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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.

Aluminum and its alloys are widely used in the nuclear industry. Therefore, it is essential to precisely measure and accurately know the neutron total cross section of aluminum in the wider energy region. The measurement is performed by using the transmission method at the Back-n White Neutron Source of CSNS. Two aluminum samples 70 mm in diameter and thicknesses of 40 and 60 mm, respectively, were positioned at 55 m from the neutron source. The transmission detector consisted of a multi-layer fast fission chamber loaded with $$^{235}$$ U and $$^{238}$$ U, and it was located at the 76-m measurement station. By applying the time-of-flight technique, it was possible to extract the n+ $$^{27}$$ Al total cross section in a wide energy region, from 1 eV to 20 MeV, after the correction for the double-bunch mode of the CSNS accelerator. The total cross sections obtained with the two Al samples are consistent and the results obtained with the $$^{235}$$ U fission cells are in good agreement with that with $$^{238}$$ U in the energy range of 1–20 MeV. The uncertainty of neutron total cross section measured with $$^{235}$$ U for 40 mm and 60 mm thick aluminum is 0.7–22.3% and 0.6–12.4% in the energy range of 10 keV–20 MeV. Results are in fair agreement with respect to previous data and evaluations.

The relative differential cross sections of the $$^{1}\hbox {H}(n, \,el)$$ reaction have been measured at the China Spallation Neutron Source (CSNS) Back-n white neutron source. A low-density polyethylene sample and a graphite foil were prepared for the foreground and background measurements, respectively. The charged particles were detected using the $${\vartriangle }E-E$$ telescope array of the Light-charged Particle Detector Array (LPDA) system. With 10 $${\vartriangle }E-E$$ telescopes, the relative differential cross sections of the $$^{1}\hbox {H}(n, \,el)$$ reaction were obtained from 70 $$^{\circ }$$ to 160 $$^{\circ }$$ in the center-of-mass system in the neutron energy ( $$E_{\mathrm{n}}$$ ) range from 6.14 to 52.48 MeV (23 energy points). The present work was the first experiment using the $${\vartriangle }E-E$$ telescope array of the LPDA system at CSNS. The present results are in good agreement with previous measurements, evaluations and theoretical calculations. Furthermore, this work is the first measurement in the 6.52 MeV $$\le E_{\mathrm{n}} \le $$ 9.09 MeV, 10.57 MeV $$\le E_{\mathrm{n}} \le $$ 12.43 MeV, and 18.05 MeV $$\le $$ $$E_{\mathrm{n}} \le $$ 20.05 MeV regions.

Back-streaming neutrons from the spallation target of the China Spallation Neutron Source (CSNS) that emit through the incoming proton channel were exploited to build a white neutron beam facility (the so-called Back-n white neutron source), which was completed in March 2018. The Back-n neutron beam is very intense, at approximately 2*10^7 n/cm^2/s at 55 m from the target, and has a nominal proton beam with a power of 100 kW in the CSNS-I phase and a kinetic energy of 1.6 GeV and a thick tungsten target in multiple slices with modest moderation from the cooling water through the slices. In addition, the excellent energy spectrum spanning from 0.5 eV to 200 MeV, and a good time resolution related to the time-of-flight measurements make it a typical white neutron source for nuclear data measurements; its overall performance is among that of the best white neutron sources in the world. Equipped with advanced spectrometers, detectors, and application utilities, the Back-n facility can serve wide applications, with a focus on neutron-induced cross-section measurements. This article presents an overview of the neutron beam characteristics, the experimental setups, and the ongoing applications at Back-n., Comment: 11 pages, 9 figures

The capture cross sections of the 169Tm reaction were measured at the back streaming white neutron beam line (Back-n) of the China Spallation Neutron Source (CSNS) using four C6D6 liquid scintillation detectors. The background subtraction, normalization, and correction were carefully considered in the data analysis to obtain accurate cross sections. For the resonance at 3.9 eV, the R-matrix code SAMMY was used to determine the resonance parameters with the internal normalization method. The average capture cross sections of 169Tm for energy between 30 and 300 keV were extracted relative to the 197Au reaction. The measured cross sections of the 169Tm reaction were reported in logarithmically equidistant energy bins with 20 bins per energy decade with a total uncertainty of 5.4% – 7.0% in this study and described in terms of average resonance parameters using a Hauser-Feshbach calculation with fluctuations. The point-wise cross sections and the average resonance parameters showed fair agreement with the evaluated values of the ENDF/B-VIII.0 library in the energy region studied.

