Neutron Time Of Flight Spectrometer Research Articles

Using neutrons and x rays to measure plasma conditions in a solid sphere of deuterated polyethylene compressed to densities of 35 g/cc at temperatures of 2 keV and pressures of 40 Gbar

This paper describes an experiment that shock compresses the center of a solid deuterated polyethylene sphere, CD2, to densities of 35 g/cc and temperatures of 2 keV with corresponding pressure of 40 Gbar. The design employs a strong spherically converging shock launched through a solid ball of material using a Hohlraum radiation drive. As the shock coalesces at the center it produces a hot spot that we characterize by measuring the x-ray self-emission and 2.45 MeV neutrons emitted. Two-dimensional images and time-resolved measurements of the x rays emitted determine the size and time duration of the hot spot, leading to an estimated 2 keV electron temperature. The neutron time of flight spectrometer measures an average ion temperature of 1.06 ± 0.15 keV and neutron yield of 7.0 (±0.5) × 109 DD neutrons. Our new distribution function tool enables us to create a forward model of the experimental data based on 1D radiation-hydrodynamic simulations, leading to a better understanding of the plasma conditions that produce the measured neutrons and x rays. Our simulations indicate that the x rays are produced in a short-lived hot-dense core over tens of picoseconds, whereas the neutron emission continues for about 200 ps, as the hot core starts to expand, thereby leading to a lower mean temperature of the plasma during neutron production. This finding is in agreement with the experimental data, and we therefore conclude that the forward-modeling is a useful tool for inferring the conditions of the hot spot in a laser-driven implosion during burn.

Recent progress in nuclear data measurement for ADS at IMP

Recent progress in nuclear data measurement for ADS at Institute of Modern Physics is reviewed briefly. Based on the cooler storage ring of the Heavy Ion Research Facility in Lanzhou, nuclear data terminal was established. The nuclear data measurement facility for the ADS spallation target has been constructed, which provides a very important platform for the experimental measurements of spallation reactions. A number of experiments have been conducted in the nuclear data terminal. A Neutron Time-of-Flight (NTOF) spectrometer was developed for the study of neutron production from spallation reactions related to the ADS project. The experiments of 400 MeV/u 16O bombarded on a tungsten target were presented using a NTOF spectrometer. Neutron yields for 250 MeV protons incident on a thick grain-made tungsten target and a thick solid lead target have been measured using the water-bath neutron activation method. Spallation residual productions were studied by bombarding W and Pb targets with a 250 MeV proton beam using the neutron activation method. Benchmarking of evaluated nuclear data libraries was performed for D-T neutrons on ADS relevant materials by using the benchmark experimental facility at the China Institute of Atomic Energy.

Conceptual design of a BackTOF neutron spectrometer for fuel ion ratio measurements at ITER

In this paper we present a conceptual design of a back scattering neutron time of flight spectrometer (BackTOF) for use at ITER. The proposed BackTOF design aims at fulfilling the requirements set on a neutron spectrometer system to be used for inferring the core fuel ion ratio in a DT plasma. Specifically we have investigated the requirements on the size, energy resolution, count rate capability, efficiency and signal to background ratio. These requirements are a compact size that fits in roughly 1 m3, an energy resolution of 4% or better, a count rate capability of at least 100 kHz, an efficiency of at least 10−5 and a signal to background ratio of 1000 or better.Using a Monte Carlo model of the BackTOF spectrometer we find that the proposed BackTOF design is compact enough to be installed at ITER while being capable of achieving a resolution of about 4% FWHM with a count rate capability of 300 kHz and an efficiency at 1.25 · 10−3. This is sufficient for achieving the requirements on the fuel ion ratio at ITER. We also demonstrate how data acquisition systems capable of providing both timing and energy information can be used to effectively discriminate random background at high count rates.

