Neutron Emission Research Articles

Gypsum and quartz specimens in compression failure: Fracto-emissions and related stoichiometric balances

Extensive experimental investigations were conducted on Gypsum and Quartz compression specimens of different sizes. They were brought to complete failure, showing two different failure modalities: (1) Very brittle loading drop for micro-crystalline Gypsum and Quartz; (2) Stable strain-softening behaviour for macro-crystalline Gypsum. All the tested specimens emitted acoustic and electromagnetic waves and the single events cumulated up to the peak load. On the other hand, neutron emissions were evident only for the largest specimens. The significant chemical composition changes occurring on the fracture surfaces are consistently explained by the assumption of Low-energy Nuclear Reactions (LENR), both fusion and fission. It is the first time that fusion reactions emerge from crushing tests, whereas fission reactions have already consistently explained the results related to other materials like the iron-rich natural rocks. Therefore, a correlation emerges between fusion nuclear reactions and strain-softening mechanical behaviour, as well as between fission nuclear reactions and brittle mechanical behaviour.

Non-destructive analysis of spent fuel samples using a gamma-blind fast neutron detector

This paper presents the capabilities of a measurement setup built to measure the axial distribution of neutron emitters in spent fuel pins from nuclear power plants. The measurement system uses a custom gamma-blind detector based on a novel combination of silver-activated zinc sulfide scintillators and wavelength-shifting fibers for direct fast neutron detection while having a low sensitivity for gamma rays even in the strong gamma fields present during the inspection of spent fuel. A collimator with an opening of 2 cm is used to create axial resolved information. The system has been tested using UOX and MOX spent fuel samples with burn-ups between 40 and 90 GWd/t and with long cooling times (20–25 y). Measurements of the total neutron emission of the samples relative to each other achieved a 1σ uncertainty of 2%. Absolute values were measured by comparison with a calibrated 252Cf source, achieving a 1σ uncertainty of 5%. The neutron emission of the samples was previously measured using a thermal neutron detector. The results from that previous measurement agree within 2.5σ with the new results. The reconstruction of the axial neutron emission profile was performed for one of the samples. Based on the edges of the sample, the resolution of the reconstruction was estimated to be 2.5 cm. These promising results are the basis for future development of the measurement setup which should not only improve the accuracy of the results but also enable the measurement of spent fuel with much shorter cooling times of ∼1 y.

Regressive Tomography and Direct Regressive Reconstruction: A Research Note

Two related methods for inverting line-integrated measurements are presented in this research paper in the context of the recent deuterium-tritium experiments in the JET tokamak. Unlike traditional methods of tomography, these methods rely on making use of a family of model distributions defining a functional space within which a solution of the inversion problem is expected to exist. This is a stronger assumption than that underlying traditional methods of tomography and requires that suitable models for the expected distribution be available. In return, the methods offer computationally efficient and robust reconstructions. Regressive tomography, as applied to the data from the JET neutron cameras, involves calculating a set of 100 or more two-dimensional (2-D) neutron emission distributions in a representative variety of conditions using the ASCOT and AFSI Monte Carlo fast ion orbit and fusion reaction codes. The distributions are line integrated to represent synthetic measurements from the 19 channels of this two-camera system. An inversion matrix is then obtained by regressing the 2-D distributions corresponding to each of the voxels against these line integrals. The second method, direct regressive reconstruction, bypasses the calculation of line integrals altogether by regressing experimental camera data against calculated neutron emission distributions. This method does not require the cameras to be calibrated, not even relatively between channels. The inversion matrices obtained by any of the two methods can then be used to provide neutron emission profiles for which ASCOT/AFSI calculations are not available.

Design of pedestrian radiation portal monitor with NaIL dual-particle detector

Radiation portal monitors (RPMs) are operated in various places such as airports, ports, and nuclear facilities to detect radioactive materials illegally possessed by pedestrians. However, most commercial RPMs can measure only gamma-rays; hence, separate neutron detectors need to be applied when neutron measurement is required. Radioactive materials including special nuclear materials (SNMs) have a high gamma-ray emission rate, but they can be concealed because gamma-rays are easily shielded. By contrast, although SNMs have a low neutron emission rate, it is difficult to shield them due to secondary radiation emission when neutrons are captured. Additionally, neutron-emitting materials can be easily detected due to the low background level of neutrons. So, measurement of both gamma-rays and neutrons is beneficial for improved detection probability of radioactive materials (i.e., SNMs). In the present study, by Monte Carlo (MC) simulations, we designed a dual-particle detection system incorporating NaIL scintillators for application as a pedestrian RPM that can detect neutrons and gamma-rays simultaneously. The simulation model was verified by experiments with a 2 inch × 2 inch cylindrical NaIL detector using gamma-ray and neutron calibration sources. The designed system is expected to offer improved detection performance over that of a commercial system, even with its smaller dimensions.

