Scintillating fibers are of growing interest in high energy physics for applications in calorimetry and in tracking detectors At present plastic scintillating fibers are mainly used in these applications because of their high light yield and their fast decay rates; however, in thin fibers, required for high spatial resolution, these suffer from low attenuation lengths. Moreover, cross-talk is still a severe problem. As alternatives we will discuss the following two concepts: (1) using Ce- and Tb-doped multicomponent glasses as active core material of glass fibers and (2) using liquid scintillator filled glass capillary arrays. The optical properties of the rare earth doped glasses are described and the scintillation efficiency of the fibers and fiber bundles utilizing these glasses as core material are presented. Broader applications appear to the possible with liquid scintillator filled capillary arrays. Suitable liquid scintillators with high refractive index solvents and locally emitting solutes with high yields, short decay times and large Stokes-shifts are available. Arrays can be produced with and without extra mural absorber in various sizes and shapes. Theoretical estimates show that reflection losses at the liquid/glass interface do not effect the overall transmission up to length/diameter ratios of 10⁵. In addition recent results have shown that the system resists radiation doses in the 100 kGy range. Further experimental results obtained at CERN with these arrays will be discussed.

A scaled version of a scintillating fiber detector (SFD) has been constructed and tested in a feasibility study at SAIC-San Diego for determining its neutron detection efficiency, directionality and gamma-ray sensitivity. This concept was supported by Monte Carlo simulations which predicted the effectiveness of the fiber bundle to discriminate against neutrons entering at directions non-parallel to the fiber axis. Fibers measuring 0.5 mm square and 10 cm long are formed into a bundle and coupled to a set of gamma-ray insensitive electro-optics intensifiers and a CCD camera. In this paper we describe the detector and present the results of the experimental tests with 14 MeV neutrons and an intense beam of ⁶⁰Co and ¹³⁷Cs gamma-rays.

A fiber tracking system was constructed at UCLA, consisting of four layers of scintillating fiber ribbons coupled to Visible Light Photon Counters (VLPC's), and was tested by measuring Cosmic-Ray tracks. The total length of the fiber array is 7 meters, 4 meters of scintillating fiber and 3 meters of clear optical fiber, 0.83 mm diameter. An average number of 6 photoelectrons were detected by the VLPC's, 7 meters from the Cosmic-ray interaction point at the end of the fibers. The details of the experimental arrangement and the test results are presented.

The recently developed plastic scintillating fiber technology started the development of a new generation of high spatial and time resolution gamma ray detectors for medical imaging, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT). A scintillating fiber PET module consisting of two 5 X 5 X 2.5 cm³ detector stacks made of parallel 1.0 mm diameter fiber, separated by 20 cm, each viewed by a Hamamatsu R2486 position sensitive photomultiplier was developed and tested. The time resolution of the coincidence system is 10 nsec. The spatial resolution and efficiency of this module turned out to be 2.3 mm (FWHM) and 2.0%, respectively, and independent of the location of the ²²Na testing source inside a sphere of 2 cm radius around the center of the two fiber stacks. The effect of gammas scattered in a 15 cm diameter water filled glass cylinder into which the ²²Na was immersed did not change the spatial resolution of the system.

We describe the current status of the development of imaging electron drift Liquid Argon Detectors (ICARUS) and the development of the Visible Light Photon Counter (VLPC) for scintillating fiber tracking for (SPC) SSC/LHC detectors. We then propose a detector that combines these two techniques to detect massive WIMPs through the possible identified Xe recoil in a liquid Xenon detector.

A short summary of the major problems of MeV and GeV gamma ray astronomy, astrophysics and cosmology is given with particular emphasis on search for Dark Matter, and study of the Large Scale Structure of the Universe. The scientific goals of the Compton Gamma Ray Observatory (GRO), and recent results on gamma ray bursts obtained by BATSE are discussed.

A new generation of large area, high resolution and improved sensitivity gamma ray telescopes are under development for the post-CGRO era in gamma ray astronomy and astrophysics, applying silicon strip detectors, scintillating fibers with position sensitive photomultipliers and cryogenic liquid drift chambers. A short review of these novel technologies is presented.