Underground Nuclear Astrophysics Experiment in China (JUNA) has been commissioned by taking the advantage of the ultra-low background in Jinping underground lab. High current mA level 400 KV accelerator with an ECR source and BGO detectors were commissioned. JUNA studies directly a number of nuclear reactions important to hydrostatic stellar evolution at their relevant stellar energies. In the first quarter of 2021, JUNA performed the direct measurements of 25Mg(p,γ)26Al, 19F(p,α)16O, 13C(α,n)16O and 12C(α,γ)16O near the Gamow window. The experimental results reflect the potential of JUNA with higher statistics, precision and sensitivity of the data. The preliminary results of JUNA experiment and future plan are given.

Differential and angle-integrated cross sections for the $^{10}$B($n, {\alpha}$)$^{7}$Li, $^{10}$B($n, {\alpha}$$_{0}$)$^{7}$Li and $^{10}$B($n, {\alpha}$$_{1}$)$^{7}$Li$^{*}$ reactions have been measured at CSNS Back-n white neutron source. Two enriched (90%) $^{10}$B samples 5.0 cm in diameter and ~85.0 ${\mu}$g/cm$^{2}$ in thickness each with an aluminum backing were prepared, and back-to-back mounted at the sample holder. The charged particles were detected using the silicon-detector array of the Light-charged Particle Detector Array (LPDA) system. The neutron energy E$_{n}$ was determined by TOF (time-of-flight) method, and the valid ${\alpha}$ events were extracted from the E$_{n}$-Amplitude two-dimensional spectrum. With 15 silicon detectors, the differential cross sections of ${\alpha}$-particles were measured from 19.2{\deg} to 160.8{\deg}. Fitted with the Legendre polynomial series, the ($n, {\alpha}$) cross sections were obtained through integration. The absolute cross sections were normalized using the standard cross sections of the $^{10}$B($n, {\alpha}$)$^{7}$Li reaction in the 0.3 - 0.5 MeV neutron energy region. The measurement neutron energy range for the $^{10}$B($n, {\alpha}$)$^{7}$Li reaction is 1.0 eV $\le$ En < 2.5 MeV (67 energy points), and for the $^{10}$B($n, {\alpha}$$_{0}$)$^{7}$Li and $^{10}$B($n, {\alpha}$$_{1}$)$^{7}$Li$^{*}$ reactions is 1.0 eV $\le$ En < 1.0 MeV (59 energy points). The present results have been analyzed by the resonance reaction mechanism and the level structure of the $^{11}$B compound system, and compared with existing measurements and evaluations., Comment: 19 pages, 34 figures, to be published in Chinese Physics C

To verify the performance of the neutron total cross-sectional spectrometer, the neutron total cross section of carbon is initially measured in the energy range of 1 eV to 20 MeV using the time-of-flight method. The measurement is performed at the Back-n white neutron source with a 76-m time-of-flight path using the China Spallation Neutron Source. A multilayer fast fission chamber with 235U and 238U is employed as the neutron detector. The diameter and thickness of the natural graphite sample are 70 mm and 40 mm, respectively. Signal waveforms are collected using a data acquisition system. Off-line data processing was used to obtain the neutron time-of-flight spectra and transmissions. The uncertainty of the counting statistics is generally approximately 3% for each bin in the energy range of 1–20 MeV. It is determined that the results for the neutron total cross section of carbon obtained using 235U cells are in good agreement with the results obtained using 238U cells within limits of statistical uncertainty. Moreover, the measured total cross sections show good agreement with the broadening evaluated data.

In the original article, there were some errors in the list of authors and affiliations. Their correct version is given in this erratum.

China Spallation Neutron Source (CSNS) has been built and commissioned successfully in 2018 which is implemented by impinging 1.6 GeV protons onto a tungsten target with 25 Hz repetition frequency. An associated white neutron beam line exploiting the back-streaming neutrons, named Back-n, with a flight path of 55 m in endstation 1 (#ES1) and 76 m in endstation 2 (#ES2) was built mainly for nuclear data measurements. The Back-n beam line started running since the beginning of 2018 and the neutron energy spectrum was measured at the very beginning since it is an essential information for feasibility study and analysis of any measurement. In this paper, the measurement of the neutron energy spectrum of Back-n #ES2 is reported. The first result of the neutron flux from 1 eV to 100 MeV measured by a fission chamber based on the 235U(n, f) reaction is presented. The total neutron flux normalized to the proton beam power of 100 kW is $ 7.03 \times 10^{6}$ neutrons/cm2/s. The results show a good agreement with that of the Monte Carlo simulation as well.

