Swiss Spallation Neutron Source Research Articles

Upgrades to the SINQ Cold Neutron Source

Changing the configuration of the cold neutron source during an extended shutdown of the Swiss Spallation Neutron Source (SINQ) at the Paul Scherrer Institut is being considered for improving performance of the instruments that use the cold source. Proposed plans include making the REH external (ensuring that it is not filled with liquid D2) and using a REH that has been optimized to provide maximum gains between 3 and 6 Å. The optimization study was done using the MCNP Monte Carlo particle transport code, but was made tenable by developing a quick flux reconstruction technique that allows the neutron guide reflectivity to be approximated and accounted for in the optimization figure of merit. Ultimately, a wedgeshaped REH that penetrates the D2 volume to about 4 cm from its center was determined to be optimal, and should provide an average gain of 24% from 3 and 6 Å and a peak gain of 29% at 5.5.

News from the Swiss Spallation Neutron Source SINQ: diffraction at non-ambient conditions

News from the Swiss Spallation Neutron Source SINQ: diffraction at non-ambient conditions

Seeking to bridge Europe’s impending neutron gap

Europe’s primacy in neutron scattering depends on maintaining a network of local and international facilities.

Benchmarking shielding simulations for an accelerator-driven spallation neutron source

The shielding at an accelerator-driven spallation neutron facility plays a critical role in the performance of the neutron scattering instruments, the overall safety, and the total cost of the facility. Accurate simulation of shielding components is thus key for the design of upcoming facilities, such as the European Spallation Source (ESS), currently in construction in Lund, Sweden. In this paper, we present a comparative study between the measured and the simulated neutron background at the Swiss Spallation Neutron Source (SINQ), at the Paul Scherrer Institute (PSI), Villigen, Switzerland. The measurements were carried out at several positions along the SINQ monolith wall with the neutron dosimeter WENDI-2, which has a well-characterized response up to 5 GeV. The simulations were performed using the Monte-Carlo radiation transport code Geant4, and include a complete transport from the proton beam to the measurement locations in a single calculation. An agreement between measurements and simulations is about a factor of 2 for the points where the measured radiation dose is above the background level, which is a satisfactory result for such simulations spanning many energy regimes, different physics processes and transport through several meters of shielding materials. The neutrons contributing to the radiation field emanating from the monolith were confirmed to originate from neutrons with energies above 1 MeV in the target region. The current work validates Geant4 as being well suited for deep-shielding calculations at accelerator-based spallation sources. We also extrapolate what the simulated flux levels might imply for short (several tens of meters) instruments at ESS.

Microstructural probing of ferritic/martensitic steels using internal transmutation-based positron source

This paper presents the use of an internal 44Ti/44Sc radioisotope source for a direct microstructural characterization of ferritic/martensitic (f/m) steels after irradiation in targets of spallation neutron sources. Gamma spectroscopy measurements show a production of ∼1MBq of 44Ti per 1 g of f/m steels irradiated at 1 dpa (displaced per atom) in the mixed proton–neutron spectrum at the Swiss spallation neutron source (SINQ). In the decay chain 44Ti → 44Sc → 44Ca, positrons are produced together with prompt gamma rays which enable the application of different positron annihilation spectroscopy (PAS) analyses, including lifetime and Doppler broadening spectroscopy. Due to the high production yield, long half-life and relatively high energy of positrons of 44Ti, this methodology opens up new potential for simple, effective and inexpensive characterization of radiation induced defects in f/m steels irradiated in a spallation target.