Can the brightness of issuing radiation be higher than that of insident. one (B B :'? In other words , can the radiation be 2 1 heated up" without. any eriercy iniection? (Obviously the br.cihtr1ess of incoherent radi ation is the most. univiver-sal parameter of r-adiation

I propose a new radiation-generating device called the laser undulator x-ray source (LUXUS). In particular, I demonstrate that LUXUS has the potential to generate a highly-directional, monochromatic beam of x-rays which is continuously tunable over multiple orders of magnitude in photon energy. In the configuration used as a model, the photons will be seen to have energies lying between 18 eV and 45 KeV when the electron accelerator energy is varied over the range 1 - 50 MeV. Reduced to its essentials, LUXUS consists of (1) a high-current, cyclic electron induction accelerator (such as a 'rebatron') in a racetrack configuration, (2) a high-finesse Fabry-Perot resonator used as a power-buildup cavity, and (3) a high-power, CW, injection-locked Nd:YAG laser to which, in turn, the Fabry-Perot resonator is locked. With a mean accelerator current of 1000 A and a Nd:YAG laser of 15 W output, an x-ray flux approximately 10¹³ photon/s should be possible at any selected energy within the x-ray range mentioned above (18 eV to 45 KeV). Important applications in medicine--including digital subtractive angiography, x-ray mammography, and general monochromatic radiography--will be discussed briefly.

Neutron imaging has been shown to be an excellent imaging tool for many nondestructive evaluation applications. Significantly improved contrast over x-ray images is possible for materials commonly found in engineering assemblies. The major limitations have been the neutron source and detection. A low cost, position sensitive neutron tomography detector system has been designed and built based on an electro-optical detector system using a LiF- ZnS scintillator screen and a cooled charge coupled device. This detector system can be used for neutron radiography as well as two and three-dimensional neutron tomography. Calculated performance of the system predicted near-quantum efficiency for position sensitive neutron detection. Experimental data was recently taken using this system at McClellan Air Force Base, Air Logistic Center, Sacramento, CA. With increased availability of low cost neutron sources and advanced image processing, neutron tomography will become an increasingly important nondestructive imaging method.

The fundamental studies for generating flash vacuum-ultraviolet (VUV) rays using a surface- discharge glass substrate are described. The experimental setup consisted of the following components: a negative high-voltage power supply, a high-voltage pulser with a condenser capacity of 14.3 nF, an oil diffusion pump, and a glass vacuum chamber for generating VUV rays. The VUV chamber employed a surface-discharge glass substrate and was connected to an oil diffusion pump which allowed operation at a pressure of 1 X 10^-3 Pa. The high-voltage pulser employed a polarity-inversion-type transmission line having a gap switch. Since the combined ceramic condenser was charged from -20 to -30 kV by a power supply, the maximum output voltages from the pulser were about -1 times the charged voltages. The VUV rays were produced after closing a gap switch. The maximum values of the discharge voltage and the current were about 17 kV and 1.8 kA, respectively. The radiation outputs with various photon energies were measured by a combination of a plastic scintillator and a photomultiplier. The pulse durations of the VUV rays were nearly equivalent to the durations of both the discharge voltage and current which displayed damped oscillations, and the widths were about 10 microsecond(s) .

The motivation of this work was to develop a non-contacting technique for rapidly measuring the density of organic material processed on a steel surface. Various alternatives were considered. The steel base effectively prevented the use of most transmission methods, while the bulk of the organics made optical and IR methods impractical. A technique based on X-ray scattering was ultimately employed. Because the intensity of Compton scattering is proportional to electron density which is in turn roughly proportional to atomic weight, this affords a method of mass measurement that is essentially independent of variations in composition to a first order of approximation. A simple one-dimensional model based on differential cross-sections and exponential attenuation law was developed and analyzed numerically. Experimental results were compared with the results of this analysis. While the model correctly predicted the general trend of the experimental data within the range of interest, it did not match the data over the full range. This was attributed to neglecting finite geometric effects in the model used.

