- Email: [email protected]
The use of amorphous Silicon flat panels as detector in neutron imaging
ARTICLE IN PRESS
Applied Radiation and Isotopes 61 (2004) 567–571
The use of amorphous Silicon flat panels as detector in neutron imaging E. Lehmann*, P. Vontobel Paul Scherrer Institute, WHGA/349, Villigen PSI CH-5232, Switzerland
Abstract A first test for neutron detection with a flat panel device based on the amorphous silicon technology is described in this report. The most important parameters defining the performance for neutron imaging are described. The first findings are encouraging for further improvements. r 2004 Elsevier Ltd. All rights reserved. Keywords: Amorphous silicon; Neutron detection; Tomography; Dynamic range; Pixel size
1. Introduction
2. Principle of amorphous silicon neutron detectors
The demand for digital imaging with neutrons is presently satisfied by CCD-based systems and by imaging plates. Whereas the first detector is limited in spatial resolution due to the scintillator properties, the second one cannot exactly be repeatedly placed for each subsequent image. It is important in neutron tomography to have the option to measure the sample at precisely the same place in many perspectives. For the option of a high-resolution detector system, which can be used as a spatially fixed system, the new approach of arrays of amorphous hydrogenated silicon (aSi:H) photodiodes is very promising Rahn et al. (1999). Such devices are in practical use in X-ray diagnostics. However, there is only limited experience with the application of this technique for investigations in neutron beams (Gibbs et al., 1999; Chapuy et al., 2001). To fill this gap, dedicated experimental investigations were made at the radiography station NEUTRA using thermal neutrons provided by the spallation neutron source SINQ at PSI. Based on a good knowledge about the conditions at this beam line, a panel delivered by THALES Electron Devices (F) was applied for this purpose. The report describes the first results obtained in November 2000.
The semiconductor material silicon is used for lightsensitive devices where photons are converted into electric charges. The chips of CCD (charged coupled devices) consist of Si single crystals providing high sensitivity especially if they are cooled down in order to reduce the dark current. However, the dimensions for single crystal arrays are limited to several square centimetres by the manufacturing process. Furthermore, there is a high damage rate in such materials when radiation is directly applied. For investigations of extended objects in the direct beam, another material is in use now—amorphous silicon doped with hydrogen. The material is deposed as thin layers (o2 mm) on extended glass substrates to produce photodiodes with pixel sizes of several hundred microns. Because of the smaller sensitivity and capacity for electric charge compared to single crystals, the options for reduction of the pixel size are limited. A scheme for the electronic arrangement for each individual pixel is given in Fig. 1. The light for a radiation detector based on a-Si is produced with a suitable scintillator. Such materials in use are Gadox (Gd2O2S) or CsI for X-ray. For neutron radiation it is necessary to convert the applied neutrons by a capture reaction into secondary radiation, which then causes the light emission. Because Gd is a neutron absorber too, Gadox could also be used
*Corresponding author. Tel./fax: +41-56-310-2963. E-mail address: [email protected] (E. Lehmann).
0969-8043/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2004.03.102
ARTICLE IN PRESS 568
E. Lehmann, P. Vontobel / Applied Radiation and Isotopes 61 (2004) 567–571 Table 1 Data sheet information about FlashScan 40 Technical specification
Fig. 1. Scheme of the electric circuit per individual pixel (taken from Rahn et al. (1999)).
as a neutron sensitive scintillator. Other materials like 6 Li-doped ZnS are much more efficient with respect to light output.
