A large tracking detector consisting of scintillating plastic optical fibers has been chosen by the D0 collaboration as a part of a planned upgrade at the Fermilab Tevatron. The tracker will utilize multiclad scintillating fibers and optical waveguides and state of the art photosensors called visible light photon counters (VLPC). In this paper we present some general characteristics of fiber detectors and then describe recent measurements of system performance based on data from the 3072 channel cosmic ray test stand. Based upon these studies, fiber detectors are expected to perform very well for collider operation, and excellent performance is also expected for fixed target applications.

Among the improvements planned for the 1997 upgrade of the D0 detector at Fermilab are installation of a new scintillating-fiber central tracker and a new lead-scintillator preshower counter read out with wave-shifting fibers. Because of space limitations, fibers in both systems may need to undergo bends of fairly small radius, and the resulting stresses and strains may cause light losses. This paper presents interim results from a study of the effects of deformation on fiber light transmission. A variety of scintillating, wave-shifting, and clear fibers with diameters near 1 mm have been examined. Particular emphasis was placed on the new, multiclad fibers developed by Kuraray. Light loss was measured by injecting light into one end of a fiber sample and measuring the exiting light before, during, and after controlled deformation of the fiber. The deformations studied include bending, tensile elongation, compression, and torsion. Generally, except for severe bending or considerable compression, light loss was found to be less than a few percent. The effect of bending were investigated using single-turn and multiple-turn loops of various radii. Light loss was found to increase with decreasing radius, but little dependence on either core dopants or diameter was observed. Generally, the light loss, L, in an N-turn loop of radius r could be parameterized by the form L equals A(root)N/rⁿ, where A is a constant and n is near 1.5. Kuraray multiclad fiber was found to be superior to single-clad fiber in that the former can be bent into single- turn loops with radii as small as 1 cm before introducing a light loss of 3%, while the latter produces this loss at a 2 cm radius. Tensile stress for forces up to 1.3 kg for 2-m-long fibers produced less than 1% light loss. On the other hand, compressive stress exerted over a 10-cm- long fiber section could cause a loss of 10%. Finally, a single observation of the effects of torsion indicated no change in light transmission for a 360 degree(s) twist at the center of a 4-m- long fiber with fixed ends. The observations made indicate that multiclad fibers produce smaller light losses under deformation than single-clad fibers, and that their use, together with avoidance of bends with radii smaller than a few centimeters, should avoid light loss due to stress and strain.

Recent advances have made scintillating-fiber technology a prominent choice for charged- particle tracking systems for high-energy physics. Such a system, containing some 81 K fibers, is planned for the 1997 upgrade of the D0 detector at Fermilab. As part of this project, a large-scale prototype containing 3072 channels has been designed and constructed. The prototype, which emulates many of the aspects of the planned upgrade tracker, is currently being tested with cosmic rays. An important feature of the prototype, as of the upgrade tracker, are clear plastic fibers, grouped into bundles, which transport scintillation light from the detector's scintillating fibers to remotely located visible-light photon counter (VLPC) photodetectors. Each of these lightguide bundles is 8 m long and contains 128 Kuraray clear multiclad fibers of 965 micrometers diameter terminated in an 128-channel optical connector at each end. This paper describes the details of the design, fabrication, and testing of 27 such bundles containing a total of 3456 channels and employing almost 17 miles of fiber. Excluding one bundle which appears to have been damaged in handling, the bad-channel frequency was found to be 0.2%, and the light loss per channel resulting from insertion of a bundle (and its two connectors) was measured to be about 5 dB. The results of these measurements validate the design and construction procedures used, and it is expected that similar procedures will be employed in fabricating more than 600 such clear lightguide bundles for the scintillating-fiber tracker for the 1997 upgrade of the D0 detector.

The visible light photon counter (VLPC) is an excellent candidate for scintillating fiber applications, meeting the requirements of high quantum efficiency, high gain with low gain dispersion, and good time resolution. The mechanism of impurity band conduction, on which the device depends, is described. Device operation is outlined, and performance characteristics are presented for a recent design. These characteristics include quantum efficiency, dark count rate, dark current, gain, and their dependence on temperature and operating voltage. Pulse height distribution and excess noise factor are also given, and shown to compare favorably with conventional avalanche photodiodes.

We have been developing and testing a scintillating fiber detector (SFD) for use as a fast neutron sensor which can discriminate against neutrons entering at angles non-parallel to the fiber axis (`directionality'). The detector/convertor component is a fiber bundle constructed of plastic scintillating fibers each measuring 10 cm long and either 0.3 mm or 0.5 mm in diameter. Extensive Monte Carlo simulations were made to optimize the bundle response to a range of fast neutron energies and to intense fluxes of high-energy gamma-rays. The bundle is coupled to a set of gamma-ray insensitive electro-optic intensifiers whose output is viewed by a CCD camera directly coupled to the intensifiers. Two types of CCD cameras were utilized: (1) a standard, interline RS-170 camera with electronic shuttering and (2) a high-speed (up to 850 frame/sec), field-transfer camera. Measurements of the neutron detection efficiency and directionality were made using 14 MeV neutrons, and the response to gamma-rays was performed using intense fluxes from radioisotopic sources (up to 20 R/hr). Recently, the detector was constructed and tested using a large 10 cm by 10 cm square fiber bundle coupled to a 10 cm diameter GEN I intensifier tube. We present a description of the current detector system and report the results of experimental tests.

