Spallation Neutron Research Articles

Neutron Irradiation Testing and Monte Carlo Simulation of a Xilinx Zynq-7000 System on Chip

The reliability of nanoscale electronic systems is important in various applications. However, they are becoming increasingly vulnerable to atmospheric neutrons. This research conducted spallation neutron irradiations on a Xilinx Zynq-7000 system on a chip using the China Spallation Neutron Source. The results were analyzed in combination with a Monte Carlo simulation to explore the impact of atmospheric neutrons on the single event effects of the target system on chip. Meanwhile, the contribution of thermal neutrons to the chip’s single event effect susceptibility was also assessed. It was found that absorbing thermal neutrons with a 2 mm Cd sheet can protect against the single event effect on the system on the chip by about 44.4%. The effects of B and Hf elements, inside the device, on a single event effect of the Xilinx Zynq-7000 system on chip were evaluated too. Additionally, it was discovered that 10B interacting with thermal neutrons was the primary cause of the thermal neutron-induced single event effect in the system on chip. Although Hf has a high neutron capture cross section, its presence does not significantly affect the sensitivity to single event effects. However, during atmospheric neutron irradiation, the presence of Hf increases the possibility of depositing the total dose in the tested chip.

Study on the failure rate of high-power thyristors irradiated by artificial neutron irradiation under different DC bias voltages

High-voltage semiconductor devices such as thyristors, due to the high voltage applied, when encountering atmospheric neutrons in the operating state, may appear single event burnout due to charge multiplication in high-altitude areas. The atmospheric neutron radiation in high-altitude areas can cause damage and interference to semiconductor devices, which seriously threatens their safe operation. However, there is little research on the influence of atmospheric neutron irradiation on the operating life of high-voltage DC transmission system thyristors in high-altitude areas. Therefore, in this paper, the neutron beam of the Atmospheric Neutron Irradiation Spectrometer (ANIS) of China Spallation Neutron Source (CSNS) was used to irradiate the high-power thyristors. The failure rates of different applied voltages under 6.74 × 106 n/cm2/s neutron flux irradiation and the leakage current changes during irradiation were obtained. The failure rate applied voltage relationship curve obtained from the artificial neutron irradiation experiment was converted to the corresponding value in Yangbajing area, China. Through the results of the artificial neutron accelerated irradiation experiment, the thyristor failure rate-voltage formula in different areas can be more accurately estimated. In this way, the reasonable working voltage can be determined according to the operating life demand of the thyristor, and determine the thyristor configuration scheme of the design of the converter station. In addition, it is found that the leakage current of thyristor increases with the increase of neutron irradiation time, which may eventually lead to the degradation of thyristor performance and affect its reliability in the DC transmission system.

Measurement of the Tb159(n,γ) cross section at the CSNS Back-n facility

The stellar ($n,\ensuremath{\gamma}$) cross section data for the mass numbers around $A\ensuremath{\approx}160$ are of key importance to nucleosynthesis in the main component of the slow neutron capture process, which occurs in the thermally pulsing asymptotic giant branch (TP-AGB). The new measurement of ($n,\ensuremath{\gamma}$) cross sections for $^{159}\mathrm{Tb}$ was performed using the ${\mathrm{C}}_{6}{\mathrm{D}}_{6}$ detector system at the back streaming white neutron beam line (Back-n) of the China spallation neutron source with neutron energies ranging from 1 eV to 1 MeV. Experimental resonance capture kernels are reported up to 1.2 keV neutron energy with this capture measurement. Maxwellian-averaged cross sections (MACS) are derived from the measured $^{159}\mathrm{Tb}(n,\ensuremath{\gamma})$ cross sections at $kT=5$--100 keV and are in good agreement with the recommended data of KADoNiS-v0.3 and JEFF-3.3, while KADoNiS-v1.0 and ENDF-VIII.0 significantly overestimate the present MACS up to $40%$ and $20%$, respectively. A sensitive test of the $s$-process nucleosynthesis is also performed with the stellar evolution code mesa. Significant changes in abundances around $A\ensuremath{\approx}160$ are observed between the ENDF/B-VIII.0 and present measured rate of $^{159}\mathrm{Tb}(n,\ensuremath{\gamma})^{160}\mathrm{Tb}$ in the mesa simulation.