3. Test program at the NEUTRA radiography station, experimental set-up The radiography beam line at SINQ has an intensity of 3 106 neutrons/cm2 s1, a high collimation (L/ D> 500) and a low gamma background. The beam diameter of 40 cm fits well to the outer dimensions of the active area of the investigated panel (284 mm 406 mm). Although the pixel array was evaluated as relatively resistant against radiation, the readout circuits at the outer edges of the panel are more likely to be damaged during exposures. It was therefore decided to shield the panel as much as possible by neutron absorbers (boron plastics) and to use an active window of only 118 mm 154 mm during the tests. The technical specifications from the manufacturer are given in Table 1. The readout process of the panel is organised in such a way that the pixels are accessed sequentially continuously (reading and erasing). Therefore, the minimal exposure time is given by this readout of the full panel (about 14 Mbytes) because equivalent exposure has to be applied for each pixel per frame. The panel was specified with a dynamic range of 2000:1 and images were provided in either 8-bit or 16-bit TIFF formats. In the last case, the data were inverted before applying the 16-bit scale where the valid range is between 61440 and 65536 grey levels (GL). The following parameters were investigated for the FlashScan30 device, operated in its standard mode with the Gadox converter under the NEUTRA conditions: sensitivity, linearity, useful dynamic range, gamma sensitivity, dark current, spatial resolution, signal-tonoise ratio, after-glow behaviour, damage indications, quantitative behaviour and readout characteristics. After taking dedicated single images for the extraction of this information, a series of projections of a test
Conversion screen Screen density Layer thickness Pixel area Total Active Pixel matrix Total Active Pixelpitch Dynamic range Signal capacity Frame rate Exposure window Limiting resolution
Gd2O2S:Tb 34 0.080
Kodak Lanex mg/cm2 mm
29.3 40.6 28.2 40.6
cm cm
2304 3200 2232 3200 0.127 >2000:1 >5.000.000 about 5 s 6.3–200 3.94
mm >11 bit Electrons/pixel s lp/mm
object were made for later tomography reconstruction. In this way, a comparison with the existing tomography system Vontobel et al. (2000) could be made.
4. Results of the investigations The general impression about data obtained with the flat panel is the generation of clear images with good resolution and contrast (e.g. Fig. 2). However, they are disturbed by ‘‘dead lines’’ and ‘‘dead pixels’’ caused by some damages in the delivered system. Therefore, the manufacturer included some correction tools for the dark field of the damaged lines and pixels, which can be applied automatically. In all our investigations, we used mainly the raw data to understand the principal behaviour of the panel. 4.1. Sensitivity and linearity The fastest readout of the panel (7.14 million pixels) is within 6.3 s. The exposure was limited in the software to 200 s (longer exposure is possible by external triggering). The experiments were carried out at the NEUTRA beam line up to 20 s of exposure when a saturation effect was found in the data. The averaged signal of the open beam is shown in Fig. 3, indicating a good linearity for low neutron dose. The manufacturer claims better linearity under X-ray exposure. The sensitivity can be calculated (in GL=grey levels) as (f=neutron flux density, t=exposure time, np=number of pixels per area, I=dark current corrected intensity): S¼
I ½GL 1100 GL ¼ f t=np 3 106 neutrons cm2 s1 5 s=6200 cm2
¼ 0:455 GL=pixel=neutron
ARTICLE IN PRESS E. Lehmann, P. Vontobel / Applied Radiation and Isotopes 61 (2004) 567–571
569
Therefore, both the halves deliver a completely different behaviour for dark current as shown in Fig. 4. The averaged signal is linear in time dependency as shown in Fig. 5. An overflow by the dark current would occur after about 500 and 800 s, respectively. For very weak neutron fields it will be a problem to obtain reasonable data due to the linearly increasing dark current. Fig. 2. Image obtained from the a-Si device (without corrections), but with adjustment of the valid dynamic range.
By means of a sharp edge made of Gd and a hole of 0.1 mm directly on the panel surface, images were made and evaluated quantitatively. From the line/point spread functions the MTF for the panel was derived (as shown in Fig. 6). Compared to the specifications of the manufacturer, these data are a little smaller than those given in Table 1, which were measured under X-ray exposure.
intensity [grey level of a 12 bit scale]
4000 3500 3000 2500
4.4. Spatial resolution
inverted gray scale dark current corrected
2000
4.5. Signal-to-noise ratio
1500 1000
This parameter was derived as the ratio of the averaged value of a representative flat field (at least
500 0 0
5
10
15
20
25
exposure time [s]
2000 1800 1600 net intensity [GL]
Fig. 3. Averaged intensity of the flat panel under the conditions provided at the NEUTRA facility: linearity, sensitivity and some saturation could be derived from these measurements (the drop down at the last point is due to saturation effects).
Higher efficiency could be obtained with better suited neutron-sensitive scintillators Chapuy et al. (2001) (by a factor of 3 about).
10 s 20 s 60 s 100 s 180 s
1400 1200 1000 800 600 400 200 0 1
501
4.2. Dynamic range
4.3. Dark current Because the panels are operating at room temperatures, charge can be collected from thermal movement, which gives a (unwanted) time-dependent background signal. In the experiments, we took dark images for time intervals from 10 to 180 s. The panel consists obviously of two different parts with independent readout systems.
