A simple model for estimating the particle size dependence of absolute efficiency of fluorescent screens

Lindström, Jan; Carlsson, Gudrun Alm

doi:10.1088/0031-9155/44/5/319

Cited by 28 publications

(26 citation statements)

References 33 publications

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“…The mean size of the powder grains was approximately 7 mm. Grain size affects both emission efficiency and spatial resolution [5,11,16,18]; however, sizes in the range from 5 to 10 mm are generally accepted as a satisfactory compromise between emission efficiency and spatial resolution [5,18]. The phosphors were used in the form of layers (screens) prepared in our laboratory [9,10,19,20,21,22] with various coating weights ranging from approximately 25 to 180 mg/ cm 2 , which are often used in various types of X-ray imaging applications.…”

Section: Methodsmentioning

confidence: 99%

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Experimental and theoretical assessment of the performance of Gd2O2S:Tb and La2O2S:Tb phosphors and Gd2O2S:Tb–La2O2S:Tb mixtures for X-ray imaging

Kandarakis

Cavouras

2001

Eur Radiol

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The purpose of this work was to investigate and compare the imaging performance of Gd2O2S:Tb and La2O2S:Tb phosphors as well as of Gd2O2S:Tb and La2O2S:Tb mixtures for use in X-ray imaging detectors (intensifying screens). Phosphors were supplied in powder form and were used to prepare test screens. Three types of screens were prepared: Gd2O2S:Tb; (Gd50La50)O2S:Tb; and La2O2S:Tb. Screens were excited by X-rays with tube voltages from 40 to 120 kV and their efficiency (light intensity or light energy flux over exposure) was measured with a photomultiplier and a dosimeter. The light spectrum was also measured with a monochromator. From these measurements, the number of emitted photons per incident X-ray (NEP) and the zero frequency detective quantum efficiency (DQE(0)) of the screens were determined. Additionally, modulation transfer function (MTF) was measured by the square wave response function (SWRF) method. A theoretical model calculating NEP and DQE was also developed to fit experimental data and predict the performance of Gd2O2S:Tb-La2O2S:Tb mixtures by weight from 10-90% to 90-10%. Gd2O2S:Tb screens exhibited highest NEP, DQE, and MTF at tube voltages higher than 55 kV and lower than 45 kV, whereas La2O2S:Tb screens had better NEP, DQE, and MTF within the 45- to 55-kV range. Maximum NEP values were higher than 700 at 100-120 kV while maximum DQE(0) was 0.314 at 80 kV. Gd2O2S:Tb screens are more efficient for high X-ray tube voltage applications (e.g., abdominal imaging, chest radiography, lumbar spine radiography, CT) and for very low voltage applications (e.g., mammography). La2O2S:Tb screens are useful for medium-range X-ray voltages (e.g., pediatric radiography).

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Section: Methodsmentioning

confidence: 99%

“…The light emission efficiency [1,2,3,4,5,6,7,8,9,10,16], which was evaluated by determining the number of emitted photons (NEP) of light per incident X-ray 2. The modulation transfer function (MTF), which describes the variation of image contrast with spatial frequency and expresses spatial resolution [5,10,11,12,13,14].…”

mentioning

confidence: 99%

Experimental and theoretical assessment of the performance of Gd2O2S:Tb and La2O2S:Tb phosphors and Gd2O2S:Tb–La2O2S:Tb mixtures for X-ray imaging

Kandarakis

Cavouras

2001

Eur Radiol

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“…According to the discrete model [7][8], the total light energy emitted per unit surface area resulting from an energy impartation of x-ray energy to the radioluminescent layer can be described…”

Section: The Discrete Model Of a Radioluminescent Layermentioning

confidence: 99%

“…The work will show that a previously verified model for establishing the extrinsic efficiency of radioluminescent layers can be used, supporting the development process and/or to check the level of optimization. It is known that luminescent polycrystalline layers of a particular phosphor and equal thickness but with varying particle size distributions will produce varying luminance for the same incident energy fluence and hence changeable extrinsic efficiency [7] [8]. The model has an optical concept expressed by the extinction factor (), which handles the light transport in one single parameter and further the particle size and layer thickness can be varied for the same basic design and extinction factor.…”