The neutron capture cross sections are very important in the field of nuclear device design and basic physics research. Hydrogen-free liquid scintillator such as C6D6 detectors are widely used in the neutron capture cross-sectional measurements for the low neutron sensitivity and fast time response. The Back-n white neutron source at China Spallation Neutron Source is the first spallation white neutron source in China, and it is suitable for neutron capture cross-sectional measurement. A C6D6 detector system was built in the Back-n experimental station. The pulse height weighting technique was used to determine the system’s detection efficiency. The response to gamma rays of the C6D6 detector was measured, and the energy resolution function was determined. Monte Carlo simulation with Geant4 code was carried out to get the weighting function of this C6D6 detector system. Additionally, the systematic uncertainty of the weighting function was also determined. According to the experimental and simulation results, this C6D6 detector system can be used to measure neutron capture cross section.

This work aims to investigate the methane emissions from integrated vertical-flow constructed wetlands (IVCWs) when ethanol is added as an external carbon source. In this study, a gradient of ethanol (0, 2, 4, 8, 16 and 32 mmol/L) was added as the carbon source in an IVCW planted with Cyperus alternifolius L. The results showed that the methane emission flux at an ethanol concentration of 32 mmol/L was 32.34 g CH4 m&minus, 2 day&minus, 1 less than that of the control experiment (0 mmol/L) and that the methane emission flux at an ethanol concentration of 16 mmol/L was 5.53 g CH4 m&minus, 1 less than that at 0 mmol/L. In addition, variations in the water quality driven by the different ethanol concentrations were found, with a redox potential range of &minus, 64 mV to +30 mV, a pH range of 6.6&ndash, 6.9, a chemical oxygen demand (COD) removal rate range of 41% to 78%, and an ammonia nitrogen removal rate range of 59% to 82% after the ethanol addition. With the average CH4-C/TOC (%) value of 35% driven by ethanol, it will be beneficial to understand that CH4-C/TOC can be considered an ecological indicator of anthropogenic methanogenesis from treatment wetlands when driven by carbon sources or carbon loading. It can be concluded that adding ethanol as an external carbon source can not only meet the water quality demand of the IVCW treatment system but also stimulate and increase the average CH4 emissions from IVCWs by 23% compared with the control experiment. This finding indicates that an external carbon source can stimulate more CH4 emissions from IVCWs and shows the importance of carbon sources during sewage treatment processes when considering greenhouse emissions from treated wetlands.

The Back-n white neutron beam line, which uses back-streaming white neutrons from the spallation target of the China Spallation Neutron Source, is used for nuclear data measurements. A Micromegas-based neutron detector with two variants was specially developed to measure the beam spot distribution for this beam line. In this article, the design, fabrication, and characterization of the detector are described. The results of the detector performance tests are presented, which include the relative electron transparency, the gain and the gain uniformity, and the neutron beam profile reconstruction capability. The result of the first measurement of the Back-n neutron beam spot distribution is also presented., Comment: 31 pages, 18 figures

Neutron capture therapy with Sulfur-33, similar to boron neutron capture therapy with Boron-10, is effective in treating some types of tumors including ocular melanoma. The key point in sulfur neutron capture therapy is whether the neutron beam flux and the resonance capture cross section of $$^{33}\hbox {S(n},\alpha )^{30}\hbox {Si}$$ reaction at 13.5 keV can achieve the requirements of radiotherapy. In this research, the authors investigated the production of 13.5 keV neutron production and moderation based on an accelerator neutron source. A lithium glass detector was used to measure the neutron flux produced via near threshold $$^{7}\hbox {Li(p,n)}^{7}\hbox {Be}$$ reaction using the time-of-flight method. Furthermore, the moderation effects of different kinds of materials were investigated using Monte Carlo simulation.

