Possibility Of The Atmospheric-like Neutron Radiation Test At Back-n

The China Spallation Neutron Source(CSNS)is a large scientific facility built in the National Twelfth Five-Year Plan.It is located in Dongguan,Guangdong province and will be completed in June 2018.It is the fourth largest spallation neutron source in the world after SNS(U.S.),J-PARC(Japan),and ISIS(U.K.).The CSNS employs the spallation reaction by bombarding a tungsten target with a high-energy proton beam,thereby to generate a large number of neutrons.The neutrons emerging from the target in the converse direction of incident protons are extracted and the back-streaming white neutron source(Back-n)is schemed.This back-streaming neutron spectrum is continuous and very broad.The Back-n is the first white neutron source for the nuclear data measurements in China.Beside the neutron nuclear data measurements,the white neutron beam has also some good other applications on the neutron photography,macroscopic experiments,atmospheric-like neutron irradiations and so on.With more and more applications ofthe highly-integrated chips and integrated circuits,there has been a strong demand from home and abroad for the neutron irradiation tests of the electronic devices in recent years.This article focuses on the feasibility to carry out the accelerating tests at the back-streaming white neutron source of CSNS.According to the neutron-irradiating experimental requirements,the neutron beam and backgrounds are evaluated and corrected.In this paper,the multi-particle transport software namely FLUKA was used to simulate the nuclear process of a 1.6GeV proton beam bombarding on the CSNS tungsten target.The neutron energy spectra,intensity and backgrounds of the white neutron beam werecalculated.The CSNS white neutron spectrum was compared with the standard atmospheric neutron energy spectra(JEDEC and IEC)and other white neutron spectra from the international white neutron sources.For several typical memory chips,the ratios of soft error rates(SER)induced by the white neutron flux of CSNS and other neutron sources to those induced by the standard atmospheric neutron fluxes,were calculated by using Weibull-formula.The resultant results show that the forward 41-degree beamline at CSNS will have the best fidelity and the highest experimental acceleration factor in the world.The fidelity of Back-n neutron spectra iscomparable to that of the ISIS white neutron spectrum,but its acceleration factor is large and the second behind the CSNS41-degreebeamline,however higher than those of other similar facilities in the world.In order to reduce the interfering effect of gamma flash for accelerated tests,in this work,the methods wereproposed to remove the gamma background in the neutron beam.It finds that the filters are effective to filter the gamma in the neutron beam.The optimizations for the filters' material and thickness are carried out.At last the gamma background flux in beam is suppressed to a level of one order of magnitude lower than the neutron flux.For the large-scale integrated circuits,the methods to expand beam spot size wereexplored by a scattering sheet.The simulated results show that the beam spot can be expanded from?100mm to ?600mm.It can meet requirements of irradiation experiments forthe large-scale integrated circuits.In this paper,it is firstly evaluated in detail the feasibility of carrying out the atmospheric-like irradiation experiments in Back-n.These studies can be as theoretical references for carrying out the accelerated tests at Back-n.And it is significant reference to construct the accelerated test platform at Back-n in the future.