Simulation of a beam rotation system for a spallation source

With a nominal beam power of nearly 1 MW on target, the Swiss Spallation Neutron Source (SINQ), ranks among the world's most powerful spallation neutron sources. The proton beam transport to the SINQ target is carried out exclusively by means of linear magnetic elements. In the transport line to SINQ the beam is scattered in two meson production targets and as a consequence, at the SINQ target entrance the beam shape can be described by Gaussian distributions in transverse $x$ and $y$ directions with tails cut short by collimators. This leads to a highly nonuniform power distribution inside the SINQ target, giving rise to thermal and mechanical stresses. In view of a future proton beam intensity upgrade, the possibility of homogenizing the beam distribution by means of a fast beam rotation system is currently under investigation. Important aspects which need to be studied are the impact of a rotating proton beam on the resulting neutron spectra, spatial flux distributions and additional---previously not present---proton losses causing unwanted activation of accelerator components. Hence a new source description method was developed for the radiation transport code MCNPX. This new feature makes direct use of the results from the proton beam optics code TURTLE. Its advantage to existing MCNPX source options is that all phase space information and correlations of each primary beam particle computed with TURTLE are preserved and transferred to MCNPX. Simulations of the different beam distributions together with their consequences in terms of neutron production are presented in this publication. Additionally, a detailed description of the coupling method between TURTLE and MCNPX is provided.

Recent progress on HYSPEC, and its polarization analysis capabilities

HYSPEC is a high-intensity, direct-geometry time-of-flight spectrometer at the Spallation Neutron Source, optimized for measurement of excitations in small single-crystal specimens with optional polarization analysis capabilities. The incident neutron beam is monochromated using a Fermi chopper with short, straight blades, and is then vertically focused by Bragg scattering onto the sample position by either a highly oriented pyrolitic graphite (unpolarized) or a Heusler (polarized) crystal array. Neutrons are detected by a bank of 3 He tubes that can be positioned over a wide range of scattering angles about the sample axis. HYSPEC entered the user program in February 2013 for unpolarized experiments, and is already experiencing a vibrant research program. Polarization analysis will be accomplished by using the Heusler crystal array to polarize the incident beam, and either a 3 He spin filter or a supermirror wide-angle polarization analyser to analyse the scattered beam. The 3 He spin filter employs the spin-exchange optical pumping technique. A 60 ∘ wide angle 3 He cell that matches the detector coverage will be used for polarization analysis. The polarized gas in the post-sample wide angle cell is designed to be periodically and automatically refreshed with an adjustable pressure of polarized gas, optically pumped in a separate cell and then transferred to the wide angle cell. The supermirror analyser has 960 supermirror polarizers distributed over 60 ∘ , and has been characterized at the Swiss Spallation Neutron Source. The current status of the instrument and the development of its polarization analysis capabilities are presented.

Neutron imaging options at the BOA beamline at Paul Scherrer Institut

The BOA beamline at the Swiss spallation neutron source SINQ at Paul Scherrer Institut is a flexible instrument used mainly for testing novel techniques and devices for neutron scattering and optics, but, due to the large and relatively homogeneous field of view, it can be successfully used for experiments in the field of neutron imaging. The beamline allows also for the exploitation of advanced imaging concepts such as polarized neutron imaging and diffractive neutron imaging. In this paper we present the characterization of the BOA beamline in the light of its neutron imaging capabilities. We show also the different techniques that can be employed there as user-friendly plugins for non-standard neutron imaging experiments.

Radiation damage and lifetime estimation of the proton beam window at the Japan Spallation Neutron Source

The proton beam window (PBW) is a component that separates the high-vacuum area of the accelerator from the target area in the Japan Proton Accelerator Research Complex’s Japan Spallation Neutron Source (JSNS). It is important to estimate the damage accumulated from proton beam irradiation to establish a safe lifetime for the window. The PBW is made of an aluminum alloy, which was chosen because of its successful use in the target safety hull of the Swiss Spallation Neutron Source (SINQ). Post-irradiation examination (PIE) performed on SINQ Target 3 after irradiation with a 0.6GeV proton beam measured the gas production in its aluminum safety hull. To estimate a safe lifetime for the JSNS PBW, we calculated the displacement per atom (DPA) and gas production rate using the Particle and Heavy Ion Transport code System (PHITS) for 0.6- and 3-GeV protons. For the hydrogen gas production rate, PHITS shows good agreement with the SINQ PIE results; however, for the helium production rate, it predicts a 45% lower value than the experimental result of 1125 appm. The calculated result for helium production was normalized to fit the experimental results of SINQ. We conservatively estimate the lifetime of the JSNS PBW using the condition that the hydrogen production rate does not exceed the value measured at SINQ. The lifetime of the PBW corresponds to a proton beam fluence of 1.8×1021cm−2, which is equivalent to an integrated beam power of 8000MWh with the designed current density of 10μAcm−2. The peak density will be reduced to 8.4μAcm−2 to suppress cavitation pitting damage in the mercury target vessel. Consequently, the lifetime of the PBW will be 9500MWh.

