Experimental Study on the Importance of Accurate Neutron Angular Distribution Measurement for Determination of Neutron Yield in a 2.5 kJ Mather type PF

Three activation counters were constructed by thin wall Geiger and were placed in different angels with respect to anode axis; 0°, 45°, 90°; where the Geigers have 20 cm distance from anode top of the 2.5 kJ SBUPF1 plasma focus device. The counters were calibrated by a 5 Ci Am–Be neutron source with source removal method. A computer program receives the Results of each plasma focus experiment and background count rates, estimates the angular distribution of neutron emission and calculates the neutron yield of each shot. The neutron yield of the device was measured about 6 × 10⁷ neutrons per shot. The results, indicate that using three counters (instead of one counter in 0°) in different angles for determination of total neutron yield, gives a more accurate measurement (up to 28% is measured in sample shots), and this error is bigger in those shots that thermonuclear fusion mechanism have greater share in neutron production.     

Angular Distribution of Argon Ions and X-Ray Emissions in the Apf Plasma Focus Device

Angular distribution of ion beam emission from an argon gas-filled plasma focus devices has been investigated using an array of five Faraday cups. The argon ion beam emission is found to be highly pressure-dependent and reaches its maximum at the pressure of 1 torr. The ions flux decreased as the working pressure increased; the maximum ion density at 1 torr was estimated to be around 9.24 × 10²⁴ ions/steradian. Also, the study on the angular distribution of X-rays has been carried out using TLD-100 dosimeters. The intensity of ions reduced significantly at angles higher than ±11° but the X-ray distribution was bimodal, peaked approximately at ±15°.     

Modified Reconstruction of Neutron Spectrum Emitted in Dense Plasma Focus Devices by MCNP Code and Monte-Carlo Method

In this study we present Monte Carlo method for obtaining the time-resolved energy spectra of neutrons emitted by D-D reaction in plasma focus devices. Angular positions of detectors obtained to maximum reconstruction of neutron spectrum. The detectors were arranged over a range of 0–22.5 m from the source and also at 0°, 30°, 60°, and 90° with respect to the central axis. The results show that an arrangement with five detectors placed at 0, 2, 7.5, 15 and 22.5 m around the central electrode of plasma focus as an anisotropic neutron source is required. As it shown in reconstructed spectrum, the distance between the neutron source and detectors is reduced and also the final reconstructed signal obtained with a very fine accuracy.     

Measurement of Double-Differential Neutron Emission Spectra from Uranium-238

We have performed the measurement of neutron emission spectra from ²³⁸U using a time-of-flight technique, and deduced the following data; (1) the prompt fission neutron spectra for 2 MeV incident neutrons at two emission angles of 90° and 135°, (2) the double-differential neutron emission cross sections at the incident energies of 1.2, 2.0, 4.2, 6.1 and 14.1 MeV. The emission spectra and the cross sections for scattering process were also deduced by subtracting the fission neutrons from the experimental spectra. The experimental results were compared with other experiments and the evaluations of JENDL-3 and ENDF/B-IV.

From the fission spectrum data ranging from 2 to 12 MeV, we have derived the best fit parameters for the Maxwellian and Watt type distribution functions. The experimental spectra are described with the Maxwellian spectrum with temperature of 1.24–1.26 MeV and are softer than both evaluations.

The spectra and cross sections for inelastic-scattering showed substantial disagreement with the evaluations concerning the discrete levels between 0.5 and 1.2 MeV, and continuum neutrons due to evaporation and pre-equilibrium processes. The secondary neutron angular distributions at 14 MeV incident energy were reproduced fairly well with the systematics.     

Effect of Neutron Irradiation on Mechanical Properties of Al-Li Alloys

An increase in yield stress at room temperature was observed in Al-0.6W/0 Li alloy irradiated to thermal neutron doses of 2.9 × 10¹⁹ to 7.2 × 10¹⁹ cm^?2. The hardening of as-irradiated specimens is accompanied with yield point followed by jerky yield-elongation in the stress-strain curve. The radiation hardening could not be annealed out by heating for 30 min at temperatures up to 350°C, whereas the yield-elongation disappeared gradually with increasing heating temperature in the l mm diam. specimens; with the 2 mm diam. specimens the yield-elongation still remained even after post-irradiation heating for 30 min at 350°C. Strengthening accompanied by jerky yield-elongation is considered to be due to He atom clusters precipitated along the dislocation. The hardening observed in the specimens heat-treated after irradiation at temperatures above 250°C is caused by randomly distributed gas bubbles.

In heavily cold-worked Al-0.6%W/o Li specimens, recovery of work hardening occurred during neutron irradiation to 4.2 × 10¹⁹ cm^?2. Hardening due to gas bubbles was also observed in the cold-worked specimens. In Al-2.7W/0 Li alloy, an increase in yield stress took place in the specimens irradiated to 4.2 × 10¹⁹ cm^?2 and heated for 30 min at temperatures of 155° to 260°C. The hardening is thought to be due to re-precipitation of β-phase resolved during the neutron irradiation.     