The Back-n white neutron source (known as Back-n) is based on back-streaming neutrons from the spallation target at the China Spallation Neutron Source (CSNS). With its excellent beam properties, e.g., a neutron flux of approximately 1.8×107 n/cm2/s at 55 m from the spallation target, energy range spanning from 0.5 eV to 200 MeV, and time-of-flight resolution of a few per thousand, along with the equipped physical spectrometers, Back-n is considered to be among the best facilities in the world for carrying out nuclear data measurements. Since its completion and commencement of operation in May 2018, five types of cross-section measurements concerning neutron capture cross-sections, fission cross-sections, total cross-sections, light charged particle emissions, in-beam gamma spectra, and more than forty nuclides have been measured. This article presents an overview of the experimental setup and result analysis on the neutron-induced cross-section measurements and gamma spectroscopy at Back-n in the initial years.

The angle-differential cross sections of neutron-induced deuteron production from carbon were measured at six neutron energies from 25 to 52 MeV relative to those of n-p elastic scattering at the China Spallation Neutron Source (CSNS) Back-n white neutron source. By employing the Δ E-E telescopes of the Light-charged Particle Detector Array (LPDA) system at 15.1° to 55.0° in the laboratory system, ratios of the angle-differential cross sections of the 12C(n, xd) reactions to those of the n-p scattering were measured, and then, the angle-differential cross sections of the 12C(n, xd) reactions were obtained using the angle-differential cross sections of the n-p elastic scattering from the JENDL-4.0/HE-2015 library as the standard. The obtained results are compared with data from previous measurements, all of which are based on mono-energic neutrons, the evaluated data from the JENDL-4.0/ HE-2015 library and the ENDF-B/VIII.0 library, and those from theoretical calculations based on INCA code and Talys-1.9 code. Being the first white-neutron-source-based systematic measurement of the angle-differential cross sections of neutron-induced deuteron production reactions on carbon in several tens of MeV, the present work can provide a reference to the data library considering the lack of experimental data.

The Back-n beam line of the China Spallation Neutron Source is the first white neutron facility in China. One of its goals is to perform radiative neutron capture cross-section ( σ nγ ) measurements. To study the experimental backgrounds of this new facility, a measurement of the σ nγ of 197Au was carried out with a C6D6 detector system at Back-n. Time-dependent backgrounds induced by the scattered neutrons and in-beam gamma-rays were measured and analyzed with nat C and nat Pb samples. The black resonance filter technique was employed to evaluate the shape of the backgrounds and perform the normalization. Besides, Monte Carlo simulations of these backgrounds were carried out with the Geant4 toolkit. The simulated results were compared with the experimental ones and the good agreement found allowed us to validate the background evaluation method.

The Back-n is a high luminosity white neutron beamline at the China Spallation Neutron Source (CSNS). It started running in 2018 for various nuclear data measurements. A Light charged Particle Detector Array (LPDA) is designed for (n, lcp) reaction experiments, which includes a group of detectors and supporting systems. The Δ E-E telescope, consisting of a Low-Pressure Multi-Wire Proportional Chamber (LPMWPC) and a Si-PIN detector, is the core detector of the LPDA. From the beginning of 2018, several measurements have been performed using the Δ E-E telescopes, and the light charged particles such as 1H, 3H, 4He, and 7Li, were identified successfully. At present, the LPMWPC can identify the protons with energy as low as 0.5 MeV. In the near future, combining with CsI(Tl) crystals, a system consisting of sixteen telescopes with an energy acceptance from 0.5 MeV to 100 MeV (proton) will be constructed for general purpose of (n, lcp) measurements.

The Back-n white neutron source at the China Spallation Neutron Source (CSNS) was put into operation in 2018, providing a good platform for the cross-section measurement of neutron induced light charged particle ( l c p ) emission ( n , l c p ) reactions. Currently, in order to detect and identify light charged particles produced in ( n , l c p ) reactions at Back-n, a silicon detector array has been developed as a part of Light-charged Particle Detector Array. Composed of 15 silicon detectors, the array can detect the emitted particles ranging from 19.2°to 160.8°. The energy resolution of each silicon detector unit is better than 1% for 5.499 MeV α particles. Adopting this silicon detector array, several experimental measurements have been completed. Differential cross sections and angle-integrated cross sections in the neutron energy region ranging from the eV to the MeV range are extracted. Compared with previous measurements and evaluations, new results are obtained in the present measurements. These experiments indicate the feasibility of the silicon detector array in ( n , l c p ) reaction cross-section measurements.