1501
2001
Fig. 4. Profiles across the image of the dark current for different time steps of accumulation.
4000 3500 net intensity [GL]
The electronic equipment of the panel provides internally 12 bit (4096 GL), (real dynamic range=pixel capacitance/read noise per pixel=11 bit) which is caused by the capacity of the pixels for storing electric charge and the digitising features of the ADC. The saturation effects for long exposure time might be due to an overflow of the charge. For some applications, higher dynamic range is required (at least 14 bit).
1001
position in axial direction [pixel number]
3000
left side right side
2500 2000 1500 1000 500 0 0
100
200
300
400
500
600
integration time [s]
Fig. 5. Averaged dark current signals for both sides of the panel showing a linear increase with time.
ARTICLE IN PRESS E. Lehmann, P. Vontobel / Applied Radiation and Isotopes 61 (2004) 567–571
570
Fig. 6. MTF of a-Si flat panel (left) compared to that of imaging plates (right).
Table 2 Signal-to-noise ratio for the flat panel device in comparison to other systems in use for neutron imaging
Mean value STD S/N ratio
Single image
16 Frames internally averaged
External sum of 16 frames
CCD With scintillator
3514 58
3507 54
56130 844
52594 824
61
65
67
64
4 cm2) and the corresponding standard deviation. As shown by the values in Table 2, the flat panel shows reasonably high values compared to the other detectors in use for neutron imaging. The S/N ratio will not be increased by further superposition of many frames, either internally or externally. 4.6. After-glow behaviour Because the scintillator (Gadox) used in this work is known to have some delayed light emission and the a-Si has a delayed signal emission from electronic traps, this so-called ‘‘afterglow’’ was measured by closing the shutter immediately after a frame readout when the flat panel was exposed for a reasonably long time (more than 20 s). The next frame was then obtained without any neutron exposure but has integrated the whole residual light during the frame transmission time (about 6.3 s). The open beam value drops down from about 2000 GL to less than 100 GL in absolute numbers of the 12bit representation (after the offset correction). The second frame after closing the shutters was completely ‘‘black’’; no deviation from the background could be found in the image.
Imaging plate
88
cross-sections compared to imaging plate data. The reason for this behaviour must be investigated in more detail. 4.8. Gamma sensitivity This parameter was measured when the thermal neutron field was shut down, but the residual gamma field passed the shutter. Because Gadox is sensitive to gamma radiation too, some signal was measured after a long exposure. However, by using a scintillator optimised for neutrons, the gamma background can be neglected during routine measurements. 4.9. Damage indication The panel was in the direct beam for at least 10 h during one week of operation. The outer part was well shielded against neutron exposure. No additional shielding against the (relatively low) gamma field was applied. At the end of the measurements, no indications of additional damage compared to the starting conditions were found.
5. Demands for further improvements 4.7. Quantitative accuracy of image data Different beam attenuation features were measured by means of iron step wedge samples. The signal obtained with the flat panel gave systematically lower attenuation
There is an urgent demand to increase the dynamic range of the panel to make it better suited as a device for tomography. Also a reduction of the pixel size would be interesting, but there is some doubt whether the capacity
ARTICLE IN PRESS E. Lehmann, P. Vontobel / Applied Radiation and Isotopes 61 (2004) 567–571
for collecting charge is sufficient to have high resolution and high dynamic range simultaneously. Because there is no shutter available to define a full frame, the readoutexposure regime must be defined more carefully. This is especially important when time-dependent investigations have to be performed. The readout speed should be as high as possible, which is very demanding for high data volumes provided. Maybe, some software features like binning or area-of-interest readout could help to gain performance.
6. Conclusions The flat panel device was found to be a suitable device for some applications in neutron imaging. If further improvements can be made regarding dynamic range,
571
readout and quantitative accuracy, the panel will be a competing tool in neutron radiography.
References Chapuy, S., et al., 2001. Real-time flat panel pixel imaging system and control for X-ray and neutron detection. IEEE Trans. Nucl. Sci. 48 (6), 2357–2364. Gibbs, K., et al. Flat panel imaging of thermal neutrons. ASNT Fall Conference October 1999. Rahn, J.T., et al., 1999. High resolution X-ray imaging using amorphous silicon flat-panel arrays. IEEE Trans. Nucl. Sci. 46 (3). Vontobel, P., et al. Neutron radiography tomography set-up at SINQ: status and first results, PSI Annual Report 1999, Vol. VI, March 2000, p. 64.
