R.D. Taylor

The layer 0 inner silicon detector of the D0 experiment

This paper describes the design, fabrication, installation and performance of the new inner layer called Layer 0 (L0) that was inserted in the existing Run IIa Silicon Micro-Strip Tracker (SMT) of the D0 experiment at the Fermilab Tevatron {bar p}p collider. L0 provides tracking information from two layers of sensors, which are mounted with center lines at a radial distance of 16.1 mm and 17.6 mm respectively from the beam axis. The sensors and readout electronics are mounted on a specially designed and fabricated carbon fiber structure that includes cooling for sensor and readout electronics. The structure has a thin polyimide circuit bonded to it so that the circuit couples electrically to the carbon fiber allowing the support structure to be used both for detector grounding and a low impedance connection between the remotely mounted hybrids and the sensors.

Ultrasound affects spermatophore transfer, larval numbers, and larval weight of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) ☆

Effects of ultrasound from a commercial device on reproduction in the Indianmeal moth, Plodia interpunctella (Hubner), were investigated in paired Plexiglas enclosures, one with ultrasound and one without (control treatment). In each of the five paired trials, 10 newly emerged male and 10 female moths were introduced into each enclosure. The commercial device produced peak frequencies at 21, 25, and 35 kHz, and a 94 dB sound pressure level at a distance of 50 cm. In enclosures with ultrasound, female moths had 27% fewer spermatophores and produced 48% fewer larvae than those not exposed to ultrasound. Furthermore, ultrasound reduced total and individual larval weights by 66% and 35%, respectively, when compared with the control treatment. About 17% more moths were found on the enclosure floor in the presence of ultrasound when compared with those not exposed to ultrasound. This is the first paper documenting the effects of ultrasound on reproductive performance of P. interpunctella. These laboratory data suggest that the use of ultrasound against P. interpunctella may be an appealing and effective behavioral management strategy.

Preliminary tests of a high efficiency 1-D silicon pixel array for small angle neutron scattering

A. first generation 120 micron pitch pixel array system for neutron detection using the PATARA amplifier chip was assembled and tested. The pixel array was tested for neutron response and spatial resolution. Pulses from the PATARA were observed at 0.5 V in height and 500 ns wide from neutron interactions. The spatial resolution of the array was determined to be 119 micrometers. Leakage current tests and alpha particle irradiation tests were conducted for a second generation prototype silicon sensor with 175 micrometer deep perforated trench structures in each pixel. The second generation sensor incorporates several design improvements to ease fabrication.

Characterization of the High-Efficiency Neutron Detector Array (HENDA)

Two new pixellated neutron detectors developed at the Semiconductor Materials and Radiological Technologies Laboratory (SMART Lab) at Kansas State University, for eventual use at Oak Ridge National Laboratory Spallation Neutron Source, were tested for resolution, count rate and efficiency.

1-D array of micro-structured neutron detectors

A 1024-channel pixel array has been constructed utilizing the perforated diode neutron detector design currently produced at Kansas State University. In this design a single pixel consists of a pn-junction diode fabricated around a single trench 4 cm long, 30 microns wide and 100 microns deep. The trench is filled with LiF powder to provide conversion of neutrons to energetic charged particles which can be captured in the diode depletion region. A pitch of 100 microns between pixels has been achieved and less than 120 micron spatial resolution has been demonstrated experimentally with a 32-channel prototype in previous work. Also, the first array demonstrated 12% thermal neutron counting efficiency. The 1024-channel array was produced by tiling 16 chips side-by-side, each containing 64 pixels. Signal processing is handled by 16 PATARA chips for amplification and thresholds, developed at University of Tennessee. The entire board assembly and digital communications to PC were handled by the KSU Electronics Design Laboratory utilizing a PCI card developed at ORNL.

Development of the dual-sided microstructured semiconductor neutron detector

Microstructured semiconductor neutron detectors (MSNDs) have long been investigated as a replacement for inefficient thin-film-coated semiconductor neutron detectors. Thin-film-coated semiconductor thermal neutron detection efficiency is restricted to 4-5%. MSNDs improved upon these devices with etched perforations into the diode backfilled with neutron conversion material. Neutron absorption and reaction-product detection efficiency was greatly improved, leading to theoretical intrinsic thermal neutron detection efficiencies greater than 45%. Previous attempts at double-stacking MSNDs to increase the detection efficiency were successful, but were accomplished with great difficulty, where device alignment and proved to be challenging. The development of the dual-sided microstructured semiconductor neutron detector (DSMSND) provides the simplicity of a single device with the detection efficiency of a double-stacked detector. Trenches were etched into the top and bottom of a single vertical pvn-junction Si diode and backfilled with 6LiF neutron conversion material. The first such devices fabricated yielded thermal neutron detection efficiencies between 9.6-16.6%. Theoretical intrinsic thermal neutron detection efficiencies of greater than 79% are possible with a single 1-mm thick silicon diode.