POWTEX visits POWGEN.

The high-intensity time-of-flight (TOF) neutron diffractometer POWTEX for powder and texture analysis is currently being built prior to operation in the eastern guide hall of the research reactor FRM II at Garching close to Munich, Germany. Because of the world-wide 3He crisis in 2009, the authors promptly initiated the development of 3He-free detector alternatives that are tailor-made for the requirements of large-area diffractometers. Herein is reported the 2017 enterprise to operate one mounting unit of the final POWTEX detector on the neutron powder diffractometer POWGEN at the Spallation Neutron Source located at Oak Ridge National Laboratory, USA. As a result, presented here are the first angular- and wavelength-dependent data from the POWTEX detector, unfortunately damaged by a 50g shock but still operating, as well as the efforts made both to characterize the transport damage and to successfully recalibrate the voxel positions in order to yield nonetheless reliable measurements. Also described is the current data reduction process using the PowderReduceP2D algorithm implemented in Mantid [Arnold et al. (2014). Nucl. Instrum. Methods Phys. Res. A, 764, 156-166]. The final part of the data treatment chain, namely a novel multi-dimensional refinement using a modified version of the GSAS-II software suite [Toby & Von Dreele (2013). J. Appl. Cryst.46, 544-549], is compared with a standard data treatment of the same event data conventionally reduced as TOF diffraction patterns and refined with the unmodified version of GSAS-II. This involves both determining the instrumental resolution parameters using POWGEN's powdered diamond standard sample and the refinement of a friendly-user sample, BaZn(NCN)2. Although each structural parameter on its own looks similar upon comparing the conventional (1D) and multi-dimensional (2D) treatments, also in terms of precision, a closer view shows small but possibly significant differences. For example, the somewhat suspicious proximity of the a and b lattice parameters of BaZn(NCN)2 crystallizing in Pbca as resulting from the 1D refinement (0.008 Å) is five times less pronounced in the 2D refinement (0.038 Å). Similar features are found when comparing bond lengths and bond angles, e.g. the two N-C-N units are less differently bent in the 1D results (173 and 175°) than in the 2D results (167 and 173°). The results are of importance not only for POWTEX but also for other neutron TOF diffractometers with large-area detectors, like POWGEN at the SNS or the future DREAM beamline at the European Spallation Source.

Terrestrial neutron induced failure rate measurement of SiC MOSFETs using China spallation neutron source

The atmospheric neutron induced single event burnout (SEB) is observed for SiC MOSFETs by conducting irradiation at China Spallation Neutron Source (CSNS) with maximum energy close to 1.6 GeV. The failure is manifested as a sudden loss of voltage blocking ability during irradiation and a melting region is observed for the device with SEB. The SEB failure rates of SiC MOSFETs are calculated based on the experimental results. It shows that the failure rates increase exponentially with operating voltages. The measured failure rates are consistent with the results obtained at the other spallation neutron sources, which proves that the neutron beam line at CSNS is suitable for SEB testing. The information of the secondary ions produced by neutron is obtained through Monte Carlo simulations and the contributors to SEB are analyzed. A simulation method is also applied to calculate SEB failure rate by considering ionization energy deposition of secondary ions in the sensitive region of SiC devices. The simulated failure rates are also consistent with the experimental results.

The multifunctional neutron imaging system at GPPD: Design, principles and applications

A multifunctional neutron imaging system (MNIS) has been built recently on the day-one instrument general purpose powder diffractometer (GPPD) at the China Spallation Neutron Source (CSNS). The sample position of MNIS is located three meters downstream of the diffraction sample position to maintain good imaging performance without changing the existing layout. MNIS can accommodate several significant neutron imaging technologies, including two-dimensional neutron radiation, three-dimensional computer tomography, neutron Talbot–Lau grating interferometer, and Bragg edge neutron imaging. The system has a largest field of view (FOV) of 6 × 6 cm2 and a best spatial resolution of 25μm by changing the magnification of the optical lens. The wavelength resolution is better than 0.2%. Additionally, MNIS serves as an initial validation for Energy-Resolved Neutron Imaging instrument (ERNI), a dedicated neutron imaging instrument currently under construction at CSNS.