Applied Radiation and Isotopes 61 (2004) 567–571
The use of amorphous Silicon flat panels as detector in neutron imaging E. Lehmann*, P. Vontobel Paul Scherrer Institute, WHGA/349, Villigen PSI CH-5232, Switzerland
Abstract A first test for neutron detection with a flat panel device based on the amorphous silicon technology is described in this report. The most important parameters defining the performance for neutron imaging are described. The first findings are encouraging for further improvements. r 2004 Elsevier Ltd. All rights reserved. Keywords: Amorphous silicon; Neutron detection; Tomography; Dynamic range; Pixel size
1. Introduction
2. Principle of amorphous silicon neutron detectors
The demand for digital imaging with neutrons is presently satisfied by CCD-based systems and by imaging plates. Whereas the first detector is limited in spatial resolution due to the scintillator properties, the second one cannot exactly be repeatedly placed for each subsequent image. It is important in neutron tomography to have the option to measure the sample at precisely the same place in many perspectives. For the option of a high-resolution detector system, which can be used as a spatially fixed system, the new approach of arrays of amorphous hydrogenated silicon (aSi:H) photodiodes is very promising Rahn et al. (1999). Such devices are in practical use in X-ray diagnostics. However, there is only limited experience with the application of this technique for investigations in neutron beams (Gibbs et al., 1999; Chapuy et al., 2001). To fill this gap, dedicated experimental investigations were made at the radiography station NEUTRA using thermal neutrons provided by the spallation neutron source SINQ at PSI. Based on a good knowledge about the conditions at this beam line, a panel delivered by THALES Electron Devices (F) was applied for this purpose. The report describes the first results obtained in November 2000.
The semiconductor material silicon is used for lightsensitive devices where photons are converted into electric charges. The chips of CCD (charged coupled devices) consist of Si single crystals providing high sensitivity especially if they are cooled down in order to reduce the dark current. However, the dimensions for single crystal arrays are limited to several square centimetres by the manufacturing process. Furthermore, there is a high damage rate in such materials when radiation is directly applied. For investigations of extended objects in the direct beam, another material is in use now—amorphous silicon doped with hydrogen. The material is deposed as thin layers (o2 mm) on extended glass substrates to produce photodiodes with pixel sizes of several hundred microns. Because of the smaller sensitivity and capacity for electric charge compared to single crystals, the options for reduction of the pixel size are limited. A scheme for the electronic arrangement for each individual pixel is given in Fig. 1. The light for a radiation detector based on a-Si is produced with a suitable scintillator. Such materials in use are Gadox (Gd2O2S) or CsI for X-ray. For neutron radiation it is necessary to convert the applied neutrons by a capture reaction into secondary radiation, which then causes the light emission. Because Gd is a neutron absorber too, Gadox could also be used
*Corresponding author. Tel./fax: +41-56-310-2963. E-mail address: [email protected] (E. Lehmann).
0969-8043/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2004.03.102
ARTICLE IN PRESS 568
E. Lehmann, P. Vontobel / Applied Radiation and Isotopes 61 (2004) 567–571 Table 1 Data sheet information about FlashScan 40 Technical specification
Fig. 1. Scheme of the electric circuit per individual pixel (taken from Rahn et al. (1999)).
as a neutron sensitive scintillator. Other materials like 6 Li-doped ZnS are much more efficient with respect to light output.