Based on the China Spallation Neutron Source (CSNS) – Back-streaming white neutron source (Back-n WNS), the measurement of the U-238/U-235 fission cross section ratio in 1–20 MeV neutron energy region has been carried out by a multi-cell fast fission ionization chamber using the time-of-flight method. The measured resonance peaks of the 235U(n, f) reaction are in good agreement with those of the ENDF/B-8.0 database. The measured six groups of the U-238/U-235 fission cross section ratios in 1–20 MeV neutron energy region agree with those of the ENDF/B-8.0 database in trend, and the average discrepancies between experiment and database are from 1.9% to 2.6%. The relative experimental uncertainties are 2.3%–3.6% (1.4–20 MeV), and the measured data agree with those of database within experimental uncertainties at most energy points. The measured U-238/U-235 fission cross section ratio could provide information and data support in relevant nuclear data evaluation.

Combined photon and neutron radiography can integrate merits of X/gamma-ray radiography and energy-selective neutron radiography and has the potential of simultaneously visualizing objects composed of high-Z materials, low-Z materials and particular isotopes that resonantly absorb neutrons at certain energies. Intense pulsed gamma bursts and wide energy spectrum neutrons at spallation sources provide a unique opportunity to perform such combined radiography research. We present the results of the combined radiography experiments performed at the back-streaming white neutron (back-n) beamline at China Spallation Neutron Source (CSNS). Gamma-ray and energy-selective neutron radiographic images of multi-element samples were taken by an ICCD camera coupled with scintillators using the time of flight (TOF) technique. High-Z (Pb, Au, W, Ta, et al.) components were visualized with the intense gamma-ray bursts. The low-Z ( 10B) component was confirmed with varied image contrast when neutrons with varied energies were selected. The specific elements ( nat In, 197Au and nat W) were identified with neutrons at corresponding resonant energies. The experimental results prove the potential for simultaneously visualizing and identifying high-Z materials, low-Z materials and particular nuclides via combined X-ray radiography and energy-selective neutron radiography.

In the past two decades cooperating with Frank Laboratory of Neutron Physics (FLNP), Joint Institute for Nuclear Research (JINR) measurements of (n, α) reaction cross sections for 6Li, 10B, 25Mg, 39K, 40Ca, 54,56,57 Fe, 58Ni, 63Cu, 64,67 Zn, 95Mo, 143Nd and 147,149 Sm nuclei were performed in the MeV neutron energy region based on the 4.5 MV Van de Graaff accelerator at Peking University. In recent years, our measurements were extended in three aspects. Firstly, measurements were expanded from two-body reactions to three-body reactions such as 10B (n, t2 α). Secondly, the neutron energy region was extended from below 8 MeV to 8 - 11 MeV by using the HI-13 tandem accelerator of China Institute of Atomic Energy (CIAE), with which cross sections of 54,56 Fe(n, α)53,51Cr reactions were measured. Thirdly, based on the newly-built China Spallation Neutron Source (CSNS) Back-n WNS (White Neutron Source), differential and angle-integrated cross sections for 6Li(n, t) and 10B(n, α) reactions were measured in the neutron energy region from 1 eV to 3 MeV.

Differential cross-section data for the n-p and n-d elastic scattering (1H(n, el), 2H(n, el)) are collected and analyzed from EXFOR library. For En > 20 MeV, the experimental results for both reactions are scarce with large uncertainties and discrepancies in general. For En ≤ 20 MeV, the experimental results lack systematicness, most of which were measured around En = 14 MeV even though the differential cross sections of n-p scattering in 1 keV ≤ En ≤ 20 MeV region are recommended as standard. Taking these facts into account, more accurate and systematic measurements are planned. The experiments will be conducted using ΔE-E detectors of the Light-charged Particle Detector Array (LPDA) system at China Spallation Neutron Source (CSNS) Back-n White Neutron Source (WNS), and simulations are carried out. Using polyethylene and deuterated polyethylene as samples, both n-p and n-d scattering reactions are simulated along with the neutron-induced 12C background reactions, and the 2-D spectra and the counting rates of the ΔE-E detectors are obtained. According to the simulations, the applicable neutron energy range and positions of the detectors are recommended, and the beam time for the event and background measurements is suggested.