Early-Stage Radiation Safety Analysis for the Spallation Neutron Source Second Target Station Bunker Operations

The Second Target Station project at Oak Ridge National Laboratory will develop a cold neutron source to meet growing experimental needs. This paper describes calculations of the residual dose rates associated with the monolith shield plug and the beamline bunker, two key conventional operations and radiation safety features. While neutron production is active, the instrument hall outside the bunker must be generally accessible with dose rates of less than 0.25 mrem/h. When neutron production is halted, the bunker must be accessible for hands-on maintenance operations. These two requirements form the cause for the assessments reported herein of residual dose rates caused by the monolith shield plug and residual dose rates in the bunker. The monolith shield plug was shown to not produce significant dose rates inside the bunker after a 20-year lifetime, and the residual dose rates inside the bunker for the case of an operating beamline were shown to reasonably allow for hands-on maintenance. These calculations are based on preliminary design models of the relevant systems. Additionally, an example showing the significance of considering neutron supermirror physics in transport calculations that track nuclide production and destruction rates to produce gamma sources for residual dose rate calculations is included. The example shows that if neutron supermirror physics is not considered, dose rate fields may be significantly underpredicted.

Glueballs at physical pion mass* *Supported by the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34030300, XDPB15), the National Key Research and Development Program of China (2020YFA0406400), and the National Natural Science Foundation of China (NNSFC) under Grants ( 11935017, 12070131001) (CRC 110 by DFG and NNSFC). The computations were performed on the CAS ORISE computing environment, the

Glueballs are investigated through gluonic operators on two RBC/UKQCD gauge ensembles at the physical pion mass. The statistical errors of glueball correlation functions are considerably reduced through the cluster decomposition error reduction (CDER) method. The Bethe-Salpeter wave functions are obtained for the scalar, tensor, and pseudoscalar glueballs by using spatially extended glueball operators defined through the gauge potential in the Coulomb gauge. These wave functions exhibit similar features of non-relativistic two-gluon systems and are used to optimize the signals of the related correlation functions at the early time regions, where the ground state masses are extracted. These masses are close to those from the quenched approximation and indicate the possible existence of glueballs at the physical point. The resonance feature of glueballs and the mixing with conventional mesons and multi-hadron systems should be considered in a more systematic lattice study.

Longitudinal bunch profile measurement of operational H− beam using laser wire and virtual slit

We propose and demonstrate a nonintrusive diagnostic technique for measuring longitudinal bunch profiles of an operational high-power hydrogen ion (${\mathrm{H}}^{\ensuremath{-}}$) beam in the Spallation Neutron Source (SNS) linear accelerator at Oak Ridge National Laboratory (ORNL). The technique consists of a laser wire formed by a picosecond pulsed laser beam and a virtual slit created by controlling the magnetic field of the electron detector. The virtual slit eliminates the influence of the transverse beam profile and size on the longitudinal bunch profile measurement. The effectiveness of the diagnostics is investigated first in numerical simulations followed by experimental demonstrations performed on the neutron production (1.4 MW on target) ${\mathrm{H}}^{\ensuremath{-}}$ beam at the SNS superconducting linac. The results from the present measurement method are verified by an independent measurement approach.

