Paul Scherrer Institut Research Articles

MuPAD: Test at the hot single-crystal diffractometer HEiDi at FRM II

Abstract The device “MuPAD” for zero-field spherical neutron polarimetry (SNP) has recently been successfully used for experiments in SANS geometry at the very cold neutron beam line MIRA at the research reactor FRM II in Munich and at the cold triple axis spectrometer TASP at Paul Scherrer Institut (PSI). At the hot neutron beam line SR 9 of FRM II, the construction of the polarised neutron single -crystal diffractometer POLI-HEiDi is under way. One of the major applications of this new instrument will be the investigation of complex magnetic structures by means of SNP. As MuPAD has originally been designed for use with thermal and cold neutrons, we carried out a first feasibility experiment with MuPAD at the existing diffractometer HEiDi in order to verify its performance when operated with short wavelength neutrons. In addition, we tested the combination of MuPAD and 3He spin filters that wherewere used as polariser and analyser. Here we present the setup of the experiment and first successful measurements of the complete polarisation tensor of the (3 3 3) Bragg reflection of a Si single-crystal. In addition, we discuss the particularities of using two 3He filter cells simultaneously. A method to perform the corrections of the data, taking into account the time dependence of the polarising efficiency in both cells, is proposed.

Determination of the hadronic width of the ground state in pionic hydrogen

In a new high-precision experiment at the Paul Scherrer Institut (PSI), the hadronic shift (e1s) and width (Γ1s) of the ground state of pionic hydrogen, which are directly connected to the pion-nucleon isospin scattering lengths, were remeasured (PSI-Experiment R-98-01 Gotta et al. 1998). The results can be confronted with recent work of effective field theories defined in the low-energy limit of quantum chromodynamics (QCD), such as, e. g., chiral perturbation theory (ChPT). In addition, Γ1s is connected to the pion-nucleon coupling constant fπN. A precisely known value for fπN allows an accurate determination of the Goldberger-Treiman discrepancy, which constitutes a measure of chiral symmetry breaking. This contribution is mainly devoted to describe a method for an accurate extraction of the hadronic width from the π −H data.

Investigation of solid [formula omitted], [formula omitted] and [formula omitted] for ultracold neutron production

We have investigated the properties of the ultracold neutron converter materials deuterium D 2 , oxygen O 2 and heavy methane CD 4 in the temperature range between 8 K and room temperature. The experimental program was performed at the FUNSPIN beamline of the Swiss Spallation Neutron Source (SINQ) at Paul Scherrer Institut (PSI). In this paper the measured cold neutron total cross-sections for D 2 , O 2 and CD 4 are presented.

Fundamental measurements with muons – View from PSI

Muons can serve as probes to precisely determine fundamental parameters of the Standard Model or search for ‘new physics’. The high intensity muon beams at the Paul Scherrer Institut (PSI) allow for precision measurements and searches for rare or forbidden processes. Both types of experiments challenge the Standard Model in a way complementary to high energy physics. We give a short overview of recent results and ongoing experiments at PSI, and of ideas for the future.

Application of Pixel array detectors at X-ray synchrotrons

Pixel array detectors have only recently been seriously used at x-ray synchrotrons. We describe the application of a digital pixel array detector (Pilatus100k) to a variety of synchrotron experiments at the Advanced Photon Source at Argonne National Laboratory. The Pilatus100k was developed at the Paul Scherrer Institut (PSI). It has been commercialized by a PSI spinoff (Dectrics Ltd.) This is the first commercially available pixel array detector for x-ray synchrotron applications. The APS synchrotron provides tunable x-ray pulses with duration of ∼80 ps and a repetition period of 153 ns (24-bunch mode). The Pilatus100k is a direct detection x-ray detector where each 172 micron pixel counts individual x-ray pulses above a lower threshold. It consists of ∼100k pixels each of which is capable of single-photon counting (>3 keV) at count rates up to ∼1 MHz. In addition, the Pilatus100k is an electronically gateable detector. We present data showing that the Pilatus100k is capable of isolating a single x-ray bunch at the APS in 24 bunch mode. We will also present a variety of different experiments exploiting the unique capabilities of the Pilatus100k.