3. Test program at the NEUTRA radiography station, experimental set-up The radiography beam line at SINQ has an intensity of 3 106 neutrons/cm2 s1, a high collimation (L/ D> 500) and a low gamma background. The beam diameter of 40 cm fits well to the outer dimensions of the active area of the investigated panel (284 mm 406 mm). Although the pixel array was evaluated as relatively resistant against radiation, the readout circuits at the outer edges of the panel are more likely to be damaged during exposures. It was therefore decided to shield the panel as much as possible by neutron absorbers (boron plastics) and to use an active window of only 118 mm 154 mm during the tests. The technical specifications from the manufacturer are given in Table 1. The readout process of the panel is organised in such a way that the pixels are accessed sequentially continuously (reading and erasing). Therefore, the minimal exposure time is given by this readout of the full panel (about 14 Mbytes) because equivalent exposure has to be applied for each pixel per frame. The panel was specified with a dynamic range of 2000:1 and images were provided in either 8-bit or 16-bit TIFF formats. In the last case, the data were inverted before applying the 16-bit scale where the valid range is between 61440 and 65536 grey levels (GL). The following parameters were investigated for the FlashScan30 device, operated in its standard mode with the Gadox converter under the NEUTRA conditions: sensitivity, linearity, useful dynamic range, gamma sensitivity, dark current, spatial resolution, signal-tonoise ratio, after-glow behaviour, damage indications, quantitative behaviour and readout characteristics. After taking dedicated single images for the extraction of this information, a series of projections of a test
Conversion screen Screen density Layer thickness Pixel area Total Active Pixel matrix Total Active Pixelpitch Dynamic range Signal capacity Frame rate Exposure window Limiting resolution
Gd2O2S:Tb 34 0.080
Kodak Lanex mg/cm2 mm
29.3 40.6 28.2 40.6
cm cm
2304 3200 2232 3200 0.127 >2000:1 >5.000.000 about 5 s 6.3–200 3.94
mm >11 bit Electrons/pixel s lp/mm
object were made for later tomography reconstruction. In this way, a comparison with the existing tomography system Vontobel et al. (2000) could be made.
4. Results of the investigations The general impression about data obtained with the flat panel is the generation of clear images with good resolution and contrast (e.g. Fig. 2). However, they are disturbed by ‘‘dead lines’’ and ‘‘dead pixels’’ caused by some damages in the delivered system. Therefore, the manufacturer included some correction tools for the dark field of the damaged lines and pixels, which can be applied automatically. In all our investigations, we used mainly the raw data to understand the principal behaviour of the panel. 4.1. Sensitivity and linearity The fastest readout of the panel (7.14 million pixels) is within 6.3 s. The exposure was limited in the software to 200 s (longer exposure is possible by external triggering). The experiments were carried out at the NEUTRA beam line up to 20 s of exposure when a saturation effect was found in the data. The averaged signal of the open beam is shown in Fig. 3, indicating a good linearity for low neutron dose. The manufacturer claims better linearity under X-ray exposure. The sensitivity can be calculated (in GL=grey levels) as (f=neutron flux density, t=exposure time, np=number of pixels per area, I=dark current corrected intensity): S¼
I ½GL 1100 GL ¼ f t=np 3 106 neutrons cm2 s1 5 s=6200 cm2
¼ 0:455 GL=pixel=neutron
ARTICLE IN PRESS E. Lehmann, P. Vontobel / Applied Radiation and Isotopes 61 (2004) 567–571
569
Therefore, both the halves deliver a completely different behaviour for dark current as shown in Fig. 4. The averaged signal is linear in time dependency as shown in Fig. 5. An overflow by the dark current would occur after about 500 and 800 s, respectively. For very weak neutron fields it will be a problem to obtain reasonable data due to the linearly increasing dark current. Fig. 2. Image obtained from the a-Si device (without corrections), but with adjustment of the valid dynamic range.
By means of a sharp edge made of Gd and a hole of 0.1 mm directly on the panel surface, images were made and evaluated quantitatively. From the line/point spread functions the MTF for the panel was derived (as shown in Fig. 6). Compared to the specifications of the manufacturer, these data are a little smaller than those given in Table 1, which were measured under X-ray exposure.
intensity [grey level of a 12 bit scale]
4000 3500 3000 2500
4.4. Spatial resolution
inverted gray scale dark current corrected
2000
4.5. Signal-to-noise ratio
1500 1000
This parameter was derived as the ratio of the averaged value of a representative flat field (at least
500 0 0
5
10
15
20
25
exposure time [s]
2000 1800 1600 net intensity [GL]
Fig. 3. Averaged intensity of the flat panel under the conditions provided at the NEUTRA facility: linearity, sensitivity and some saturation could be derived from these measurements (the drop down at the last point is due to saturation effects).
Higher efficiency could be obtained with better suited neutron-sensitive scintillators Chapuy et al. (2001) (by a factor of 3 about).
10 s 20 s 60 s 100 s 180 s
1400 1200 1000 800 600 400 200 0 1
501
4.2. Dynamic range
4.3. Dark current Because the panels are operating at room temperatures, charge can be collected from thermal movement, which gives a (unwanted) time-dependent background signal. In the experiments, we took dark images for time intervals from 10 to 180 s. The panel consists obviously of two different parts with independent readout systems.
1501
2001
Fig. 4. Profiles across the image of the dark current for different time steps of accumulation.
