Back-n White Neutron Source Research Articles

$$^{10}$$B-doped MCP detector developed for neutron resonance imaging at Back-n white neutron source

$$^{10}$$B-doped MCP detector developed for neutron resonance imaging at Back-n white neutron source

Measurement of the neutron total cross section of 9Be at the Back-n white neutron source of CSNS* *Supported by the National Key Research and Development Plan (2016YFA0401603), the National Natural Science Foundation of China (11675155, 11790321) and Foundation of President of China Academy of Engineering Physics (YZJJLX2016003)

The neutron total cross section data of 9Be are essential in the nuclear structure model research of light nuclei and nuclear power installations. The neutron total cross section of 9Be in the 0.3 eV−120 MeV energy region has been measured using time-of-flight and transmission methods with the Neutron Total Cross Sectional Spectrometer (NTOX) based on the multi-cell fast fission chamber at the China Spallation Neutron Source (CSNS)-Back-n white neutron source (Back-n). The fission count-neutron energy distributions of 235U and 238U without samples and with Be samples with three thicknesses were measured in the double-bunch operation mode for a beam power of 100 kW. The Bayesian method was used to eliminate the influence of the double-bunch problem on neutron measurement in the energy region above 10 keV. The neutron total cross section of 9Be results was consistent with ENDF/B-VIII.0 evaluation library data in the 0.3 eV−20 MeV energy region. In the energy ranges of 0.3 eV to 10 keV and 0.01 to 20 MeV, the deviations between our results and the evaluation results of ENDF/B-VIII.0 were within 2.5% and 15%, respectively. In the resonance energy region, the measured resonance energies in our experiment were 0.63, 0.82, and 2.8 MeV, respectively. The results showed that the total cross section uncertainties of three Be samples were within 2.2% in the energy region below 1 MeV. The total cross section uncertainty of 30 mm Be from 235U was the smallest and less than 5% in the energy region of 0.3 eV−120 MeV. The results of this experiment can provide technical support for further data analysis and related nuclear data evaluation.

SEU protection design for the prototype readout electronics of MAPS-based STCF inner tracker

The Super Tau Charm Facility (STCF) is a high-luminosity electron-positron collider experiment operating at center-of-mass energy of 2–7 GeV. Its primary goal is to explore flavor physics, CP-violations, and investigate physics beyond the Standard Model. The inner tracker (ITK) is a crucial component of the STCF tracking system, which is responsible for detecting particle hits, especially those with low momentum below 100 MeV/c. Its primary objectives include providing high detection efficiency and spatial resolution for charged particle tracks. However, the electronics of ITK is susceptible to single-event upset (SEU) caused by beam-related background. To address this, this paper presents a prototype of FPGA (Field Programmable Gate Array)-based electronics that can detect and automatically repair SEU induced soft errors in its Configuration Random Access Memory (CRAM) and whose Block Random Access Memory (BRAM) has been also subjected to commonly used hardening techniques. Importantly, the prototype's corrective operations do not result in any dead time due to hot redundancy backup. In the laboratory environment, we measured the bit error rate of the data transmission to be lower than 10-12 with a confidence level of 99.99%. Through neutron beam experiments conducted at China Spallation Neutron Source (CSNS) back-n white neutron source. We demonstrated that the readout electronics can effectively restore correct functionality and promptly rectify soft errors.

Measurement of the neutron energy response curve of 4H-SiC detector based fission target detection system at the CSNS Back-n white neutron source

