This paper addresses the use of Visible Light Photon Counters (VLPCs) for detection of light induced in light arrays of small scintillating crystals for gamma ray imaging. The use of plastic step-index-of-refraction fibers for collecting the scintillation light for detection by a VLPC is examined and data obtained in initial exploratory experiments are discussed. The results are compared with the number of detectable scintillation photons predicted by a model that in essence treats the crystal as an integrating cavity with highly efficient diffuse reflecting surfaces.

Scintillating fibers enable the experimentalist to gather time and energy information on particles entering a large array of fibers. The ideal detector therefore has a large input size, and should be capable of handling as many scintillating fibers as possible. This paper outlines the latest developments in photon counting tubes and camera systems. Developments include ruggedized intensifiers for space applications of fiber scintillators, and systems with improved pixel capacity. Centroiding intensified CCD systems are capable of resolving more than 4 million pixels, but with time resolution no better than a TV frame period. At the other end of the time/resolution spectrum, we have developed multi anode photomultipliers with 96 pixels, and subnanosecond time resolution.

The paper presents advances in two sensor technologies: (1) Mercuric Iodide (HgI₂) X-ray Detector Technology and, (2) Large Area Silicon Avalanche Photodiode (APD) Technology, which after years of development have recently produced commercially viable devices. Large Area Silicon Avalanche Photodiodes, which are solid-state light sensitive devices with internal amplification, combine the convenience, ruggedness and low power consumption of traditional semiconductor p-n and p-i-n photodiodes with the high light sensitivity and large photosensitive area approaching the active areas of traditional vacuum photomultiplier tubes. Device approaching 1-inch diameter with internal gain of up to 1000, have been developed by utilizing a beveled edge structure. By combining APD's with scintillation crystals, resolution of 6% (FWHM) was obtained for 662 keV energy line of ¹³⁷Cs using a CsI(Tl) scintillator, and 7% (FWHM) was obtained using a NaI(Tl) scintillator. Resolution of 14% (FWHM) at room temperature and 11% (FWHM) at 0 degree(s)C have been obtained for APD's coupled to BGO scintillators. Rise times of 3 ns were measured by applying an impulse signal input, to a 200 mm² device.

Tracking detectors based on scintillating-fiber technology are being developed for the Solenoidal Detector Collaboration at the Superconducting Super Collider and for the D0 collaboration at Fermilab. An important aspect of this work is the effect of the intense radiation environment existing in the detector cores on the fibers. This paper presents preliminary results of a 2 MeV x-ray irradiation of selected fibers to a dose of 140 Krad, corresponding to some ten years of detector operation. Primary emphasis was placed on studying new Kuraray multiclad scintillating and clear fibers which have superior brightness, attenuation lengths, and mechanical robustness. Two types of Bicron single-clad scintillating fibers were also investigated.

Tracking detectors based on scintillating-fiber technology are being developed for the Solenoidal Detector Collaboration at the Superconducting Super Collider and for the D0 collaboration at Fermilab. An important part of the work is to insure that the fibers will not be damaged by environmental conditions in the course of detector construction. This paper presents preliminary results of the effects of ambient fluorescent light on scintillating fibers containing 3-hydroxyflavone (3HF) waveshifter. Six fiber types having 3HF concentrations between 100 ppm and 6000 ppm were studied; both single-clad fibers from Bicron and Kuraray and a new Kuraray multiclad fiber were included. A blue fiber containing no 3HF was used to provide a comparison.

Visible Light Photon Counters (VLPCs), which were produced by Rockwell International Science Center for UCLA, can detect visible light down to the single photon level with a quantum efficiency approaching 80%. They were produced for the SSC Laboratory for a proposed scintillating fiber tracking detector. The VLPCs were tested and characterized at Rockwell and UCLA. They have better than 3 ns time resolution, and demonstrate count rate capabilities on the order of 3 X 10⁷ mm^-2s^-1. Some test results, characteristics of the VLPCs, and applications will be discussed.

Issues necessary for good charged particle tracking in a solenoidal magnetic field are discussed. The advantages to high energy physics experiments of using a tracking detector made using scintillating fibers are presented. Upon passage of a charged particle through a fiber, light is emitted. For a fraction of the photons, the fiber acts like a wave guide, transmitting the photons to a transducer outside the active detection region. The design uses scintillating fibers of approximately 1 mm diameter and is highly segmented as well as capable of very high data rates. Systems with up to 10⁶ channels are simple in design so that `industrialization' can easily be accomplished. Results from the production of prototypes are presented.

A 96-channel, 3-superlayer scintillating fiber tracking system has been tested in a 5 GeV/c (pi) ^- beam. The scintillating fibers were 830 micrometers in diameter, spaced 850 micrometers apart within a layer, and 4.3 m in length. These were coupled to 6 m long clear waveguides and finally to Visible Light Photon Counters. A spatial resolution of approximately 150 micrometers for a double-layered ribbon was achieved with this tracking system.