Development of transient Monte Carlo in a fissile system with β-delayed emission from individual precursors using modified open source code OpenMC(TD)

In deterministic and Monte Carlo transport codes, β-delayed emission is included using a group structure where all of the precursors are grouped together in 6 groups or families, but given the increase in computational power, nowadays there is no reason to keep this structure. Furthermore, there have been recent efforts to compile and evaluate all the available β-delayed neutron emission data and to measure new and improved data on individual precursors. In order to be able to perform a transient Monte Carlo simulation, data from individual precursors needs to be implemented in a transport code. This work is the first step towards the development of a tool to explore the effect of individual precursors in a fissile system. In concrete, individual precursor data is included by expanding the capabilities of the open source Monte Carlo code OpenMC. In the modified code – named Time Dependent OpenMC or OpenMC(TD)– time dependency related to β-delayed neutron emission was handled by using forced decay of precursors and combing of the particle population. The data for continuous energy neutron cross-sections was taken from JEFF-3.1.1 library. Regarding the data needed to include the individual precursors, cumulative yields were taken from JEFF-3.1.1 and delayed neutron emission probabilities and delayed neutron spectra were taken from ENDF-B/VIII.0. OpenMC(TD) was tested in a monoenergetic system, an energy dependent unmoderated system where the precursors were taken individually or in a group structure, and in a light-water moderated energy dependent system, using 6-groups, 50 and 40 individual precursors. Neutron flux as a function of time was obtained for each of the systems studied. These results show the potential of OpenMC(TD) as a tool to study the impact of individual precursor data on fissile systems, thus motivating further research to simulate more complex fissile systems.

Potential uses of different sustainable concrete mixtures in gamma and neutrons shielding purposes

Gamma and neutron radiation causes severe effects on human health; many nuclear accidents led to radiation leakage affecting the environment and human health during the last century. Therefore, a great need for radiation shielding is now in demand. Concrete is the main constituent in any shielding design. This research investigates the mechanical properties of traditional concrete mixtures incorporating ilmenite or tourmaline aggregates. The crushing value of tested aggregates, along with the compressive and tensile behavior of concrete samples, was evaluated. Test results showed a general reduction in compressive and tensile strength of ilmenite concrete compared to conventional concrete by up to 18.2% and 27.5%, respectively.In contrast, tourmaline concrete achieved superior compressive and tensile strength than its conventional counterpart by up to 26.23% and 23.79%, respectively. The new concrete samples (Ilmenite and Tourmaline) are used in gamma and neutrons emission attenuation. Results show high gamma attenuation for both ilmenite (23–73%) and Tourmaline (32–79%). As for neutrons, the attenuation when using ilmenite was (9–37%) and for Tourmaline (13–42%).

Probing local electron temperature and density inside a sheared flow stabilized Z-pinch using portable optical Thomson scattering.

We report the first optical Thomson scattering measurements inside a high electron temperature (≳1 keV) and moderate electron density (mid 1016 cm-3) plasma. This diagnostic has been built to provide critical plasma parameters, such as electron temperature and density, for Advanced Research Projects Agency-Energy-supported fusion-energy concepts. It uses an 8J laser at 532nm in 1.5ns to measure the high frequency feature of the Thomson scattering profile at 17 locations along the probe axis. It is able to measure electron density from 5 × 1017 cm-3 to several 1019 cm-3 and electron temperatures from tens of eV to several keV. Here, we describe the design, deployment, and analysis on the sheared flow stabilized Z-pinch machine at Zap Energy named FuZE. The probe beam is aimed at an axial distance of 20cm from the central electrode and is timed within the temporal envelope of neutron emission. The high temperature and moderate density plasmas generated on FuZE lie in an unconventional regime for Thomson scattering as they are between tokamaks and laser-produced plasmas. We described the analysis considerations in this regime, show that the electron density was below 5 × 1016 cm-3 at all times during these measurements, and present a sample shot where the inferred electron temperature varied from 167 ± 16eV to 700 ± 85eV over 1.6cm.