Sustainability of electricity supply technology portfolio

This paper outlines the approach to the evaluation of sustainability of current and future electricity supply options of interest for a major Swiss utility Axpo Holding AG. The motivation behind this effort has been to provide a solid basis for a state-of-the-art interdisciplinary assessment and use this framework within a dialog with a wide spectrum of stakeholders. The development and implementation of the methodology was coordinated by Axpo in co-operation with the Paul Scherrer Institut (PSI) and other scientific institutions. The evaluation covers environmental, social and economic dimensions of sustainability. Methods used include among others life cycle assessment (LCA), impact pathway approach (IPA) and probabilistic safety assessment (PSA). The associated databases developed by PSI have been extensively used, subject to major extensions necessary for analyzing the future technologies. Learning curves were employed for future cost estimates. Furthermore, particularly in the social area expert surveys were used. The results were aggregated using total (internal plus external) costs approach and multi-criteria decision analysis (MCDA). For MCDA a set of criteria and the associated indicators was established. In total 75 indicators were quantified, including 11 environmental, 33 social and 31 economic. Eighteen current and 18 future technologies have been analysed including nuclear as well as fossil and renewable technologies. Total costs were estimated for these technologies providing a clear ranking with nuclear having the lowest costs and some of the renewables showing remarkable cost reductions until 2030. This ranking is partially controversial mainly due to the limited representation of social aspects in the total costs. The results of MCDA-applications involving elicitation of preferences from a relatively homogeneous stakeholder group, i.e. 85 employees of the Axpo Group (including also NOK, EGL, CKW and Axpo IT), are summarized. In addition, sensitivity of technology ranking to preference profiles is demonstrated. Broader consideration of social factors favours renewables and depending on the specifics of preference profiles may lower the ranking of nuclear. Further applications of the MCDA-approach with various stakeholder groups are planned.

Scoping-level Probabilistic Safety Assessment of a complex experimental facility: Challenges and first results from the application to a neutron source facility (MEGAPIE)

This paper presents a scoping-level application of Probabilistic Safety Assessment (PSA) to selected systems of a complex experimental facility. In performing a PSA for this type of facility, a number of challenges arise, mainly due to the extensive use of electronic and programmable components and of one-of-a-kind components. The experimental facility is the Megawatt Pilot Target Experiment (MEGAPIE), which was hosted at the Paul Scherrer Institut (PSI). MEGAPIE demonstrated the feasibility of a liquid lead-bismuth target for spallation facilities at a proton beam power level of 1 MW. Given the challenges to estimate initiating event frequencies and failure event probabilities, emphasis is placed on the qualitative results obtainable from the PSA. Even though this does not allow a complete and appropriate characterization of the risk profile, some level of importance/significance evaluation was feasible, and practical and detailed recommendations on potential system improvements were derived. The second part of the work reports on a preliminary quantification of the facility risk. This provides more information on risk significance, which allows prioritizing the insights and recommendations obtained from the PSA. At the present stage, the limited knowledge on initiating and failure events is reflected in the uncertainties in their probabilities as well as in inputs quantified with bounding values. Detailed analyses to improve the quantification of these inputs, many of which turn out to be important contributors, were out of the scope of this study. Consequently, the reported results should be primarily considered as a demonstration of how quantification of the facility risk by a PSA can support risk-informed decisions, rather than precise figures of the facility risk.