Using neutrons to measure keV temperatures in highly compressed plastic at multi-Gbar pressures

We have designed an experiment for the National Ignition Facility to measure the Hugoniot of materials such as plastic at extreme pressures. The design employs a strong spherically converging shock launched through a solid ball of material using a hohlraum radiation drive. The shock front conditions can be characterized using X-ray radiography until background from shock coalescence overtakes the backlit signal. Shock coalescence at the center is predicted to reach tens of Gbars and can be further characterized by measuring the X-ray self-emission and 2.45MeV neutrons emitted from the shock flash region. In this simulation design work the standard plastic sphere is replaced with a deuterated polyethylene sphere, CD2, that reaches sufficiently high densities and temperatures in the central hot spot to produce neutrons from Deuterium-Deuterium (DD) fusion reactions that can be measured by a neutron time of flight spectrometer (nTOF) and act as a temperature diagnostic. This paper focuses on the design of these experiments, based on an extensive suite of radiation-hydrodynamics simulations, and the interpretation of the predicted DD neutron signals. The simulations predict mean temperatures of 1keV in the central hot spot with mean densities of 33g/cc and mean pressures of 25Gbar. A preliminary comparison with early experimental results looks promising with an average ion temperature of 1.06±0.15keV in the central hot spot estimated from the nTOF spectral width and measured neutron yield of 7.0 (±0.5)×109 DD neutrons.

Neutron time-of-flight spectrometer based on HIRFL for studies of spallation reactions related to ADS project

A Neutron Time-of-Flight(NTOF) spectrometer, based at the Heavy Ion Research Facility in Lanzhou(HIRFL) was developed for studies of neutron production of proton induced spallation reactions related to the ADS project. After the presentation of comparisons between calculated spallation neutron production doubledifferential cross sections and the available experimental data, a detailed description of the NTOF spectrometer is given. Test beam results show that the spectrometer works well and data analysis procedures are established.The comparisons of the test beam neutron spectra with those of GEANT4 simulations are presented.

A Monte Carlo Simulation of Neutron Instrument Resolution Functions

In this paper we demonstrate that the Monte Carlo simulation package McStas is a useful tool, not only for instrument design, but also for resolution function calculation. It has been possible to determine analytically the 4 dimensional resolution function of both a direct geometry time of flight neutron spectrometer and a triple axis spectrometer. The obtained resolution functions are directly comparable to and in agreement with the Monte Carlo simulated results. These results are a step towards incorporating a 4 dimensional resolution function into data analysis. For each instrument we show an example of the resolution function calculated at a particluar point in (Q, omega) space.

Fundamental ion cyclotron resonance heating of JET deuterium plasmas

Radio frequency heating of majority ions is of prime importance for understanding the basic role of auxiliary heating in the activated D–T phase of ITER. Majority deuterium ion cyclotron resonance heating (ICRH) experiments at the fundamental cyclotron frequency were performed in JET. In spite of the poor antenna coupling at 25 MHz, this heating scheme proved promising when adopted in combination with D neutral beam injection (NBI). The effect of fundamental ICRH of a D population was clearly demonstrated in these experiments: by adding ∼25% of heating power the fusion power was increased up to 30–50%, depending on the type of NBI adopted. At this power level, the ion and electron temperatures increased from Ti ∼ 4.0 keV and Te ∼ 4.5 keV (NBI-only phase) to Ti ∼ 5.5 keV and Te ∼ 5.2 keV (ICRH + NBI phase), respectively. The increase in the neutron yield was stronger when 80 keV rather than 130 keV deuterons were injected in the plasma. It is shown that the neutron rate, the diamagnetic energy and the electron as well as the ion temperature scale roughly linearly with the applied RF power. A synergistic effect of the combined use of ICRF and NBI heating was observed: (i) the number of neutron counts measured by the neutron camera during the combined ICRF + NBI phases of the discharges exceeded the sum of the individual counts of the NBI-only and ICRF-only phases; (ii) a substantial increase in the number of slowing-down beam ions was detected by the time of flight neutron spectrometer when ICRF power was switched on; (iii) a small D subpopulation with energies slightly above the NBI launch energy was detected by the neutral particle analyzer and γ-ray spectroscopy.

Utilization of high-energy neutrons for the detection of fissionable materials

The detection of high-energy prompt fission neutrons was investigated as a method of fissionable material detection. Neutron energy spectra of U238 and several nonfissionable materials were measured using a neutron time of flight spectrometer. The photonuclear reactions were induced in the targets using a pulsed bremsstrahlung beam for several endpoint energies between 8 and 15MeV. While fission neutrons can have energies in excess of 10MeV, neutrons emitted from nonfissionable materials have distinct energy limits that depend upon binding and incident particle energies. Hence the presence of high-energy neutrons can be used to discriminate fissionable from most nonfissionable materials.