Calibration sources for the LEGEND-200 experiment

In the search for a monochromatic peak as the signature of neutrinoless double beta decay an excellent energy resolution and an ultra-low background around the Q-value of the decay are essential. The LEGEND-200 experiment performs such a search with high-purity germanium detectors enriched in 76Ge immersed in liquid argon. To determine and monitor the stability of the energy scale and resolution of the germanium diodes, custom-made, low-neutron emission 228Th sources are regularly deployed in the vicinity of the crystals. Here we describe the production process of the 17 sources available for installation in the experiment, the measurements of their alpha- and gamma- activities, as well as the determination of the neutron emission rates with a low-background LiI(Eu) detector operated deep underground. With a flux of ( 4.27 ± 0.60stat ± 0.92syst) × 10-4 n / (kBq·s), approximately one order of magnitude below that of commercial sources, the neutron-induced background rate, mainly from the activation of 76Ge, is negligible compared to other background sources in LEGEND-200.

Estimation of double-differential cross-sections of 9Be(p,xn) reaction for new nuclear data library JENDL-5

Double-differential cross-sections of the 9Be(p,xn) reaction are newly evaluated based on the Wakabayashi’s function and neutronics analysis up to 12 MeV for a new nuclear data library, JENDL-5. We devoted our efforts especially to the re-optimization of the absolute cross-sections and the interpolation of the neutron energy spectra. Through the comparisons between the thick target yield measurements and Monte-Carlo simulations at different proton energies and neutron emission angles, we conclude that JENDL-5 gives the best evaluation in the world.

Post-Neutron Mass Yield Distribution in the Thermal Neutron Induced Fission of 233U

In the thermal neutron–induced fission of 233U, the cumulative and independent yields of various fission products within the mass ranges of 77 to 109 and 123 to 155 have been measured by using an off-line gamma-ray spectrometric technique. The lower yields of 86Br and 136I than usual trend indicate the formation of delayed neutron emitters 87Br and 137I. From the cumulative yields, the post-neutron mass yield distribution was obtained after applying the charge distribution correction. The data from the present and earlier work of our laboratory in the 233U(nth,f) reaction were compared with similar data of 232,235U(nth,f) and 238U(n,f) reactions to examine the effect of mass difference of the fissioning systems on the fine structure of the mass yield distribution. The mass yield distribution in the 233U(nth,f) reaction was also compared with those of 229Th(nth,f), 241Pu(nth,f), and 245Cm(nth,f) reactions to examine the effect of charge and mass difference of the fissioning systems and also to examine the different behaviors of standard I and standard II asymmetric modes of fission.

Operator Protection from Gamma Rays Using Ordinary Glass and Glass Doped with Nanoparticles

Radiation-shielding glass is utilized in a few applications such as nuclear medicine, (PET) scans, x-rays, or treatment use. Nuclear reactors additionally require shielding from radiation types such as gamma, x-rays, and neutron emissions. Radiation-shielding glass is additionally utilized in the exploration and industry fields, for example, in cyclotron support testing of non-destructive materials, and the improvement of airport x-ray machines. Notwithstanding, radiation-shielding glass utilizes space innovation to protect both the astronauts and tools from cosmic rays. Nanoparticles have been involved recently in those applications. Several simulations using MCNP 6 have been used in this study to compare a variety of conventional and nanoparticle-doped glass, including silicate glass (containing BiO or PbO), BZBB5, and glass containing nanoparticles, including Na2Si3O7/Ag, Al2H2Na2O13Si4/HgO, and lead borate glass containing ZrO2 to detect shielding properties for operators at different gamma energies. We investigated the percentage of transmitted photons, linear attenuation coefficient, half-value layer, and mean free path for the selected glass. Several shielding properties were not significantly different between the simulated results and the theoretical data available commercially. Based on the results, those parameters depend on the glass material due to their densities and atomic number. It has been found that 70 Bismuth(III) oxide:30 Silica has the best shield properties from gamma rays, such as a low percentage of transmitted photons, low HVL, and low MFP, which is due to its high density and atomic number.

