A method for determining the intensity of concomitant neutron source D(d, n)3He when studying the characteristics of delayed neutrons from nuclear fission induced by neutrons from reaction T(d, n)4He

A factor that may be responsible for the discrepancies in the total delay neutron yields, the relative yields of separate groups of delayed neutrons, and half-lives of their precursors has been investigated. These discrepancies are shown to be attributable to the effect of a concomitant neutron source—reaction D(d, n)³He. Such a source is unavoidably present in an experiment where reaction T(d, n)⁴He on a solid-state target is used as a neutron source. A method has been developed to calculate the contribution of neutrons from the reaction D(d, n)³He to the measured total and relative yields of delayed neutrons and the half-lives of their precursors in heavy nuclei fission induced by neutrons with energies of 14–18 MeV. The energy dependence of the parameters of delayed neutron groups from the neutron-induced fission of ²³⁸U nuclei in the energy range of 14.2–17.9 MeV is presented.     

A spectrometer of polarized neutrons

A polarized neutron spectrometer intended for studies of interactions of nuclei and condensed matter with polarized neutrons with energies in the range from thermal energies to several electron volts was designed at the IBR-2 pulsed reactor (JINR, Dubna). Diffraction on magnetized Co(92%)–Fe(8%) single crystals was used to polarize neutrons and analyze the polarization. The attained neutron polarization was ∼95% within the entire energy range.     

A Hemispherical Fission Chamber for the Neutron-Flux Monitoring

A fission ionization chamber has been designed to monitor neutron fluxes produced by the proton beam of the Van de Graaf accelerator in the ⁷Li(p, n)⁷Be nuclear reaction. A target producing neutrons is placed at the center of the chamber, which has a hemispherical shape. The neutrons escaping from the target are detected within the limits of a space angle a little larger than 2 sr. A ²³⁵U isotope is used as a fissile material. A U₃O₈ layer with a thickness of 300 g/cm² and an area of 80 cm² has already been deposited on the surface of the inner hemisphere using electrolysis. The chamber is filled with a gas mixture of 97% Ar + 3% CO₂. The detection efficiency of the chamber for neutrons with 1- to 150-keV energies is found to be 1.6 × 10^–5. Using this chamber, it is possible to measure (with a statistical accuracy of 1%) the integrated neutron yield in a thick target exposed for 20 min to a proton beam with a current of 3 A and an energy of 1942 keV, which is 60 keV above the threshold of the ⁷Li(p, n)⁷Be reaction. The design of the fission chamber is described, and the test results are presented.     

Detection of neutrons and γ rays by a xenon pulsed ionization chamber

The applicability of a xenon γ-ray spectrometer based on a high-pressure (50 atm) xenon cylindrical ionization chamber to thermal neutron detection is discussed. The reaction of radiative capture of thermal neutron capture ¹³¹Xe(n, γ)¹³²Xe* followed by emission of 668-keV γ rays detectable by the spectrometer is used. The response of the xenon spectrometer with a sensitive volume of 0.2 L is analyzed. The measured thermal neutron detection efficiency is 0.08%. The advantage of the detector is its capability of simultaneously detecting both thermal neutrons and γ rays, which allows precise and high-efficiency identification of radioactive and fissile materials.     

Determining the singlet nn -scattering length from data on the n + d → p + n + n reaction yield by solving the inverse problem

The possibility of determining the nn-scattering length in the n + d → p + n + n reaction is considered. An inverse problem of reconstructing the dependence of the reaction yield on the energy of relative motion of two neutrons in the region of the nn final state interaction peak is solved. The proposed technique is tested using results of simulation of the nd breakup reaction. Original Russian Text ? S.V. Zuyev, E.S. Konobeevski, M.V. Mordovskoy, 2008, published in Pribory i Tekhnika Eksperimenta, 2008, No. 3, pp. 5–8.     

High-Intensity Neutron Fields at the Center of the Metallic Core of Fast Reactors as the Primary Standard Neutron Fields

It is proposed to use high-intensity neutron fields with an average neutron energy of 0.7–1.5 MeV at the center of the metallic core of fast reactors as the primary standard neutron fields along with the known standard fields of fission neutrons with average energies of 1.93 and 2.13 MeV, respectively, from ²³⁵U and ²⁵²Cf nuclei, which are used in the world practice of taking neutron measurements. It is also proposed to create standard fields of nuclear fission neutrons with an average energy of 2 MeV by the bombardment of ²³⁵U converters with a beam of fast monoenergetic neutrons with energies of 2.5 and 14 MeV and 50-MeV protons.     

Studying the spectrum of neutrons emitted from the LSDS-100 using a multiwire proportional fission chamber

A fast multiwire proportional fission chamber capable of detecting ∼10⁶ fission fragments per second was produced. Heptane vapor at a pressure of 15 mbar was used as a working gas. The full width at the base of the pulse from a fission fragment was ≤0.2 μs. The spectrum of the neutron flux density on the spectrometer surface was measured by the neutron slowing-down time in the lead of the LSDS-100 at neutron energies ranging from 18 eV to 11.3 keV.     

