Showing papers on "Scintillation published in 1990"

Scintillation characteristics of pure and Tl-doped CsI crystals

Abstract: The scintillation characteristics of pure and Tl-doped CsI were investigated. The scintillation light was detected with photomultipliers and silicon photodiodes. The influence of the Tl concentration on the light yield and on the decay times was studied upon excitation with gamma -rays and alpha -particles. The origin of the different emission components is discussed. >

Simulation of point-source scintillation through three-dimensional random media

Abstract: We have calculated intensity spectra and variances for waves emanating from a point source and propagating through extended three-dimensional random media by simulation. Spectra of the medium fluctuations considered were power-law, power-law with inner scale, and Gaussian spectra. The simulations covered the regimes of weak fluctuations and strong focusing, including the peak of the intensity variance and beyond. The intensity variances are substantially larger than both the corresponding results for plane-wave incidence and the theoretical calculations for point sources by other authors. Our simulation results agree reasonably closely with the results of laserpropagation experiments over kilometer-length paths in the atmosphere.

The MSU Miniball 4π fragment detection array

Abstract: A compact and highly granular charged particle detection array, covering 89% of 4π in solid angle, is described. In its present configuration, the array consists of 188 fast-plastic CsI(Tl) phoswich detectors arranged in 11 rings coaxial about the beam axis. Each phoswich detector is comprised of a 40 μm thick plastic scintillator foil and a 2 cm thick CsI(Tl) crystal selected for good scintillation uniformity. The detectors are read out by photomultiplier tubes. Elemental identification up to Z ≈ 18 and isotopic identification of H and He nuclei is achieved by exploiting pulse shape discrimination techniques.

Determination of solar-wind velocities using single-station measurements of interplanetary scintillation.

Abstract: Un methode de determination de la vitesse du vent solaire basee sur les mesures de scintillation interplanetaire des radiosources compactes de regions a faible diffusion est presentee. Les vitesses obtenues a partir des donnees d'une seule station, d'une part, et de trois stations, d'autre part, sont trouvees en bon accord.

Case study of intense scintillation events on the OTS path

Abstract: Selected events of enhanced field amplitude fluctuations recorded on the Orbital Test Satellite (OTS) path have been analyzed. The statistical properties of the beacon signals together with their correlation with the concurrent radiometric signal suggest that both scintillation and a variable attenuation mechanism act to produce the field fluctuations. Analysis of the coherence between the beacon and the radiometric signals gives an indication of the fluctuation frequency range over which each effect prevails. The comparison between scintillation data collected by a large (17 m) and a small (3 m) antenna indicates that the turbulence of the refractive index was particularly high during the course of the considered events. >

Cerium fluoride: A scintillator for high-rate applications

Abstract: Measurements of the temperature dependence, over a 400°C range, of the scintillation yield of CeF3 are presented. A separation of the fast (≈ 5 ns) and slow (30 ns) components is made at room temperature and at liquid nitrogen temperature. It is estimated that the fast component increases from 33% to 60% when the crystal is cooled. The use of inexpensive starting material reduces the slow component with little or no loss of fast component. Applications for CeF3, primarily high-rate PET, are also discussed.

Optical diagnostics of random phase objects.

Abstract: Possibilities of optical noncontact diagnostics of random phase objects are studied, based on measurements of transverse coherence function, scintillation index, and amplitude and phase dispersion of the field resulting from interaction with the object. The advantages of these methods are increased speed and accuracy compared with commonly used methods. Interference measurements of second-and higher-order correlation parameters of the field phase is demonstrated which can be used to find the corresponding probability density distribution function for objects with phase statistics differing from Gaussian. The sensitivity threshold of the methods is estimated to be ~0.005 microm when measuring surfaces with slight roughness.