Severe accident risks in fossil energy chains: A comparative analysis

Accidents in the energy sector have been identified as one of the main contributors to man-made disasters. The present work focuses on the assessment of severe accident risks relating to fossil energy chains. Evaluations were based on the highly comprehensive Energy-related Severe Accident Database (ENSAD), which was established at the Paul Scherrer Institut (PSI). The historical experience represented in this database allows a detailed comparison of severe accident risks in the broader energy sector. The analyses are not limited to power plants, but cover full energy chains, showing that immediate fatality rates are much higher for full fossil chains than expected if only power plants are considered. The different energy chains were analyzed separately, addressing selected technical aspects of severe accidents, followed by comparative evaluations. Generally, immediate fatality rates are significantly lower for countries of the Organization for Economic Co-operation and Development (OECD) and European Union 25 countries (EU25) than for non-OECD countries. In addition to aggregated values, frequency-consequence curves are also provided, since they not only reflect implicitly a ranking based on aggregated values, but also include information such as the maximum credible extent of damages.

Response study of fission track detectors using two different moderator designs in a high-energy radiation field

Fission track detectors in the center of moderating spheres are routinely used to measure the ambient dose equivalent due to neutrons in the environmental dosimetry at Paul Scherrer Institut (PSI). Originally, the system was designed to cope with neutrons from skyshine effects. Later, the system was also adapted behind the shielding of PSI's accelerators. Nowadays, as a consequence of continuously upgrading accelerator energies and intensities, the neutron energy behind thick shielding can range from fractions of eV to about 1 GeV (e.g. at CERN). For this reason a measurement campaign in a high-energy stray radiation field at CERN's High-Energy Reference Field Facility (CERF) was initiated to study and compare the response of the already existing detector-moderator configuration and a new design, the “GSI ball”. Employing an additional lead layer in a moderator sphere of 32.5 cm diameter, the GSI ball was primarily designed for the use with thermoluminescent based dosimeters in its center in order to optimize the response for the measurement of H * ( 10 ) to higher neutron energies. In this work, the measurement results for fission track detectors using two different radiator materials in the PSI and the GSI moderator are presented. Based on these studies, on the one hand, field calibration factors for the use in presumably similar high-energy fields around accelerators could be deduced. On the other hand, it could be shown that there is no need to replace the established PSI moderator by the GSI moderator since the combination of fission track detector and GSI moderator does not result in a significant sensitivity improvement.

Spatial and model-order based reactor signal analysis methodology for BWR core stability evaluation

A new methodology for the boiling water reactor core stability evaluation from measured noise signals has been recently developed and adopted at the Paul Scherrer Institut (PSI). This methodology consists in a general reactor noise analysis where as much as possible information recorded during the tests is investigated prior to determining core representative stability parameters, i.e. the decay ratio (DR) and the resonance frequency, along with an associated estimate of the uncertainty range. A central part in this approach is that the evaluation of the core stability parameters is performed not only for a few but for ALL recorded neutron flux signals, allowing thereby the assessment of signal-related uncertainties. In addition, for each signal, three different model-order optimization methods are systematically employed to take into account the sensitivity upon the model-order. The current methodology is then applied to the evaluation of the core stability measurements performed at the Leibstadt NPP, Switzerland, during cycles 10, 13 and 19. The results show that as the core becomes very stable, the method-related uncertainty becomes the major contributor to the overall uncertainty range while for intermediate DR values, the signal-related uncertainty becomes dominant. However, as the core stability deteriorates, the method-related and signal-related spreads have similar contributions to the overall uncertainty, and both are found to be small. The PSI methodology identifies the origin of the different contributions to the uncertainty. Furthermore, in order to assess the results obtained with the current methodology, a comparative study is for completeness carried out with respect to results from previously developed and applied procedures. The results show a good agreement between the current method and the other methods.

