Analysis of displacement damage effects on the charge-coupled device induced by neutrons at Back-n in the China Spallation Neutron Source

Displacement damage effects on the charge-coupled device(CCD)induced by neutrons at the back-streaming white neutron source(Back-n)in the China Spallation Neutron Source(CSNS)are analyzed according to an online irradiation experiment.The hot pixels,random telegraph signal(RTS),mean dark signal,dark current and dark signal non-uniformity(DSNU)induced by Back-n are presented.The dark current is calculated according to the mean dark signal at various integration times.The single-particle displacement damage and transient response are also observed based on the online measurement data.The trends of hot pixels,mean dark signal,DSNU and RTS degradation are related to the integration time and irradiation fluence.The mean dark signal,dark current and DSNU2 are nearly linear with neutron irradiation fluence when nearly all the pixels do not reach saturation.In addition,the mechanisms of the displacement damage effects on the CCD are demonstrated by combining the experimental results and technology computer-aided design(TCAD)simulation.Radiation-induced traps in the space charge region of the CCD will act as generation/recombination centers of electron-hole pairs,leading to an increase in the dark signal.

Silicon photomultiplier based scintillator thermal neutron detector for China Spallation Neutron Source(CSNS)

The energy-resolved neutron imaging spectrometer(ERNI)will be installed in 2022 according to the spectrometer construction plan of the China Spallation Neutron Source(CSNS).The instrument requires neutron detectors with the coverage area of approximately 4 m^(2)in 5°-170°neutron diffraction angle.The neutron detection efficiency needs to be better than 40%at 1 A neutron wavelength.The spatial resolution should be better than 3 mm×50 mm in the horizontal and vertical directions respectively.We develop a one-dimensional scintillator neutron detector which is composed of the^(6)Li F/Zn S(Ag)scintillation screens,the wavelength-shifting fiber(WLSF)array,the silicon photomultipliers(Si PMs),and the self-designed application-specific integrated circuit(ASIC)readout electronics.The pixel size of the detector is designed as 3 mm×50 mm,and the neutron-sensitive area is 50 mm×200 mm.The performance of the detector prototype is measured using neutron beam 20#of the CSNS.The maximum counting rate of 247 k Hz,and the detection efficiency of63%at 1.59 A are obtained.The test results show that the performance of the detector fulfills the physical requirements of the ERNI under construction at the CSNS.

Displacement damage in optocouplers induced by high energy neutrons at back-n in China Spallation Neutron Source

Neutron radiation experiments of optocouplers at back-streaming white neutrons(back-n)in China Spallation Neutron Source(CSNS)are presented.The displacement damages induced by neutron radiation are analyzed.The performance degradations of two types of optocouplers are compared.The degradations of current transfer ratio(CTR)are analyzed,and the mechanisms induced by radiation are also demonstrated.With the increase of the accumulated fluence,the CTR is degrading linearly with neutron fluence.The radiation hardening of optocouplers can be improved when the forward current is increased.Other parameters related to CTR degradation of optocouplers are also analyzed.

Development of a ~3He Gas Filling Station at the China Spallation Neutron Source

At the China Spallation Neutron Source(CSNS), we have developed a custom gas-filling station, a glassblowing workshop, and a spin-exchange optical pumping(SEOP) system for producing high-quality ^(3)He-based neutron spin filter(NSF) cells. The gas-filling station is capable of routinely filling ^(3)He cells made from GE180 glass of various dimensions, to be used as neutron polarizers and analyzers on beamlines at the CSNS. Performance tests on cells fabricated at our gas-filling station are conducted via neutron transmission and nuclear-magneticresonance measurements, revealing nominal filling pressures, and a saturated ~3He polarization in the region of 80%, with a lifetime of approximately 240 hours. These results demonstrate our ability to produce competitive NSF cells to meet the ever-increasing research needs of the polarized neutron research community.