Note: Versatile sample stick for neutron scattering experiments in high electric fields

We present a versatile high voltage sample stick that fits into all cryomagnets and standard cryostats at the Swiss Spallation Neutron Source, Paul Scherrer Institut, and which provides a low effort route to neutron scattering experiments that combine electric field with low temperature and magnetic field. The stick allows for voltages up to 5 kV and can be easily adapted for different scattering geometries. We discuss the design consideration and thermal behavior of the stick, and give one example to showcase the abilities of the device.

Production and segregation of transmutation elements Ca, Ti, Sc in the F82H steel under mixed spectrum irradiation of high energy protons and spallation neutrons

Ferritic/martensitic steel F82H was irradiated at 345°C in a mixed proton–neutron spectrum in the Swiss spallation neutron source up to 20.3dpa. Nanoscale investigations using the atom probe tomography (APT) technique were performed in order to study the atomic scale evolution of the microstructure of the F82H steel under irradiation.Spallation products Ca, Ti and Sc have been detected. The irradiation led to the production of about 370appm of Ca, 90appm of Sc and 800appm of Ti. APT experiments revealed that regardless their low bulk concentrations, the spallation products extensively participate in the evolution of the microstructure: formation of radiation-induced clusters, segregation at the dislocation loops and alteration of the microchemistry of carbides. In this paper, a quantitative description of the observed features is presented and results are compared with TEM data of the literature obtained on the same steel and under similar irradiation conditions.

Bend-fatigue properties of JPCA and Alloy800H specimens irradiated in a spallation environment

To evaluate the lifetime of the beam window of an accelerator-driven transmutation system (ADS) and spallation neutron source, post irradiation examination (PIE) of the STIP (SINQ target irradiation program, SINQ; Swiss spallation neutron source) specimens has been carried out. The specimens tested in this study were made from the austenitic steel JPCA (Japan Primary Candidate Alloy) and high-Ni steel Alloy800H. The specimens were irradiated at SINQ Target 4 (STIP-II) with high-energy protons and spallation neutrons. The irradiation conditions were as follows: the proton energy was 580MeV, irradiation temperatures ranged from 120 to 350°C and displacement damage levels ranged from 7.0 to 19.3dpa. Bend-fatigue tests were performed in air at room temperature under deflection control mode. The wave form of the control signal was a sine curve with a frequency of 26Hz. Fracture surface observation after the tests was done by SEM.The results on the irradiated JPCA in this study are identical to with the result of STIP-I specimens (−11dpa). Namely, the numbers of cycles to failure (Nf) were not changed by irradiation. Dpa dependence of Nf was not clearly seen in the irradiation conditions. In spallation environment, He atom production ratio is very high and most of He atoms are retained in the materials. In spite of large number of He atoms, all JPCA specimens show transgranular fracture surface.