The fission target detection system, which is based on U-235(or U-238)fission target and large area 4H-SiC detector, has been developed for pulsed neutron detection. However, calibration of its neutron energy response curve is challenging due to its very low detection efficiency to fast neutrons. In the past, the calibration of the neutron sensitivity for the fission target detection system was limited to using ∼ 14 MeV neutrons generated by the Cockcroft-Walton accelerator. To obtain the response function for the complete range of neutron energies, extrapolation based on neutron fission cross sections was required. In this paper, we present the calibration of its energy response at the China Spallation Neutron Source (CSNS) Back-n beam line using the time of flight method, both with double-bunch and single-bunch mode in end-station 1(with a flight path of ∼ 55 m). The SiC detector with a thin sensitive thickness of 30 μm has lower scattering background than the traditional Si-PIN detector . As a result, the energy response curve of the fission target detection system above 0.26 MeV has been successfully acquired. The spectrum of the double-bunch mode was unfolded using the Bayesian algorithm, and the results indicate that, under conditions of sufficient counts, this method can yield results similar to those obtained from the single-bunch mode. The issue of pulse height defect of SiC detector to fission fragments is discussed. This experiment confirms that our detection system of SiC+fission target has a strong signal-to-noise ratio and anti-interference capability. At the same time, it demonstrates that this device has its own advantages in measuring the energy response of low sensitivity detectors.

Design and Testing of a Prototype ASIC for the MTPC Readout at CSNS Back-n White Neutron Source

In this paper, a prototype Application Specific Integrated Circuit (ASIC) for the Multi-purpose Time Projection Chambers (MTPC) at Back-n White Neutron Source is presented. The ASIC integrates 16 readout channels and is fabricated in a 0.18 μm CMOS process. Each channel consists of a Charge Sensitive Amplifier (CSA), a Pole-Zero Cancellation (PZC), two bridged-T shapers, a baseline holder, and a fully differential output buffer. It provides selectable charge ranges of 2 pC and 10 pC, programmable peaking times from 110 ns to 1 μs, and an adjustable output common-mode voltage from 0.7 V to 1.25 V. The ASIC has already been tested and all the results meet the requirements. In the case of 100 pF input capacitance, 2 pC charge range, and 1 μs peaking time, it features a maximum Integral Non-Linearity (INL) of 0.48% and an Equivalent Noise Charge (ENC) of 0.749 fC, which makes the Signal-to-Noise Ratio (SNR) at full-scale input over 2600. In particular, a crosstalk rejection ratio of 63 dB is obtained in this prototype ASIC by using the baseline holder circuit in each channel to generate references for single-ended to differential conversion, isolating noise and crosstalk from the reference path.

Progress in measurements of fission cross sections and total cross sections at CSNS Back-n white neutron source

The neutron-induced cross sections are of great significance for the design of nuclear devices and advanced reactors for the nuclear energy production. At CSNS Back-n white neutron source, new measurements of the fission cross sections and total cross sections are performed with two sets of Day-one spectrometers based on the multi-cell fast fission ionization chamber (FIC). The neutron-induced 236,238U fission cross sections relative to 235U from the fission threshold energy to 200 MeV were measured by using the TOF method and the Fast Ionization Chamber Spectrometer for Fission Cross Section Measurement (FIXM) in the single/double bunch mode of Back-n. The experimental uncertainties are analyzed in detail, and the results from the two modes are consistent. The measured 236,238U/235U fission cross section ratios are compared with previous experiments and evaluations. The 236,238U(n,f) cross sections are obtained based on the standard 235U fission cross section. The neutron total cross sections of carbon and aluminum in the energy region from 1 eV to 20 MeV have been measured by using the TOF method and transmission method based on the Neutron Total Cross Section Spectrometer (NTOX) in the double bunch mode. The total cross section results after unfolding are in good agreement with the previous measurements as well as the broadening of the ENDF/B-Ⅷ.0 evaluation with Gaussian function within the experimental uncertainty. The present results provide the experimental data for further measurements, relevant evaluations and the design of nuclear system.

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.

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.

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.

Detector development at the Back-n white neutron source

PurposeBack-n is a white neutron beamline at China spallation neutron source, which was established in the year of 2018. It is a powerful facility for nuclear data measurement, neutron detector calibration, and radiation effect research.MethodA series of detectors were built for different experiments, including beam monitoring, beam profile measurement, neutron induced secondaries (fission fragments, light charged particles and gamma) cross section measurement, and neutron resonance radiography, etc. A common digitization electronics and a cluster-based DAQ were developed for these detector systems. Most detectors have been employed at Back-n and serviced for experiments from the beginning of the beamline running.Results and conclusionAs an overview of detectors of Back-n, the details of the detector design and the experiment performing are described in this paper. Some developing systems, e.g., MTPC and B-MCP, are also included.