Upgrade of the sextupole field for beam instability mitigation in rapid cycling synchrotron of China Spallation Neutron Source

Background The China Spallation Neutron Source incorporates a rapid cycling synchrotron(RCS)that operates by accumulating protons at 80 MeV and subsequently accelerating them to 1.6 GeV within a time span of 20 ms.The beam is guided to striking the tungsten target for neutron source.Purpose As a space charge dominated machine,the RCS is subject to space charge effects and momentum spread,hereby influencing the tune spread.To address this issue,sextupole magnets,powered by two families of DC power supply,were initially employed to decrease the absolute value of chromaticity and to control the tune spread.The head-tail instability has been observed during the RCS beam commissioning.Method The beam tests and simulations were conducted,revealing that tuning the chromaticity proved to be an effective mitigation strategy.However,to achieve better control over the tune spread and further suppress the instability,the DC sextupole field has been upgraded to an AC sextupole field,aiming to provide dynamic for controlling the chromaticity over an acceleration cycle.Results and conclusion Thanks to the upgraded of AC field,the instability has been fully mitigated with beam power of 100 kW and the transmission in the RCS has been improved by~2%from 96 to 98%.With help of AC sextupole at present,the beam power in the RCS is increased to 140 kW.

China's Spallation Neutron Source Goes Operational

It is a hot summer morning amid the endless greenness of lychee orchards 30 km southeast of downtown Dongguan,near China’s southern coastline,when project manager CHEN Hesheng and his team gathered with excitement in the control room of the China Spallation Neutron Source(CSNS)to witness a historic moment:the production of the first neutron beam lines from the machine they had just completed after more than six years of construction.

Measurement of the relative neutron sensitivity curve of a LaBr_(3)(Ce)scintillator based on the CSNS Back-n white neutron source

A scintillator detector consisting of a LaBr_(3)(Ce)(0.5%)scintillator,a photomultiplier tube(PMT),and an oscilloscope were used to study the neutron sensitivities of the LaBr_(3)(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 LaBr_(3)(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 LaBr_(3)(Ce)scintillator and those of other scintillators with a similar neutron response signal intensity.

Measurements of the ^(107)Ag neutron capture cross sections with pulse height weighting technique at the CSNS Back-n facility

Silver indium cadmium(Ag–In–Cd) control rod is widely used in pressurized water reactor nuclear power plants,and it is continuously consumed in a high neutron flux environment. The mass ratio of ^(107)Ag in the Ag–In–Cd control rod is 41.44%. To accurately calculate the consumption value of the control rod, a reliable neutron reaction cross section of the ^(107)Ag is required. Meanwhile,^(107)Ag is also an important weak r nucleus. Thus, the cross sections for neutron induced interactions with ^(107)Ag are very important both in nuclear energy and nuclear astrophysics. The(n, γ) cross section of ^(107)Ag has been measured in the energy range of 1–60 eV using a back streaming white neutron beam line at China spallation neutron source. The resonance parameters are extracted by an R-matrix code. All the cross section of ^(107)Ag and resonance parameters are given in this paper as datasets. The datasets are openly available at http://www.doi.org/10.11922/sciencedb.j00113.00010.

Analysis of radiation environmental safety for China's Spallation Neutron Source (CSNS)

The China Spallation Neutron Source（CSNS） is going to be located in Dalang Town,Dongguan City in the Guangdong Province.In this paper we report the results of the parameters related with environment safety based on experiential calculations and Monte Carlo simulations.The main project of the accelerator is an under ground construction.On top there is a 0.5 m concrete and 5.0 m soil covering for shielding,which can reduce the dose out of the tunnel＇s top down to 0.2 μSv/h.For the residents on the boundary of the CSNS,the dose produced by skyshine,which is caused by the penetrated radiation leaking from the top of the accelerator,is no more than 0.68 μSv/a.When CSNS is operating normally,the maximal annual effective dose due to the emission of gas from the tunnel is 2.40×10-3 mSv/a to the public adult,and 2.29×10-3 mSv/a to a child,both values are two orders of magnitude less than the limiting value for control and management.CSNS may give rise to an activation of the soil and groundwater in the nearest tunnels,where the main productions are 3H,7Be,22Na,54Mn,etc.But the specific activity is less than the exempt specific activity in the national standard GB13376-92.So it is safe to say that the environmental impact caused by the activation of soil and groundwater is insignificant.To sum up,for CSNS,as a powerful neutron source device,driven by a highenergy high-current proton accelerator,a lot of potential factors affecting the environment exist.However,as long as effective shieldings for protection are adopted and strict rules are drafted,the environmental impact can be kept under control within the limits of the national standard.

