Energy Of Emitted Neutrons Research Articles

First measurement in a magnetic confinement fusion experiment of the H3+H3→He5+n intermediate two-body resonant reaction

We report on the first experimental measurements made at a magnetic confinement fusion device of the tritium(T)-tritium(T) reaction T+T→He4+2n indicating the presence of the intermediate two-body resonant reaction T+T→He5+n. During the second deuterium-tritium campaign (DTE2) at the Joint European Torus, measurements of fusion plasmas with high tritium concentrations, nT/(nT+nD)≈0.99, heated with tritium neutral beam injection, were performed using the neutron time-of-flight (TOF) spectrometer TOFOR. We detect a peak in the neutron emission TOF spectrum consistent with the two-body resonant reaction. The TT neutron emission energy spectrum is modeled using an R-matrix framework where the distributions of the most likely model parameters given our experimental TOF data are determined utilizing a Markov chain Monte Carlo approach. We compare our best estimate of the T+T neutron emission energy spectrum with results obtained at inertial confinement fusion experiments at the OMEGA facility and find a spectral shape that is consistent with the energy dependency in the neutron spectrum observed at OMEGA. Published by the American Physical Society 2024

Design and simulated performance of a high-resolution magnetic proton recoil spectrometer for deuterium–tritium neutrons

Neutron emission energy and time spectra of deuterium–tritium plasma contain abundant information about the fusion yield, ion temperature, and nuclear burn history. Magnetic recoil spectrometers have been employed in measuring time-integrated energy spectra in inertial confinement fusion (ICF) experiments. As the fusion yield increases, time-resolved neutron diagnostics is urgently desired for understanding complex fusion physics. Herein, we design a compact magnetic proton recoil (MPR) spectrometer based on a 90 degree permanent magnet. The entrance and exit of the magnet are second-order shapes to eliminate two major second-order aberrations. The energy resolution and time resolution for 14MeV neutrons achieve 97keV and 1.6ns, respectively, under the detection efficiency of 7.4×10−8cm2. A quadratic relation is found between detection efficiency and energy resolution when configurations are optimal. Monte Carlo simulations are accomplished to study the performance in measuring time-integrated energy spectra, emission time spectra, and time-resolved energy spectra, demonstrating the potential of high-resolution MPR spectrometers in future high-yield ICF experiments.

Characterization of the LUNA neutron detector array for the measurement of the 13C([formula omitted], [formula omitted])16O reaction

We introduce the LUNA neutron detector array developed for the investigation of the 13C(α, n)16O reaction towards its astrophysical s-process Gamow peak in the low-background environment of the Laboratori Nazionali del Gran Sasso (LNGS). Eighteen 3He counters are arranged in two different configurations (in a vertical and a horizontal orientation) to optimize neutron detection efficiency, target handling and target cooling over the investigated energy range Eα,lab=300−400 keV (En=2.2−2.6MeV in emitted neutron energy). As a result of the deep underground location, the passive shielding of the setup and active background suppression using pulse shape discrimination, we reached a total background rate of 1.23±0.12 counts/hour. This resulted in an improvement of two orders of magnitude over the state of the art allowing a direct measurement of the 13C(α, n)16O cross-section down to Eα,lab=300 keV. The absolute neutron detection efficiency of the setup was determined using the 51V(p,n)51Cr reaction and an AmBe radioactive source, and completed with a Geant4 simulation. We determined a (34 ± 3)% and (38 ± 3)% detection efficiency for the vertical and horizontal configurations, respectively, for En=2.4MeV neutrons.

Simulation of a rotating neutron moderator

This concept study demonstrates numerically the neutronic properties of a rotating neutron moderator, a device designed to moderate neutrons from a primary source and to emit the neutrons preferentially in a plane within a narrow energy band. The guiding principles are that a narrow energy band is achieved by cooling the moderator to cryogenic temperatures while the directionality and emitted neutron energy are attained by rotating the moderator at an appropriate angular velocity. Proof-of-principle simulations using GEANT4 demonstrate that the number of neutrons emitted at the desired energy and direction from the rotating moderator is about 60 times higher than that emitted by a static room temperature moderator of the same geometry.

Development of MC-based uncertainty estimation technique of unfolded neutron spectrum by multiple-foil activation method

Unfolding process plays an important role in neutron energy distribution measurement by means of the multiple-foil activation method. We have developed an algorithm for estimating uncertainty of resultant neutron distribution. For the demonstration of the algorithm, we have conducted an experiment to measure thick-target neutron yield (TTNY) of the C(d,n) reaction induced by 20-MeV deuterons with the multiple-foil activation method. The experiment was conducted at Cyclotron and Radioisotope Center, Tohoku University in Japan. The obtained experimental data were analyzed by the algorithm. As a result, we found that uncertainty of derived TTNY has dependency on neutron emission energy. In addition, the dependency is caused by excitation functions of activation reactions. Therefore, we found the particular reactions causing large uncertainty in TTNY. The result of present study shows that the algorithm can evaluate uncertainty and its causes.

