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Single scintillation crystal versus Phoswich detectors for in vivo low- energy photon detection

Description: The development of in vivo body-count measurement systems for the detection of low-energy photons from americium and plutonium has stressed the importance of low background counting rates for better sensitivity. The measurement systems are develeped for use in the body-counting facility, which has been in operation at the Rocky Flats Plant, to detect exposures in humans from radioactive materials. The facility is in a separate building and houses the body courter which consists of thick steel walls. The detectors within the body counter section are arranged over a table or couch and can be positioned over various parts of the body of an individual being checked for the presence of radioactive materials. The systems in current use provide an improvement in background counting rates for sodium-iodide thallium detectors with the two- crystal sandwich or Phoswich scintillator. The two types of electronic configurations used with the Phoswich detectors demonstrate improvements in background counting rates over results from a single crystal detector. Tabulated data comparing the operating parameters of a single crystal and a dual-crystal configuration are included. (auth)
Date: January 1, 1974
Creator: Tyree, W. H.
Partner: UNT Libraries Government Documents Department

Scintillator Evaluation for High-Energy X-Ray Diagnostics

Description: This report presents results derived from a digital radiography study performed using x-rays from a 2.3 MeV, rod-pinch diode. Detailed is a parameter study of cerium-doped lutetium ortho-silicate (LSO) scintillator thickness, as it relates to system resolution and detection quantum efficiency (DQE). Additionally, the detection statistics of LSO were compared with that of CsI(Tl). As a result of this study we found the LSO scintillator with a thickness of 3 mm to yield the highest system DQE over the range of spatial frequencies from 0.75 to 2.5 mm{sup -1}.
Date: September 1, 2001
Creator: Lutz, S. S. & Baker, S. A.
Partner: UNT Libraries Government Documents Department

Monolithic circuits for barium fluoride detectors used in nuclear physics experiments. CRADA final report

Description: Custom monolithic electronic circuits have been developed recently for large detector applications in high energy physics where subsystems require tens of thousands of channels of signal processing and data acquisition. In the design and construction of these enormous detectors, it has been found that monolithic circuits offer significant advantages over discrete implementations through increased performance, flexible packaging, lower power and reduced cost per channel. Much of the integrated circuit design for the high energy physics community is directly applicable to intermediate energy heavy-ion and electron physics. This STTR project conducted in collaboration with researchers at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory, sought to develop a new integrated circuit chip set for barium fluoride (BaF{sub 2}) detector arrays based upon existing CMOS monolithic circuit designs created for the high energy physics experiments. The work under the STTR Phase 1 demonstrated through the design, simulation, and testing of several prototype chips the feasibility of using custom CMOS integrated circuits for processing signals from BaF{sub 2} detectors. Function blocks including charge-sensitive amplifiers, comparators, one shots, time-to-amplitude converters, analog memory circuits and buffer amplifiers were implemented during Phase 1 effort. Experimental results from bench testing and laboratory testing with sources were documented.
Date: February 1, 1998
Creator: Varner, R.L.; Blankenship, J.L.; Beene, J.R. & Todd, R.A.
Partner: UNT Libraries Government Documents Department

Development of a long-term post-closure radiation monitor: Phase 2, Topical report, March 1994--July 1995

Description: The long-term monitoring of a hazardous waste site for migration of radionuclides requires installation of radiation sensors at a large number of subsurface locations. The concept under development employs a passive in-ground measurement probe which contains a scintillator coupled to an optical lightguide. The overall goal of the Long-Term Post-Closure Radiation Monitor System (LPRMS) development program is to configure a long-term radiation monitor using commercially available, demonstrated components to the largest extent possible. The development program is planned as a three phase program spanning a total time of 53 months. The problems to be solved during Phase 1 were primarily those associated with selection of the most appropriate components (scintillator, coupling optics, optical fiber, and opto-electronics) to maximize the signal reaching the detectors and thereby minimizing the integration time required to obtain a reliable measure of radiation. Phase 2 (the current Phase) encompassed the fabrication and testing of the prototype LPRMS probe at a contaminated DOE site, the Fernald Environmental Management Project, in southwestern Ohio. Uranium isotopes are the primary contaminants of concern at this site. The single probe and opto-electronic device were used to made measurements in-situ at relatively shallow subsurface depths. The end objective of Phase 2 was the design of a full-scale prototype system which incorporates all the features expected to be necessary on a commercial system, including 50 meter depth of measurement, multiplexing of multiple probes, and remote transmission of data. This full-scale prototype will be fabricated and field tested for 12 months during Phase 3, and a commercial design will be developed based upon the data gathered and experience gained during the entire program.
Date: July 1, 1995
Creator: Reed, S.E.
Partner: UNT Libraries Government Documents Department