Portable neutron energy spectrometer utilizing microstructured semiconductor neutron detectors (MSND)

The portable neutron energy spectrometer is designed to identify an unknown neutron source. The spectrometer is cylindrical in shape with a diameter of 12 cm and a length of 33 cm. This allows for a large surface area for incident neutrons to interact with and sufficient moderating material to thermalize neutrons up to 14.1 MeV in energy. The spectrometer utilizes eleven 2 cm × 2 cm high-efficiency microstructured semiconductor neutron detector (MSND) devices. The detectors are arranged linearly along the central axis of the spectrometer. The spectrometers volume consists of alternating layers of MSNDs, high-density polyethylene (HDPE), and cadmium. The HDPE acts as a moderator for the epithermal and fast neutrons, allowing them to disperse energy linearly within the spectrometers volume thereby, becoming thermalized and counted by the detectors. The 2 mm thick cadmium layer after each detector prevents thermal neutrons from backscattering to a previous detector. Extensive modeling of the portable spectrometer was conducted using MCNPS. The modeling was used to optimize the number of MSNDs and the thickness of the HDPE layers. Also, reference library templates for a variety neutron sources were simulated, including; 252Cf, 252Cf + D2O, PuBe, AmBe, and a 14.1 MeV fusion neutron source. A Figure-of-Merit calculation was used to identify the experimental neutron source. The spectrometer is a light-weight, portable, self-contained unit, weighing less than 20 lbs. It is powered by a rechargeable 6V battery contained within the main housing. The measurement data and identified neutron source information is displayed on the built-in LCD screen.

Fabrication of present-generation microstructured semiconductor neutron detectors

Microstructured semiconductor neutron detectors with large aspect-ratio, straight trenches backfilled with neutron sensitive material exhibit superior detection efficiencies over traditional thin-film-coated diodes for solid-state thermal neutron detection. The detectors operate as partial-conformal diffused pin-junction diodes with low leakage current and capacitance. The solid-state silicon substrate detectors operate on a zero to 2.7 V bias and are coupled with signal amplifying and electronic readout components. The intrinsic thermal neutron detection efficiency for a 4-cm2 single-sided MSND reported here is 30.0±0.9% for a neutron beam with normal incidence to the detector surface. The intrinsic thermal neutron detection efficiencies for 0.0253 eV neutrons were determined by calibrating against a calibrated helium-3 gas-filled proportional detector at the Kansas State University TRIGA Mk II nuclear reactor diffraction beam port.

Preliminary results of KSU Frisch-collar CZT array

Cadmium zinc telluride (CdZnTe or CZT) is a well-known problematic material once dimensions exceed ∼1cm∧3, due to material imperfections that cause severe charge carrier (hole) trapping, compromising the energy resolution for basic planar detector designs. Advances in CZT detector design at Kansas State University (KSU) have demonstrated that room-temperature energy resolution less than 0.9% for 662 keV gamma rays can be consistently achieved. The Frisch-collar detector, developed at KSU, is a design based on the Frisch grid effect, which changes a basic planar detector from a low-resolution device into a high-resolution device by suppressing deleterious effects from charge carrier (hole) losses. We studied the application of Frisch-collar CZT detectors to hand-held or remotely-deployable rapid spectroscopic devices, designed to operate in signal-summation and Compton-suppression modes, employed for greater counting efficiency and improved energy resolution, respectively. The array is made from small volumes of Frisch-collar CZT, lowering cost and easing purity requirements for ingot growth. Timing resolution for signals arising from Compton-scattered gamma rays as a function of detector bias voltage will be discussed.

PATARA II: A 64-channel solid-state Neutron Detector readout system with integrated analog and digital processing for the SNS

The High Efficiency Neutron Detector Array (HENDA) project at the Spallation Neutron Source (SNS), Oak Ridge Tennessee, has driven the need for state of the art radiation detector readout electronics. Readout electronics of this class must support multi-channel inputs while providing a high level of integration and precision. The Patara II ASIC targets this need by integrating a charge sensitive front end followed by analog and digital signal processing that supports the connectivity of 64 detectors. A monolithic biasing system and digital programmability was integrated in order to reduce the amount of required external components on the end system motherboard.