Readout techniques and radiation damage of undoped cesium iodide

Abstract: Several readout techniques for undoped CsI have been studied which utilize the fast scintillation component for speed and the high photon yield for good energy resolution. Quantum yields have been measured for samples up to 30 cm in length using photomultiplier tubes, wavelength shifters, and silicon photodiodes. A study has also been made of the scintillation properties of undoped CsI. It is found that the light output and decay time of the 310-nm fast component increases and the emission spectrum shifts to longer wavelengths at lower temperatures. The effects on the optical transmission and scintillation light output due to radiation damage from /sup 60/Co gamma rays have been measured for doses up to approximately 10/sup 6/ rad. It is found that the radiation resistance of undoped CsI is substantially higher than has been reported for thallium-doped CsI. >

Decay time and light yield measurements for plastic scintillating fibers

Abstract: We have studied light production and propagation in three different samplesof plastic scintillating fibers manufactured by Kyowa Gas Co.: SCSF-81, SCSF-38 and SCSF-38 with afquenching additive. The emissio time distribution is described phenomenologically by a fast two-step scintillation process and an additional slow component, the time constants of which are determined. The light yield from the fibers is measured as a function of distance for the two light components which propagate by total internal reflection from the core-clad interface and from the clad-air interface. We obtain the absolute light yield and attenuation lengths for the different fibers.

Radiation detector using scintillator array

Abstract: A radiation detector comprising a scintillator array for emitting scintillation light upon incidence of radiation to a scintillator and distributing the scintillation light to the other scintillators at a predetermined distribution ratio and plural photomultiplier tubes optically coupled to the scintillator array for converting the scintillation light into an amplified electrical signal representing an incident position of the radiation to the scintillator array. The scintillator array comprises plural scintillators, and each pair of neighboring scintillators have coupling surface on both of confronting surfaces thereof for optically coupling the neighboring scintillators therethrough, each of the coupling surfaces having at least one of a roughened surface and a mirror-polished surface having different transmissivities to light passing therethrough to thereby adjust the distribution ratio of the scintillation light transmitted from one of the scintillators to another.

A study of the scintillation light induced in liquid xenon by electrons and alpha particles

Abstract: The time dependence and the intensity of the primary scintillation light in liquid xenon excited by /sup 241/Am alpha particles and /sup 207/Bi internal conversion electrons were measured at different electric field strengths. High-purity liquid xenon was used to fill a parallel-plate ionization chamber equipped with a CaF/sub 2/ window coupled to a UV (ultraviolet) sensitive photomultiplier tube. The effect of the specific ionization density on the scintillation light as well as the time correlation between the light signal and the charge signal is reported. It is demonstrated that the fast scintillation signal produced in liquid xenon by an ionizing particle provides an ideal trigger in a detector aiming at a complete three-dimensional event reconstruction with an excellent background rejection capability. >

Large area silicon avalanche photodiodes for scintillation detectors

Abstract: Large area (≈1 cm 2 ) silicon avalanche photodiodes (SiAPDs) have been fabricated and their performance as optical detectors for use with scintillating crystals has been measured. Light sensitivity is measured for hexagonal SiAPDs of 1.57 cm 2 total package area, and the energy and timing resolution is measured for these devices coupled to CsI(Tl) scintillators operating as gamma spectrometers.

Scintillation properties of Ce/sup 3+/ doped BaF/sub 2/ crystals

Abstract: The scintillation properties of cylindrically shaped, 1-in*1-in, and 30-mm*30-mm*4.5-mm BaF/sub 2/ crystals doped with 0.2-, 0.3-, 0.5-, 0.8-, and 1.0-mol.% Ce/sup 3+/ have been studied by means of X-ray and gamma-ray excitation. Optical transmission, X-ray-induced emission, and decay time spectra are presented. The photoelectron (phe) yield/MeV was measured with an XP2020Q photomultiplier tube. The 1-in*1-in, 0.2-mol.% doped crystal has a light yield of 1790 phe/MeV, which is larger than the total light yield (1570 phe/MeV) of a pure BaF/sub 2/ crystal of the same dimensions. The crystal shows two main scintillation decay times of 47+or-5 ns and 260+or-40 ns. For the 1.0-mol.% doped crystal, a light yield of 1210+or-80 phe/MeV and a dominating decay time of 81+or-7 ns were observed. The crystals scintillate at wavelengths larger than 300 nm, and the scintillation light can be detected with glass-windowed photomultiplier tubes. >

Effects of saturation on the optical scintillometer.