Section: Introductionmentioning

confidence: 99%

Optimizing two radioluminescence based quality assurance devices for diagnostic radiology utilizing a simple model

et al. 2014

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The extrinsic (absolute) efficiency of a phosphor is expressed as the ratio of light energy emitted per unit area at the phosphor surface to incident x-ray energy fluence. A model described in earlier work has shown that by knowing the intrinsic efficiency, the particle size, the thickness and the light extinction factor ξ, it is possible to deduce the extrinsic efficiency for an extended range of particle sizes and layer thicknesses for a given design. The model has been tested on Gd 2 O 2 S:Tb and ZnS:Cu fluorescent layers utilized in two quality assurance devices, respectively, aimed for the assessment of light field and radiation field congruence in diagnostic radiology. The first unit is an established device based on both fluorescence and phosphorescence containing an x-ray sensitive phosphor (ZnS:Cu) screen comprising a long afterglow. Uncertainty in field edge position is estimated to 0.8 mm (k=2). The second unit is under development and based on a linear CCD sensor which is sensitized to x-rays by applying a Gd 2 O 2 S:Tb scintillator. The field profiles and the corresponding edge location are then obtained and compared. Uncertainty in field edge location is estimated to 0.1 mm (k=2).The properties of the radioluminescent layers are essential for the functionality of the devices and have been optimized utilizing the previously developed and verified model. A theoretical description of the maximization of phosphorescence is also briefly discussed as well as an interesting finding encountered during the development processes: focal spot wandering. The oversimplistic physical assumptions made in the radioluminescence model have not been found to lead the optimizing process astray. The obtained functionality is believed to be adequate within their respective limitations for both devices.

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“…When comparing the relative light output of (Gd,Y) 2 O 3 :Eu to other sintered ceramic scintillators, it is the third best material after CsI:Tl and doped Gd 2 O 2 S [1,3] and it is the best material with a simple oxide character. Its synthesis is straight forward and the average particle size can easily be controlled, making it a good model system for studying size effects.…”

Section: Introductionmentioning

confidence: 99%

Light Emission Intensities of Luminescent Y2O3:Eu and Gd2O3:Eu Particles of Various Sizes

et al. 2017

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There is great technological interest in elucidating the effect of particle size on the luminescence efficiency of doped rare earth oxides. This study demonstrates unambiguously that there is a size effect and that it is not dependent on the calcination temperature. The Y2O3:Eu and Gd2O3:Eu particles used in this study were synthesized using wet chemistry to produce particles ranging in size between 7 nm and 326 nm and a commercially available phosphor. These particles were characterized using three excitation methods: UV light at 250 nm wavelength, electron beam at 10 kV, and X-rays generated at 100 kV. Regardless of the excitation source, it was found that with increasing particle diameter there is an increase in emitted light. Furthermore, dense particles emit more light than porous particles. These results can be explained by considering the larger surface area to volume ratio of the smallest particles and increased internal surface area of the pores found in the large particles. For the small particles, the additional surface area hosts adsorbates that lead to non-radiative recombination, and in the porous particles, the pore walls can quench fluorescence. This trend is valid across calcination temperatures and is evident when comparing particles from the same calcination temperature.

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A simple model for estimating the particle size dependence of absolute efficiency of fluorescent screens

Cited by 28 publications

References 33 publications

Experimental and theoretical assessment of the performance of Gd2O2S:Tb and La2O2S:Tb phosphors and Gd2O2S:Tb–La2O2S:Tb mixtures for X-ray imaging

Experimental and theoretical assessment of the performance of Gd2O2S:Tb and La2O2S:Tb phosphors and Gd2O2S:Tb–La2O2S:Tb mixtures for X-ray imaging

Optimizing two radioluminescence based quality assurance devices for diagnostic radiology utilizing a simple model

Light Emission Intensities of Luminescent Y2O3:Eu and Gd2O3:Eu Particles of Various Sizes

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