A PHYSICAL DESIGN OF A NEUTRON IRRADIATION SPECTROMTER AT CSNS FACILITY* Q. Z. Yu †, W. Yin and T. J. Liang# Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China Abstract technology is trending towards smaller size, higher We have physically designed a full spectrum neutron density and larger number of memory bits. These factors irradiation spectrometer, which is proposed by China increase the potentially disastrous impact on memory and Spallation Neutron Source (CSNS) facility to single-event chip functions. Rapid testing the susceptibility of each effect (SEE) test in semiconductor device and to other new generation of electron devices to the neutron related researches. Based on the overall layout of the radiation effects is highly needed in many fields such as target station and the neutronic performance, CSNS aviation, automotive, electronic medical device, high neutron irradiation spectrometer lies in the forward reliability computer users and so on. direction with 41 degrees to the proton beam, facing the Accelerator based neutron sources are favorite because front part of the W-Ta spallation target directly. The key the spallation neutron spectrum is similar to the components in the target station have been designed and atmosphere neutron spectrum produced by cosmic rays, manufactured to meet the special requirements of this but usually have more than five to six orders of spectrometer. At high energy region (>10 MeV), the magnifications of neutron flux. It implies that the SEE spectrum of the CSNS irradiation spectrometer calculated effects with 1 hour at test facilities equals to tens or by Monte Carlo code MCNPX2.5, is very similar to hundreds years in the real atmospheric environments. JEDEC standard at ground level with 3×109 magnification. Such kinds of rapid test can greatly satisfy the The integrated neutron flux at high energy region is requirements of government and semiconductor industries. 2.3×106 n/cm2/s at 14 m from the centre of the target There are several neutron irradiation facilities in the station. This spectrometer can also provide broad region worldwide, such as ICE 1 & 2 (Irradiation of Chips and of thermal neutrons in addition to high region of neutrons, Electronics) at Weapons Neutron Research (WNR) [5], covering neutron energy from meV to 1.6 GeV for NIF (Neutron Irradiation Facility) at TRIUMF [6], TSL different kinds of irradiation test and research. The single- ANITA at The Svedberg Laboratory [7], and CHIPIR event upset (SEU) in a static random access memory (Chip Irradiation) at ISIS-TS2 [8]. They provide the good (SRAM) cell is calculated by Monte Carlo code neutron spectra with high neutron flux to perform the SEE PHITS2.24. Results confirm that with neutron spectrum test of electronic devices and integrate circuits all over the similar to the atmosphere environment while high neutron world. flux, CSNS neutron irradiation spectrometer can give a China Spallation Neutron Source (CSNS) Facility [9] reliable SEE test for electronic devices and systems at provides an excellent capability of neutron irradiation greatly accelerated rate. environment for time-saving cosmic ray neutron filed testing. A new generation of neutron irradiation INTRONDUCTION spectrometer was recently proposed by the government. The main goals of this spectrometer are to predict the When high energy cosmic rays reach the earth’s electronic experiences in different irradiation atmosphere, they collide with the oxygen and nitrogen atoms, producing secondary cascade particles including environments, and find ways to overcome the irradiation protons, neutrons and pions. Neutrons have been affects caused by cosmic ray induced neutrons. This paper recognized as the main particles that reach to the aircraft will present the physical design of the CSNS neutron irradiation spectrometer. The structures of this altitudes and below [1,2]. When high energy neutrons spectrometer at the target station are presented. The interact with the silicon nuclei in semiconductor device, charged particles are produced and deposit their energy by neutron spectrum and flux calculated by the Monte Carlo ionizing radiation, inducing a great deal of electron-hole code MCNPX2.5 [10], are analyzed and compared with pairs. If the total number of the induced charge collected other accelerator based neutron facilities. The single- event upset (SEU) in a static random access memory in a sensitive region exceeds its critical value of the (SRAM) cell is calculated by Monte Carlo code device, a single-event effect (SEE) is occurred [3,4]. As PHITS2.24 to assess the test ability of CSNS neutron the fast developments of the electronic systems, irradiation spectrometer. ______________________ *Work supported by the National Science Foundation of China (Grant Nos. 11075203, 91026009 and 11174358). † [email protected], #[email protected] STRUCTURE OF CSNS NEUTRON during evaporation process. Based on the overall layout