Scintillation response of lithium fluoride

Description: Thesis. Lithium fluoride crystals, with TlF added to the charge, were prepared by the Bridgman- Stockbarger method. The scintillation response to photon energies between 25 and 1250 keV for these crystals and a commercially prepared LiF (Ti) crystal was studied. The response of the LiF (Ti) crystal was compared to the response of an NE109 scintillator at 1250 keV. The dose response of the LiF (Ti) crystal was evaluated over the energy range 25 to 1250 keV. The absorption and emission spectra of the LiF (Ti) crystal are discussed. A historical review precedes the discussion. (auth)
Date: February 11, 1974
Creator: Kloepping, R.J.
Partner: UNT Libraries Government Documents Department

Measurement of electromagnetic shower position and size with a saturated avalanche tube hodoscope and a fine grained scintillation hodoscope

Description: A hodoscope has been constructed from 100 ..mu.. m diameter wires and brass tubes (1.2 x 0.7 cm/sup 2/ cross section) filled with a mixture of argon, ethane and ethyl alcohol. It has been tested in the saturated avalanche mode in an SCG1-C electromagnetic shower detector to determine its properties for the measurement of the position and size of electromagnetic showers. Two of these tube hodoscopes were positioned 3.5 radiation lengths deep in the detector and the profiles of 1 to 25 GeV electromagnetic showers were measured. Simultaneous measurements were performed using a plane of twenty, 0.5 cm wide scintillation counters positioned immediately behind the gas tube hodoscope. In addition the transition between saturated avalanche and limited streamer modes has been measured for the tube hodoscopes.
Date: January 1, 1984
Creator: Rameika, R.; Cox, B.; Jenkins, C.M.; Judd, D.J.; Hale, G.; Mazur, P.O. et al.
Partner: UNT Libraries Government Documents Department

Integrated constant-fraction discriminator shaping techniques for the PHENIX lead-scintillator calorimeter

Description: The suitability of several on-chip constant-fraction discriminator (CFD) shaping methods for use in the multichannel PHENIX Lead- Scintillator detector has been investigated. Three CFD circuits utilizing a distributed R-C delay-line, a lumped-element R-C delay- line and the Nowlin shaping method have been realized in a standard 1. 2-{mu} n- well CMOS process. A CFD using ideal delay-line shaping was also studied for comparison. Time walk for 5 ns risetime input signals over a dynamic range of - 2 V to - 20 mV was less than {+-} 175 ps, {+-} 150 ps, {+-} 150, and {+-} 185 ps while worst case rms timing jitter measured 85 ps, 90 ps, 100 ps, and 65 ps, respectively, for the four methods mentioned above. Area requirements for the three candidate methods tested including the fraction circuit were 172 {mu} X 70 {mu}, 160 {mu} X 65 {mu}, 179 {mu} X 53 g, respectively. The fraction circuit area for the external delay-line circuit was 67 {mu} X 65 {mu}. Each shaping method studied consumed no power from the dc supply.
Date: December 31, 1996
Creator: Jackson, R.G.; Blalock, T.V.; Simpson, M.L.; Wintenberg, A.L. & Young, G.R.
Partner: UNT Libraries Government Documents Department

Recent results in a search for inorganic scintillators for x- and gamma-ray detection

Description: We present recent results from an ongoing search for inorganic scintillators for gamma ray detection in which we measure the scintillation properties (luminous efficiency, decay time, and emission wavelength) of powdered samples excited by brief x-ray pulses. Recent promising candidates include cerium doped lutetium borate (LuBO{sub 3}) and the lutetium double phosphates K{sub 3}Lu(PO{sub 4}){sub 2} and Rb{sub 3}Lu(PO{sub 4}){sub 2}, which have luminous intensities above 25,000 photons/MeV. In order to find scintillators that are compatible with silicon photodetectors, we have tested over 1,100 samples using a photomultiplier tube with a GaAs:Cs photocathode, which is sensitive to emissions from 200-950 nm. While many samples exhibited strong emissions in the 600-900 nm range, all had decay times that were larger than 10 {mu}s.
Date: October 1997
Creator: Moses, W. W.; Weber, M. J.; Derenzo, S. E.; Perry, D. & Berahl, P.
Partner: UNT Libraries Government Documents Department