Investigation of the Neutron Production Mechanism in a 20 kJ Plasma Focus Device

Neutron production mechanisms in a medium energy plasma focus device (20 kJ) were investigated. The time-resolved hard X-ray, neutron signals were obtained with two detectors based on a plastic scintillator–photomultiplier combination located at two different angles (0°, 90°) to the plasma chamber and 10 m from the top of the anode. Neutron signal intensities at 0° and 90° were recorded for comparison. Neutron intensity width results in a distribution of neutron energy in the 0°, direction greater than the energy of thermonuclear neutrons (2.45 MeV).     

Neutron Scaling Laws from Numerical Experiments

Experimental data of neutron yield Y _n against pinch current I _pinch is assembled to produce a more global scaling law than available. From the data a mid-range point is obtained to calibrate the neutron production mechanism of the Lee Model code. This code is then used for numerical experiments on a range of focus devices to derive neutron scaling laws. The results are the following: Y _n = 2 × 10¹¹ I _pinch ^4.7 and Y _n = 9 × 10⁹ I _peak ^3.9. It is felt that the scaling law with respect to I _pinch is rigorously obtained by these numerical experiments when compared with that obtained from measured data, which suffers from inadequacies in the measurements of I _pinch.     

Neutron Irradiation Effects on Thermally Activated Process of Tensile Properties of Titanium

This paper deals with the relationship between mechanical properties and irradiation, effects for titanium irradiated to fast neutron fluxes. The neutron fluences applied are 6.9×10¹⁸, 8.6 × 10¹⁸ and 3.0 × 10¹⁹ n/cm². Tensile deformation is carried out over the temperature range of 77–about 600°K retaining the strain rate constant on one hand and changing the strain rate by a factor of about 5 and 10 on the other.

The fluence (φ) dependence of the yield stress at room temperature for an athermal component of the stress, σμ is greater than that for a thermal component σ* which does not change remarkably after irradiation. Their increments Δσ, Δμ and Δ σ* are proportional toσ ^1/3, σ^1/2σ^1/4 and, respectively.

The relationship between activation volume V* and effective shear stress τ* is investigated for both the unirradiated and irradiated specimens. In terms of the τ*/τ*₀ analysis (τ*_o is the value of τ* at T = 0°K), V* shows a tendency to decrease with increase in neutron fluence.

Irradiation defects observable by electron microscopy seem to be related to the athermal activation stress (σ_u) and those too small to be observed by electron microscopy to the thermal activation stress. The yield stress in the thermal activation can be given by Conrad's formula. The activation energy H₀ shows a constant value of about 1.8 eV irrespective of the neutron fluence applied. This value is 0.3–0.4eV higher than that for unirradiated specimens.     

Measurement and Calculation of Neutron Diffusion Parameters in Water

Neutron diffusion parameters in water at a room temperature of 10°C have been measured by the pulsed neutron method for the range of geometrical buckling from 0.093 to 1.36 cm^-2. The results are 205±4 μ60 for the neutron mean life time due to absorption, 34,120±610 cm²·sec^-1 for the diffusion coefficient and 3,350±560 cm⁴·sec^-1 for the diffusion cooling coefficient.

The decay constant has been calculated as a function of buckling for the Nelkin and the Rad-kowsky scattering models of water on the assumption of linear anisotropic scattering. The calculated diffusion coefficients, 36,290 cm²·sec^-1 for the Nelkin model and 37.610 cm²·sec^-1 for the Radkowsky model, are somewhat higher than the experimental result.

It is shown that the calculated diffusion coefficient approaches the experimental value if we use μ-(E), the mean value of cosine of scattering angle, obtained from the Beyster's experiment instead of that for the Nelkin model.     

Calculations to support JET neutron yield calibration: Neutron scattering in source holder

After the coated CFC wall to ITER-Like Wall (Beryllium/Tungsten/Carbon) transition in 2010–11, confirmation of the neutron yield calibration will be ensured by direct measurements using a calibrated ²⁵²Cf neutron source deployed by the in-vessel remote handling boom and Mascot manipulator inside the JET vacuum vessel.The paper describes preliminary calculations and the results of numerical study of the effect of source holder on neutron detector response. The source baton was designed in such a way, that it does not significantly affect the neutron spectrum, angular neutron flux distribution or activation detector response. All effects are approximately equal to or less than 1%. The largest disturbance to the neutron flux angular distribution and to the neutron spectrum arises from the source capsule. Hence one should obtain as much information as possible about the capsule and the ²⁵²Cf source material in order to avoid additional systematic errors.     