The 6Li(n, t)4He reaction was measured as the first experiment involving neutron-induced charged particle emission reactions at the CSNS (China Spallation Neutron Source) Back-n white neutron source. The differential cross-sections of the 6Li(n,t)4He reaction at 15 detection angles ranging from 19.2° to 160.8° are obtained from 1.0 eV to 3.0 MeV at 80 neutron energy points; for 50 energy points below 0.1 MeV they are reported for the first time. The results indicate that the anisotropy of the emitted tritium is noticeable above E n = 100 eV. The angle-integrated cross-sections are also obtained. The present differential cross-sections agree in general with the previous evaluations, but there are some differences in the details. More importantly, the present results indicate that the cross-sections of the 6Li(n, t)4He reaction might be overestimated by most evaluations in the 0.5 − 3.0 MeV region, although they are recommended as standards below 1.0 MeV.

Back-n is a white neutron experimental facility at China Spallation Neutron Source (CSNS). The time structure of the primary proton beam make it fully applicable to use TOF (time-of-flight) method for neutron energy measuring. We implement the electronics of TOF measurement on the general-purpose readout electronics designed for all of the seven detectors in Back-n. The electronics is based on PXIe (Peripheral Component Interconnect Express eXtensions for Instrumentation) platform, which is composed of FDM (Field Digitizer Modules), TCM (Trigger and Clock Module), and SCM (Signal Conditioning Module). T0 signal synchronous to the CSNS accelerator represents the neutron emission from the target. It is the start of time stamp. The trigger and clock module (TCM) receives, synchronizes and distributes the T0 signal to each FDM based on the PXIe backplane bus. Meantime, detector signals after being conditioned are fed into FDMs for waveform digitizing. First sample point of the signal is the stop of time stamp. According to the start, stop time stamp and the time of signal over threshold, the total TOF can be obtained. FPGA-based (Field Programmable Gate Array) TDC is implemented on TCM to accurately acquire the time interval between the asynchronous T0 signal and the global synchronous clock phase. There is also an FPGA-based TDC on FDM to accurately acquire the time interval between T0 arriving at FDM and the first sample point of the detector signal, the over threshold time of signal is obtained offline. This method for TOF measurement is efficient and not needed for additional modules. Test result shows the accuracy of TOF is sub-nanosecond and can meet the requirement for Back-n at CSNS., 4 pages, 13 figures, 21st IEEE Real Time Conference

It is very important to control methane emissions to mitigate global warming. An intermittent micro-aeration control system was used to control methane emissions from an integrated vertical-flow constructed wetland (IVCW) to treat agricultural domestic wastewater pollution in this study. The optimized intermittent micro-aeration conditions were a 20-min aeration time and 340-min non-aeration time, 3.9 m3 h−1 aeration intensity, evenly distributed micro-aeration diffusers at the tank bottom, and an aeration period of every 6 h. Methane flux emission by intermittent micro-aeration was decreased by 60.7% under the optimized conditions. The average oxygen transfer efficiency was 26.73%. The control of CH4 emission from IVCWs was most strongly influenced by the intermittent micro-aeration diffuser distribution, followed by aeration intensity, aeration time, and water depth. Scaling up of IVCWs is feasible in rural areas by using intermittent micro-aeration control as a mitigation measure for methane gas emissions for climate change.

A white neutron source for nuclear data measurement has been built and put into operation on China Spallation Neutron Source (CSNS). We developeda beam monitor for real-time online monitoring of neutron flux on the white neutron source. The beam monitor work simultaneously with other nuclear data measurement detectors to provide neutron flux for data analysis. To minimize beam disturbance and reduce the background generated by the monitor, a structure in which neutron conversion layer and Si detectors are separated is employed: A 6LiF film with a mass thickness of 360 μ g/cm 2 was deposited on a 10 μ m aluminum foil and placed inside the beam line. Eight Si-detectors with a size of 20 × 20 mm2 were placed around the film outside the beam to maximize the reception of secondary particles from the conversion layer and to avoid neutron beam irradiation. The simulation of the beam monitor (layout, counting rate, neutron disturbance, etc.), construction and online performance are described in the paper. Good online performance of the monitor was achieved during the CSNS white neutron source flux calibration experiment in March, 2018: The counting rate for the beam line operating at Ф30 mm and Ф60 mm beam pattern modes was normalized to 100 kW proton beam power, and the result is consistent with the simulation. The total uncertainty of the normalized counting rate is less than 1%. Moreover, the measurement of neutron flux in low energy region below 10 keV of the white neutron source by the monitor is discussed.