Growth of large detector crystals. CRADA final report

Description: In the course of a collaborative research effort between L.A. Boatner of Oak Ridge National Laboratory and Prof. Alex Lempicki of the Department of Chemistry of Boston University, a new highly efficient and very fast scintillator for the detection of gamma-rays was discovered. This new scintillator consists of a single crystal of lutetium orthophosphate (LuPO{sub 4}) to which a small percentage of trivalent cerium is added as an activator ion. The new lutetium orthophosphate-cerium scintillator was found to be superior in performance to bismuth germanium oxide--a material that is currently widely used as a gamma-ray detector in a variety of medical, scientific, and technical applications. Single crystals of LuPO{sub 4} and related rare-earth orthophosphates had been grown for a number of years in the ORNL Solid State Division prior to the discovery of the efficient gamma-ray-scintillation response of LuPO{sub 4}:Ce. The high-temperature-solvent (flux-growth) method used for the growth of these crystals was capable of producing crystals in sizes that were adequate for research purposes but that were inadequate for commercial-scale production and widespread application. The CRADA between ORNL and Deltronic Crystal Industries of Dover, NJ was undertaken for the purpose of investigating alternate approaches, such as top-seeded-solution growth, to the growth of LuPO{sub 4}:Ce scintillator crystals in sizes significantly larger than those obtainable through the application of standard flux-growth methods and, therefore, suitable for commercial sales and applications.
Date: June 18, 1997
Creator: Boatner, L.A. & Samuelson, S.
Partner: UNT Libraries Government Documents Department

Small inorganic scintillators as neutron detectors

Description: Small organic scintillators that exhibit pulse shape differences (PSD) in response to charged particles have been investigated as possible neutron detectors in the energy range from 1 to 200 MeV. Neutrons in this energy range can induce reactions such as (n,p) and (n,alpha) in these scintillators, and the cross sections for these reactions vary with energy. Pulse-height and PSD distributions were measured as a function of neutron energy for small crystals of NaI(Tl) and CsI(Tl) at the LANSCE-WNR pulsed spallation neutron source. PSD information indicating the relative numbers of protons and alphas produced can give information about the neutron spectrum in fast-neutron radiation fields such as those encountered in space exploration.
Date: December 1, 1998
Creator: Bartle, C.M. & Haight, R.C.
Partner: UNT Libraries Government Documents Department

Neutron scintillators using wavelength shifting fibers

Description: A proposed design for an optically-based, one-dimension scintillation detector to replace the gas-filled position-sensitive proportional counter currently used for a wide-angle neutron detector (WAND) at the high-Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (ORNL) is presented. The scintillator, consisting of a mixture of {sup 6}LiF and ZnS(Ag) powders in an epoxy binder, is coupled to an array of wavelength shifting optical fibers which provide position resolution. The wide-angle neutron detector is designed to cover a 120 degree arc with a 75 cm radius of curvature. The final detector design provides for 600 optical fibers coupled to the scintillator screen with an angular resolution of 0.2 degrees. Each individual pixel of the detector will be capable of operating at count rates exceeding 1 MHz. Results are presented from the measurement of neutron conversion efficiencies for several screen compositions, gamma-ray sensitivity, and spatial resolution of a 16 element one-dimensional array prototype.
Date: June 1, 1995
Creator: Hutchinson, D.P.; Miller, V.C. & Ramsey, J.A.
Partner: UNT Libraries Government Documents Department