In-beam superfluid-helium ultracold neutron source for the ESS

This paper discusses design principles and possible performances of an “in-beam” ultracold neutron (UCN) source for the European Spallation Source (ESS). The key components of the proposed neutron delivery system are nested-mirror optics (NMO), which image the bright neutron emission surface of the large liquid-deuterium moderator, studied within the HighNESS project, onto a remotely located superfluid-helium converter. Bandpass supermirrors, with optional polarization capability, enable the selective transport of those neutrons that are most effective for UCN production, exploiting the single-phonon conversion process that is possible for neutrons having wavelengths within a narrow range centered on 8.9 A ˚. NMO are capable of extracting and refocusing neutrons with small transport losses under the large solid angle available at the ESS Large Beam Port (LBP), allowing the converter to be placed far away from the high-radiation area in the ESS shielding bunker, where the source stays accessible for trouble-shooting while facilitating a low-background environment for nearby UCN experiments. Various configurations of the beam and converter are possible, including a large-volume converter – with or without a magnetic reflector – for a large total UCN production rate, or a beam focused onto a small converter for highest possible UCN density. The source performances estimated by first simulations of a baseline version presented in this paper, including a saturated UCN density on the order of 10 5 cm − 3 , motivate further study and the development of NMO beyond the first prototypes that have been recently investigated experimentally.

Measurement of the delayed-neutron yield in the thermal neutron induced fission of 239Pu

This article presents an experimental effort to provide high-quality data to improve the evaluation of the 239Pu delayed neutron yield in the thermal energy range. The set-up is composed of a long counter with sixteen 3He tubes, a fast shutter system to produce irradiation cycles with short rising/falling times, and a miniature fission chamber containing 114μg of 239Pu. The whole system was installed in the PF1B experimental zone of the Institut Laue-Langevin, which provides a cold neutron beam. The repetition of irradiation/decay cycles enables to saturate the delayed neutron precursors and to measure their yield through the observed activity, shortly after the beam-stop. The innovation of our measurement technique relies on the clear distinction between prompt and delayed neutron counting, thanks to boron absorbers, without the necessity to move the sample. In such a way, it is possible to normalize the counting of delayed neutron emission to the one of total neutron emission, based on the well-known value of the prompt neutron multiplicity. The present work provides a delayed neutron yield value of vd = 0.642(5)%. The latter is in 1σ agreement with the IAEA recommendation of 0.628(38)%, with a strongly reduced uncertainty thanks to our normalization technique.

A Problem in the Statistical Description of Beta-Delayed Neutron Emission

Reaction measurements on fission products are being planned at both Argonne National Lab and at the Facility for Rare Isotope Beams. These indirect experiments produce specific short-lived nuclei via beta decay, and the subsequent neutron and gamma emission are studied. Some initial experiments found a surprising overabundance of gamma emission, which theory has yet to explain. To remedy this, we are developing an integrated nuclear data workflow that connects advanced nuclear shell model codes for describing the beta decay with a contemporary nuclear reaction model code.

Results of the 244Cm, 246Cm and 248Cm neutron-induced capture cross sections measurements at EAR1 and EAR2 of the n_TOF facility

Accurate neutron capture cross section data for minor actinides (MAs) are required to estimate the production and transmutation rates of MAs in light water reactors, critical fast reactors like Gen-IV systems, and other innovative reactor systems such as accelerator driven systems (ADS). In particular, 244Cm, 246Cm and 248Cm play a role in the transport, storage and transmutation of the nuclear waste of the current nuclear reactors, due to the contribution of these isotopes to the radiotoxicity, neutron emission, and decay heat in the spent nuclear fuel. Also, capture reactions in these Cm isotopes open the path for the formation of heavier elements. In this work, the results of the capture cross section measurement on 244Cm, 246Cm and 248Cm performed at the CERN n_TOF facility are presented. It is important to notice that the Cm samples used in the experiment at n_TOF have been used previously in an experiment at J-PARC, this experiment and the previous one done in the 70s with a nuclear explosion were the only previous capture experiments for these isotopes. At n_TOF, the capture cross section measurements of 244Cm, 246Cm and 248Cm were performed at the 20 m vertical flight path (EAR2) with three C6D6 total energy detectors. In addition, the cross section of 244Cm was measured at the 185 m flight path (EAR1) with a Total Absorption Calorimeter (TAC). The combination of measurements in EAR1 and EAR2 has contributed to controlling and reducing the systematic uncertainties in the results. The compatibility of the different measurements performed and the techniques to obtain the results are presented in this paper as well as the procedure to obtain the resonance parameters.

