William L. Bryan

Multiple-input microcantilever sensors

A surface-micromachined micro-electro-mechanical-system (MEMS) process has been used to demonstrate multiple-input chemical sensing using selectively coated cantilever arrays. Cantilever motion due to absorption-induced stress was readout using a custom-designed, eight-channel integrated circuit. Combined hydrogen and mercury vapor detection was achieved with a palm-sized, self-powered module with spread-spectrum telemetry reporting.

Fast neutron - gamma pulse shape discrimination of liquid scintillation signals for time correlated measurements

We describe a neutron/gamma pulse shape discrimination (PSD) system that overcomes count rate limitations of previous methods for distinguishing neutrons from gammas in liquid scintillation detectors. Previous methods of PSD usually involve pulse shaping time constants that allow throughput of tens of thousands counts per second. Time correlated measurements require many millions of counts per second to accurately characterize nuclear material samples. To rapidly inspect many test articles, a high-throughput system is desired. To add neutron - gamma distinction to the analysis provides a much desired enhancement to the characterizations. However, if the PSD addition significantly slows down the inspection throughput, this PSD feature defeats any analysis advantage. Our goal for the fast PSD system is to provide sorted timing pulses to a fast, multi-channel, time-correlation processor at rates approaching several million counts per second enabling high throughput, enhanced inspection of nuclear materials.

ASIC for Small Angle Neutron Scattering Experiments at the SNS

We present an ASIC for a 3He gas detector to be used in small angle neutron scattering experiments at the Spallation Neutron Source in Oak Ridge. The ASIC is composed of 64 channels with low noise charge amplification, filtering, timing and amplitude measurement circuits, where an innovative current-mode peak-detector and digitizer (PDAD) is adopted. The proposed PDAD provides at the same time peak detection and A/D conversion in real time, at low power, and without requiring a clock signal. The channels share an efficient data sparsification and derandomization scheme, a 30-bit 256 deep FIFO, and low voltage differential signaling.

A preamplifier-shaper-stretcher integrated circuit system for use with germanium strip detectors

A 16-channel integrated circuit readout electronics chip is being developed for use with a germanium strip detector. Such a system will provide superior energy resolution with 2-dimensional imaging in a single instrument that can be used for X-ray imaging and nuclear line gamma-ray spectroscopy. As part of the total ASIC development, prototype ICs of a typical channel have been designed, fabricated and tested. These integrated circuits include a low-noise, variable gain, preamplifier circuit that can detect both positive and negative going input charges, a 4-pole pulse shaper with variable peaking times and a stretcher circuit that can do a peak detect and hold for the different peaking times. The integrated circuits are fabricated in a 1.2 micron n-well CMOS process. The noise performance for this system was measured to be 185erms +14e/pF for a 2 /spl mu/s peaking time and gain at /spl sim/200 mV/fC. Linearity measurements in both inverting and non-inverting modes of operation were approximately +/-1%. Peaking times from 0.5 microseconds to 8 microseconds and gain adjustments to get up to 400 mV/fC per channel were done through digital switching.

TGLD: a 16 channel charge readout chip for the PHENIX Pad Chamber detector subsystem at RHIC

This paper describes TGLD, a charge readout chip for the PHENIX Pad Chamber (PC) subsystem at Brookhaven National Laboratorys Relativistic Heavy Ion Collider (RHIC) in Upton, NY. Due to the PCs high channel density, the TGLD and associated circuitry operate within the active detector region as permanent, zero access components, with remote set-up and test during collider operation. The TGLD design accommodates varying pad capacitance and charge gain for three detector subassemblies that detect particles at three different distances from the PHENIX collision vertex. The design also provides adjustable discrimination thresholds from MIP/10 to 2 MIP (Minimum Ionizing Particle). Three TGLD chips operate with a complimentary digital memory unit (DMU) to form 48 channel low power, low mass, readout cards. Partitioning of readout electronics and address control for robust remote operation are discussed. Component and system test results are also reported.

A discriminator with a current-sum multiplicity output for the PHENIX multiplicity vertex detector

pitch constraints, the discriminator (as well as all other MVD FEE) must be arrayable within an 85 p pitch. A current output multiplicity discriminator for use in the front-end electronics (FEE) of the Multiplicity Vertex Detector (MVD) for the PHENIX detector at RHIC has been fabricated in the a 1.2-p CMOS, n-well process. The discriminator is capable of triggering on input signals ranging from 0.25 MIP to 5 MIP. Frequency response of the discriminator is such that the circuit is capable of generating an output for every bunch crossing (105 ns) of the RHIC collider. Channel-to-channel threshold matching was adjustable to f 4 mV. One channel of multiplicity discriminator occupied an area of 85 p x 630 p and consumed 515 pW from a single 5-V supply. Details of the design and results from prototype device testing are presented.

Telesensor integrated circuits.

Progress in personal computing has recently permitted small research programs to design and simulate application-specific integrated circuits (ASICs). Inexpensive fabrication of silicon chips can then be obtained using chip foundries, and quite complex circuits can be greatly reduced in size with an accompanying increase in certain performance characteristics. Within the past 5 years it has also become possible to design ASICs which can transmit and receive radio signals and which thus may be employed in applications in which wired connections for input and output of signals are not practicable. We are currently developing research-grade prototype ASICs for the monitoring of human vital signs. In this case one or more sensors placed on an ASIC provides a signal to be transmitted a distance of 2-3 meters to a receiver/display unit. The use of ASIC telesensors provides the possibility of wireless monitoring, including long-term monitoring, with inexpensive and unencumbering devices. Their self-contained nature permits a number of potential uses in future biomedical applications as new sensors are devised which are amenable to deployment on silicon.

A detector for 2-D neutron imaging for the spallation neutron source

We have designed, built, and tested a 2-D pixellated thermal neutron detector. The detector is modeled after the MicroMegas-type structure previously published for collider-type experiments. The detector consists of a 4/spl times/4 square array of 1 cm/sup 2/ pixels each of which is connected to an individual preamplifier-shaper-data acquisition system. The neutron converter is a /sup 10/B film on an aluminum substrate. We describe the construction of the detector and the test results utilizing /sup 252/Cf sources in Lucite to thermalize the neutrons.

A front-end ASIC for use with large-pixel array detectors

An Integrated Circuit (IC) readout chip with four channels arranged so as to receive input charge from the corners of the chip was designed for use with 5- to 7-mm pixel detectors. This Application Specific IC (ASIC) can be used for cold neutron imaging, for study of structural order in materials using cold neutron scattering or for particle physics experiments. The ASIC is fabricated in a 0.5-/spl mu/m n-well AMI process. The design of the ASIC and the test measurements made will be reported. Noise measurements will also he reported.

Advantages of a modular design approach for radiological instrumentation

The application of a modular design approach to the development and implementation of radiological instrumentation provides significant improvements over conventional instrument design in terms of capability, maintainability, and overall system costs. Two implementations utilizing this approach are discussed: a multifunction survey meter system developed for the US Navy RADIAC (radiation detection, indication and computation) program, and a stationary workplace monitoring system under development for use at Oak Ridge National Laboratory. By designing modular, functionally partitioned hardware and software subsystems incorporating standard interfaces, it is possible to generate whole families of instrumentation systems in a building block fashion. >