Effect of the energy spectrum and angular momentum of pre-scission neutrons on the prediction of fission fragment angular anisotropy by the models

Effects of the various neutron emission energy spectra, as well as the influence of the angular momentum of pre-scission neutrons on theoretical predictions of fission fragment angular anisotropies for several heavy-ion induced fission systems are considered. Although theoretical calculations of angular anisotropy are very sensitive to neutron emission correction, the effects of the different values of kinetic energy of emitted neutrons derived from the various neutron emission energy spectra before reaching to the saddle point on the prediction of fission fragment angular distribution by the model are not significant and can be neglected, since these effects on angular anisotropies of fission fragments for a wide range of fissility parameters and excitation energies of compound nuclei are not more than 10%. Furthermore, the theoretical prediction of fission fragment angular anisotropy is not sensitive to the angular momentum of emitted neutrons.

Dynamics of neutron-induced fission ofU235using four-dimensional Langevin equations

Background: Langevin equations have been suggested as a key approach to the dynamical analysis of energy dissipation in excited nuclei, formed during heavy-ion fusion-fission reactions. Recently, a few researchers theoretically reported investigations of fission for light nuclei in a low excitation energy using the Langevin approach, without considering the contribution of pre- and post-scission particles and $\ensuremath{\gamma}$-ray emission.Purpose: We study the dynamical evolution of mass distribution of fission fragments, and neutron and $\ensuremath{\gamma}$-ray multiplicity for $^{236}\mathrm{U}$ as compound nuclei that are constructed after fusion of a neutron and $^{235}\mathrm{U}$.Method: Energy dissipation of the compound nucleus through fission is calculated using the Langevin dynamical approach combined with a Monte Carlo method. Also the shape of the fissioning nucleus is restricted to ``funny hills'' parametrization.Results: Fission fragment mass distribution, neutron and $\ensuremath{\gamma}$-ray multiplicity, and the average kinetic energy of emitted neutrons and $\ensuremath{\gamma}$ rays at a low excitation energy are calculated using a dynamical model, based on the four-dimensional Langevin equations.Conclusions: The theoretical results show reasonable agreement with experimental data and the proposed dynamical model can well explain the energy dissipation in low energy induced fission.

Neutron intensity monitor with activation foil for p-Li neutron source for BNCT – Feasibility test of the concept

Proton-lithium (p-Li) reaction is being examined worldwide as a candidate nuclear production reaction for accelerator based neutron source (ABNS) for BNCT. In this reaction, the emitted neutron energy is not so high, below 1MeV, and especially in backward angles the energy is as low as about 100keV. The intensity measurement was thus known to be difficult so far. In the present study, a simple method was investigated to monitor the absolute neutron intensity of the p-Li neutron source by employing the foil activation method based on isomer production reactions in order to cover around several hundreds keV. As a result of numerical examination, it was found that 107Ag, 115In and 189Os would be feasible. Their features found out are summarized as follows: 107Ag: The most convenient foil, since the half life is short. 115In: The accuracy is the best at 0°, though it cannot be used for backward angles. And 189Os: Suitable nuclide which can be used in backward angles, though the gamma-ray energy is a little too low. These would be used for p-Li source monitoring depending on measuring purposes in real BNCT scenes.

The Prompt Fission Neutron Spectrum (PFNS) Measurement Program at LANSCE

The prompt neutron spectrum from neutron-induced fission needs to be known in designing new fast reactors, predicting criticality for safety analyses, and developing techniques for global security application. A program to measure this spectrum for neutron-induced fission of 239Pu is underway at the Los Alamos Neutron Science Center. The goal is to obtain data on the shape of the spectrum with a small uncertainty over the emitted neutron energy range of 100 keV to 12 MeV with additional data below and above this range. The incident neutron energy range will be from 0.5 to 30 MeV. The status of this program including results of initial experimental measurements is described here.

Statistical and evaporation models for the neutron emission energy spectrum in the center-of-mass system from fission fragments

Abstract The neutron emission energy spectra in the CMS (center-of-mass) frame from two compound nuclei produced by fission are studied. The neutron spectra calculated with the Hauser–Feshbach statistical model are compared with the evaporation theory, and the definition of the temperature is revisited. Using the Monte Carlo technique we average the CMS neutron spectra from many fission fragments to construct the representative CMS spectrum from both the light and heavy fragments. The CMS spectra for each fission fragment pair are also converted into the laboratory frame to calculate the total prompt fission neutron spectrum that can be observed experimentally. This is compared to measured laboratory data for thermal neutron induced fission on 235 U. We show that the Hauser–Feshbach calculation gives a different spectrum shape than the Madland–Nix model calculation.