Photon detectors

Description: J. Seguinot and T. Ypsilantis have recently described the theory and history of Ring Imaging Cherenkov (RICH) detectors. In this paper, I will expand on these excellent review papers, by covering the various photon detector designs in greater detail, and by including discussion of mistakes made, and detector problems encountered, along the way. Photon detectors are among the most difficult devices used in physics experiments, because they must achieve high efficiency for photon transport and for the detection of single photo-electrons. For gaseous devices, this requires the correct choice of gas gain in order to prevent breakdown and wire aging, together with the use of low noise electronics having the maximum possible amplification. In addition, the detector must be constructed of materials which resist corrosion due to photosensitive materials such as, the detector enclosure must be tightly sealed in order to prevent oxygen leaks, etc. The most critical step is the selection of the photocathode material. Typically, a choice must be made between a solid (CsI) or gaseous photocathode (TMAE, TEA). A conservative approach favors a gaseous photocathode, since it is continuously being replaced by flushing, and permits the photon detectors to be easily serviced (the air sensitive photocathode can be removed at any time). In addition, it can be argued that we now know how to handle TMAE, which, as is generally accepted, is the best photocathode material available as far as quantum efficiency is concerned. However, it is a very fragile molecule, and therefore its use may result in relatively fast wire aging. A possible alternative is TEA, which, in the early days, was rejected because it requires expensive CaF{sub 2} windows, which could be contaminated easily in the region of 8.3 eV and thus lose their UV transmission.
Date: October 1, 1995
Creator: Va`vra, J.
Partner: UNT Libraries Government Documents Department

Scintillators for positron emission tomography

Description: Like most applications that utilize scintillators for gamma detection, Positron Emission Tomography (PET) desires materials with high light output, short decay time, and excellent stopping power that are also inexpensive, mechanically rugged, and chemically inert. Realizing that this ``ultimate`` scintillator may not exist, this paper evaluates the relative importance of these qualities and describes their impact on the imaging performance of PET. The most important PET scintillator quality is the ability to absorb 511 keV photons in a small volume, which affects the spatial resolution of the camera. The dominant factor is a short attenuation length ({le} 1.5 cm is required), although a high photoelectric fraction is also important (> 30% is desired). The next most important quality is a short decay time, which affects both the dead time and the coincidence timing resolution. Detection rates for single 511 keV photons can be extremely high, so decay times {le} 500 ns are essential to avoid dead time losses. In addition, positron annihilations are identified by time coincidence so {le}5 ns fwhm coincidence pair timing resolution is required to identify events with narrow coincidence windows, reducing contamination due to accidental coincidences. Current trends in PET cameras are toward septaless, ``fully-3D`` cameras, which have significantly higher count rates than conventional 2-D cameras and so place higher demands on scintillator decay time. Light output affects energy resolution, and thus the ability of the camera to identify and reject events where the initial 511 keV photon has undergone Compton scatter in the patient. The scatter to true event fraction is much higher in fully-3D cameras than in 2-D cameras, so future PET cameras would benefit from scintillators with a 511 keV energy resolution < 10--12% fwhm.
Date: September 1, 1995
Creator: Moses, W.W. & Derenzo, S.E.
Partner: UNT Libraries Government Documents Department

Experimental efforts and results in finding new heavy scintillators

Description: New heavy scintillators are being discovered with increasing frequency. In recent years NaI(Tl) (with its high light output and energy resolution) has been joined by BGO (with its high stopping power), BaF{sub 2} (with its excellent timing resolution), and CeF{sub 3} (with its speed and short Moliere radius). More than 10 potentially useful scintillators have been under development in the past five years, such as PbSO{sub 4} and Lu{sub 2}SiO{sub 5}(Ce). We tabulate the characteristics of these and other scintillators, including wavelength, luminous efficiency, decay time, and initial intensity. We describe a search strategy and the prospects for finding the ``ideal`` heavy scintillator, which would combine the light output of NaI(Tl) and CsI(Tl), the stopping power of BGO, and the speed of BaF{sub 2} and ZnO(Ga).
Date: September 1, 1992
Creator: Derenzo, S. E. & Moses, W. W.
Partner: UNT Libraries Government Documents Department

Ultrafast readout of scintillating fibers using upgraded position-sensitive photomultipliers. Progress report, FY 1993

Description: Experimental results obtained with commercially available position-sensitive photomultipliers (PSPM) coupled with 0.5 mm diameter scintillating fiber arrays show some promising performances such as space resolution better than 200 {mu}m and time resolution {approx} 1.5 ns with a detection efficiency higher than 90%. Major progress has also been recently achieved with an upgrade of a PSPM based on new grid dynode structures. Two-track spatial resolution has been studied using the upgraded PSPM. Initial studies demonstrate that two tracks separated by a minimum distance of 3 mm are resolved.
Date: January 1, 1994
Creator: Onel, Y.
Partner: UNT Libraries Government Documents Department

Design and characterization of a pulsed x-ray source for fluorescent lifetime measurements

