designed to study small-volume samples at high pressure and consists of 16 sections, each one of which is divided into six independent detector elements. We present the main design features of the detector, detecting electronics, data-acquisition and visualization software, and software system for experiment management. The results of the first neutronographic experiments that were carried out with the use of the detector are also presented.

Two-coordinate position-sensitive monitor-detector of thermal neutrons

Development of new high-flux-intensity neutron sources and the need to equip them with efficient spectrometers raises the problem of designing special-purpose direct-beam monitors-detectors. These detectors feature an extremely low efficiency and a very low attenuation of the incident neutron beam. In this work, a two-coordinate position-sensitive monitor-detector is described that was developed for real-time recording of the profile of neutron beams generated by both steady and pulsed neutron sources. The basic parameters of this device are the following: a coordinate resolution of 4 × 4 mm2, a sensitive area of 100 × 100 mm2, and a recording efficiency of 10−6−10−2. Use of nitrogen as a converter makes it possible to achieve a record low efficiency and still maintain other parameters at a desired level. The device can be combined not only with high-flux-intensity neutron sources already in use worldwide but also with next-generation sources being developed in the United States (SNS) and Japan (JPARC).

A test setup for the bead cryogenic neutron moderator of the IBR-2 reactor

The design and main characteristics of a test setup for studying the serviceability of the bead cryogenic neutron moderator and determining its optimal operating conditions on the fast pulsed IBR-2 reactor are presented. Using the test setup, the possibility has been demonstrated of filling the moderator chamber with the working medium—beads of a mixture of aromatic hydrocarbons, delivered to the chamber by a cold (T < 85 K) helium gas flow over an intricately shaped cryogenic pipeline system.

An automation system for experiments with a neutron powder diffractometer

The modernization of the detector system and control system of the neutron powder diffractometer (NPD) in the GEK-5 channel of the VVR-c reactor (Obninsk Branch, Karpov Institute of Physical Chemistry) is described. The PC-connected hardware and software complex, which ensures data acquisition and storage and control of the experiments, is created. The main modules of the NPD automation system and Sonix+ control software package, designed at the Frank Laboratory of Neutron Physics at JINR, are briefly described. The modernization has made it possible to increase the luminosity of the diffractometer and completely automatize the measurement process.

A One-Dimensional Position-Sensitive Detector for Thermal Neutrons

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).

A Low-Noise Fast Eight-Channel Preamplifier

A preamplifier with a rise and fall time of ∼2.5 ns is described. At the output of a transmitting 50-Ω cable with matched terminations at both ends, and the input-equivalent circuit noise is 20 μV at an amplification factor of 7.5. Eight such preamplifiers are placed inside a unit with dimensions of 8 × 16 × 4 cm.

Multi-Section Ring-Shaped Detector for Thermal Neutrons

Volume 24 • Number 3 • 2013 Neutron News 28 A new gas multi-section ringshaped 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 a new neutron diffractometer at the IBR-2M nuclear reactor for studying small-volume samples at high pressures. The MSRD is divided into 16 sections, which share the same gas volume. The outer radius of the ring detector is 800 mm and the inner one is 637 mm. Each sector of the detector consists of a frame with six anode wires separated by millimeter-thick textolite plates serving as cathodes. The total number of independent detecting elements in the ring detector volume is 96. A detector element (point detector) has approximately a parallelepiped shape measuring 123 × 40 × 12 mm. A solid angle of the detector element is ΔΩf = 0.054 str and the angular ratio of the element width to its distance to the center of the ring is ΔΩq = 0.005 str. At an operating pressure of 3He of 4 atm the detection effi ciency of neutrons with a wavelength of 1.8 Å coming into the detector volume is ~89% (without regard for absorption in the detector wall). The advantages of the MSRD detector are: large size of its working volume, which allows the neutron count rate to be increased several times; shared working volume makes it possible to have practically the same effi ciency for all sections; smaller sizes of “dead zones” of the detector. The photos of MSRD are shown in Figure 1. To optimize the detection channel separation and to reduce electronic noise, charge-sensitive preamplifi ers are located inside the gas volume on the frame with anode wires. Signals from the preamplifi ers of the two pair sections come into leak-proof multiple output connectors that connect 12-channel amplifi ers-shapers attached directly to the detector housing. Amplifi ed and shaped signals (96 channels altogether) come to a data acquisition and accumulation system. At FLNP (starting from 2012) all DAQ systems for multipoint detectors (MPD) are unifi ed and consist of two types of units ─ one digital unit capable of registering and accumulating data from 1 to 240 point detector elements and several (depending on the real number of detector elements) 32-channel analog units in which data acquisition, discrimination, transformation and transfer are performed using lowMulti-Section Ring-Shaped Detector for Thermal Neutrons

Neutron Spectrometer Based on a Proton Telescope with Electronic Collimation of Recoil Protons

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.

Spectrometry and Performance Characteristics of a BGO–ФЭУ-165 Scintiblock in a Temperatire Range of +25 to –140°C

The possibility of the joint operation of a ФЭУ-165 photomultiplier based on microchannel plates and a BGO crystal, which are cooled to a temperature required for the operation of a semiconductor Ge detector, is investigated taking into account the temperature dependence of proper PMT characteristics. The system was cooled from room temperature to –140°C for 8 h. The limiting temperature at which the PMT holds its serviceability was determined, and the temperature changes in the spectroscopic characteristics of the system (the energy resolution and signal-to-noise ratio) were studied.