Measurement of the relative neutron sensitivity curve of a LaBr3(Ce) scintillator based on the CSNS Back-n white neutron source

A scintillator detector consisting of a LaBr3(Ce) (0.5%) scintillator, a photomultiplier tube (PMT), and an oscilloscope were used to study the neutron sensitivities of the LaBr3(Ce) scintillator at the China Spallation Neutron Source (CSNS) Back-n white neutron source in the double-bunch and single-bunch operation modes, respectively. Under the two operational modes, the relative neutron sensitivity curves of the LaBr3(Ce) scintillator in the energy regions of 1–20 MeV and 0.5–20 MeV were obtained for the first time. In the energy range of 1–20 MeV, the two curves were nearly identical. However the relative neutron sensitivity uncertainties of the double-bunch experiment were higher than those of the single-bunch experiment. The above results indicated that the single-bunch experiment’s neutron sensitivity curve has a lower minimum measurable energy than the double-bunch experiment. Above the minimum measurable energy of the double-bunch experiment, there is little difference between the measured relative neutron sensitivity curves of the single-bunch and double-bunch experiments of the LaBr3(Ce) scintillator and those of other scintillators with a similar neutron response signal intensity.

Special Topic on “Initial instruments at the Second Target Station of the Spallation Neutron Source”

Special Topic on “Initial instruments at the Second Target Station of the Spallation Neutron Source”

Erratum: Development of a Spin-Exchange Optical Pumping-Based Polarized 3He System at the China Spallation Neutron Source (CSNS) [Chin. Phys. Lett. 38, 092801 (2021)

Abstract

Conceptual Polarization Setup at CENTAUR, the SANS/WANS Instrument at the Second Target Station of SNS

CENTAUR is a multifunctional general purpose small-angle and wide-angle neutron scattering instrument with diffraction and spectroscopic capability in the future Second Target Station at the Spallation Neutron Source of the Oak Ridge National Laboratory. To fill a gap in neutron polarization capability, the instrument will be designed to provide polarization analysis. Here we present the conceptual polarization setup at CENTAUR, as well as the Spin Echo Modulated Small-Angle Neutron Scattering setup which will further expand the length scale covered by the instrument.

The light charged particle detector array at the CSNS Back-n white neutron source

The Back-n white neutron source at the China Spallation Neutron Source (CSNS) provides neutrons in the continuous energy region from 0.5 eV to 200 MeV. A spectrometer named Light charged Particle Detector Array (LPDA) is designed for the study of (n, lcp) reactions at Back-n. The main detector of the LPDA spectrometer, a 16-unit ΔE-ΔE-E telescope array, is composed of two arrays of 8-unit ΔE-ΔE-E telescope. Each telescope unit consists of a Low-Pressure Multi-Wire Proportional Chamber (LPMWPC), a Si-PIN detector, and a CsI(Tl) scintillator detector. In 2021, a neutron-proton (n-p) scattering reaction cross-section measurement experiment was accomplished as the first experiment of the telescope array. Protons can be clearly identified in the ΔE-E spectrum (LPMWPC + Si-PIN) and the ΔE-E spectrum (Si-PIN + CsI(Tl)). Cross sections of the n-p scattering reaction in the neutron energy range of several MeV are extracted. The ΔE-E method also provides new measurement opportunities for many-body neutron induced light charged-particle emission reactions.

Design and verification of a high-gradient and high-power 2nd harmonic cavity for the China Spallation Neutron Source upgrade project

Here, we report our recent progress in the design, fluid thermodynamics simulation, and high-power test of the2nd harmonic cavity for the China Spallation Neutron Source Phase II. A high-performance and large-size magnetic alloy (MA) core was developed as the load material for the radiofrequency cavity to achieve a high gradient of 40 kV/m. The water-cooling structure and cooling efficiency were studied and improved through numerical analysis and thermal experiments. The long-term stability of the cavity, especially the waterproofness of the MA cores with high heat load, was verified by high power tests.

Development of polarized neutron techniques at the China Spallation Neutron Source

In this article, the ongoing development progress of the polarized neutron technique developments at the China Spallation Neutron Source (CSNS) is presented. The general goal of establishing polarized neutron capability in parallel to CSNS beamline construction is also explained. The key instrument development projects of developing the Spin-Exchange Optical Pumping (SEOP) 3He systems, polarized neutron devices, and their application on neutron beamlines are demonstrated. Performance parameters of the developed techniques are also discussed.