Monte Carlo simulations for instrumentation at SINQ

The Paul Scherrer Institut (PSI) operates a spallation source SINQ equipped with 11 different neutron scattering instruments. Beside the optimization of the existing instruments, the extension with new instruments and devices are continuously done at PSI. For design and performance studies different Monte Carlo packages are used. Presently two major projects are in an advanced stage of planning. These are the new thermal neutron triple-axis spectrometer Enhanced Intensity and Greater Energy Range (EIGER) and the ultra-cold neutron source (UCN-PSI). The EIGER instrument design is focused on an optimal signal-to-background ratio. A very important design part was to realize a monochromator shielding which covers best shielding characteristic, low background production and high instrument functionality. The Monte Carlo package MCNPX was used to find the best choice. Due to the sharp energy distribution of ultra-cold neutrons (UCN) which can be Doppler-shifted towards cold neutron energies, a UCN phase space transformation (PST) device could produce highly monochromatic cold and very cold neutrons (VCN). The UCN-PST instrumentation project running at PSI is very timely since a new-generation superthermal spallation source of UCN is under construction at PSI with a UCN density of 3000–4000 n cm −3. Detailed numerical simulations have been carried out to optimize the UCN density and flux. Recent results on numerical simulations of an UCN-PST-based source of highly monochromatic cold neutrons and VCN are presented.

Proton irradiation of EMCCDs

This paper describes the irradiation of 95 electron multiplication charge coupled devices (EMCCDs) at the Paul Scherrer Institut (PSI) in Switzerland, to investigate the effects of proton irradiation on the operational characteristics of CCDs featuring electron multiplication technology for space use. This work was carried out in support of the CCD development for the radial velocity spectrometer (RVS) instrument of the European Space Agency's cornerstone Gaia mission. Previous proton irradiations of EMCCDs, have shown the technology to be radiation hard to /spl sim/10/spl times/ the required six-year Gaia lifetime proton fluence, with no device failures or unexpected operational changes. The purpose of the study described in this paper was to further investigate the statistical probability of device failure as a result of radiation damage, the large number of devices and high proton fluence used, making the study equivalent to testing /spl sim/50 complete RVS CCD focal planes to the expected end of life proton dose. An outline of the earlier EMCCD proton irradiations is given, followed by a detailed description of the proton irradiation and characterization of the 95 devices used in this latest study.

The Digital User Office (DUO)

The Digital User Office (DUO) has been developed at the Swiss Light Source (SLS) of the Paul Scherrer Institut (PSI) in order to deal efficiently with the large number of users typical of a synchrotron radiation facility. DUO is based on an Oracle database. Thus, in addition to the canonical functions expected from such a system, such as support of the proposal processing and preparation of conferences, it offers additional novel functions. Active linking of the DUO database to other databases permits the creation of computer accounts, automatic setup of experiment parameters at the start of a measurement or preparing information on publications for reporting semi-automatically. Developed initially for the SLS at the Paul Scherrer Institut, DUO is currently being extended to include in an integrated central PSI user office the user communities of the other large facilities at PSI: the neutron spallation source SINQ, the μSR facility SμS, and the proton accelerator. Currently, the system is dealing effectively with far over one thousand users per year and hundreds of proposals so that in terms of scalability the multiplication of these numbers expected in coming years should present no problem.

Results of spot-scanning proton radiation therapy for chordoma and chondrosarcoma of the skull base: The Paul Scherrer Institut experience

To assess the clinical results of spot scanning proton beam radiation therapy (PT) in the treatment of skull base chordomas and low-grade chondrosarcomas (CS). Between October 1998 and October 2003, 29 patients (median age, 39 years) with chordomas (n = 18) and CS (n = 11) were treated at the Paul Scherrer Institut (PSI) with protons using the main 510-MeV cyclotron. Tumor conformal application of proton beams was realized by spot scanning technology. The median chordoma and CS dose was 74 and 68 cobalt Gy equivalent, respectively (cobalt Gy equivalent = proton Gy x 1.1). Median gross tumor volumes (GTV) were 16.4 mL (range, 1.8-48.1 mL) and 15.2 mL (range, 2.3-57.3 mL) for chordoma and CS, respectively. Late toxicity was assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE, v3.0) grading system. The median follow-up time was 29 months (range, 6-68 months). Actuarial 3-year local control rates were 87.5% and 100% for chordoma and CS, respectively. We observed one surgical pathway and one marginal failure in patients with chordomas. No regional failure or distant metastasis was observed. At 3 years, actuarial PFS and OS for the entire cohort was 90% and 93.8%, respectively. Actuarial 3-year complication-free survival was 82.2%. Radiation-induced pituitary dysfunction was observed in 4 (14%) patients (CTCAE Grade 2). No patient presented with post-PT brainstem or optic pathways necrosis or dysfunction. In univariate analysis, age < or =40 years at the time of PT affected favorably on PFS (p = 0.09). Spot-scanning PT offers high tumor control rates of skull base chordoma and CS. These results compare favorably to other combined proton-photon or carbon ion irradiation series. Observed toxicity was acceptable. Younger age (< or =40 years) was a favorable prognostic factor of PFS. These preliminary results are encouraging but should be confirmed during a longer follow-up.

