Recent progress in a single-pulse Nanosecond Impulse Neutron Investigation System (NINIS) intended for interrogation of hidden objects by means of measuring elastically scattered neutrons is presented in this paper. The method uses very bright neutron pulses having duration of the order of 10 ns only, which are generated by dense plasma focus (DPF) devices filled with pure deuterium or DT mixture as a working gas. The small size occupied by the neutron bunch in space, number of neutrons per pulse and mono-chromaticity (ΔE/E∼1%) of the neutron spectrum provides the opportunity to use a time-of-flight (TOF) technique with flying bases of about a few metres. In our researches we used DPF devices having bank energy in the range 2–7 kJ. The devices generate a neutron yield of the level of 108–109 2.45 MeV and 1010–1011 14 MeV neutrons per pulse with pulse duration ∼10–20 ns. TOF base in the tests was 2.2–18.5 m. We have demonstrated the possibility of registering of neutrons scattered by the substances under investigation—1 litre bottles with methanol (CH3OH), phosphoric (H2PO4) and nitric (HNO3) acids as well as a long object—a 1 m gas tank filled with deuterium at high pressure. It is shown that the above mentioned short TOF bases and relatively low neutron yields are enough to distinguish different elements’ nuclei composing the substance under interrogation and to characterize the geometry of lengthy objects in some cases. The wavelet technique was employed to ‘clean’ the experimental data registered. The advantages and restrictions of the proposed and tested NINIS technique in comparison with other methods are discussed.
Abstract:Neutron well logging is one of the basic methods for the determination of the characteristic parameters of rock samples. The neutron source and neutron detectors are elements of Neutron-Neutron Thermal-Epithermal logging tool (NNTE) of significant importance. A neutron source creates the neutron field in the nearest environment. Detectors placed at specified distances from the source register neutrons from this space. A signal of a Neutron-Neutron Thermal-Epithermal tool in specific geological conditions was numerically calculated by means of the Monte Carlo (MC) codes. The main aim of this paper is to show the potential for using the Monte Carlo N-Particle Transport Code (MCNP) software in nuclear well logging prospection methods. The results of this MC modelling are presented in this paper.
An activation of fissionable materials with neutrons has been considered as a possible neutron diagnostic of D-D and D-T fusion plasma. Fission reaction caused by fusion neutrons leads up to emission of secondary neutrons: prompt and delayed. Physical assumptions have been outlined to design a new device (DET-12) for measurements of delayed neutrons emitted from samples of fissionable materials activated with neutrons at big fusion-plasma devices. The aim is to support a classic neutron activation method used as one of plasma diagnostics at tokamaks or stellarators. An interpretation of the time decay of delayed neutrons enables an assessment of the primary neutron flux which induced fission reaction. Monte Carlo calculations have been carried out in order to elaborate the method considered. Nuclides like: pure 235 U, 238 U and 232 Th, have been selected as possible materials to be irradiated. Physical fundamentals of generation of the delayed neutrons are mentioned and a resulting concept of the DET-12 device, built in the Institute of Nuclear Physics, Poland, is presented. A general size and dimensions of particular constituent material layers, and a number and placement of neutron detectors are optimized by means of Monte Carlo modelling. Recommendations for a technical design of the measuring chamber were formulated. Detection efficiency of DET-12 has been also estimated.
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