Tensile mechanical properties of a stainless steel irradiated up to 19 dpa in the Swiss spallation neutron source

To evaluate the lifetime of the beam window of an accelerator-driven transmutation system (ADS), post irradiation examination (PIE) of the STIP (SINQ target irradiation program, SINQ; Swiss spallation neutron source) specimens was carried out. The specimens tested in this study were made from the austenitic steel Japan primary candidate alloy (JPCA). The specimens were irradiated at SINQ Target 4 (STIP-II) with high-energy protons and spallation neutrons. The irradiation conditions were as follows: the proton energy was 580MeV, irradiation temperatures ranged from 100 to 430°C, and displacement damage levels ranged from 7.1 to 19.5dpa. Tensile tests were performed in air at room temperature (RT), 250°C and 350°C. Fracture surface observation after the tests was done by Scanning electron microscope (SEM). Results of the tensile tests performed at R.T. showed the extra hardening of JPCA at higher dose compared to the fission neutron irradiated data. At the higher temperatures, 250°C and 350°C, the extra hardening was not observed. Degradation of ductility bottomed around 10dpa, and specimens kept their ductility until 19.5dpa. All specimens fractured in ductile manner.

Materials issues of the SINQ high-power spallation target

Abstract The Swiss spallation neutron source SINQ operated at the Paul Scherrer Institut is driven by PSI's 590 MeV proton accelerator at a beam power of 0.8 MW, as such being the most powerful (CW) spallation source worldwide. The core element of such a facility is the neutron production target. Since the commissioning in 1997, PSI has always fostered combined efforts in the development of the spallation target, including dedicated materials research for high dose radiation environments. The overall goal was to achieve optimized neutron production, combined with sufficient robustness, thermo-mechanical stability and radiation resistance to withstand the severe loads of high-dose irradiation and frequent thermal cycling over an acceptable lifetime. The target itself has been improved in several steps by searching for the optimal materials and geometries. In parallel, numerous experiments have been conducted in the targets of SINQ for studying radiation damage effects induced by high energy protons and spallation neutrons.

The ICON beamline – A facility for cold neutron imaging at SINQ

The beamline for Imaging with COld Neutrons (ICON) at Swiss spallation neutron source (SINQ) at Paul Scherrer Institut has a flexible design to meet the requests from a wide user community. The current status of the beamline and its characteristics are described. The instrumentation includes three experimental positions from which two are equipped with digital camera based imaging detectors. Tomographic imaging is among the standard methods available at the beamline. Advanced methods such as energy-selective imaging and grating interferometry are available as instrument add-ons which are easily installed.

EFFECTS OF RADIATION AND He ON MICROSTRUC- TURES OF LOW ACTIVE FERRITIC/MARTENSITIC STEEL F82H

Low active ferritic/martensitic steel,F82H,has been developed as a candidate material for structural applications of fusion reactors because it has relatively low shifts in ductile-to-brittle transition temperature(DBTT) and excellent irradiation swell resistance.More works have been done in recent years on the microstructure and mechanical properties of F82H steel before and after irradiation,but most of the tested samples were irradiated at low temperature(400℃).In this work,the microstructure of F82H steel irradiated in the Swiss spallation neutron source SINQ in a temperature range of 150—450℃and a dose range of 6.1—20.2 dpa was studied.Defect clusters and He bubble were observed by TEM in the irradiated specimens.The results showed that there existed high density He bubbles with size of 1.6 nm under irradiation temperature higher than 208℃, irradiation dose higher than 9.5 dpa and He concentration 680×10~(-6).The effects of irradiation dose, irradiation temperature and He concentration on microstructure of F82H steel were discussed.

Helium-induced hardening effect in ferritic/martensitic steels F82H and Optimax-A irradiated in a mixed spectrum of high energy protons and spallation neutrons

Ferritic/martensitic (FM) steels, F82H and Optimax-A, were irradiated up to 11.3dpa/1175appm He in Target-3 of the Swiss Spallation Neutron Source (SINQ). To investigate helium-induced hardening effect, micro-hardness and microstructure of the irradiated specimens were investigated in as-irradiated condition and after annealing at 600°C. The results show that the hardening in the as-irradiated specimens increased linearly with √dpa at low doses and more rapidly at higher doses, which is contributed by both defect clusters and helium bubbles. After annealing, although the hardening decreased greatly, a significant amount remained, which is proportional to √CHe (CHe is helium concentration) and essentially contributed by helium bubbles. From the results of the annealed specimens, it is deduced that the helium bubbles with sizes 1–1.5nm are weak obstacles with barrier strength about 0.1. The significant hardening in the annealed specimens can be attributed to the high density of bubbles.