4000 3500 net intensity [GL]
The electronic equipment of the panel provides internally 12 bit (4096 GL), (real dynamic range=pixel capacitance/read noise per pixel=11 bit) which is caused by the capacity of the pixels for storing electric charge and the digitising features of the ADC. The saturation effects for long exposure time might be due to an overflow of the charge. For some applications, higher dynamic range is required (at least 14 bit).
1001
position in axial direction [pixel number]
3000
left side right side
2500 2000 1500 1000 500 0 0
100
200
300
400
500
600
integration time [s]
Fig. 5. Averaged dark current signals for both sides of the panel showing a linear increase with time.
ARTICLE IN PRESS E. Lehmann, P. Vontobel / Applied Radiation and Isotopes 61 (2004) 567–571
570
Fig. 6. MTF of a-Si flat panel (left) compared to that of imaging plates (right).
Table 2 Signal-to-noise ratio for the flat panel device in comparison to other systems in use for neutron imaging
Mean value STD S/N ratio
Single image
16 Frames internally averaged
External sum of 16 frames
CCD With scintillator
3514 58
3507 54
56130 844
52594 824
61
65
67
64
4 cm2) and the corresponding standard deviation. As shown by the values in Table 2, the flat panel shows reasonably high values compared to the other detectors in use for neutron imaging. The S/N ratio will not be increased by further superposition of many frames, either internally or externally. 4.6. After-glow behaviour Because the scintillator (Gadox) used in this work is known to have some delayed light emission and the a-Si has a delayed signal emission from electronic traps, this so-called ‘‘afterglow’’ was measured by closing the shutter immediately after a frame readout when the flat panel was exposed for a reasonably long time (more than 20 s). The next frame was then obtained without any neutron exposure but has integrated the whole residual light during the frame transmission time (about 6.3 s). The open beam value drops down from about 2000 GL to less than 100 GL in absolute numbers of the 12bit representation (after the offset correction). The second frame after closing the shutters was completely ‘‘black’’; no deviation from the background could be found in the image.
Imaging plate
88
cross-sections compared to imaging plate data. The reason for this behaviour must be investigated in more detail. 4.8. Gamma sensitivity This parameter was measured when the thermal neutron field was shut down, but the residual gamma field passed the shutter. Because Gadox is sensitive to gamma radiation too, some signal was measured after a long exposure. However, by using a scintillator optimised for neutrons, the gamma background can be neglected during routine measurements. 4.9. Damage indication The panel was in the direct beam for at least 10 h during one week of operation. The outer part was well shielded against neutron exposure. No additional shielding against the (relatively low) gamma field was applied. At the end of the measurements, no indications of additional damage compared to the starting conditions were found.
5. Demands for further improvements 4.7. Quantitative accuracy of image data Different beam attenuation features were measured by means of iron step wedge samples. The signal obtained with the flat panel gave systematically lower attenuation
There is an urgent demand to increase the dynamic range of the panel to make it better suited as a device for tomography. Also a reduction of the pixel size would be interesting, but there is some doubt whether the capacity
ARTICLE IN PRESS E. Lehmann, P. Vontobel / Applied Radiation and Isotopes 61 (2004) 567–571
for collecting charge is sufficient to have high resolution and high dynamic range simultaneously. Because there is no shutter available to define a full frame, the readoutexposure regime must be defined more carefully. This is especially important when time-dependent investigations have to be performed. The readout speed should be as high as possible, which is very demanding for high data volumes provided. Maybe, some software features like binning or area-of-interest readout could help to gain performance.
6. Conclusions The flat panel device was found to be a suitable device for some applications in neutron imaging. If further improvements can be made regarding dynamic range,
571
readout and quantitative accuracy, the panel will be a competing tool in neutron radiography.
References Chapuy, S., et al., 2001. Real-time flat panel pixel imaging system and control for X-ray and neutron detection. IEEE Trans. Nucl. Sci. 48 (6), 2357–2364. Gibbs, K., et al. Flat panel imaging of thermal neutrons. ASNT Fall Conference October 1999. Rahn, J.T., et al., 1999. High resolution X-ray imaging using amorphous silicon flat-panel arrays. IEEE Trans. Nucl. Sci. 46 (3). Vontobel, P., et al. Neutron radiography tomography set-up at SINQ: status and first results, PSI Annual Report 1999, Vol. VI, March 2000, p. 64.