Indirect (n,γ) cross sections of thorium cycle nuclei using the surrogate method

Indirect neutron capture ($n$,$\ensuremath{\gamma}$) cross sections have been extracted for the key thorium cycle nuclei ${}^{232}$Th, ${}^{231}$Pa, and ${}^{230}$Th using the surrogate reaction method. Final nucleus $\ensuremath{\gamma}$-decay probabilities were measured between the neutron binding energy and around 1 MeV above it using the ${}^{232}$Th(d,p)${}^{233}$Th, ${}^{232}$Th(${}^{3}$He,t)${}^{232}$Pa, and ${}^{232}$Th(${}^{3}$He,$\ensuremath{\alpha}$)${}^{231}$Th reactions in experiments with the CACTUS $\ensuremath{\gamma}$-detector array and Silicon Ring charged-particle detectors at the Oslo Cyclotron Laboratory. Because the neutron capture cross section for ${}^{232}$Th is already well known from direct measurements a comparison with these results provides a stringent test of the applicability of the surrogate method in the actinide region for indirect ($n$,$\ensuremath{\gamma}$) cross-section measurements. In addition, a new technique for correcting measured $\ensuremath{\gamma}$-ray decay probabilities below the neutron emission energy threshold is proposed and used. We find good agreement between indirect and direct ($n$,$\ensuremath{\gamma}$) cross-section measurements in the range 500 keV--1 MeV, but large discrepancies outside this range. Explanations for the observed differences are proposed.

Direct neutron spectrum measurement to validate natZr(n,2n) reaction cross-section at 14 MeV

Lithium zirconate, Li 2ZrO 3, is known as a candidate blanket material in a fusion reactor. Various neutronics benchmark experiments for zirconium have thus been carried out so far. According to the independent benchmark studies by two parties, the neutron spectrum calculations show fairly large overestimation for most evaluated nuclear data libraries. However, the reason has not yet been made clear up to now. The author's group expects it would be due to a problem of evaluation for the natZr(n,2n) reaction cross-section, because the cross-section measurement is basically not possible with the foil activation method for zirconium isotopes except for 90Zr. In the present study, two neutrons emitted from natZr(n,2n) reaction have been measured directly to investigate the reason for the above overestimation. The measurement was done with our own special technique of detecting angle-correlated neutrons by the coincidence detection technique and the pencil-beam DT neutron source of FNS, JAEA. Angle-correlated energy differential cross-sections for natZr(n,2n) reaction were successfully measured. The obtained total cross-section above the emitted neutron energy of 800 keV was fairly larger than the one evaluated in JENDL-3.3. The total cross-section of natZr(n,2n) reaction was estimated by extrapolating the spectrum down to zero energy taking into account the nuclear temperature. The estimated cross-section value with the nuclear temperature of 1 MeV, which is larger than the one adopted in JENDL-3.3, was in acceptable agreement with JENDL-3.3. It is suggested from the result that the disagreement pointed out in the previous benchmark studies may be due to inappropriate nuclear temperature used in the evaluation. Further investigation of the nuclear temperature employed in the nuclear data evaluation should thus be carried out once again.

Additional evidence of nuclear emissions during acoustic cavitation

Time spectra of neutron and sonoluminescence emissions were measured in cavitation experiments with chilled deuterated acetone. Statistically significant neutron and gamma ray emissions (with more than 25 standard deviation accuracy) were measured with a calibrated liquid-scintillation detector. The neutron and sonoluminescence emissions were found to be time correlated over the time of significant bubble cluster dynamics. The neutron emission energy was at and below 2.45 MeV and the neutron emission rate was up to ∼400<th>000 n/s. Measurements of tritium production were also performed and these data implied a neutron emission rate due to D-D fusion which agreed with what was measured. In contrast, control experiments using normal acetone did not result in statistically significant tritium activity, or neutron or gamma ray emissions. The talk will highlight significant details of the acoustic chamber design, characterization and qualification along with the nuclear data obtained.

Additional evidence of nuclear emissions during acoustic cavitation.

Time spectra of neutron and sonoluminescence emissions were measured in cavitation experiments with chilled deuterated acetone. Statistically significant neutron and gamma ray emissions were measured with a calibrated liquid-scintillation detector, and sonoluminescence emissions were measured with a photomultiplier tube. The neutron and sonoluminescence emissions were found to be time correlated over the time of significant bubble cluster dynamics. The neutron emission energy was less than 2.5 MeV and the neutron emission rate was up to approximately 4 x 10(5) n/s. Measurements of tritium production were also performed and these data implied a neutron emission rate due to D-D fusion which agreed with what was measured. In contrast, control experiments using normal acetone did not result in statistically significant tritium activity, or neutron or gamma ray emissions.