The visible light photon counters (VLPCs) have been developed as a result of the joint work between the UCLA and the Rockwell International Science Center since 1988. The VLPCs with quantum efficiencies approaching 80% and having avalanche gains of 30000, rate capabilities of 50 millions per second per millimeter square with a time resolution better than one nanosecond have been applied to high energy particle physics research, medical imaging and particle astrophysics. A survey of VLPC development with some results and applications is presented.

The energy resolution is measured for a plastic scintillating fiber detector coupled to position sensitive photomultiplier tubes. A point source (Mn-54) is placed at a distance in front of an xy plastic scintillating fiber stack which is coupled to two Hamamatsu R2486 position sensitive photomultiplier tubes. At some distance behind this detector another plastic scintillating detector coupled to another position sensitive photomultiplier is placed. Gamma rays interacting in the first detector are scattered, and interact with the second detector. By the knowledge of the source location, the Compton interaction location in the first detector, and the interaction location of the scattered gamma in detector two, the scattering angle of the Compton interaction in detector one can be determined. From this scattering angle and the known primary gamma energy the Compton electron energy can be calculated. The energy resolution of the scintillating fiber stack-photomultiplier unit of detector one for different Compton electron energies is determined by plotting the experimentally measured electron energies obtained from the light output of the photomultiplier tubes of detector one, comparing them with the electron energy calculated above, and expressed in terms of the FWHM.

The design considerations for a megavoltage imager based on the distribution of pair production events in tissues are explored. Optical scintillating fibers utilizing electronic collimation are used to detect the 0.511 MeV annihilation radiation from the pair production events. The resolution, efficiency, and signal-to-noise ratio characteristics of this imaging modality are discussed and compared to conventional computed tomography (CT) and positron emission tomography (PET) imagers. A proof of principle small animal imager experiment is discussed.

A small animal whole body imaging device was built with plastic scintillating fibers and application of this system to image folate receptors in mice is described. The prototype imaging device consisted of two layers of 1 mm BCF-10 fibers laid on 6.98 cm acrylic core, one layer with a right handed pitch and the other with a left handed pitch. The fiber readout was performed with a position sensitive photomultiplier and a specialized flash ADC. A coaxial brass mesh collimator (1 mm thick) was used to increase spatial resolution. Histamine- folate conjugate was labeled with I-125 and was found to have receptor binding properties similar to ³H labeled compound. Imaging studies were performed in mice bearing folate receptor +ve (IGROV) tumor and receptor -ve (Meth-A) tumor. In situ imaging of animals sacrificed at 30 min post injection of the tracer showed the localization of the tumor in animals with the folate receptor +ve tumors and the results were negative in animals with receptor -ve tumor. The biodistribution studies confirmed these observations. Our initial studies demonstrate the prospects for development of agents for imaging folate receptors that may have application in drug development and the application of the small animal imaging device built with plastic scintillating detectors in imaging with low energy photons (25 - 35 keV).

This paper describes for construction a prototype version of a new type of liquid xenon detector, specifically capable of distinguishing low energy (keV-range) nuclear recoil events from background events. Such a detector would be ideally suited to the detection of weakly interacting massive particles (WIMPS) which may constitute a significant part of the galactic dark matter. The same principle could be used also for the coherent detection of neutrinos from a supernova burst.

We review several new applications of scintillating fibers. One application is to be used in the experiment E803 at Fermilab which is designed to detect the neutrino oscillations (nu) _(mu ) yields (nu) _(tau ). A fiber tracker is to be used to localize the interaction inside a ton of nuclear emulsion and to help carry out real time detection of this process. Another application is to measure the emittance change of a cooling (mu) ^+/- beam for a (mu) ⁺(mu) ^- collider that is being studied by a group of scientists from US institutions. Scintillating fiber tracking could also be used in a detector for the (mu) ⁺(mu) ^- collider and for the UCLA Asymmetric (phi) Factory due to unusual requirements.

We have created a detector to image the neutrons emitted by imploded inertial-confinement fusion targets. The 14-MeV neutrons, which are produced by deuterium-tritium fusion events in the target, pass through an aperture to create an image on the detector. The neutron radiation is converted to blue light (430 nm) with a 20-cm-square array of plastic scintillating fibers. Each fiber is 10-cm long with a 1-mm-square cross section; approximately 35-thousand fibers make up the array. The resulting blue-light image is reduced and amplified by a sequence of fiber-optic tapers and image intensifiers, then acquired by a CCD camera. The fiber-optic readout system was tested optically for overall throughput and resolution. We plan to characterize the scintillator array using an ion-beam neutron source as well as DT-fusion neutrons emitted by inertial confinement targets. Characterization experiments will measure the light-production efficiency, spatial resolution, and neutron scattering within the detector. Several neutron images of laser-fusion targets have been obtained with the detector. We describe the detector and our characterization methods, present characterization results, and give examples of the neutron images.