New diagnostic techniques and technologies at JET (invited)

The European Fusion Development Agreement’s mission for JET is the development of ITER scenarios exploiting the specific properties of the device. This task requires significant improvements in the measuring techniques. The most innovative diagnostic upgrades are in the fields of edge measurements, detection of fast magnetohydrodynamics modes and “burning plasma” diagnostics. The importance of plasma-wall interactions, and, in particular, the issue of tritium inventory promoted the development of the quartz microbalance, a detector with improved time resolution to measure material redeposition in the remote areas of the inner divertor. Measurement of Alfvén cascades with unprecedented spectral resolution, reaching a toroidal n number of up to 16, was obtained using an O-mode microwave reflectometer as an interferometer. For the diagnosis of the fusion products, a new approach is being developed to measure the He ash based on double charge exchange between thermalized particles and neutrals from JET beams. There have been several upgrades of the neutron diagnostic systems, one of which, the new time of flight neutron spectrometer designed for high counting rates is described.

The TOFOR neutron spectrometer and its first use at JET

A time-of-flight neutron spectrometer (TOFOR) has been developed to measure the 2.45 MeV d+d→3He+n neutron emission from D plasmas. The TOFOR design features the capability to operate at high rates in the 100 kHz range, data collection with fast time digitizing and storing, and monitoring of the signals from the scintillation detectors used. This article describes the principles of the instrument and its installation at JET and presents preliminary data to illustrate the TOFOR performance as a neutron emission spectroscopy diagnostic.

Advanced neutron diagnostics for JET and ITER fusion experiments

The diagnostics functions of neutron measurements as well as the roles played by neutron yield monitors, cameras and spectrometers are reviewed. The importance of recent developments in neutron emission spectroscopy (NES) diagnostics is emphasized. Results are presented from the NES diagnosis of the Joint European Torus (JET) plasmas performed with the magnetic proton recoil (MPR) spectrometer during the first deuterium tritium experiment of 1997 and the recent trace tritium experiment of 2003. The NES diagnostic capabilities at JET are presently being enhanced by an upgrade of the MPR (MPRu) and a new 2.5 MeV time-of-flight (TOF) neutron spectrometer (TOFOR). The principles of MPRu and TOFOR are described and illustrated with the diagnostic role they will play in the high performance fusion experiments in the forward programme of JET largely aimed at supporting the International Thermonuclear Experimental Reactor (ITER). The importance of the JET NES effort for ITER is discussed.

Neutron time-of-flight spectrometer for high rate diagnosis of deuterium plasmas

The new concept for the design of a neutron time of flight spectrometer operating at high rates of events has been studied based on instrumental modeling and neutron transport calculations. The aim is to find an optimized design for an instrument that can measure the 2.5 MeV neutron emission from deuterium plasmas and attain diagnostics capabilities comparable to those as has been demonstrated possible with the 14 MeV magnetic proton recoil spectrometer for deuterium–tritium plasmas at Joint European Torus. Preliminary results are presented and used to project the potential for realizing an advanced neutron emission spectrometry diagnosis of plasmas.

Inelastic neutron scattering and prompt fission neutron spectra for 237Np

The secondary neutron spectra (inelastic, elastic, fission) for 237Np were measured by the neutron time of flight spectrometer of the IPPE at the incident energy range 1–2.5 MeV. The solid tritium target was used as a neutron source. The neptunium oxide (189 g) packed in the low mass stainless steel container was used as a scattering sample. The neutron background due to scattering on the target environment and tritium into the target backing was measured and was calculated with the appropriate model of the neutron source. The data were corrected for neutron background, the scattering on the oxygen and iron nuclei, and the effect of the finite sample size. The fission neutron spectra were measured, evaluated and subtracted from the emission neutron spectra to estimate inelastic neutron spectra and cross-sections. The experimental results were compared with ENDF/B-VI, BROND-2, JENDL-3 neutron data libraries.

Experimental mass excess of 49K and 50K.