Ultimate characteristics of an X-ray prism spectrometer

X-ray prism spectrometry schemes for experimental investigations of fast processes are considered. Diamond and beryllium prism dispersion parameters and special features of transmission spectra for crystal prisms are analyzed. It is shown that relative energy resolution E/ΔE at photon energies E ∼ 10 keV may reach 10³–10⁴ and the total working spectral band is ∼100 keV. This opens unique possibilities for measuring fine structures of single-shot absorption spectra for quasi-parallel beams and continuous monitoring of the fundamental and high-frequency harmonics of an X-ray free electron laser. Original Russian Text ? A.G. Tur’yanskii, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 4, pp. 150–158.     

Measuring the neutron spectrum of the accelerator-based source using the time-of-flight method

The time-of-flight technique with a new method for generating short radiation bursts has been used to measure the neutron spectrum of the accelerator-based source with a stationary proton beam. Specific problems arising thereby and methods for solving them are described. The measured spectrum of neutrons in the reaction ⁷Li(p, n)⁷Be at a proton energy of 1.915 MeV is presented and compared to the calculation. This spectrum is shown to comply with the requirements for the neutron beam used in neutron capture therapy.     

A protective subsurface container for holding and temporary storage of activated targets

An accelerator-driven source of epithermal neutrons has been developed by the Budker Institute of Nuclear Physics for carrying out investigations into neutron capture therapy of malignant tumors. Safe handling of targets with ⁷Be radionuclide accumulated in them is one of the problems encountered in generation of neutrons in the ⁷Li(p, n)⁷Be reaction. It is proposed that targets will be decontaminated in a natural course, being placed in a subsurface container located in the room of the accelerating facility. The maximum activity of the targets enclosed in the container after scheduled generation of neutrons at the facility is estimated. Analytical estimates and Monte Carlo calculation of γ-ray transport are performed to determine the optimum container size, such that the γ-ray flux from its contents is reduced to the acceptable level. The preliminary design of the container and its embodiment are presented.     

Discrimination of particles by the scintillation pulse shape (in the electron energy range of 0.5–4.0 MeV) using the zero-crossing method

The ratios of the fast to slow components of scintillation pulses produced by neutrons and γ rays have been calculated on the basis of experimental data for several energies in the range of 0.5-4.0 MeV of the electron equivalent. The procedure for discriminating between neutrons and γ rays by measuring the zero-crossing time of a bipolar pulse formed by RC circuits has been simulated for organic scintillators using the Monte Carlo method in the range of 0.012-4.000 MeV of the electron equivalent. It is shown that pulse shape discrimination of particles based on the zero-crossing technique allows rejection of γ-ray background down to a level of 10-4 at particle energies of >100 keV of the electron equivalent (for energies of <50 keV, the γ-ray background is suppressed to a level of 10^-1- 10^-2 and this technique becomes ineffective in principle).     

Fast X-ray and Neutron Detectors Based on Natural Diamond

Fast-response detectors based on natural diamond, which has a long charge-carrier lifetime, have been developed and manufactured for performing time-of-flight measurements of the parameters of plasma and other pulsed sources of ultrasoft X-ray and neutron radiations. Detectors of two types—volumetric detectors for detecting neutrons and X rays with quantum energies of >1 keV and surface detectors for detecting ultrasoft X rays with quantum energies of 200–1000 eV—have been manufactured. Their response time is 1–2 ns (the FWHM duration of a current response). The sensitivity of the volumetric detectors to neutrons with an energy of 14 MeV is at a level of 10^–18 C cm²/neutron. The sensitivity of the surface detectors to X rays with an energy of 580 eV is above 5 mA/W.     

A source of broad homogeneous beams of low-energy (∼0.5 keV) gas ions

A source of gas ions (argon, oxygen, nitrogen, etc.), the operating principle of which is based on the use of a glow discharge in an electrode system of a wide-aperture hollow cathode and anode in a magnetic field, is described. The exit aperture diameter of the hollow cathode, increased up to a size close to the ion beam diameter (10 cm), ensures the uniform ion emission of the plasma generated in the discharge region near the anode. A decreased angular divergence or increased ultimate ion-beam current density is achieved by a change in the potential drop in the space charge sheath between the plasma and the ion optics. The source generates broad (50 cm²) slightly diverging (ω/2∼3°–5°) ion beams with energies of 300–1000 eV at a beam current density of ∼0.5 mA/cm².     

