Kent Charles Burr

Scintillation detection using 3 mm × 3 mm silicon photomultipliers

A silicon photomultiplier (SiPM) consists of an array of independent Geiger-mode avalanche photodiodes, each with an integrated quenching resistor. SiPMs have many potential attractive features, including high photon detection efficiency, high gain, low timing jitter, compact design, and low operating voltage. We are evaluating SiPMs for use in scintillation detectors, and present results using 3 mm x 3 mm Multi-Pixel Photon Counter (MPPCTM)prototypes from Hamamatsu Photonics K. K. coupled to LYSO scintillator crystals. Our evaluation includes energy resolution, timing resolution, and the sensitivities of these measurements to bias voltage and temperature variations. We have also used simulations to try to understand the impact of avalanche photodiode reset time and cross-talk on the observed non- linearity of the pulse-height spectrum.

Dependence of timing resolution on crystal size for TOF PET

Recently, with the prospect of great improvement in image quality, the development of time of flight technology has become an exciting topic for positron emission tomography. The excitement was further accelerated by the introduction of various fast and high light output scintillators as well as photosensors. However, the development of improved time of flight detectors is not only about the selection of crystals and photosensors, but also about how detectors are assembled to optimize their performance. For example, depending on crystal block structure, photo-sensor layout, and coupling methods, a detectors timing resolution can be drastically different. Since the effect of block structure for timing resolution is complex and less understood it is essential to first dissect the block structure and understand the impact of its basic components on timing resolution. In this paper, we will present the dependence of timing resolution on varying the dimensions of the scintillator crystals that are the main component of a block detector.

Depth of interaction effect on timing resolution in PET block detectors

We have investigated the effect of the depth of interaction (DOI) on the coincidence timing distribution of a PET block detector excited with 511 keV photons. Measurements were performed with a detector consisting of a quad photomultiplier tube (PMT) optically coupled to a 6times6 array of mixed lutetium silicate (MLS) scintillator crystals with different surface treatments. The PET detector was side-illuminated with an electronically collimated beam and the coincidence timing distribution was recorded at different DOI as the detector block was stepped through the beam. The shift of the timing distribution peak measured the variation of the average propagation time of the scintillation photons within the block. From top to bottom (30 mm distance), the average delay ranged from 120 ps for polished crystals up to 350 ps for crystals with all sides roughened. The results of this study allowed modeling the effect of DOI delay on timing performance for front-end irradiation with 511 keV photons, assuming a range of different values for the intrinsic timing resolution of the detector. The relative contribution from DOI effects to the total time coincidence resolution was found to be significant only for detectors with an intrinsic time resolution less than 250 ps FWHM

Evaluation of position sensitive avalanche photodiodes for PET

A gamma ray detector for PET, consisting of an array of mixed lutetium oxyorthosilicate (MLS) scintillator crystals coupled to a position sensitive avalanche photodiode (PSAPD), was evaluated. The scintillator array was constructed from individual MLS crystals with dimensions of 1.5 mm/spl times/1.5 mm/spl times/15 mm. The assembled 7/spl times/7 array, including inter-crystal reflector material, had a pitch of 1.79 mm. The low noise, high gain PSAPD had dimensions of 14 mm/spl times/14 mm. Peaks associated with each of the 49 scintillator crystals were readily identifiable in flood histograms, and most of the crystals demonstrated energy resolution in the range of 15% to 20% at 511 keV. Preliminary measurements of the timing of the PSAPD in coincidence with a fast-scintillator/PMT detector indicated a timing resolution of approximately 4 ns. The operating characteristics and design attributes, such as compactness and reduced readout channel requirements, of the PSAPD make it attractive for high resolution PET applications.

Design of a Modular and Efficient CAMAC/Lab VIEW-Based Data Acquisition System for a Time of Flight PET Test-Bed

A high-speed data acquisition (DAQ) system has been designed for a time of flight PET test-bed. The requirements of the system were flexibility, data throughput and data integrity. The software is modular so that modifications and additions can be integrated easily into the existing software architecture. The program operation is driven by commands read from a script file, simplifying implementation of complex acquisition sequences. The heart of the program is the DAQ module, which efficiently transfers data from CAMAC to file. Another software module offers online or offline analysis capabilities. The software, written in LabVIEW, communicates with a novel high-speed USB2 CAMAC controller (CCUSB). The CCUSB offers significant improvements over its GPIB predecessor, supporting FIFO buffered DAQ and a variety of data readout modes. Four readout modes have been evaluated in order to maximize the DAQ rate for this particular system. A highest sustained data rate of 15.7 k events/s was achieved for approximately 60 input channels using a 22Na flood phantom. Flexibility in the software design accommodates both current and future hardware configurations without the need to edit the LabVIEW code.

SiC photodetectors for industrial applications

Silicon carbide is a wide bandgap semiconductor with highly robust properties lending its applicability to robust electronics and sensors. Ultraviolet detection in particular is of interest for several industrial applications including those requiring a rugged sensing device. SiC photodetectors and their applications will be discussed, including examples of device design, fabrication and testing. Also, the fabrication and testing of separate avalanche and multiplication region avalanche photodiodes will be highlighted.