The Extension of the Hauser-Feshbach Fission Fragment Decay Model to Multi-chance Fission and its Application to 239Pu

The Hauser-Feshbach fission fragment decay model, HF3D, calculates the statistical decay of fission fragments through both prompt and delayed neutron and γ-ray emissions in a deterministic manner. While previously limited to the calculation of only first-chance fission, the model has recently been extended to include multi-chance fission, up to neutron incident energies of 20 MeV. The deterministic decay takes as input prescission quantities–fission probabilities, pre-fission neutron energies, and the average energy causing fission– and post-scission quantities–yields in mass, charge, total kinetic energy, spin, and parity. From those fission fragment initial conditions, the full decay is followed through both prompt and delayed particle emissions. The evaporation of the prompt neutrons and γ rays is calculated through the Hauser-Feshbach statistical theory, taking into account the competition between neutron and γ-ray emission, conserving energy, spin, and parity. The delayed emission is taken into account using time-independent calculation using decay data. This whole formulation allows for the calculation of prompt neutron and γ-ray properties, such as multiplicities and energy distributions, both independent and cumulative fission yields, and delayed neutron observables, in a consistent framework. Here, we describe the implementation of multi-chance fission into the HF3D model, and show an example of prompt and delayed quantities beyond first-chance fission, using the example of neutron-induced fission on 239Pu. This expansion represents significant progress in consistently modeling the emission of prompt and delayed particles from fissile systems.

Investigation of $$\beta ^-$$-decay half-life and delayed neutron emission with uncertainty analysis

Investigation of $$\beta ^-$$-decay half-life and delayed neutron emission with uncertainty analysis

Tomography of fast ion distribution function under neutral beam injection and ion cyclotron resonance heating on EAST

In magnetic confinement fusion devices, velocity-space tomography of fast-ion velocity distribution function is crucial for investigating fast-ion distribution and transport. In the neutral beam injection (NBI) and ion cyclotron resonance heating (ICRF) synergistic heating experiments in Experimental Advanced Superconducting Tokamak (EAST), high-energy particles with energy exceeding the particle energy in NBI are observed. Simulations of synergistic effect on fast-ion velocity distribution function given by TRANSP also show the existence of particles with energy higher than the particle energy in NBI. To investigate the behaviors of fast ion distribution and calculate the velocity distribution functions under different heating conditions, the first-order Tikhonov regularization tomographic inversion method with higher inversion accuracy is introduced by comparing various regularization techniques. The limitations of the dual-view fast-ion D<sub>α</sub> (FIDA) diagnostic measurements in velocity space are addressed by incorporating prior information such as null measurement and the known peaks and effectively mitigate the occurrence of artifacts. This method is first employed in the case of NBI heating. The NBI peak is successfully reconstructed at the expected location in velocity space, which shows significant improvement in the inversion results. In order to further validate the synergistic effect of NBI-ICRF heating and study the mechanism of fast ion distribution under synergistic heating, the combination of FIDA and neutron emission spectrometer (NES) is applied to the first-order Tikhonov regularization tomographic inversion method for enhancing the coverage of velocity space, through which the issue of artifacts in the inversion results is significantly improved, and thus the precision of the obtained fast-ion velocity distribution functions is enhanced. Based on the benefit described above, the method of combining NES diagnosis and FIDA diagnosis is used to obtain fast-ion velocity distribution functions in the NBI and ICRF synergistic heating discharge. The synergistic heating effect is manifested in the fast-ion velocity distribution. The availability of this inversion method in reconstructing fast-ion velocity distribution functions during high-performance operation of NBI-ICRF synergistic heating in the EAST experiment is confirmed. In the next-step EAST research, high performance discharge will demand more efficiency NBI and ICRF synergistic heating, the present work builds the stage for investigating the underlying mechanism of synergistic heating and the intricate behaviors associated with fast ion distribution and transport.

Characterization of Liquid Scintillator-Based CNES for Deuterium–Deuterium Neutron Emission Spectroscopy in the LHD

Characterization of Liquid Scintillator-Based CNES for Deuterium–Deuterium Neutron Emission Spectroscopy in the LHD

β-delayed neutron spectroscopy of 85,86As with MONSTER

The β-delayed neutron emission in the 85,86As β-decays has been measured at the IGISOL facility of the Accelerator Laboratory of the University of Jyväskylä (JYFL-ACCLAB). The complete β-decays have been studied with a complex setup that consists of a plastic scintillator, the MOdular Neutron time-of-flight SpectromeTER (MONSTER), and two types of γ-ray detectors—an HPGe clover and four LaBr3 crystals. The β-delayed neutron energy distributions have been determined by unfolding the TOF spectra with an innovative methodology based on the iterative Bayesian unfolding method and accurate Monte Carlo simulations.