Over 7200 hours commissioning of RF-driven negative hydrogen ion source developed at CSNS

The China Spallation Neutron Source project Phase-II (CSNS-II) aims to deliver a proton beam of 500 kW on the tungsten target. To accomplish this goal, an RF-driven negative hydrogen ion source was developed to replace the penning ion source used in CSNS-I. The RF-driven ion source has been put into commissioning on CSNS accelerator since September 8th, 2021. And it was shut down on July 26th, 2022, together with the whole accelerator for the annual maintenance in summer. In this run cycle it has accumulated service time of over 7200 hours without major maintenance. The availability of the ion source is above 99.99%, except for one or two sparks per day of the 50 kV high voltage platform, each spark causing 1 second trip of the accelerator. The RF-driven ion source has an external antenna winding around a silicon nitride plasma chamber, which is quite robust in high duty-factor operation. In this paper, we present the structure of the ion source, the improvements over other ion sources, and the issues met in the commissioning.

An unstructured mesh based neutronics optimization workflow

We have developed a fully automated workflow to optimize the neutronics performance of the Second Target Station (STS) at the Oak Ridge National Laboratory’s Spallation Neutron Source. The optimization workflow starts with the parametrized solid CAD engineering models and converts them into the unstructured mesh (UM) models for the neutronics calculations with MCNP6.2. Calculations are executed and their results are loaded into the Dakota optimization toolkit. Dakota analyzes the results and proposes new geometry parameters for the next design iteration. The cycle repeats until the optimal parameters are found. The automated CAD to MCNP conversion, the use of high-fidelity UM models, and the use of modern optimizer are the key elements that advance the entire optimization workflow in comparison with the original workflow. The original workflow was based on a simplified constructive solid geometry (CSG) modeling with MCNPX, mcnp_pstudy tool, and an in-house optimizer. To demonstrate the new workflow, we present a case of neutronics optimization of the moderator–reflector assembly (MRA). Apart from the MRA, the workflow can optimize other major STS components, such as the spallation target, neutron beamlines, radiation shielding, and various accelerator components. Importantly, the new workflow opens the door to the advanced multi-physics multi-parameter optimization and has the potential for use in other nuclear physics and accelerator applications.

Design and performance characterization of the time-of-flight liquid neutron reflectometer at the China spallation neutron source

The full design of a liquid neutron reflectometer for China spallation neutron source is reported. The horizontal sample geometry enables studies on both solid and liquid samples. A neutron beam with a wavelength range from 1 to 10 Å and neutron flux intensity of 4 × 107 n/cm2/s was optimized for the classical specular reflection. A multi-blade detector with high detection efficiency and a high neutron counting rate was used to ensure the performance of neutron detection. Data acquisition and reduction routines were demonstrated to confirm the reliability of the measurements. The design and algorithms developed in this study pave the way for the future construction of liquid reflectometry for high-performance neutron scattering measurements.

Research on the application of pulse shape discrimination method in (n, lcp) reaction cross-section measurements

The China Spallation Neutron Source Back-n white neutron source supplies neutrons with a wide energy range for nuclear data measurements and nuclear techniques. In cross-section measurements of neutron induced light charged-particle emission (n, lcp) reactions at Back-n, the identification of charged particles are usually achieved with the ΔE-E method or a two-dimensional spectrum of the signal amplitude of the particles deposited in the detector and the corresponding neutron energies derived from the time of flight, called amplitude-En method. Nevertheless, a deficiency still exists in the measurement range and the identification performance with these methods. The pulse shape discrimination (PSD) method with a silicon detector is supposed to be a supplement to the amplitude-En and ΔE-E methods. With silicon detectors, experiments have been performed to compare the performance of the amplitude-En and the PSD methods. The PSD method shows a good performance in identifying light charged particles in the MeV neutron energy region. Alphas and tritons emitted from 6Li(n, t) reaction can be identified with the low energy threshold around 2.5 MeV. This provides an effective method for the cross-section measurement of (n, lcp) reactions at Back-n.