The beta decay energy ${Q}_{\ensuremath{\beta}}$ of the delayed neutron emitters $^{49}$,50K produced by fragmentation of a uranium target with a 600 MeV proton beam has been determined. Energies of the beta transitions to well-located neutron emitting levels in the daughter nuclei have been measured by means of a scintillation telescope in coincidence with a large solid angle neutron time of flight spectrometer. The $^{49}\mathrm{K}$ and $^{50}\mathrm{K}$ inferred mass excesses, -30.33\ifmmode\pm\else\textpm\fi{}0.07 and -25.5\ifmmode\pm\else\textpm\fi{}0.3 MeV, respectively, are compared with mass predictions.

The production and measurement of ultra-short intense electron and neutron bursts at gelina

Abstract By means of a post-acceleration pulse compression system electron pulses of about 600 picosecond (FWHM) and more than 100 A peak current are now available at the Geel Electron Linear Accelerator (GELINA). The pulse compression method (1) is reviewed and results of neutron measurements demonstrating the exceptional resolution power of the neutron time of flight spectrometer are given.

A ROTATING CRYSTAL NEUTRON TIME-OF-FLIGHT SPECTRO-METER FOR CONDENSED MATTER INVESTIGATION

A rotating single crystal thermal neutron time of flight spectrometer was constructed in IAB for the study of various dynamic process in condensed matter. The surplus reflections from undesired crystallographic planes in the rotating monochromator (Ge) is eliminated by carefully choosing a proper orientation of the rotating axis in the (Ⅲ) plane. The range of incident initial neutron energy is from 10 meV to 100 meV; The corresponding energy resolution is 2.5 to 7.2% with intensities adequate for inelastic scattering studies. Based on the work of Brockhouse et al., we have calculated a theoretical value of the resolution for neutrons scattered from the sample and compared it with measured results. Inelastic neutron scattering spectra from vanadium sample is presented and comparison with other spectrometers of similar type is given.

Neutron scattering simulation in a time-of-flight spectrometer using a Monte Carlo method

The neutron scattering in a time-of-flight (TOF) spectrometer has been studied using a Monte Carlo method. The program has been written so that any neutron TOF spectrometer can be introduced. The code is applied in order to obtain the transfer function of the cold-neutron spectrometer which operates in the CAMEN centre at San Piero a Grado, Pisa. A quasi-elastic scattering simulation is also presented.

Neutron Diffraction Utilizing the T-O-F Method

Characteristic features of the TOF (time of flight) neutron diffraction are summarized. In this method, i) all the reciproal points on the rod passing through the origin in the reciprocal space can be scanned by each burst of white neutrons, ii) it is easy to measure high index reflections at the large scattering angle, iii) each reflection is not affected by the higher-order harmonics, and iv) it is easy to measure the physical properties depending on the neutron wavelength.The pulse neutron generator as well as the data acquisition system in the Laboratory of Naclear Science of Tohoku University is described.The TOF method seems to be very powerful if it is applied to the accurate structure analysis. The data correction methods are discussed. The TOF method is prospective to the study of transient phenomena. In this method one can apply to the crystalline sample an external field pulsed with the same frequency as the neutrons. By using this method, the transient state of the polarization reversal of the ferroelectric NaNO2 has been observed.The magnetically pulsed neutron TOF spectrometer is briefly introduced after a review of the choper history.

An associated particle 14-MeV neutron time of flight spectrometer for use with small accelerators

The 14-MeV neutron time of flight spectrometer used with a 150-keV SAMES type J accelerator at the University of Aston is described. The use of the associated particle technique to provide a zero time signal is shown to produce count rates near to that produced by klystron bunching techniques and angular resolutions at least equal to those achieved on larger accelerators. The way in which the spectrometer is used to measure the differential cross-sections for elastic and inelastic scattering of 14-MeV neutrons for 14N is described.

The total neutron cross-sections of cobalt, silver, iodine, aluminium, nickel and gallium between 1 eV and 5 keV

This paper presents experimental results of total neutron cross-section measurements made with a neutron time of flight spectrometer at the Atomic Energy Research Establishment, Harwell. Six elements, Co, Ag, I, Al, Ni and Ga, have so far been studied over the range of neutron energies from 1 eV to 5 keV. The main interest of the measurements lies in the use of improved resolution at the higher energies with the result that certain levels have now been more clearly resolved. The results are presented as curves showing the variation of total cross-section with neutron energy. For certain levels, the strength of the resonance is calculated. The spectrometer is briefly described and some reference made to previous work in the same field.