Ch. Brönnimann

Mythen detector system

Time-resolved experiments in powder diffraction are limited by the long time required to record spectra with current detectors. A major improvement can be made by using a massively parallel X-ray detection system together with a fast read out. The Mythen detector (Microstrip system for time-resolved experiments) has been built for the Powder Diffraction Station of the Material Science beamline at the Swiss Light Source to meet these requirements. The specifically developed read out chip (Mythen chip), the detector system and first measurements are shown.

PILATUS: a two-dimensional X-ray detector for macromolecular crystallography

A large quantum-limited area X-ray detector for protein crystallography is under development at the Swiss Light Source. The final detector will be 2k � 2k pixels covering 40 � 40 cm 2 : A three-module prototype with 1120 � 157 pixels covering an active area of 24:3 � 3: 4c m 2 has been tested. X-rays above 6 keV with peak count rates exceeding 5 � 10 5 X-ray/pixel/s could be detected in single photon counting mode. Statistics of module production and results of threshold trimming are presented. To demonstrate the potential of this new detector, protein crystal data were collected at beamline 6S of the SLS. r 2002 Elsevier Science B.V. All rights reserved. PACS: 87.64.Bx

Improved data acquisition in grazing-incidence X-ray scattering experiments using a pixel detector

The use of an area detector in grazing-incidence X-ray experiments lends many advantages in terms of both speed and reliability. Here a discussion is given of the procedures established using the PILATUS pixel detector developed at the Swiss Light Source for optimizing data acquisition and analysis of surface diffraction data at the Materials Science beamline, especially with regard to reflectivity measurements, crystal truncation and fractional order rods, and grazing-incidence diffraction experiments.

Precise measurement of the pi+ ---> pi0 e+ nu branching ratio

Using a large acceptance calorimeter and a stopped pion beam we have made a precise measurement of the rare pi(+)-->pi(0)e(+)nu (pi(beta)) decay branching ratio. We have evaluated the branching ratio by normalizing the number of observed pi(beta) decays to the number of observed pi(+)-->e(+)nu (pi(e2)) decays. We find the value of Gamma(pi(+)-->pi(0)e(+)nu)/Gamma(total)=[1.036+/-0.004(stat)+/-0.004(syst)+/-0.003(pi(e2))]x10(-8), where the first uncertainty is statistical, the second systematic, and the third is the pi(e2) branching ratio uncertainty. Our result agrees well with the standard model prediction.

A pixel detector for the protein crystallography beamline at the SLS

At the Paul Scherrer Institute a new synchrotron light source is currently under construction, the Swiss Light Source (SLS), which will be operational in summer 2001. Among the first beamlines is a high brightness, micro-focusing protein crystallography beamline. It will be equipped with a pixel detector, which has several features of interest for the next generation of protein crystallography detectors. The point spread function and the effect of charge sharing was measured with a prototype detector in a test experiment at the European Synchrotron Radiation Facility in Grenoble. The concepts of the SLS pixel detector is presented as well as test results from radiation hard prototype chips.

Continuous sample rotation data collection for protein crystallography with the PILATUS detector

The PILATUS detector (pixel apparatus for the SLS) is a large all silicon quantum-limited area X-ray detector for protein crystallography. A three-module array with 1120 � 157 pixels covering an active area of 24.3 � 3.6 cm 2 is in operation. Its main features are an excellent point-spread function, a very high dynamic range and a readout time of o7 ms. X-rays with energy above 6 keV can be detected in single photon counting mode. To demonstrate the potential of the detector, fine f-sliced protein crystal data were collected in continuous sample rotation mode at beamline X06SA of the SLS. r 2003 Elsevier B.V. All rights reserved.

Design, commissioning and performance of the PIBETA detector at PSI

Abstract We describe the design, construction and performance of the PIBETA detector built for the precise measurement of the branching ratio of pion beta decay, π + →π 0 e + ν e , at the Paul Scherrer Institute. The central part of the detector is a 240-module spherical pure CsI calorimeter covering ∼3 π sr solid angle. The calorimeter is supplemented with an active collimator/beam degrader system, an active segmented plastic target, a pair of low-mass cylindrical wire chambers and a 20-element cylindrical plastic scintillator hodoscope. The whole detector system is housed inside a temperature-controlled lead brick enclosure, which in turn is lined with cosmic muon plastic veto counters. Commissioning and calibration data were taken during two 3-month beam periods in 1999/2000 with π + stopping rates between 1.3·10 3 π + / s and 1.3·10 6 π + / s . We examine the timing, energy and angular detector resolution for photons, positrons and protons in the energy range of 5– 150 MeV , as well as the response of the detector to cosmic muons. We illustrate the detector signatures for the assorted rare pion and muon decays and their associated backgrounds.

Synchrotron beam test with a photon-counting pixel detector

Synchrotron beam measurements were performed with a single-photon-counting pixel detector to investigate the influence of threshold settings on charge sharing. Improvement of image homogeneity by adjusting the threshold of each pixel individually was demonstrated. With a flat-field correction, the homogeneity could be improved. A measurement of the point spread function is reported.

Protein crystallography with the PILATUS 1M detector at the Swiss Light Source

2. Excellent point spread function of one pixel. 3. High quantum efficiency. At 8 keV the absorption of a 0.3 mm thick Si-Sensor is 100%, at 12 keV 75% of the incoming radiation. This exceeds the quantum-efficiency of direct-coupled CCDs.

Cosmic muon tomography of pure cesium iodide calorimeter crystals

Abstract Scintillation properties of pure CsI crystals used in the shower calorimeter being built for precise determination of the π + →π 0 e + ν e decay rate are reported. Seventy-four individual crystals, polished and wrapped in Teflon foil, were examined in a multiwire drift chamber system specially designed for transmission cosmic muon tomography. Critical elements of the apparatus and reconstruction algorithms enabling measurement of spatial detector optical nonuniformities are described. Results are compared with a Monte Carlo simulation of the light response of an ideal detector. The deduced optical nonuniformity contributions to the FWHM energy resolution of the PIBETA CsI calorimeter for the π + → e + ν 69.8 MeV positrons and the monoenergetic 70.8 MeV photons were 2.7% and 3.7%, respectively. The upper limit of optical nonuniformity correction to the 69.8 MeV positron low-energy tail between 5 and 55 MeV was +0.2%, as opposed to the +0.3% tail contribution for the photon of the equivalent total energy. Imposing the 5 MeV calorimeter veto cut to suppress the electromagnetic losses, GEANT -evaluated positron and photon lineshape tail fractions summed over all above-threshold ADCs were found to be 2.36±0.05 (stat) ±0.20 (sys)% and 4.68±0.07 (stat)±0.20 (sys)%, respectively.