Experimental studies on nuclide identification radiography with a CMOS camera at Back-n white neutron source

As an advanced neutron imaging technique, nuclide identification radiography (NIR) using neutron resonance or cross-section differences is a promising technique for investigating nuclide spatial distribution inside samples. Since its proposal in 1980s, this technique has advanced very slowly due to many limitations in neutron source, detector efficiency and resolution. At the Back-n white neutron source at China Spallation Neutron Source, the NIR technique based on gated CMOS camera has been developed by taking the advantage of very high neutron flux and suitable energy spectrum of the Back-n neutron beam. Heavy nuclides, medium-mass nuclides and light nuclides have been tested to validate the effectiveness of the technique, covering the resonances from eV to MeV regions. Typical heavy elements such as Ag, In, Au and W, medium-mass elements such Al, Fe and Cu, light elements such as O have been used for experiments. The study shows, that nuclides with resonance peaks in the eV region can be easily identified, while the nuclides with resonance peaks above keV are difficult to be identified individually due to their narrow resonance peaks affecting the signal-to-noise ratio in the camera measurements. However, these nuclides can be differentiated for imaging by using adjacent multiple resonance peaks or distinct cross-section differences over wider energy ranges. The experiments are perhaps the first ones that demonstrate the NIR technique for the identification and imaging of nuclides with cross-section resonances covering from eV to several MeV.

Direct measurement of an energy-dependent single-event-upset cross-section with time-of-flight method at CSNS

To predict the soft error rate for applications, it is essential to study the energy dependence of the single-event-upset (SEU) cross-section. In this work, we present a direct measurement of the SEU cross-section with the Back-n white neutron source at the China Spallation Neutron Source. The measured cross section is consistent with the soft error data from the manufacturer and the result suggests that the threshold energy of the SEU is about 0.5 MeV, which confirms the statement in Iwashita’s report that the threshold energy for neutron soft error is much below that of the (n, α) cross-section of silicon. In addition, an index of the effective neutron energy is suggested to characterize the similarity between a spallation neutron beam and the standard atmospheric neutron environment.

A study on relative neutron sensitivity of Yb:YAG with CSNS Back-n white neutron source

Two inorganic scintillator detectors consisting of Yb:YAG scintillators and photomultiplier tubes, and an oscilloscope were used to studied the neutron sensitivities of Yb:YAG scintillators at the China Spallation Neutron Source (CSNS) Back-n white neutron source. The relative neutron sensitivity curves of two Yb:YAG scintillators in the energy region between 0.5 and 20 MeV were obtained for the first time. As the measured relative neutron sensitivity curves of Yb:YAG scintillators cannot be verified by the Monte Carlo method and there was no referable data, the neutron sensitivity curve of a ST401 scintillator was also studied in the same method and a Geant4 simulation of ST401 scintillator was conducted to verify the experiment method in this paper. The result showed that the experimental and simulation results were approximately consistent between 17–20 MeV, and agreed well between 1–17 MeV. A comparison between the experimental result and references of ST401 scintillator was also applied and the result showed that the curve tendency of the experimental result and references was matched. The above results imply that the measured relative neutron sensitivity curves and the experimental method used herein were reliable. It also demonstrated the feasibility of studying the neutron sensitivity of inorganic scintillator based on the white neutron source.

An SCA ASIC-based multi-channel readout system for a prototype multi-purpose TPC at CSNS Back-n white neutron source

The back-streaming white neutron source (Back-n) at China Spallation Neutron Source (CSNS), which has excellent energy spectrum and good time resolution, provides superior conditions for neutron induced light charged particle tracking experiment. To track light charged particles, CSNS has proposed a project named Multi-purpose Time Projection Chambers (MTPC) and completed a 1519-channel prototype. A multi-channel readout system based on Switched Capacitor Arrays (SCA) waveform sampling ASIC was designed to meet the requirements of the prototype MTPC. This paper presents the structure of this readout system and the results of the beam test with MTPC at CSNS. Time of Flight spectrum of neutron beam and 3D-track of neutron induced light charged particles were successfully reconstructed. These test results prove the feasibility of large-scale MTPC.