Abstract: Measurements of the level of turbulence Cn2 have been successfully performed with the optical scintillometer. The success of this instrument is based on the observed fact that the variance of aperture averaged scintillation is described by weak scattering theory even for conditions in which strong scintillation is observed for point detectors. However, for sufficiently long propagation paths, the aperture averaged variance is affected by strong scattering. The effects of strong scattering are calculated theoretically and compared to experimental results. The physics of this regime are discussed and the important parameters investigated. The new range of validity of the optical scintillometer is discussed.

Prospects of CsJ(Tl)-photodiode detectors for low level spectroscopy

Abstract: Abstract A detailed study of the potential of CsI(Tl)—photodiode detectors for applications in low-level spectroscopy was carried out. The energy resolution of small crystals (few cm 3 ) for γ-rays in the MeV range can be parametrized as ΔE (FWHM)/ E = 5% × E [MeV] −0.69 . In kg size detectors, where resolution is limited by electronic noise, the use of new large-area low-capacitance pin Si photodiodes led to a significantly improved energy precision of ΔE (FWHM) = 150 keV, nearly independent of energy. Unfavourable light collection geometries, like in large-acceptance well detectors, do not substantially degrade the energy measurement. Scintillation light yields vary slowly with temperature and time so excellent long-term stability can be expected. For the first time a systematic investigation of inherent crystal radioactivity was possible due to the improved energy resolution obtained with large crystals. Six α-active radionuclides of the Th-decay-chain were identified. The isotopes are in equilibrium with each other but not in secular equilibrium with 232 Th. The total α-activity varies from crystal to crystal between 2.4 and 5.5 decays/h cm 3 ) corresponding to 228 Th concentrations of 1.1–2.5×10 −18 g/g. Activity from 238 U-chain isotopes is not sent at a level two orders of magnitude below the Th-activity. Prospects are discussed for further improved energy resolution and for applications in low-level spectroscopy, specifically for a search for 100 Mo double beta decay.

Recent results in scintillation detection with silicon avalanche photodiodes

Abstract: An investigation of silicon avalanche photodiodes (APDs) in scintillation detection for potential applications in medical imaging and nuclear spectroscopy is reported. Experimental measurements were performed on bismuth germanate (BGO), CdWO/sub 4/, plastic, NaI(Tl) and CsI(Tl) scintillators, geometrically optimized for light collection. Results show the advantages of a solid-state photodetector having an internal gain for the detection of low-energy gamma and X-rays. When coupled to CsI(Tl), X-ray energies as low as 5.9 keV can be discriminated from the noise. The results demonstrate the suitability of APDs for many applications in scintillation detection and, in particular, their distinct advantage over other unity gain photodiodes for the detection of low-energy radiation in scintillation spectroscopy: unequaled energy thresholds have been demonstrated. >

High-latitude irregularity spectra deduced from scintillation measurements

Abstract: High-latitude scintillation data show that the strength and spectral index of intensity scintillation are dependent on the propagation geometry. It will be shown that anisotropic irregularity spectra, with different indices along and across the magnetic field, lead to geometrical effects similar to those observed. In general, the spectrum along the magnetic field is steeper than that across the field, and the difference is more pronounced for nighttime conditions. Spectral anisotropy can be interpreted as a size-dependent irregularity anisotropy. Our data indicate that large-scale irregularities in the daytime and nighttime ionosphere are almost isotropic, while small-scale irregularities are anisotropic and considerably more so at night than during the day. It will be shown that anisotropic irregularity spectra could account for the observed scintillation and in situ temporal spectra with frequency-dependent slope. The effect depends strongly on the geometry.