Neutron emission study of DT plasmas heated with tritium neutral beams

The neutron emission energy spectrum from deuterium–tritium fusion reactions has been measured in experiments carried out at the Joint European Torus for plasmas heated with high power neutral beam (NB) injection of tritium beams at Eb≈150 keV using a magnetic proton recoil neutron spectrometer. High quality data were obtained in which up to three spectral components due to different ion reactions could be distinguished with the help of dedicated model calculations of the fusion neutron emission based on Monte Carlo simulations. The analysis model involved neutrons from reactions of NB ions on passing and trapped orbits interacting with thermal bulk ions. Moreover, a narrow Gaussian component, due to neutrons from thermal d+t→α+n reactions, could be resolved in some cases. Results are presented and the plasma information obtained is discussed as an illustration of the capabilities of neutron emission spectroscopy diagnostics.

Simultaneous Measurement of Prompt Neutrons and Fission Fragments for 239Pu(nth,f)

The multiplicity and energy of the prompt neutrons emitted from the fission fragments for 239Pu(nth, f) were measured as functions of the fragment mass and total kinetic energy. The results were compared with those for 233U(nth, f) and with the predicted values by the multi-channel fission theory with the random neck rupture model. The measured and predicted values of the neutron multiplicity, ⟨V⟩(m*), show the saw-tooth trend and agree with each other. The total neutron multiplicity decreases linearly with increasing total kinetic energy resulting in —d⟨TKE⟩/d⟨Vtot⟩=16.5±0.4MeV/neutron. The slope of the neutron multiplicity vs. the total kinetic energy, —d⟨V⟩/d⟨TKE⟩, was plotted against the fragment mass. Its shape agrees with that for 233U(nth, f). The average neutron emission energy, ⟨η⟩(m*), follows a bell shape about the symmetric fission accompanying higher values for very asymmetric fissions and agrees with that for 233U (nth, f). The total excitation energy (TXE)(m*) was determined by two manners: (1) neutron data and (2) Qmax—⟨TKE⟩. Both results satisfactorily agree with each other as the case of 233U( nth, f), and thereby the present derivation of ⟨TKE⟩ from the neutron data is confirned.

Measurement of Neutron-Production Double-Differential Cross Sections for Nuclear Spallation Reaction Induced by 0.8, 1.5 and 3.0 GeV Protons

Neutron-production double-differential cross sections were measured for the spallation reaction induced by 0.8, 1.5 and 3.0GeV protons on C, Al, Fe, In and Pb targets. The experiments were performed by time-of-flight technique with a typical flight path length of 1 m, and the cross sections were obtained with energy resolutions better than 8% at neutron energies below 100MeV. The experimental data were compared with the results of calculation codes based on an intranuclear-cascade-evaporation model. Adoption of the in-medium effect on nucleon-nucleon cross section in the cascade calculation improves the agreement between the calculated results and experimental data particularly in the case of 0.8-GeV proton incidence. For protons above 1GeV, however, the calculations typically twice overestimate the cross sections in the emitted neutron energy region of 10 to 30MeV.

Measurement of Neutron-Production Double-Differential Cross Sections for Nuclear Spallation Reaction Induced by 0.8, 1.5 and 3.0 GeV Protons.

Neutron-production double-differential cross sections were measured for the spallation reaction induced by 0.8, 1.5 and 3.0GeV protons on C, Al, Fe, In and Pb targets. The experiments were performed by time-of-flight technique with a typical flight path length of 1 m, and the cross sections were obtained with energy resolutions better than 8% at neutron energies below 100MeV. The experimental data were compared with the results of calculation codes based on an intranuclear-cascade-evaporation model. Adoption of the in-medium effect on nucleon-nucleon cross section in the cascade calculation improves the agreement between the calculated results and experimental data particularly in the case of 0.8-GeV proton incidence. For protons above 1GeV, however, the calculations typically twice overestimate the cross sections in the emitted neutron energy region of 10 to 30MeV.

Neutron emission spectra obtained by a double neutron-gamma discrimination technique

A technique to obtain neutron emission energy spectra above 2 MeV from (x,n) nuclear reactions using NE-213 liquid scintillator and a pulsed accelerator was investigated. After selection of the neutron light pulses both by pulse shape discrimination and time correlation with the cyclotron microstructure pulses, the light output spectrum is unfolded to yield the energy spectrum. Neutron background, flight paths, beam current pulse time resolution and time uncorrelated gamma-ray light pulses are discussed. It is concluded that it is feasible with this technique to obtain double differential neutron emission spectra to measure nuclear level densities.

Neutron emission cross section measurements with a 14 MeV neutron generator

The PINSTECH 14 MeV Neutron Generator Facility has been used for the measurements of double differential neutron emission cross sections of Al, Cu and Pb in the emitted neutron energy range of 3–14 MeV and in the 30°–130° range. Integrated neutron emission cross sections are given and compared with previously reported values.