Design and Preliminary Property Research of Double-Grid Ionization Chamber for CSNS Back-n White Neutron Source

Design and Preliminary Property Research of Double-Grid Ionization Chamber for CSNS Back-n White Neutron Source

Gap uniformity study of a resistive Micromegas for the Multi-purpose Time Projection Chamber (MTPC) at Back-n white neutron source

A Multi-purpose Time Projection Chamber prototype based on a resistive Micromegas technique has been proposed, designed and fabricated at China Spallation Neutron Source to measure the cross sections of neutron-induced light-charged particle emission reactions and fission reactions at the Back-n white neutron source. For the requirements of working stability with high voltage and high granularity of readout, the prototype is fabricated by applying a resistive Micromegas with high-density pixelated anode plane. In order to fully understand the process of charge spreading and signal induction on the anode plane covered by a resistive layer, a simulation method is developed and the energy correction function is then obtained, which can be used in the further energy correction in the experimental data analysis. Measured with a 55Fe X-ray source, the uniformity of gain and avalanche gap are specially analyzed by combining the simulated gas avalanche parameters with fitting of experimental data in which the parallel plate avalanche model is adopted.

Measurement of total neutron cross section of natural lithium at China Spallation Neutron Source Back-n facility

Lithium is one of the main materials of fuel carrier salt in molten salt reactors. Its neutron cross section provides an important basic datum for physical design of molten salt reactor core and for evaluating the safety of the core during operation. The total neutron cross sections of natural lithium samples with thickness values of 8.00 mm and 15.0 mm are measured, respectively, in an energy range from 0.4 eV to 20 MeV by using a neutron total cross section spectrometer (NTOX) with the transmission method at the Back-n white neutron source of China Spallation Neutron Source (CSNS Back-n) with a 76.0 m time-of-flight path. High quality experimental data are obtained, especially in the energy region of keV and below, which supply a significative supplement of the data, thereby providing more abundant and reliable experimental data for nuclear data evaluation of lithium. Additionally, a theoretical analysis is carried out under the guidance of 1/<i>v</i> law and the multilevel R-matrix theory. And the resonance parameters of n+<sup>6,7</sup>Li reaction around the energy of 260 keV are extracted from the measured data.

Real-time digital trigger system for GTAF-II at CSNS Back-n white neutron source

A 4-π detector array composed of 40 BaF_2 crystals named Gamma Total Absorption Facility II (GTAF-II) is designed for neutron capture cross-section (n, γ) measurements at Back-n white neutron source in China Spallation Neutron Source. The waveform digitizing (WFD) method is used to acquire the detector signals from GTAF-II accurately. To reduce the high data rate caused by the WFD method, a real-time digital trigger system is proposed in this paper. The trigger system is divided into local and global trigger processing to distinguish desired signals from various noises. The local trigger processing rejects photomultiplier noises and α particles by signal characteristics. The global trigger verification eliminates natural γ-rays according to the (n, γ) reaction mechanism. In order to realize the interaction between the local and global trigger processing, a high-precision global synchronization and trigger exchange network is constructed. Experiments with beams at back-n show that the trigger system provides a high data reduction factor. This trigger system covers the entire neutron energy range of 25 ms without dead time, and desired signals are acquired with full waveforms.

Erratum to: Measurement of the neutron total cross sections of aluminum at the back-n white neutron source of CSNS

Erratum to: Measurement of the neutron total cross sections of aluminum at the back-n white neutron source of CSNS

Measurement of the neutron total cross sections of aluminum at the back-n white neutron source of CSNS

Measurement of the neutron total cross sections of aluminum at the back-n white neutron source of CSNS