The constructions and the radiographic characteristics of a flash x-ray generator having a liquid-anode radiation tube are described. This generator consisted of the following essential components: a high-voltage power supply, a combined ceramic condenser of 10.7 nF, an oil- diffusion pump, an oil circulator, a trigger device, and a flash x-ray tube. The x-ray tube was of a triode and was composed of the following major devices: a mercury anode, a rod-shaped graphite cathode, a trigger electrode made from a copper wire, an x-ray window made from a polyethyleneterephthalate film, and a glass tube body. The ceramic condenser was charged from 40 to 60 kV by a power supply, and the electric charges in the condenser were discharged to the x-ray tube after the triggering. The maximum tube voltage was equivalent to the initial charged voltage of the condenser, and the tube current was less than 0.7 kA. The pulse widths of the flash x rays had values of about 1 microsecond(s) , and the time-integrated x-ray intensity was about 2.4 (mu) C/kg at 0.26 m per pulse with a charged voltage of 60 kV.

We developed a high-durability flash x-ray tube with a plate-shaped ferrite cathode for the use in the field of biomedical engineering and technology. The surface-discharge cathode was very useful for generating stable flash x rays. This flash x-ray generator consisted of the following essential components: a high-voltage power supply, an energy-storage condenser of 97 nF, a two-stage Marx type pulser, an oil diffusion pump, and a flash x-ray tube. This x-ray tube was of a diode which was connected to the turbo molecular pump and had plate-shaped anode and cathode electrodes. The cathode electrode was made of ferrite, and its edge was covered with a thin gold film by means of the spattering in order to decrease contact resistance. The space between the anode and cathode electrodes could be regulated from the outside of the x-ray rube. The two condensers in Marx circuit were charged from 50 to 70 kV by a power supply, and the condensers were connected in series after closing a gap switch. Thus the maximum output voltages from the pulser were about two times the charged voltages. In this experiment, the maximum tube voltage and the current were about 110 kV and 0.8 kA, respectively. The pulse widths were less than 140 ns, and the maximum x-ray intensity was 1.27 (mu) C/kg at 0.5 m per pulse. The size of the focal spot and the maximum repetition rate were about 2 X 2.5 mm and 50 Hz (fps), respectively.

A general systematic method to characterize the material composition of an object to be interrogated is posed and discussed. It employs neutrons to provide for the excitation of the nuclear isomer states of the isotopes constituting the body. Observation of the characteristic energies of the gamma rays emitted during the prompt relaxation identifies the isotope species. The intensity of the gamma rays together with neutron cross section data allows for the determination of species abundance. Measurements using multiple detectors that are spatially offset allows for the generation of images of the body composition isotope by isotope. This isomer excitation technique enables isotope identification for species of Z >= 3. Observation of neutron capture (gamma) emission supplements the method for hydrogen and helium-3. Several applications of the technique are described.

A recently developed neutron diagnostic probe system has the potential to satisfy a significant number of van-mobile and fixed-portal requirements for nondestructive detection, including monitoring of contraband explosives, drugs, and weapon materials, and treaty verification of sealed munitions. The probe is based on a unique associated-particle sealed-tube neutron generator (APSTNG) that interrogates the object of interest with a low-intensity beam of 14- MeV neutrons generated from the deuterium-tritium reaction and that detects the alpha-particle associated with each neutron. Gamma-ray spectra of resulting neutron reactions identify nuclides associated with all major chemicals in explosives, drugs, and chemical warfare agents, as well as many pollutants and fissile and fertile special nuclear material. Flight times determined from detection times of the gamma-rays and alpha-particles yield a separate coarse tomographic image of each identified nuclide. The APSTNG also forms the basis for a compact fast-neutron transmission imaging system that can be used along with or instead of the emission imaging system. Proof-of-concept experiments have been performed under laboratory conditions for simulated nuclear and chemical warfare munitions and for explosives and drugs. The small and relatively inexpensive APSTNG exhibits high reliability and can be quickly replaced. Surveillance systems based on APSTNG technology can avoid the large physical size, high capital and operating expenses, and reliability problems associated with complex accelerators.

