C. J. Schmidt

Surface science using molecular beam spin echo

Abstract We have developed a new experimental method for measuring extremely small changes in kinetic energy in a flux of atoms or molecules. Here, we manipulate the magnetic moments of the species so as to create an echo signal. Using the nuclear spins in an atomic beam of 3 He we have demonstrated the power of this method, by resolving a change in energy of several neV. Due to the exclusive surface sensitivity and complete inertness of He atoms as a probe, 3 He spin echo ( 3 He-SE) seems an ideal method for studying slow motion in and on surfaces (e.g. diffusion). Therefore, we have added UHV surface science capabilities to the 3 He-SE setup. We present the first results obtained with the completed apparatus and show that 3 He-SE may give information on the dynamics at the surface on length scales up to tens of μm.

MSGCROC -a selftriggered ASIC for readout of hybrid gas microstrip neutron detectors for event rates of 10 8 /s and 2D spatial resolutions ≪100 μm FWHM

In the frame of the DETNI project a 32-channel ASIC suitable for readout of a novel 2D thermal neutron detector type based on a hybrid low-pressure micro-strip gas chamber (MSGC) with solid 157Gd converter has been developed. Each microstrip and ASIC channel delivers position information, a fast time stamp of 2 ns resolution and the signal amplitude. The time stamp T is used for correlating the signals from the X and Y strips with low chance coincidence rate while the amplitude E is used for finding the center of gravity of a cluster of strips. The T and E information are stored in derandomizing buffers and read out via a token ring architecture.

Development of very high rate and resolution neutron detectors with novel readout and DAQ hard- and software in DETNI

In the Joint Research Activity DETNI (DETectors for Neutron Instrumentation) of the FP6 EU Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy (NMI3) prototypes of three novel modular thermal neutron area detector types, based on thin solid neutron converters, were built and tested, which were developed for time- and wavelength resolved neutron detection with 2-D spatial and time resolutions of 50–1000 µm (FWHM) and of up to 2 ns, respectively, and for counting rates in the 107 – 108 cps range, i.e. for coping with the highest resolution and rate requirements at pulsed spallation neutron sources with MW average proton beam power like ESS. The detector types are (i) four-fold segmented modules of Silicon microstrip detectors (Si-MSD) with 157Gd converter layer between two double-sided Si sensors with 80 ¼m strip pitch, (ii) hybrid low-pressure microstrip gas chamber (MSGC) detectors with three-stage gas amplification and 2-D position-sensitive MSGC plates either side of a composite 157Gd/CsI converter, (iii) CASCADE detectors with cascaded 10B-coated GEM (Gas Electron Multiplier) foils either side of a 2-D position-sensitive readout electrode. For readout in DETNI prototypes of two novel, channel-wise self-triggered high-rate ASICs, of ADC-FPGA boards with Gigabit glass fiber readout and of the necessary data acquisition firmware and software have been developed. The ASICs, i.e. the 128-channel n-XYTER ASIC, optimized for the Si-MSD and strip hit rates of 200 khits/s, and the 32-channel MSGCROC ASIC for the MSGC with variable amplification and strip rates of 900 khits/s, deliver for each strip spatial and 4 (2) ns time stamp resolution, respectively, the latter e.g. for correlating x and y strips unambiguously, as well as analog amplitude resolution for center-of-gravity interpolation and gating. In this paper the current status of prototyping will be reported.

Development of a selftriggered high counting rate ASIC for readout of 2D gas microstrip neutron detectors

In the frame of the DETNI project a 32-channel ASIC suitable for readout of a novel 2D thermal neutron detector based on a hybrid low-pressure Micro-Strip Gas Chamber with solid 157 Gd converter has been developed. Each channel delivers position information, a fast time stamp of 2 ns resolution and the signal amplitude (called energy below). The time stamp is used for correlating the signals from X and Y strips while the amplitude is used for finding the center of gravity of a cluster of strips. The timing and energy information are stored in derandomizing buffers and read out via token ring architecture.