A. I. Klimov

A combined spectrometric detector of fast neutrons

A combined spectrometric detector consisting of two subdetectors for fast and thermal neutrons has been developed. The fast neutron detector is a total absorption detector with a polystyrene-based scintillator generating a signal proportional to the absorbed energy of a fast neutron. The thermal neutron detector based on a 6LiF/ZnS(Ag) scintillator in the form of a thin screen detects neutrons that have lost almost all their energy in the first detector and have been thermalized. The electronics of the combined detector operates in coincidence: if a neutron has been detector by the thermal neutron detector, the signal from the fast neutron detector participates in the formation of the amplitude spectrum within a predetermined time interval (fast neutron moderation time). The methods for reconstructing the neutron spectrum by the spectrum recorded using the combined detector are considered. The measured neutron spectra from various sources are presented.

An experimental setup for studying spectra of β particles emitted by mixtures of 235U and 239Pu thermal neutron fission products

An experimental setup on the thermal neutron beam of the IR-8 reactor at the National Research Centre Kurchatov Institute is described. This setup has been designed to precisely measure the ratio of spectra of β particles emitted by mixtures of 235U and 239Pu fission products. The experiment is based on simultaneous measurements of β spectra from fissile isotopes 235U and 239Pu and the background spectrum in the same neutron beam. Measurements of the β spectra are taken by a high-selectivity β spectrometer in the time interval when the neutron beam is intercepted by a mechanical chopper. The evolution of the measurement technique is considered.

A monitoring and measuring module for tagged neutron experiments

A tagged neutron technology for remote neutron monitoring is used to reduce the background counting rate in recording of useful events. The key elements of the technology are a neutron generator with a built-in α-particle detector, nanosecond electronic system, and fast detectors of secondary radiation produced by emitted neutrons. A module for monitoring and measuring the pulse-height and time parameters of the secondary radiation detector with a time reference to the α-particle detector is described. A prototype of the experimental setup comprising the main components of a standard system based on the tagged neutron technology has been designed to test the module. Numerical calculations have been performed to simulate the γ-ray and neutron transport and the event recording procedure as applied to the geometry of the experimental setup. The time errors and the main sources of background events in measurements using the tagged neutron technology have been investigated. Background counts are shown to affect only slightly the useful data acquired in this geometry.

A high-selectivity β spectrometer

Measurements of β spectra from fission fragments are complicated by high background of γ rays and neutrons. A scintillation β spectrometer capable of precisely reconstructing the β particle spectra in the energy range of >1 MeV has been developed to reduce the effect of this background without deteriorating the high detection efficiency for β particles. The functional diagram of the spectrometer is described, and the results of spectrometer testing using radioactive electron sources are presented.

Angular correlations in detection of α-γ coincidences in the nanosecond tagged neutron technology

The characteristics of the setup for analyzing the elemental composition of organic substances using spectroscopy of γ rays induced by tagged neutrons with an energy of ∼14 MeV in an inelastic neutron scattering reaction are discussed. An ING-27 D-T neutron generator with a built-in position-sensitive α detector, fast neutron and γ detectors, and a multichannel detecting system providing a subnanosecond time resolution are parts of the experimental setup. The correlation between the exit angle of a neutron and the number of the α pixel, as well as the anisotropy in emission of γ rays in the inelastic neutron scattering reaction, are measured, and the errors of these measurements are estimated.

A study of the possibility of improving the time resolution of the PHOS spectrometer

Experimental investigations have shown that a timing device based on a constant-fraction discriminator is capable of providing a time resolution of approximately 0.5 ns and a timing error of approximately ±0.25 ns in the energy range of 0.8−1.8 GeV. In the region of “low” energies (<0.6 GeV), the time resolution is decreased by the influence of detector noise, whose level is ~3–5 mV for most scintillation detectors under investigation.

A multichannel spectrometer for detecting γ rays in a wide range of time intervals during pulse neutron irradiation

A versatile spectrometer has been developed for measuring the nuclear radiation spectrum in discrete time intervals. The design and operating principle of the spectrometer are described. Since the main logical part is based on a field programmable gate array, time intervals may be tuned in a wide range without changing the spectrometer hardware. The test experiments have demonstrated the spectrometer applicability for measuring the amplitude and timing parameters of the γ response when an analyzed sample is irradiated with a pulsed neutron flux. This device can be used to solve many problems of nondestructive testing, e.g., spectrometric neutron logging, detection of explosives, identification and characterization of fissile materials.

High-speed electronics of the T0 detector for the ALICE experiment (CERN)

The design and special features of the main units of high-speed electronics for the trigger subsystem of the T0 detector of the ALICE experiment are considered. Its characteristic time resolution is 50 ps. The dead time does not exceed 25 ns.

Characteristics of the detecting equipment for the nanosecond tagged-neutron technology

Detecting equipment for the nanosecond tagged-neutron technology has been developed, and its characteristics have been studied. The principles of arrangement and operation of the readout electronics based on the selection of useful events according to specified criteria and data accumulation by a buffer-memory unit with subsequent transfer of data arrays to a remote computer for processing and visualization. The main selection criterion is the presence of signals from α- and γ detectors within the time gate and amplitude ranges in the absence of overlapped events. A prototype of a setup for testing the developed equipment was assembled and experimental studies of its characteristics were performed. The time resolution attained in the recording of α-γ coincidences is 1.0 ± 0.1 ns at an amplitude resolution of the γ detector of 3.6–3.8%.

A fast electronic system of the T0 start trigger detector for the ALICE experiment

A fast electronic system of the T0 start trigger detector for the ALICE experiment has been developed, assembled, and adjusted using a pulsed laser. The system is composed of 24 independent detection channels for secondary particles (this number corresponds to the number of individual Cherenkov counters in the detector); common modules, which generate the signal of the event detection time with an error of <50 ps, the trigger of the interaction vertex position with an error of ∼2 cm, and triggers of two independent levels of the event multiplicity in the range of 1–150 minimum ionizing particles (MIP); and several auxiliary modules. A total of 109 channels are used in the time-to-digital converters to record time, amplitude, and auxiliary data. The time resolution of the detector for single MIP is 38 ps.