Chaotic behaviour of ionospheric turbulence from scintillation measurements

Abstract: Ionospheric amplitude and phase scintillation data have been analysed to estimate the ‘information dimension’ associated with the attractor of the system. For weak scintillations, both amplitude and phase data yield identical results which demonstrate that spatial fluctuations of electron density in the ionosphere may be characterized by a few degrees of freedom. Stronger scintillations are attributed to steepened density irregularities which cause ‘focusing’ of the incident radio wave. This results in the amplitude scintillations exhibiting higher dimensional chaos but spatial fluctuations in ionospheric density still involve low dimensional chaos.

A fundamental limit on timing performance with scintillation detectors

Abstract: A new lower bound on the mean-squared error of postdetection gamma -ray time-of-flight estimators has been derived. Previously, the Cramer-Rao bound has been used, but for nearly exponentially decaying scintillation pulses it gives an extremely optimistic picture of the achievable performance, depending critically on the dark current and photomultiplier characteristics. The new bound has been derived under the assumption that excited states in the scintillator leading to the emission of scintillation photons have an exponential lifetime density. The bound is a function of the mean state lifetime, the spectrum of energy deposited, and the energy conversion efficiency of the scintillator, and it is exact for the observation of a mono-exponentially decaying photoelectron rate at the first dynode of the photomultiplier tube given the gamma -ray arrival time. >

Lead carbonate, a new fast, heavy scintillator

Abstract: The authors describe the scintillation properties of lead carbonate (PbCO/sub 3/), a newly discovered, heavy (6.6 g/cm/sup 3/), inorganic scintillator. Its fluorescence decay lifetime, measured with the delayed coincidence method, is described by a sum of three exponentials. The emission spectrum peak is centered at a wavelength of 475 nm and drops to less than 10% of its peak value at 370 nm and 580 nm. The authors were unable to obtain an optical quality crystal of pure PbCO/sub 3/, but when a 3 mm cube of a cerussite (a naturally occurring mineral form of PbCO/sub 3/) is excited with 511 keV photons, a photopeak with a 42% full width at half maximum is observed at approximately 9% the light output of a bismuth germanate (BGO) crystal with similar geometry. The light output increases rapidly with decreasing temperature, plateauing at twice the light output of BGO at approximately -40 degrees C. The short fluorescence lifetime, high density, and reasonable light output of this new scintillator suggest that it would be useful for applications where high counting rates, good stopping power, and nanosecond timing are important, such as medical imaging and nuclear science. >

The response function of a CsI(Tl) scintillator with photodiode readout to light and heavy ions in the intermediate energy range

Abstract: The luminescent response of a CsI(Tl) crystal has been determined for light and heavy ions (Z ≤ 14) with energies up to 800 MeV. These fragments were produced in a 28Si + 28Si reaction at beam energies between 22 and 35 MeV/nucleon. A nonlinear response was observed over the entire energy range. A parametrization of the light output, L(Z, E), is given. The scintillator response was found to be proportional to E1.3 for Z ⩾ 3. The scintillation efficiency has been determined. The overall features can be described within an existing model, if the effect of secondary electrons is taken into account.

Light yield as a function of gas pressure and electric field in gas scintillation proportional counters

Abstract: We have investigated the dependence of the scintillation light output for Xe on gas pressure in the range 0.14–1.4 bar, using a gas scintillation proportional counter, in different experimental configurations. We have compared our work with that of previous workers, and have shown that both our results and the results of previous authors are compatible with the intrinsic light output being independent of gas pressure, with any observed dependence being a pure experimental effect due to the spectral response of the various UV detectors used. We also use our experimental data for determining the ratio between the cross section of the Xe 2 ∗∗ + Xe → Xe 2 ∗ + Xe reaction and the rate of the Xe 2 ∗ → 2 Xe +γ UV reaction.