PIONIC HYDROGEN

The measurement of the pion–nucleon scattering lengths constitutes a high–precision test of the methods of Chiral Pertubation Theory (χPT), which is the low–energy approach of QCD. The πN s–wave scattering lengths and the pion–nucleon coupling constant are related to the strong–interaction shift ∊1s and width Γ1s of the s–states in the pionic hydrogen atom. ∊1s and Γ1s are determined from the measured energies and line widths of X–ray transitions to the 1s ground state when compared to the calculated electromagnetic values. A new experiment, set up at the Paul–Scherrer–Institut (PSI), has completed a first series of measurements.

Materials for Polymer Electrolyte Fuel Cells

The commercial success of the polymer electrolyte fuel cell (PEFC) will to a large extent be determined by the nature, properties, functionality, and cost of the electrochemical sub-components used in the membrane electrode assembly (MEA). Materials research activities in Switzerland for the PEFC are being pursued at the Paul Scherrer Institut (Villigen AG) and the Swiss Federal Institute of Technology in Lausanne with different objectives. The radiation grafted proton exchange membrane developed at the Paul Scherrer Institut (PSI) has been brought to a near-product-like quality level with encouraging performance close to state-of-the-art materials and a life-time of several thousand hours. Furthermore, the membrane shows low methanol crossover in the direct methanol fuel cell. In addition, polyarylene block copolymer membranes have been investigated as an option for fluorine-free membranes. The electrocatalysis of Pt in acidic solution and in contact with a solid electrolyte, the development of new methanol oxidation and oxygen reduction catalysts, and co-sputtering of Pt and carbon as an alternative method for catalyst preparation are areas of fundamental research. More applied research is performed in the characterization of commercial electrodes in single cells, using standard as well as advanced diagnostic tools developed in-house. This article gives an overview over the research and development projects in Switzerland related to materials and components for the PEFC.

Peach Bottom BWR Turbine Trip Benchmark Analyses with RETRAN-3D and CORETRAN

This paper presents results from Paul Scherrer Institut (PSI) on the three phases of the Peach Bottom Boiling Water Reactor Turbine Trip Benchmark. The first part of the paper presents the PSI analysis using RETRAN-3D of Phase 1, where the system pressure is predicted based on a predefined core power distribution. These calculations elucidate the importance of accurate modeling of the steam separator region and of nonequilibrium effects. In the second part, the CORETRAN results of Phase 2 are summarized and the core 3-D response to the pressurization transient prior to SCRAM is discussed. The CORETRAN results show a slight axial flux redistribution toward the top of the core, while radially a flux redistribution is observed toward core regions with assemblies that are initially moderately voided and where the axial power shape is increasingly top-peaked. The impact of the control rod configuration as well as the assembly coolant inventory dynamics on the 3-D flux redistribution is also discussed. The third part presents results of the Phase 3 calculation using RETRAN-3D, which is a culmination of the analytical work of Phases 1 and 2.