Measurements of the neutron yield and the neutron energy distribution from the 9Be(d,n)10B reaction on a thick Be target at an incident deuteron energy of 20.2 MeV

A fast neutron irradiation facility has been set up at the SARA cyclotron located in Grenoble. This facility provides the possibility to carry out fast neutron irradiation tests at both cryogenic and ambient temperatures. Neutrons are produced by stopping a 20.2 MeV deuteron beam in a 3 mm thick beryllium target. The angular distribution of the neutron flux and the energy spectra from 0° to 40° with respect to the deuteron beam axis were measured. A neutron fluence in the range of 10¹⁴ cm⁻² is available per day, with a small gamma contamination and a small thermal neutron flux.     

Neutron Resonance Parameters of Silver-107 and Silver-109

Neutron transmission measurements were carried out on the separated isotopes of silver using the time-of-flight facility at the Japan Atomic Energy Research Institute electron linear accelerator. Neutrons were detected with the ⁶Li-glass detectors at 56 and 191 m. The samples used were metallic powder enriched to 98.2% for ¹⁰⁷Ag and 99.3% for ¹⁰⁹Ag. Transmission data were analyzed with the multi-level Breit-Wigner formula incorporated in a least squares fitting program. Resonance energies and neutron widths were determined for the large number of resolved resonances in the neutron energy region of 400 eV~7 keV. The s-wave strength functions and average level spacings were obtained to be; S₀= (0.43±0.05) × 10^?4, D₀ = 20±2 eV for ¹⁰⁷Ag and S₀= (0.45 ± 0.05) × 10^?4, D₀ = 20 ± 2eV for ¹⁰⁹Ag.     

Measurement of thermal neutron cross section and resonance integral for 165Ho(n, γ)166gHo reaction by the activation method

The thermal neutron cross section and the resonance integral of the reaction ¹⁶⁵Ho(n, γ)^166gHo were measured by the activation method using ⁵⁵Mn(n,γ)⁵⁶Mn monitor reaction. The sufficiently diluted MnO₂ and Ho₂O₃ samples with and without a cylindrical Cd case were irradiated in an isotropic neutron field of the ²⁴¹Am–Be neutron sources. The γ-ray spectra from the irradiated samples were measured with a calibrated n-type high purity Ge detector. Thus, the thermal neutron cross section for ¹⁶⁵Ho(n,γ)^166gHo reaction has been determined to be 59.2 ± 2.5 b relative to the reference thermal neutron cross section value of 13.3 ± 0.1 b for the ⁵⁵Mn(n,γ)⁵⁶Mn reaction, and it generally agrees with the recent measurements within about 1 to 12%. The resonance integral has also been measured relative to the reference value of 14.0 ± 0.3 b for the ⁵⁵Mn(n,γ)⁵⁶Mn reaction using an epithermal neutron spectrum of the ²⁴¹Am–Be neutron source. The resonance integral for ¹⁶⁵Ho(n, γ)^166gHo reaction obtained was 667 ± 46 b at a cut-off energy of 0.55 eV for 1 mm Cd thickness. The existing experimental and evaluated data for the resonance integral are distributed from 618 to 752 b. The present resonance integral value agrees with most of the previously reported values obtained by ¹⁹⁷Au standard monitor within the limits of error.     

Construction of Neutron Guide Tubes in Upgraded JRR-3

Five neutron guide tubes have been installed in the upgraded JRR-3 (Japan Research Reactor No. 3). Two of them are for thermal neutrons and the other three are for cold ones. The characteristic wavelength of the thermal neutron guide tubes is 2 Å, and those of the cold neutron guide tubes are 4 and 6 Å. The longest guide tube is 59.9 m long and the total length of guide tubes is 232.1 m.

The beam sizes are 2 cm × 20 cm for the thermal neutron beams and 2 cm × 12 cm for the cold neutron beams. A curved part of the neutron guide is assembled by a polygonal approximation with use of 85 cm long straight units. The neutron mirrors of these units are made of natural Ni deposited borosilicate glasses. The Ni layer is about 2,000 Å in thickness.

The mean fabrication error of guide tube units is 4 μm. The mean installation errors are 8 μm for the positional abutment error and 5 × 10^?6 rad for the angular error. The neutron losses by these errors will be about 5%, and the neutron fluxes at the exits of the neutron guides are estimated to be about 2 × 10⁸ n/cm²·s.     

