Andrey Kuznetsov

Neutron and fragment yields in proton-induced fission of 238U at intermediate energies

The primary fission fragment mass and kinetic energy distributions, and neutron multiplicities as function of fragment mass have been measured in the proton-induced fission of 238 U at energies Ep ¼ 20, 35, 50 and 60 MeV using time-of-flight technique. Pre-scission and post-scission neutron multiplicities have been extracted from double differential distributions. The fragment mass dependence of the post-scission neutron multiplicities reveals the gross nuclear shell structure effect even at the higher proton energies we measured. The yields ofneutron-rich fission products in the fission of 238 U by 25 MeV protons were measured using an ion guide-based isotope separator technique. The results indicate enhancement for superasymmetric mass division at intermediate excitation energy of the fissioning nucleus. The experimental results have been analysed in the framework of a time-dependent statistical model with inclusion ofnuclear f effects in the fission process. # 2001 Elsevier Science B.V. All rights reserved.

Neutron multi-detector system: mutual influence of its modules

Abstract A position-sensitive neutron detector (PSND) has been designed and tested as a module of a multi-detector array. “Cross-talk” effects, contributing a major distortion factor for all closely packed neutron detector systems, have been measured. It was established, using neutrons from the spontaneous fission of 252 Cf (setting neutron energy threshold at 0.7 MeV), that the distortions of neutron energy and of neutron angular distribution are insignificant (within the level of statistical accuracy). The influence of cross-talk on the coincidence counting rate was measured to range from 48% to 16% for distances between detectors axes of 12 to 24 cm.

DETECTION OF HIDDEN EXPLOSIVES BY NANOSECOND NEUTRON ANALYSIS TECHNIQUE

One of the most promising methods of detection of hidden explosives and other dangerous substances is the so-called, “neutron in, gamma out” technique. The main idea of this method consists in irradiation of suspicious object or volume with neutrons and measurement of secondary γ-radiation caused by interaction of neutrons with the material of the irradiated object. Different chemical elements produce different characteristic γ-radiation as a result of inelastic scattering or capture of neutrons. By decomposing measured γ-spectra into contributions from different chemical elements, one can obtain elemental composition of the explored object and thus determine whether it contains hazardous (e.g. explosive) material or not.

SENNA: device for explosives' detection based on nanosecond neutron analysis

Portable device for explosives detection (SENNA) based on Nanosecond Neutron Analysis (NNA) / Associated Particles Technique (APT) has been created and tested. SENNA is a single suitcase weighting 35 kg; it is remotely controlled from any PC-compatible computer. Inside is an APT neutron generator with a 3×3 matrix of semiconductor detectors of associated alpha-particles, two BGO-based detectors of gamma-rays, fully-digital data acquisition electronics, data analysis and decision-making software, and batteries. Detection technology is based on determining chemical composition of the concealed substance by analyzing secondary gamma-rays from interaction of tagged fast neutrons with its material. A combination of position-sensitive alpha-detector and time-of-flight analysis allows one to determine the location of the detected material within the inspected volume and its approximate mass. Fully digital data acquisition electronics is capable of performing alpha-gamma coincidence analysis at very high counting rates, which leads to reduction of the detection time down to dozens of seconds. SENNAs scenario-driven automatic decisionmaking algorithm based of fuzzy logic mechanism allows one to detect not only standard military or industrial explosives, but also improvised explosives (including those containing no nitrogen), even if their chemical composition differs from that of standard explosives. SENNA can also be trained to detect other hazardous materials, such as chemical/toxic materials, if their chemical composition is in any way different from that of the surrounding materials.

Position sensitive neutron detector

Abstract A position-sensitive neutron detector has been developed for use in nuclear physics research. The detector consists of a ∅5.5xa0cm×100xa0cm long quartz tube filled with liquid scintillator viewed from both ends by photomultipliers and enclosed in a light-tight titanium container. The properties of the detector were determined both experimentally and by Monte Carlo simulations (EFEN code). A time resolution of 0.4xa0ns was reached resulting in the position resolution of less than 4xa0cm. The neutron registration efficiency varies from 36% to 20% within neutron energy range 1–10xa0MeV and is practically independent of the position along the detector length. Good n–γ separation is achieved for neutron energies greater than 0.5xa0MeV.

Decision-Taking Procedure for Explosives Detection by Nuclear Technique

One of the most promising techniques of explosives detection is based on detection of secondary γ-rays that are induced in the inspected object or area by a flux of neutrons (the so-called “neutron-in gamma-out” method). Fast neutrons undergo mostly inelastic scattering (n,n’γ) while thermal neutrons undergo mostly radiation capture (n,γ) reactions on nuclei inside the object. Spectra of secondary γ-rays contain information about the isotopic composition of the object. By using narrow (few nanoseconds) time gates one can determine the time of arrival of the given γ-quantum with respect to a particle which accompanies neutron emission from the neutron source, and thus split the total γ-spectrum into fast (inelastic scattering) and slow (radiation capture) components.

Fragment mass distribution in superasymmetric region in proton-induced fission of U and Th

SummaryFission fragment mass distributions down to super-asymmetric mass region and both pre- and post-scission neutron multiplicity for238U(p,fission) reaction atEp = 20, 35, 50, 60 MeV and for232Th(p, fission) reaction atEp = 50, 60 MeV were measured using HENDES set-up. The results indicate enhancement for super-asymmetric mass division at intermediate excitation energies.

Detector of Hazardous Substances Based on Nanosecond Neutron Analysis

Feasibility of Nanosecond Neutron Analysis/Associated Particle Technique for detection of explosive and flammable liquids has been experimentally demonstrated. Experimental results with imitators and real liquids are discussed.

Detection of Explosives Using Continuous Microwaves

Application of ultra-high frequency (microwave) electromagnetic radiation for detection of explosive objects is based on the possibility to determine two parameters: a) shape and size of the object, and sometimes b) its dielectric constant. This can be achieved by using two kinds of systems: either pulsed radars or continuous-wave radars.

HENDES-high efficiency neutron detection system for correlation measurements with HI beams

HENDES is a new device for correlation measurements of fission fragments, neutrons and light charged particles produced in HI induced reactions. Double differential neutron spectra are measured with the help of Position Sensitive Neutron Detectors, fission fragment spectra are recorded with large Position Sensitive Avalanche Counters, and light charge particle spectra are measured with arrays of dE-E telescopes. Collective dynamical parameters of nuclear matter are extracted from the data. New results were obtained from 40Ar+180Hf reaction at EAr=190–250u2009MeV. Work is in progress to study the influence of neutron excess on the fusion-fission dynamics in different combinations of Ni beams on Sn targets.