On a concept of electromagnetic pump for the liquid metal target for routine operation in the Swiss Spallation Neutron Source

On a concept of electromagnetic pump for the liquid metal target for routine operation in the Swiss Spallation Neutron Source

Achievements and perspectives of ERAWAST

The ERAWAST initiative (Exotic Radionuclides from Accelerator Waste for Science and Technology) was started at PSI in 2006 and is aimed to acquire resources from the PSI accelerator facilities for the preparation of rare long-lived radionuclides for several scientific purposes [1]. One of the application fields where such radionuclides like 60 Fe, 53 Mn, 44 Ti, 26 Al, 7/10 Be are urgently needed is nuclear astrophysics.First laboratory-scale separations have been carried out, with the result that two samples of around 1016 atoms of 60 Fe each could be provided for experiments [2]. A re-determination of the half-life of 60 Fe was performed with the first one [3], and the neutron capture cross section of 60 Fe at stellar energies was measured for the first time [4] using the second one.These successes encouraged us to put more efforts into the development of remote- controlled separation systems in order to gain higher amounts and the exploitation of new sources of the desired isotopes. These works are currently ongoing and for the first time, separation of about 5 GBq 7 Be from the cooling water of the Swiss Spallation Neutron Source (SINQ) was succeeded. Moreover, about 50 g of 10 Be are now available after its separation from graphite samples of the target E station at PSI [5]. Considerable amounts of 60 Fe, 53 Mn, 26 Al and others from an irradiated copper beam dump can be expected in the near future.In addition, a scientific program was originated to determine half-lives and neutron capture cross-section of astrophysical interesting radionuclides. In a first step a confirmation of the new measured 60 Fe half-life in two independent experiments was started. First studies aimed to re-measure the half-life of 10 Be are currently ongoing. Experiments to determine the neutron capture cross-section of 53 Mn using cold and ultra-cold neutrons as well as its half-life at PSI are planned.

Proton irradiation effects on tensile and bend-fatigue properties of welded F82H specimens

In several institutes, research and development for an accelerator-driven transmutation system (ADS) have been progressed. Ferritic/martensitic (FM) steels are the candidate materials for the beam window of ADS. To evaluate of the mechanical properties of the irradiated materials, the post irradiation examination (PIE) work of the SINQ (Swiss spallation neutron source) target irradiation program (STIP) specimens was carried out at JAEA. In present study, the results of PIE on FM steel F82H and its welded joint have been reported. The present irradiation conditions of the specimens were as follows: proton energy was 580 MeV. Irradiation temperatures were ranged from 130 to 380 °C, and displacement damage level was ranged from 5.7 to 11.8 dpa. The results of tensile tests performed at 22 °C indicated that the irradiation hardening occurred with increasing the displacement damage up to 10.1 dpa at 320 °C irradiation. At higher dose (11.8 dpa) and higher temperature (380 °C), irradiation hardening was observed, but degradation of ductility was relaxed in F82H welded joint. In present study, all specimens kept its ductility after irradiation and fractured in ductile manner. The results on bend-fatigue tests showed that the fatigue life ( N f) of F82H base metal irradiated up to 6.3 dpa was almost the same with that of unirradiated specimens. The N f of the specimens irradiated up to 9.1 dpa was smaller than that of unirradiated specimens. Though the number of specimen was limited, the N f of F82H EB (15 mm) and EB (3.3 mm) welded joints seemed to increase after irradiation and the fracture surfaces of the specimens showed transgranular morphology. While F82H TIG welded specimens were not fractured by 10 7 cycles.