Effect of Lithium on Pressure of Hydrogen in Liquid Sodium

Abstract

Neutron spectra in a cylindrical straight duct and in bent ducts with angles of 30°, 60° and 90° have been measured by the multiple foil activation and thermoluminescence dosimetry methods. Two-dimensional discrete ordinates and three-dimensional Monte Carlo calculations are executed, and the results are compared with the measurements. The flow rate at the duct entrance calculated by the DOT3.5 code is underestimated by approximately 30%, due to a conversion of the core and reflector geometry from XY to RZ geometry. The fast neutron flux in the ducts is underestimated by 20% by the MORSE-SGC/S code due to a too coarse angular mesh of the source, which does not properly represent the actual angular distribution of the fast flux, which is highly peaked forwardly into the ducts. The thermal neutron flux was overestimated by the Monte Carlo calculation. A method is proposed to calculate the angular distribution of the flow rate at the duct entrance and to calculate the source strength and the angular distribution of the flow rate at the entrance of the second leg of the duct. The results are compared with those of the transport calculations. Generally, the agreement is quite satisfactory.     

Slow Neutron Resonances in Terbium-159

An experiment of neutron resonances in ¹⁵⁹Tb was carried out using the Japan Atomic Energy Research Institute linac time-of-flight facility. Transmission and capture measurements were made on terbium samples of two thicknesses, using ⁶Li-glass and Moxon Rae detectors at the 47 m station; the neutron flux was monitored with a ⁶Li-glass transmission type flux monitor. Transmission data were analyzed with an area program up to 1.2 keV, and capture data with Monte-Carlo program CAFIT, to obtain 2gΓ⁰ _n Γ and Γ_γ Resonance parameters of 209 levels below 1.2 keV are obtained, and 52 levels between 754eV and 1.2keV are new ones. The results are; average level spacing <D>=4.4±0.4eV below 600 eV, s-wave strength function S₀=(1.55 ±0.15)10⁴ below 1.2 keV, and average radiation width <Γ_γ>=107±7 meV for lower 25 levels. Average capture cross section <σ_c> were obtained from 50 eV to 30keV.     

Determining the irradiation temperature of witness samples of VVER-1000 AND -440 reactor vessel steel

The most convenient methods for measuring the temperature in nuclear reactors are enumerated in this paper, specifically thermocouples, fusible metal inserts, and diamond probes. Their advantages and disadvantages are listed and data are presented on their use for measuring the irradiation temperatures of containers with witness samples of steel in VVER-1000 and -440 reactor vessels. It is found that the sample temperature in these assemblies in the VVER-1000 is 300 ± 2°C, as measured by fusible inserts, while thermocouples in chains in the VVER-440 indicated 270°C. The advantage of the method employing diamond probes is their small size, but the range of possible direct measurements for this technique is restricted to a maximum neutron fluence of 10¹⁸ cm⁻² (for neutron energies above 0.5 MeV). Translated from Atomnaya énergiya, Vol. 105, No. 3, pp. 145–150, September, 2008.     

Neutron diagnostics on the Angara-5 assembly

Conclusions The neutron diagnostics complex, developed on the Angara-5 assembly, enables determining the total yield, the spectrum, and the time dependence of the neutron yield of the source. In experiments with superfast deuterium Z pinch a neutron yield of 10¹² and spatial anisotropy of the neutron spectrum were recorded with the help of the described diagnostics system. The anisotropy of the neutron spectrum indicates that at least some of the neutrons were produced by an acceleration mechanism.Affiliate of the I. V. Kurchatov Institute of Atomic Energy. Translated from Atomnaya Énergiya, Vol. 71, No. 6, pp. 516–523, December, 1991.     

Interaction of fast hydrogen ions with silicon surface at glancing angles of incidence

Angular distributions of 380 keV protons reflected from (1 1 1) surface of Si monocrystal were measured in the range of projectiles glancing angle from 0.3° up to 0.8°. It is shown that increase of glancing angle causes non-linear change of such distribution parameters as angular width of the front rise, angular width of the distribution, the maximum yield value. Registered energy spectrum of reflected particles for glancing angle of 0.5° consists of several peaks with practically constant angular intervals between them and maxima weakly reducing towards lower energy region. It is experimentally shown that the most energetic peak relates to the reflection from the very surface and the rest ones are caused by successive scattering of ions by inner silicon crystallographic planes.     

Energy Response of Neutron Area Monitor with Silicon Semiconductor Detector

Abstract

A prototype neutron area monitor with a silicon semiconductor detector has been developed which has the energy response of 1 cm dose equivalent recommended by the 1CRP-26. Boron and proton radiators are coated on the surface of the silicon semiconductor detector. The detector is set at the center of a cylindrical polyethylene moderator. This moderator is covered by a porous cadmium board which serves as the thermal neutron absorber. Neutrons are detected as α-particles generated by the nuclear reaction ¹⁰B(n, α)⁷Li and as recoil protons generated by the interaction of fast neutrons with hydrogen.

The neutron energy response of the monitor was measured using thermal neutrons and monoenergetic fast neutrons generated by an accelerator. The response was consistent with the 1cm dose equivalent response required for the monitor within ±34% in the range of 0.025–15 MeV.