Measurements of strong pulsed magnetic fields by Hall effect devices

The possibility of using Hall effect devices for measuring strong pulsed magnetic fields is studied. The Hall effect devices with a∼10-mV/T sensitivity, based on 1- to 3-μm-thick n-type InAs polycrystalline films with a 10³-cm²/(Vs) electron mobility and ∼10¹⁸-cm-³ concentration, are used. It is established that the Hall effect voltage of these devices is a linear function of the field in magnetic fields with an induction of up to 56 T, and they are suitable for measuring unipolar strong pulsed magnetic fields at induction variation rates of up to ~10⁵T/s. It is necessary to use more sensitive Hall effect devices to obtain higher signal-to-noise ratios for rapidly measuring alternating fields.     

Energy spectra of neutrons escaping from light and heavy fragments with asymmetric <Superscript>235</Superscript>U and <Superscript>252</Superscript>Cf nuclear fission

The neutron-activation analysis is used to determine the energy spectra of neutrons escaping from light and heavy fragments from nuclear fission of ²³⁵U by thermal neutrons and spontaneous fission of ²⁵²Cf nuclei. It is shown that the difference of the spectra obtained is slight, ∼90.6 keV. The 28-group energy spectra of instantaneous neutrons from fission of ²³⁵U and ²⁵²Cf nuclei, which were reconstructed using four-component a priori spectra, are presented.     

Numerical Simulation of a Fusion Power Measurement Using Inelastic Neutron Scattering by Carbon Nuclei

The possibility of using prompt rays from the 4.439-MeV excited level of carbon nuclei in the ¹²C(n, n)¹²C reaction and scattered neutrons for measuring the power of a thermonuclear facility is studied. It is shown that the angular distributions of rays and scattered neutrons can be measured using three -ray spectrometers and three neutron detectors. The detectors must be installed around the carbon sample at angles of 140.8°, 90.0°, and 39.2°. The obtained total cross sections of the scattered-neutron and -ray angular yields are compared to the published data.     

A calorimetric spectrometer measuring single pulses of relativistic microwave generators

A calorimetric spectrometer measuring individual pulses radiated by wideband relativistic microwave oscillators is described. The calorimetric spectrometer comprises two calorimeters and a set of low-pass filters. In the development of such a spectrometer, the basic feature consists in the high radiation power (∼10⁸ W) and low pulse energy (∼1 J). To prevent the microwave surface discharge, the calorimeters have a rather large area (∼0.1 m²). The calorimeters’ sensitivity is 0.05 J. Frequency responses of the filters were measured experimentally and calculated with the help of a three-dimensional version of the KARAT computer code. The experimental spectrum of a wideband relativistic microwave plasma oscillator measured in a frequency range of 5–40 GHz is presented.     

A method for measuring the energy spectrum of neutrons with energies of 1–15 MeV

The characteristics of the detector prototype for 1–15 MeV neutrons are described. The prototype is a full absorption detector consisting of interlaced plastic scintillators and ⁶Li doped glasses. A neutron incident on the detector deposits all its energy in the plastic scintillator, is moderated to thermal energies, and detected in the lithium glass. The measured time of complete neutron moderation is ～60 μs. Recording two signals in this time interval from the first event of neutron scattering in the plastic scintillator and from the neutron absorption by a lithium atom in the glass, it is possible to effectively suppress background thermal neutrons and γ rays and, therefore, detect low-intensity neutron sources. Owing to the proposed detector design, the direction toward the neutron source can be determined.     

Effects of fluid-structure interaction on trailing-edge noise

This study numerically investigates the effects of fluid-structure interaction (FSI) on the trailing-edge noise, particularly for the cases of wake instability and Karman vortex shedding. The trailing edge is modeled as a flat plate with an elastic cantilever end and its flow-induced vibration is solved by an eigenmode analysis with the Galerkin method. The flow and sound coupled in the FSI analysis are computed on the moving grid by a direct numerical simulation (DNS) procedure. The computed result of wake instability shows that when the first-eigenmode natural frequency ω _n of the cantilever is close to be resonant with the wake characteristic frequency ω _c , the sound pressure level (SPL) is significantly reduced by 20 dB at ω _n /ω _c =0.95, or increased by 15 dB at ω _n /ω _c =1.05, for all angles. For the Karman vortex shedding, a similar frequency modulation occurs via FSI, if ω _n is close to ω _c . The flow and acoustic details are somewhat different for this case but a considerable noise reduction was also possible for angles from −120° to +120°.     

First results of use of a scintillating-fiber position-sensitive detector for recording the target image in a 14-MeV neuron beam at the ISKRA-5 facility

The design of the scintillating-fiber detector is described, and the first results obtained in recording the target image in a 14-MeV neutron beam at the ISKRA-5 facility are presented. The scintillating-fiber position-sensitive detector has been designed for diagnosing laser fusion processes by recording the spatial distribution of thermonuclear neutrons escaping from the target. Position-sensitive detection is effected by conversion of neutron radiation into light in a scintillating fiber array. Discrimination of neutrons from γ rays by their time of flight and image intensification are performed with the aid of a frame camera. Images are recorded by a CCD camera. A technique for recording penumbra images is used for imaging at low neutron yields (3 × 10⁸−10¹¹).