The Chinese spallation neutron source was completed in May 2018 and then subsequently commissioned. The Back-streaming white neutron beam line can be used in neutron nuclear data measurement, neutron physics research, and nuclear technology. In these experiments, it is necessary to know the neutron energy spectrum, the neutron flux, and the neutron beam profile of the neutron beam. In this paper, we present the preliminary measurements of these parameters. The neutron energy spectrum and neutron flux are measured by the time-of-flight method with a fission chamber equipped with 235U and 238U samples and a 6Li-Si detector. The neutron beam profile is measured by a scintillator-CMOS detection system. The preliminary experimental measurements of the beam line are obtained. Among them, the energy spectrum measurement range of white neutrons is from eV to more than 100 MeV, which also gives an uncertainty analysis; the neutron fluence rate gives the full power value of the two experimental halls; the collimated white neutron beam spot is given under a diameter of 60 mm. The future plan is also given. The results of these experimental parameters can serve as the foundation for the future nuclear data measurement and detector calibration experiments of the beam line.

237Np (≃2.14 × 106 yr half-life) is potentially applicable in studies on nuclear safeguards and radioactive waste migration. The atomic ratio of 237Np/U in nature is 10−12 or even lower, depending strongly on the integral neutron flux received by the material. As an ultra-sensitive technique, accelerator mass spectrometry (AMS) is the best for measuring ultratrace 237Np. By extracting negative molecular ions NpO– from the oxide sample using 238UO– and 208Pb16O2– pilot beams for the simulation of 237Np ion transport, identifying the interference isotopes by high-resolution dedicated injector, electrostatic analyzer, and time of flight (TOF) detector, a method for AMS measurement of 237Np was set up on the HI-13 accelerator at the China Institute of Atomic Energy (CIAE). A sensitivity of –11 has been achieved for the isotopic ratio 237Np/238U.

In order to improve the accuracy of accelerator mass spectrometry (AMS) measurement for 182Hf/180Hf, a series of measurements have been taken in the AMS laboratory at the China Institute of Atomic Energy (CIAE). The major ones include the instantaneous monitoring of 180HfF−5 current, testing the stability of transmission, the alternate measurements of an unknown sample and standard, and the origin identification and minimization of background 182W. The experimental details and the improvement in the measurement accuracy, as well as some useful suggestions for better satisfying the requirements of certain practical applications, are presented in this paper.

A new method was developed for AMS measurement of 126Sn. Major features of the method include the preparation of SnF2 samples, the use of SnF2 as target material, the selection of SnF 3 - molecular ions for the AMS measurements, and the quantitative calibration of our Beijing HI-13 AMS measurements by using samples with 126Sn determined by γ-ray spectrometry. The results indicate that the relative uncertainty of the 126Sn/Sn calibrated by γ-ray spectrometry is better than 4% for samples with 126Sn/Sn of 10−8 to −9. A beam current of 126Sn up to 400 nA can be obtained by the combination of SnF2/ SnF 3 - (target sample, selected ions), while 126Te interference was reduced by 2–3 orders of magnitude. A perfect linearity (R2 = 0.99975) between measured and nominal 126Sn/Sn values was obtained by using three standard samples (diluted from the one calibrated by γ-ray spectrometry) with 126Sn/Sn ratios of 1.033 × 10−8, 4.54 × 10−9, 6.43 × 10−10, respectively. A sensitivity of (1.92 ± 1.13) × 10−10 (126Sn/Sn) has been reached by measuring a blank sample.

Isobar interference is the main obstacle for AMS measurement, especially in the case of very strong isobaric interference, such as in the measurement of 32 Si, 53 Mn, 60 Fe, 63 Ni, etc. An isobar separation method with Q3D magnetic spectrometer was developed aiming at AMS measurements for the above-mentioned nuclides. Based on a method of (ΔE-Q3D) the isobaric events can be largely rejected from the region of the nuclide of interest on the focal plane of a Q3D magnetic spectrometer. As a result, the isobaric interference can be reduced by more than three orders of magnitude. Further reduction of isobaric interference can be achieved by the use of a multi-anode ionization chamber placed at the position of collecting the nuclide of interest. The performance of the ΔE-Q3D system for isobar separation was tested by the above-mentioned nuclides with atomic numbers from 14 to 42. The results showed that ΔE-Q3D method has strong capability for separating isobars, as detailed in this paper.