A 25-kV 75-kHz Kicker for Measurement of Muon Lifetime

An international collaboration plans to measure the lifetime of the muon to a precision of 1 part per million . The "MuLan" experiment will take place at the Paul Scherrer Institut (PSI) in Northern Switzerland. The MuLan experiment requires a fast beam line kicker, which can turn the beam on and off, to invoke an artificial time structure on the continuous beam which has a 50.6-MHz time microstructure. The kicker needs to run with a standard "on-off time cycle" or in a "Muon on Request" mode. The MuLan kicker consists of two pairs of deflector plates mechanically in series, driven by four modulators. Each modulator consists of two stacks of MOSFETs operating in push-pull mode. The specifications for the kicker demand that the rise and fall times of the deflector plate voltage do not exceed 45 ns. There is a requirement for an adjustable output voltage from 0 V to /spl plusmn/12.5 kV per deflector plate, a minimum pulse duration of 200 ns, and adjustable repetition rate up to a maximum of 50 kHz, continuous. Short turn-on and turn-off delays are required for the "Muon on Request" mode; the measured propagation delay is 200 ns. The specifications also require that the polarity of the pulses on the plates be selectable, although not on a pulse-by-pulse basis. This paper describes the novel design of the kicker and presents both predictions and measurements.

Severe accidents in the energy sector: comparative perspective

This paper addresses one of the controversial issues in the current comparative studies of the environmental and health impacts of energy systems, i.e. the treatment of severe accidents. The work covers technical aspects of severe accidents and thus primarily reflects an engineering perspective on the energy-related risk issues, though some social implications are also touched upon. The assessment concerns fossil energy sources (coal, oil and gas), nuclear power and hydro power. The scope is not limited to the power production (conversion) step of these energy chains but, whenever applicable, also includes exploration, extraction, transports, processing, storage and waste disposal. With the exception of the nuclear chain the focus of the work has been on the evaluation of the historical experience of accidents. The basis used for this evaluation is a comprehensive database ENSAD (Energy-related Severe Accident Database), established by the Paul Scherrer Institut (PSI). For hypothetical nuclear accidents the probabilistic technique has also been employed and extended to cover the assessment of economic consequences of such accidents. The broader picture obtained by coverage of full energy chains leads on the world-wide basis to aggregated immediate fatality rates being much higher for the fossil chains than what one would expect if only power plants were considered. Generally, the immediate fatality rates are for all considered energy carriers significantly higher for the non-OECD countries than for OECD countries. In the case of hydro and nuclear the difference is in fact dramatic. The presentation of results is not limited to the aggregated values specific for each energy chain. Also frequency-consequence curves are provided. They reflect implicitly the ranking based on the aggregated values but include also such information as the observed or predicted chain-specific maximum extents of damages. This perspective on severe accidents may lead to different system rankings, depending on the individual risk aversion.

CFD Design Support at PSI for the International MEGAPIE Liquid-Metal Spallation Target

The MEGAPIE (Megawatt Pilot Experiment) Project has been primarily initiated in response to interest in the Accelerator Driven System (ADS). The ADS is a nuclear reactor concept with a fuel cycle which can burn minor actinide waste products from conventional reactors, while also taking advantage of the safety characteristics of a sub-critical reaction process. By this means, the fission chain reaction is maintained by additional neutrons generated by protons in a liquid-metal spallation target. The goal of the international MEGAPIE project is to design and construct such a target and install and test it over a period of one year in the SINQ spallation neuron source facility at the Paul Scherrer Institut (PSI). To aid the design process, Computational Fluid Dynamics (CFD) is being used to optimise the thermal- hydraulic behaviour of the target. Results obtained so far indicate that it should be possible to remove 700 kW of heat deposited by the proton beam in the target, under steady-state conditions (40kg/s total Lead Bismuth Eutectic flow rate), without peak window temperature rising above about 385°C, when using a bypass flow of 2.5 kg/s and a slanted- end guide tube. A tentative peak window temperature of 400°C is currently considered allowable, on the basis of material strength after irradiation, and CFD simulation is currently being validated by suitable LBE experiments in similar geometry.