B. Yu

Front-end electronics for imaging detectors

Abstract Front-end electronics for imaging detectors with large numbers of pixels (10 5 –10 7 ) is reviewed. The noise limits as a function of detector capacitance and power dissipation are presented for CMOS technology. Active matrix flat panel imagers (AMFPIs) are discussed and their potential noise performance is illustrated.

Active pixel sensors on high resistivity silicon and their readout

The concept of X-ray active matrix pixel sensor (XAMPS) is introduced. XAMPSs are direct illumination, position sensitive X-ray detectors with the possibility of containing 1000 000 pixels. They count the number of diffracted X-rays in each pixel by measuring the total charge released by converted X-rays in the body of the sensor. Readout is accomplished with a relatively small number of channels equal to the square root of the number of pixels. The estimated readout time can be about 1 ms. Noise of the readout electronics can be so low that practically no additional fluctuations in the number of incident X-rays per pixel are added and, therefore, the XAMPS performance is very close to that of an ideal detector for X-ray crystallography.

High-performance, imaging, thermal neutron detectors

Abstract Existing and planned spallation neutron sources require two-dimensional detectors for many experiments. Unlike the requirements for steady-state neutron sources, it is essential that these detectors possess good time resolution to determine neutron energy. A range of detectors based on gas proportional chambers, with low-noise encoding electronics, has been fabricated at this laboratory, with properties well suited for use at spallation sources. These high-performance detectors possess outstanding qualities in terms of dynamic range and stability of both recorded neutron positions and response (efficiency), in addition to normal attributes such as good position resolution, high detection efficiency and insensitivity to γ-rays. We review here some of the major characteristics of the detectors, describe recent advances, and illustrate their high level of performance with neutron scattering results. While relatively few such detectors are required world wide, specialized efforts are required for their development. The additional opportunities provided by new spallation sources will need continued advances in detector performance.

A large, high performance, curved 2D position-sensitive neutron detector ☆

Abstract A new position-sensitive neutron detector has been designed and constructed for a protein crystallography station at LANLs pulsed neutron source. This station will be one of the most advanced instruments at a major neutron user facility for protein crystallography, fiber and membrane diffraction. The detector, based on neutron absorption in 3He, has a large sensitive area of 3000 cm 2 , angular coverage of 120°, timing resolution of 1 μs , rate capability in excess of 10 6 s −1 , position resolution of about 1.5 mm FWHM, and efficiency >50% for neutrons of interest in the range 1– 10 A . Features that are key to these remarkable specifications are the utilization of eight independently operating segments within a single gas volume, fabrication of the detector vessel and internal segments with a radius of curvature of about 70 cm , optimized position readout based on charge division and signal shaping with gated baseline restoration, and engineering design with high-strength aluminum alloy.

Study of GEM characteristics for application in a MicroTPC

The Gas Electron Multiplier (GEM) may provide a convenient method for obtaining significant electron multiplication over large detector areas. An important potential application of the GEM is for readout of microTPCs. We are conducting a study of a multi-GEM structure with particular emphasis on the following characteristics: gain uniformity/stability, ion feedback and position readout. In particular, we present the first experimental results of interpolating anode pad readout. Initial results provide encouragement that the GEM application in microTPCs may be realized.

A method for reduction of parallax broadening in gas-based position sensitive detectors

A description is given of the principle and experimental verification of a new method which significantly reduces broadening of the position response, due to parallax, for radiation incident on a detector at finite angles of incidence. The technique, which can be implemented in gas-based position-sensitive detectors with planar geometry, substantially improves position resolution for scattering experiments using X-rays and neutrons, and will permit larger angular coverage than has previously been possible. An improvement of nearly a factor four in rms position resolution is predicted, which is confirmed by measurements using a gas proportional X-ray detector with delay-line position encoding.

Digital centroid-finding electronics for high-rate detectors

Fast centroid-finding electronics are being developed for a range of position-sensitive gas proportional detectors. Each cathode strip feeds a preamplifier, shaper and a free-running ADC. Increased total count rate is achieved by dividing the detector into several segments with parallel processing that introduces no common dead time. Each segment has central-channel finding logic and event listing realized in a FPGA, followed by a DSP that performs the centroid calculation and histogramming. Measured count-rate per segment exceeds 10/sup 6/ per second, with virtually no dead time.

High rate, high resolution, two-dimensional gas proportional detectors for X-ray synchrotron radiation experiments

Two-dimensional, gas proportional detectors are being developed for use with X-ray synchrotron radiation. Two new types of interpolating cathode structures have been investigated, both of which can operate with a significantly smaller number of readout nodes along each sensing axis than previous cathodes. Lumped parameter delay lines are used as the position encoders. Timing signals from fast, low noise shaping electronics are fed to a new, dual TDC system developed for this purpose. Operating with a clock frequency of 500 MHz, the TDCs have an intrinsic differential non-linearity of 0.1%. The complete system can handle X-ray fluxes in excess of 10{sup 6} per sec without distortion of the position information. A resolution of approximately 100 {mu}m FWHM and differenfial non-linearity of {plus minus}4% have been achieved. Application of a detector with active area 10 cm {times} 10 cm using synchrotron radiation is described.

High resistivity silicon active pixel sensors for recording data from STEM

An X-ray Active Matrix Pixel Sensor (XAMPS) for recording Data from the Scanning Transmission Electron Microscope (STEM) was designed, produced and tested. The reason for measuring scattering angle of all STEM electrons is given together with the requirement on the performance of the XAMPS. Principles of the measurement of the number of STEM electrons scattered in a particular direction are summarized. Results of tests performed on a produced detector are described and the problem with the formation of an insulation layer between silicon and aluminum is identified. A change in the design of the pixel is proposed which results in a fully functioning XAMPS even with the insulation layer present.

Front-end electronics for high rate, position sensitive neutron detectors ☆

Advanced neutron detectors for experiments at new spallation sources will require greater counting rate capabilities than previously attainable. This necessitates careful design of both detector and readout electronics. As part of a new instrument for protein crystallography at LANSCE, we are constructing a detector whose concept was described previously (IEEE Trans. Nucl. Sci. NS-46 (1999) 1916). Here, we describe the signal processing circuit, which is well suited for 3He detectors with a continuous interpolating readout. The circuit is based on standard charge preamplification, transmission of this signal over 20 meters or so, followed by sample and hold using a second order gated baseline restorer. This latter unit provides high rate capability without requiring pole-zero and tail cancellation circuits. There is also provision for gain-adjustment. The circuits are produced in surface mounted technology.