This paper sets forth the fundamental principles governing the development of position- sensitive detection systems for slow neutrons. Since neutrons are only weakly interacting with most materials, it is not generally practical to detect slow neutrons directly. Therefore all practical slow neutron detection mechanisms depend on the use of nuclear reactions to 'convert' the neutron to one or more charged particles, followed by the subsequent detection of the charged particles. The different conversion reactions which can be used are discussed, along with the relative merits of each. This is followed with a discussion of the various methods of charged particle detection, how these lend themselves to position-sensitive encoding, and the means of position encoding which can be applied in each case. Detector performance characteristics which may be of importance to the end user are discussed and related to these various detection and position-encoding mechanisms.

The ISIS Single Crystal Diffractometer SXD is a time-of-flight Laue instrument exploiting the pulsed nature of the ISIS beam along with large area detectors. This means that the data collected on SXD is in the form of reciprocal space volumes. The development of the large area position-sensitive detectors used on ISIS are outlined, and results obtained from both the Anger camera and later fiber-optic encoded scintillator detectors are used to illustrate the performance of these.

The main problem in neutron protein crystallography is the low flux of present reactor based or pulsed neutron sources. This low flux is however well matched with presently available multiwire area detectors. One way to increase the flux at the sample is to increase the wavelength bandwidth. The conventional technique uses a monochromator with a bandwidth of the order of 1%. This bandwidth can be increased by using a multilayer monochromator composed of different 'd' spacings. This provides a large delta lambda increasing the flux manifold. In this case a reflection in diffraction condition is scanned by the wavelength bandwidth and not by rotation of the reciprocal lattice point through the Ewald sphere. In order to collect most of the simultaneous diffraction a large cylindrical area detector covering an angular width of 120 degree(s) with a height of approximately 20 cm is needed. Such a detector should have a spatial resolution of 1.1 mm, an efficiency of 80% at 2.0 A and a counting rate of one million events per second. This detector will be subdivided into 4 sectors that will be decoded simultaneously into a Motorola based computer system. This data acquisition system allows time slicing and this detector is therefore useful for similar experiments using pulsed neutron sources.

The Small Angle Diffractometer (SAD) at the Intense Pulsed Neutron Source (IPNS) utilizes a 20 X 20 cm² Borkowski-Kopp type ³He position sensitive detector (PSD) which has reliably performed small-angle neutron scattering experiments for more than a decade. The pulsed-source based SAD employs a small, but fixed, sample-to-detector distance and a pulsed polychromatic neutron beam. The neutron energies are resolved through time-of- flight (TOF) measurements so that a much wider range of momentum transfer is probed in a single measurement compared to the range of spectrometers using monochromatic incident beams. However, the pulsed source requires a short sample-to-detector distance so that the detector covers a large solid angle, but with lower angular resolution, and this situation puts stringent demands on the spatial resolution of the detector. Previously, nonlinearities in the position encoding of detected neutrons required that the outer channels of the detector, representing 40% of the detector area, be discarded. This paper presents a technique to characterize both the position encoding and the position resolution of the entire detector so that the whole detector can be used for SANS measurements.

A two-dimensional position-sensitive neutron detector (PSD) was constructed using a scintillator attached to a position-sensitive photo-multiplier with 100 mm diameter. Position determination is based on charge division. Spatial resolution, gamma sensitivity, linearity, temperature dependence and radiation shielding have been investigated. The shaping amplifiers used in the detection electronics were optimized. Two kinds of scintillators were examined: LiI(Eu) crystal and Li-glass. Concerning the gamma sensitivity and resolution, the best performance was obtained using the LiI. A spatial resolution with full width half maximum of 1.3(1) mm was measured. A good shielding against gamma radiation was found to consist out of three layers: 5 mm of boron rubber, 5 cm of lead and 5 mm of boron rubber. The influence of the temperature on the PSD signal output was measured and indicates that a stabilization is necessary. The PSD will be used in a time-of-flight neutron reflectometer.