We have measured the performance of scintillating fiber detectors read out with visible light photon counters (VLPCs). Both single clad and multiclad scintillating fibers have been tested. For a system comprised of 3 m long multiclad scintillating fibers of 830 micrometers diameter optically coupled to 8 m long multiclad waveguide fibers of 965 micrometers diameter and read out with HISTE-IV VLPCs, we detect an average of 6.2 photoelectrons from the far end of the scintillating fiber if the fiber end is unmirrored and 10 photoelectrons if the fiber end is mirrored. A minimum of 2.4 detected photoelectrons is required for efficient particle detection in high energy physics tracking applications. Hence our result indicates a factor of 2.5 and 4 safety margin in required light yield for the unmirrored and mirrored cases respectively. Given this substantial detected photoelectron yield, cosmic ray tracks are easily detected in fiber arrays, and excellent performance characteristics are expected for the fiber trackers designed for the D0 experiment at the Fermilab Tevatron Collider and SDC experiment at the SSC laboratory.

We propose a detector that combines two techniques to detect massive WIMPs through the possible identified Xe recoil in a liquid Xenon detector. The detector is based on ionization readout (like ICARUS) and a light collection using scintillating fibers and VLPCs.

We discuss the upcoming Plasma Lens experiment at SLAC and speculate on the possibility that some type of scintillating fiber telescope can be used for a beam monitor.

The CERN WA95/CHORUS Collaboration has been constructing a detector to search for neutrino oscillations. An essential component of the detector is a scintillating fiber tracker system for precise track reconstruction of particles. An overview of the tracker system design, its opto-electronics readout, data processing and test beam measurements is presented.

Detectors of varying dimensions and geometry may be built using plastic scintillating optical fibers. This paper presents a study of the imaging properties of these detectors, directed at assessing the relative advantages of different designs. To this end, the radionuclide source distribution in the object is reconstructed by solving the inverse problem, using generalized matrix inversion. Photon detection matrices, as is well known, are ill-conditioned, a problem which may be dealt with by using truncated singular value decomposition. The design of the imaging device is investigated in term of minimizing these effects on the system matrix, and the effect of different geometric design parameters is examined. Experimental data obtained with small-scale cylindrical and planar devices are presented for different collimation schemes.

Scintillating optical fibers have been used to build small detectors for whole-body imaging of small rodents by nuclear medicine techniques. Cylindrical detectors with entrance apertures of 6.8 cm and active lengths of 11.3 cm were constructed using both 3 mm and 1 mm BCF-10 fibers. Fiber readout was performed using position sensitive photomultipliers and a specialized flash ADC system. The efficiencies of these detectors were determined as a function of energy, their resolution was studied, and their potential use for SPECT (single photon emission computed tomography) was explored.

We are continuing the characterization of a PET module using plastic scintillating fibers coupled to position sensitive photomultipliers. The sensitivity in air and the resolution in air and water are tabulated for a source positioned at nine locations within the detector field of view. The full width half maximum resolution for a 0.5 mm diameter Na-22 source in air and water is approximately 2.5 m. The sensitivity is 19 c.p.s./(mu) Ci.

A scaled version of a scintillating fiber detector using a high-speed CCD camera has been constructed in a feasibility study at SAIC-San Diego for characterization of its response to fast neutrons and to high energy gamma-rays. The detector concept relies on the combination of long, thin plastic fibers and the kinematics of the neutron-proton reaction to provide an effective means to discriminate against background (non-target) neutrons entering at directions non-parallel to the fiber axis. In the present study, the detector was modified to accept a commercially available high-speed CCD camera capable of frame rates up to 850 Hz. We describe here measurements for determining the neutron detection efficiency, directionality, and gamma-ray sensitivity and discuss improvements which were made to enhance the fiber bundle performance.

An improved scintillator fiber optic long counter for neutron detection, which uses ⁶Li- loaded, Tb³⁺-doped glass scintillator fibers as the detection element has been fabricated and tested. By determining the position of an absorbed neutron along the fiber axis, the system is capable of performing low resolution neutron spectroscopy based on thermalization depth, while retaining the flat efficiency of the conventional long counter. The system offers improved gamma ray/neutron discrimination capability and more efficient signal processing electronics.

One of the leading candidate technologies being considered for use in the forward region at both the Superconducting Supercollider and the Large Hadron Collider is liquid scintillating fiber spaghetti calorimetry in which the fibers are constructed using liquid scintillator as the core in combination with a tube or channel with a lower refractive index for the cladding. In this report, R&D results on some of the most critical issues will be reviewed, including findings concerning attenuation lengths and radiation damage. Results from in situ tests used to study liquid fiber performance while in an intense radiation environment are also discussed.

A small selection of some typical tracker systems is presented, followed by the latest developments around the Hybrid Photodiode. The latter device might replace PMTs in many physics applications.