First neutron Bragg-edge imaging experimental results at CSNS

The neutron Bragg-edge imaging is expected to be a new non-destructive energy-resolved neutron imaging technique for quantitatively two-dimensional or three-dimensional visualizing crystallographic information in a bulk material,which could be benefited from pulsed neutron source.Here we build a Bragg-edge imaging system on the General Purpose Powder Diffractometer at the China Spallation Neutron Source.The residual strain mapping of a bent Q235 ferrite steel sample has been achieved with a spectral resolution of 0.15%by the time-of-flight neutron Bragg-edge imaging on this system.The results show its great potential applications in materials science and engineering.

Mechanical research and development of a monocrystalline silicon neutron beam window for CSNS

The monocrystalline silicon neutron beam window is one of the key components of a neutron spectrom- eter. Monocrystalline silicon is brittle and its strength is generally described by a Weibull distribution due to the material inhomogeneity. The window is designed not simply according to the mean strength but also according to the survival rate. The total stress of the window is stress-linearized into a combination of membrane stress and bending stress by finite element analysis. The window is a thin circular plate, so bending deformation is the main cause of failure and tensile deformation is secondary and negligible. Based on the Weibull distribution of bending strength of monocrystalline silicon, the optimized neutron beam window is designed to be 1.5 mm thick. Its survival rate is 0.9994 and its transmittance is 0.98447, which meets both physical and mechanical requirements.

Introduction to the overall physics design of CSNS accelerators

The China Spallation Neutron Source (CSNS) is an accelerator-based facility. The accelerator of CSNS consists of a low energy linac, a Rapid Cycling Synchrotron (RCS) and two beam transport lines. The overall physics design of CSNS accelerator is described, including the design principle, the choice of the main parameters and design of each part of accelerators. The key problems of the physics design, such as beam loss and control, are also discussed. The interface between the different parts of accelerator, as well as between accelerator and target, are introduced.

The machine protection system for CSNS

Background The China Spallation Neutron Source(CSNS)accelerator consists of an 80 MeV H-LINAC,a 1.6 GeV rapid cycling synchrotron(RCS)and two beam transport lines.The uncontrolled beam may permanently damage the components or lead to very high residual radiation dose along the beam line.So the equipment protection must be deliberately designed and implemented.Purpose The machine protection system(MPS)protects components from being damaged by the beam.The response time requirement for the CSNS MPS is less than 20 ms,so the PLC(programmable logic controller)was adopted to implement the interlock logic.Methods The MPS was implemented as a two-tier architecture system,and developed through utilizing PLC and Experimental Physics and Industrial Control System(EPICS)software toolkits.The application logic was taken into careful consideration during the implementation stage.An embedded CPU module can function as an IOC accessing PLC I/O modules through the sequence CPU,with an embedded Linux operation system.Results The interlock logic and heartbeat functions were tested with all functions ok.Time consumption has been measured thoroughly since the important requirement,which is around 15 ms to stop the beam.Conclusions MPS was completed in Sep.2017 and then put into operation.It has been operating smoothly for more than 3 years.MPS has played an important role in every stage of CSNS’s commissioning and operation and achieved high reliability during the user’s experiment operation.The accelerator recently runs stably with low equipment failure.