We report on progress in different domains of n-detection: (1) High gain image intensifiers coupled to n-scintillators enable small size n-monitors with high spatial resolution. (2) Standard CCD cameras combined with special frame grabbers provide low cost n-image processing. (3) Progress in diode technology allows direct light detection from n-scintillators with the aim of low effort and very thin n-detectors. (4) New foils with X-ray photography combined with n-converters can be used for efficient large area position-sensitive detectors. The stored information is read out by laser-stimulated emission of light.

Resistive Plate Chambers, RPC, are wireless gaseous detectors working with a uniform field generated by two parallel electrode plates of high bulk resistivity. They can be made sensitive to thermal neutrons by a thin layer of boron carbide coating the electrode internal surface and acting as neutron converter. This presentation describes the performance of a neutron sensitive RPC and discusses possible ideas concerning RPC's optimization as neutron detectors. The purpose of this research is to realize an inexpensive position sensitive neutron detector suitable for applications where large detection areas are required.

The light emission of a microstrip-anode in noble gas mixture, with a gas amplification of 4(DOT)10⁴, is 60 times higher than the light emission of NaI(Tl) scintillator.

Existing neutron imaging detectors have limited count rates due to inherent property and electronic limitations. The popular multiwire proportional counter is qualified by gas recombination to a count rate of less than 10⁵ n/s over the entire array and the neutron Anger camera, even though improved with new fiber optic encoding methods, can only achieve 10⁶ cps over a limited array. We present a preliminary design for a new type of neutron imaging detector with a resolution of 2 - 5 mm and a count rate capability of 10⁶ cps per pixel element. We propose to combine optical and electronic processing to economically increase the throughput of advanced detector systems while simplifying computing requirements. By placing a scintillator screen ahead of an optical image processor followed by a detector array, a high throughput imaging detector may be constructed.

Microchannel plates (MCPs) are compact electron multipliers of high gain, widely used for the high resolution imaging of charged particles and photons. In this paper, we consider the use of lead glass MCPs for the imaging of thermal neutrons. Two contrasting techniques are described. The first method involves direct neutron detection within a special channel plate structure containing lithium and/or boron. We review the constraints of glass chemistry on the attainable lithium oxide and boron oxide fractions and, hence, on the maximum neutron detection efficiency. The second method involves the detection, using MCPs of standard glass composition, of the internal conversion electrons from a thin gadolinium foil. We present the first measurements of the detection efficiency, pulse height resolution and imaging properties of a pulse-counting MCP/Gd detector system.

A charge injection device (CID) camera and image processing system have been used as a position sensitive detector for energetic charged particles and low energy neutrons. This video radiation detector (VRD) is simple in design but highly effective for real-time radiography and dosimetry with many advantages characteristics. The VRD currently has a dynamic range of 65,000 intensity levels for a 755 X 484 pixel matrix, an active area of 7 mm X 9 mm, a spatial mapping resolution of about 14 micrometers for single detected events (7 micrometers for radiation from a point source), and is sufficiently radiation-hard to be operated in a neutron beam for extended periods of time. Radiation images are updated at a rate of thirty frames per second. The VRD is sensitive to fission fragments, alpha particles, and slow neutrons. Using commercially available image processing hardware and software and an off-the-shelf camera, the system is inexpensive, easy to use with simple interpretation of data, and is capable of performing radiography with only minimal adaptations. Applications in our laboratory include the characterization of focused cold neutron beams, the mapping of uranium and lithium distributions in samples by the detection of neutron absorption reaction products, and the mapping of spontaneous alpha radioactivity from environmental samples. Results provide information on x-y position, counts received, and energy deposited per count, each as a function of time.