Description: To search for new, fast, inorganic scintillators, the author and his colleagues have developed a bench-top pulsed x-ray source for determining fluorescent lifetimes and wavelengths of compounds in crystal or powdered form. This source uses a light-excited x-ray tube which produces x-rays when light from a laser diode strikes its photocathode. The x-ray tube has a tungsten anode, a beryllium exit window, a 30 kV maximum tube bias, and a 50 HA maximum average cathode current. The laser produces 3 {times} 10{sup 7} photons at 650 nm per {approximately}100 ps pulse, with up to 10{sup 7} pulses/sec. The time spread for the laser diode, x-ray tube, and a microchannel plate photomultiplier tube is less than 120 ps fwhm. The mean x-ray photon energy, at tube biases of 20, 25, and 30 kV, is 9.4, 10.3, and 11.1 keV, respectively. They measured 140, 230, and 330 x-ray photons per laser diode pulse per steradian at tube biases of 20, 25, and 30 kV, respectively. Background x-rays due to dark current occur at a rate of 1 {times} 10{sup 6} and 3 {times} 10{sup 6} photons/sec/steradian at tube biases of 25 and 30 kV, respectively. Data characterizing the x-ray output with an aluminum filter in the x-ray beam are also presented.
Date: December 1, 1993
Creator: Blankespoor, S. C.
Partner: UNT Libraries Government Documents Department

Timing resolution of ``Shisk-Kebab`` lead scintillator sandwich calorimeters

Description: We have constructed lead scintillator sandwich calorimeters with 1/4 {chi}{sub o} sampling frequency and total thickness {approximately}16{chi}{sub o}. The 4 mm thick scintillator plates are read out by wavelength shifter fibers 1 mm in diameter which pass through holes penetrating the plates on a .95 cm {times} .95 cm grid (Shish-Kebab geometry). We tested these modules in the A2 test beam at Brookhaven using low energy electrons and hadrons. Results are here presented on electron energy and time-of-flight resolution obtained with various combinations of scintillators and wavelength shifters. We also describe results on e/{pi} separation obtained with a new technique for the longitudinal segmentation.
Date: December 31, 1992
Creator: Kistenev, E.; White, S.; Pischalnikov, Y.; Protopopov, Y. & Rykalin, V.
Partner: UNT Libraries Government Documents Department

Calibration of scintillation detectors for MeV charged fusion products

Description: The light output of ZnS scintillators used to detect escaping fusion products in the TFTR Tokamak is studied with 3.5 MeV alpha and 3 MeV proton beams. The emitted light first increases linearly with beam current and then saturates. In all cases investigated, the onset of the saturation corresponds to a power of about 1 mW absorbed within the ZnS powder. The scintillators have adequate time response up to 50--100 kHz.
Date: December 31, 1991
Creator: Tuszewski, M. & Zweben, S. J.
Partner: UNT Libraries Government Documents Department

Measurements of charged fusion product diffusion in TFTR

Description: The single particle confinement of charged fusion products, namely the 1 MeV triton and the 3 MeV proton, has been studied using a detector located near the outer midplane of TFTR. The detector, which measure the flux of escaping particles, is composed of a scintillator [ZnS(Ag)] and a system of collimating apertures, which permit pitch angle, energy and time resolution. It is mounted on a movable probe which can be inserted 25 cm into the vacuum vessel. Measurements indicate a level of losses higher than expected from a first-orbit loss mechanism alone. The primary candidate for explaining the observed anomalous losses is the toroidal field (TF) stochastic ripple diffusion, theoretically discovered by Goldston, White and Boozer. This loss mechanism is expected to be localized near the outer midplane where, at least at high current ({approx_gt} 1.0 MA) it would locally dominate over first-orbit losses. Calculations made with a mapping particle orbit code (MAPLOS) show a semi-quantitative agreement with the measurements. The predominant uncertainties in the numerical simulations were found to originate from the modeling of the first wall geometry and also from the assumed plasma current and source profiles. Direct measurements of the diffusion rate were performed by shadowing the detector with a second movable probe used as an obstacle. The diffusion rate was also measured by moving the detector behind the radius of the RF limiters, located on the outer wall. Comparisons of these experimental results with numerical simulations, which include diffusive mechanisms, indicate a quantitative agreement with the TF stochastic ripple diffusion model.
Date: December 1991
Creator: Boivin, R. L.
Partner: UNT Libraries Government Documents Department