Effects of scintillation light collection on the time resolution of a time-of-flight detector for annihilation quanta

Abstract: Monte Carlo methods were used to simulate the production and collection of scintillation light in a BaF/sub 2/ crystal The calculated results were compared to measured values for detectors with different heights Based on this simulation, a TOF (time-of-flight) detector consisting of two conical BaF/sub 2/ crystals (base radius 18 mm, top radius 15 mm, height 25 mm) was assembled The total time resolution of this system was (210+or-5) ps FWHM (full width at half maximum) for 511-keV annihilation quanta and was found to be independent of the source position between the detectors Since the time resolution of the TOF detector system consisting of two conical BaF/sub 2/ crystals is sufficiently constant in the volume of interest and does not change during operation, this detector meets the requirements for application in a clinical routine >

Gamma camera device

Abstract: A radiation ray (gamma ray) radiated from a test subject previously dosed with radioisotope is incident on a scintillator and converted into scintillation light. A plurality of photomultipliers arranged in a hexagon receive and convert the scintillation light into electrical signals. Photomultipliers arranged in parallel with sides of the hexagon constitute a group. Output signals of the photomultipliers are supplied to a first position detector for detecting a group of photomultipliers which receives the scintillation light and deriving position information Xo and Yo representing the approximate gamma ray incident position. The position information Xo and Yo and the output signals of the photomultiplier are supplied to a second position detector for deriving position information x and y representing the precise gamma ray incident position. Outputs of the photomultiplier are supplied to a pulse height analyzer which derives incident radiation energy information z.

CsI-based scintillators in γ-detection systems

Abstract: Scintillation characteristics of a mixed CsICsBr crystal have been studied. The crystal luminescence spectrum is 280–340 nm; the decay time is 11 ns; the relative light yield is 0.18 of NaI(Tl). The parameters of the γ-quantum hodoscope based on CsICsBr and hodoscopic PMTs (HPMTs) have been measured. The hodoscope spatial resolution is shown to be 2 σ = 2.4 mm. A design of a positron emission tomograph ring on the basis of CsICsBr and HPMTs is proposed. It is suggested that the CsICsBr scintillator may be used in electromagnetic calorimeters at counting rates greater than 10 7 s −1 .

Monte Carlo simulation of BaF/sub 2/ detectors used in time-of-flight positron emission tomography

Abstract: To better understand the performance of the SP3000 time-of-flight PET (positron emission tomography), machine, the authors performed Monte Carlo calculations of photon interactions in a BaF/sub 2/ detector module and calculations of crystal optics for BaF/sub 2/ UV scintillation light. Evaluated were photon detection sensitivities, the amount of photon spillover, crystal crosstalk, interring miscodes, and true-to-random coincidence ratios as a function of the lower-level energy discriminator setting and crystal/photomultiplier tube energy resolution. UV light collection efficiencies for the timing tube and decode tube were calculated assuming different crystal geometries, reflective materials, and reflectances. For a typical SP3000 detector module the detection efficiency for single 511-keV photons varied between 20 and 60% depending on the angle of incidence. >

Scintillation camera gantry supporting a plurality of detector heads between two parallel plates

Abstract: A gantry for a multi-head scintillation camera including a pair of vertically disposed annular plates between which are mounted the scintillation camera heads. The plates are supported on their peripheral edges by rollers which both provide load bearing support and allow plate rotation. A pulley is mounted on one of the plates and is belt-driven by a motor.

Coupling type scintillator

Abstract: PURPOSE:To perform two kinds of radiation measurements with one PM system and a pulse amplifier system by measuring the intesities of the two or more kinds of radiations by using one photomultiplier tube (PM) and one pulse amplifier system. CONSTITUTION:An NaI scintillator 1 and a plastic scintillator 2 are formed in a disk shape, respectively. Both scintillators are coupled in the stacked state in two stages. Thus, a series coupling type scintillator 3 is constituted. The NaI scintillator 1 receives gamma rays and emits scintillation light. The scintillation light is inputted into a photomultiplier tube PM 4 through the plastic scintillator 2. Meanwhile, the plastic scintillator 2 receives neutron rays and the gamma rays and emits scintillation light. The scintillation light is inputted into the PM 4. In this way, the detected signal component of the gamma rays from the NaI scintillator 1 and the detected signal component of the neutron rays from the plastic scintillator can be taken out in a separated pattern.