of IRRADIATION SPECTROMETER the target station, and the neutronic performance of CSNS neutron irradiation spectrometer, the beam port is CSNS is an accelerator based neutron facility being designed in the forward direction with 41 degrees to the constructed in south of China. It is intended to start proton beam, viewing the front part of the spallation operation in 2018. An accelerator delivers a 1.6 GeV target directly. The distance from the target window to the proton beam at 25 Hz frequency to a spallation target. The nearest beam port is 13.3 cm. In the Be/Fe reflectors with initial design proton beam power is 100 kW and will be radius of 50 cm, the beam port is 8×8 cm2. It is expanded upgraded to 500 kW after several years operation. The 2 to 10×10 cm from the helium vessel, passing through the key components at the target station are the W-Ta target, shielding to the outside of the target station. The three hydrogen-rich moderators, beryllium plus iron irradiated samples are positioned at 14 m from the centre (Be/Fe) reflectors and biological shielding. Detailed of the target station to experience the irradiation test. The description of the target station was once presented at geometry of the neutron irradiation spectrometer at the elsewhere [11,12]. There are 20 neutron spectrometers to target station is presented in Fig. 1. be designed in total. 19 thermal neutrons extracting from three different moderators are used for neutron scattering Beam shutter of CSNS neutron irradiation scientific research, while one fast neutron spectrometer in spectrometer at target station addition with thermal neutrons facing the front part of the spallation target directly, is used for SEE test and other There are 20 neutron beam shutters corresponding to irradiation researches. Three neutron scattering each spectrometer at CSNS Facility. Neutron beam spectrometers are being instructed at Stage-One, which shutters, which begin from 2.25 m to 4.25 m relative to are the General Purpose Powder Diffractometer (GPPD), the center of the target station, are used to ensure the the Multi-Purpose Reflectometer (MR) and the Small safety environment during sample replacements. Because Angle Neutron Scattering spectrometer (SANS). The CSNS neutron irradiation spectrometer supplies high CSNS neutron irradiation spectrometer is proposed to be energy neutrons and thermal neutrons with high constructed at Stage-Two. Since this neutron irradiation integrated fluxes, material and structure of the beam stop spectrometer is extracted from the target instead of the used in the neutron shutter is greatly different to the other moderators, its structure is greatly different from other 19 beam stops. Figure 2 shows the structure of the beam neutron scattering spectrometers. stop used in the beam shutter, together with the main structures of the beamline at the target station. The beam Beam port of CSNS neutron irradiation stop consists a 1.4 m stainless steel (SS316) block and a spectrometer in target station 60 cm W block. Heavy concrete used as the biological shielding, origins from 4.8 m to 6 m, while ordinate A 1.6 GeV proton beam bombards the W-Ta target, spallation reactions take place, producing high energy neutrons via cascade process and low energy neutrons Neutron Irradiation Spectrometer Biological shielding W-Ta target Fe/ Be reflectors Proton beam Fig. 2 Structure of neutron beam shutter in CSNS neutron Fig.1 The schematic of CSNS neutron irradiation irradiation spectrometer. It begins from 2.25 m to 4.25 m spectrometer at the target station. It is extracted from relative to the center of the target station, with 1.4 m the front part of the W-Ta target directly, at 41 SS316 plus 60 cm W. There are 1.8 m heavy concrete degrees in the forward direction of the proton beam. shielding and 3 m ordinate concrete pre-shielding. concrete from 6 m to 9 m is used as the pre-shielding. involves simulating the differential neutron spectrum Figure 3 shows the dose map corresponding to the including both thermal and high energy neutrons. The structure in Fig.2. One can see that near the spallation Monte Carlo code MCNPX2.5 is used to simulate the target, the dose rate is at 109 µSv/h. Since the beam stop proton beam interacting with the W-Ta target. Bertini of SS316&W can greatly shield high energy neutrons, the intranuclear cascade model coupled with RAL dose rate decrease sharply to several µSv/h at the end of evaporation model is used to simulate the productions of the beam stop, ensuring the safety environment in the high energy neutrons, while the nuclear data library experimental hall. ENDF-B/VI is used to calculate the productions of low energy neutrons. For the neutronic performance of the neutron irradiation spectrometer, the calculations are based on a 1.6 GeV, 100 kW (3.9×1014 p/s) proton beam with Gaussian distributions of 9.42 cm and 3.53 cm full width at half maximum, irradiating the 17×7×60 cm3 W- Ta target.