Measurements have been made on optical properties of Bicron BCF-91 waveshifting optical fiber. This fiber is proposed as a means of converting UV and blue light emitted from liquid scintillator when exposed to ionizing radiation. The conversion is accomplished by coiling the fiber in a reservoir filled with liquid scintillator and coated internally with reflective paint. UV and blue light is absorbed by the waveshifting dyes in the fiber and reemitted light is channeled into the core of the fiber and output to photo detectors. It has been proposed to outfit the hadron calorimeter sub-system of the GEM detector to be built at the Superconducting Super Collider with 800,000 separate liquid scintillator/waveshifting fiber cells. The measurements described in this work deal with the optical performance of the fiber: spectral emission, response as a function of input wavelengths, response as a function of irradiated length, propagation length and output numerical aperture. The theoretical response of an ideal calorimeter cell is studied based on the results of the measurements presented in this paper.

The three levels of thermal neutron sources are introduced--University laboratory sources, infrastructure sources and world-class sources--and the needs for each kind and their inter- dependence will be emphasized. A description of the possibilities for University sources based on a (alpha) -Be reactions or spontaneous fission emission is given, and current experience with them is described. A new generation of infrastructure sources is needed to continue the regional programs based on small reactors. Some possibilities for accelerator sources that could not meet this need are considered.

Small accelerator neutron sources offer considerable potential for applied neutron radiography applications. Among the desirable features are relatively low costs, limited operating hazards, opportunities for tailoring primary neutron spectra, compactness and portability, and modest licensing requirements (compared to fission reactors). However, exploitation of this potential has been somewhat limited, in part, by incomplete knowledge of the primary-neutron yields and energy spectra from the favorable source reactions. This work describes an extensive experimental determination of zero-degree neutron yields and energy spectra from the ⁹Be(d,n)¹⁰B source reaction, for incident deuterons of 2.6 to 7.0 MeV on a thick beryllium metal target. This information was acquired by means of time-of-flight measurements that were conducted with a calibrated uranium fission detector. Tables and plots of neutron-producing reaction data are presented. This information provides input which will be essential for applications involving the primary spectrum as well as for the design of neutron moderators and for calculation of thermal-neutron yield factors. Such analyses will be prerequisites in assessing the suitability of this source for various possible neutron radiography applications and, also, for assisting in the design of appropriate detectors to be used in neutron imaging devices.

Several d,n reaction reactions using pulsed deuteron beams have been investigated for possible pulsed 'white neutron' sources for use in a Fast Neutron Spectrometer to be used in an airport security system. It was found that a 5 to 6.6 MeV pulsed deuteron beam incident on a thick Beryllium target generates a good 'white neutron' source.

The feasibility of utilizing real-time computed tomography (CT) to characterize and monitor the growth of defects in composite materials as they undergo destructive testing was investigated. The equipment consisted of an Imatron C-100 Ultrafast CT Scanner, a modified high-temperature laboratory oven, and a motor driven hydraulic ram. Three types of composites were studied: carbon-carbon, carbon-phenolic, and glass-phenolic. Time-density profiles were obtained for each type. In general, the density of the samples decreased slightly upon impact of the ram, then sharply increased before dropping back to a slightly lower constant value.

Research is being conducted on a new type airport security system based on pulsed fast neutron spectroscopy. A pulsed 'white neutron' source is produced from the ⁹Be(d,n) reaction by allowing a pulsed 5 MeV deuteron beam to impinge on a thick beryllium target. By performing sample in/sample out experiments, the neutron attenuation as a function of neutron energy is determined. From the attenuation curves, the presence and amount of hydrogen, carbon, nitrogen and oxygen in the neutron beam is determined. The determination of these four elements allows one to determine with high probability the presence of explosives.

Several d,n reaction reactions using pulsed deuteron beams have been investigated for possible pulsed 'white neutron' sources for use in a Fast Neutron Spectrometer to be used in an airport security system. It was found that a 5 to 6.6 MeV pulsed deuteron beam incident on a thick Beryllium target generates a good 'white neutron' source.

Neutron Laue diffraction patterns have been recorded using a gadolinium scintillator and X- ray image plate. The optimization of scintillator and storage phosphor are discussed.