Parameters of CCD/CMOS detectors for Neutron or X-ray Imaging
- Big pixels are needed, or the ability to combine (bin) small pixels, since light gathering capacity depends on pixel area.
- Big detectors are better for a large Field-Of-View, since efficiency depends on the ratio of the areas of the detector to FOV.
- Monochrome detectors don't have colour filters that absorb light, and neutrons or x-rays are colour-blind.
- 14- 16-bit readout is needed to increase the number of observable intensity levels, or dynamic range.
- Cooled cameras reduce thermal noise, increasing the signal/noise ratio and the dynamic range.
- Electron/Photon multiplication is not needed, since the scintillator multiplies a single neutron to thousands of photons.
- Moderate cost is important since the detector is eventually damaged in a radiation environment.
The largest markets are for consumer cameras, industrial or security applications, and biological science, all of which have different requirements to neutron imaging. We use cameras designed for amateur astronomy, where the technical requirements are closest to those needed for neutron imaging (longer, low noise exposures with high dynamic range). We make small cameras for beam alignment, and large cameras for tomographic imaging.
In general, choose the smallest, cheapest camera compatible with your requirements, and eventually trade-up if necessary.
Our Choice of CCD and CMOS detectors.
Detector |
Slim CCD |
Slim CMOS |
Fast CMOS |
Square CMOS |
FS60 |
VS60 |
CMOS7.1 |
4/3" CMOS |
APS-C CMOS |
FullFrame |
ICON-L |
Type |
Interline ICX829 |
Pregius IMX174 |
Pregius IMX432 |
Pregius IMX533 |
Interline ICX694 |
Interline ICX694 |
Pregius IMX428 |
Pregius IMX294 |
Pregius IMX571 |
Pregius IMX455 |
Andor ICON-L |
Lens Type & aperture |
C- Tam f/1.0 |
C- Tam f/1.2 |
C- Fuji f/1.4 |
C- Fuji f/1.4 |
C- Fuji f/1.4 |
C- Fuji f/1.4 |
C- Fuji f/1.4 |
MFT 35mm f/0.95 |
MFT 35mm f/0.95 |
Nikon 50mm f/1.2 |
Nikon 50mm f/1.2 |
|
Typ Optical Path length |
150mm |
150mm |
200mm |
200-500mm |
200-500mm |
200-500mm |
200-500mm |
200-500mm |
350-500mm |
500mm |
500mm |
|
Typ FOV mm scintillator |
75 x 50 |
100x100 |
100x100 |
100x100 |
100x100 |
200x250 |
200x250 |
200x250 |
200x250 |
200x250 |
200x250 |
Pixel size at FOV |
150µm |
85µm |
90µm |
35-70µm |
45-90µm |
90µm |
90µm |
60µm |
50µm |
30µm |
100µm |
Resolution pixel |
752 x 580 |
1920x1200 |
1600x1100 |
3000x3000 |
2759x2200 |
2759x2200 |
3208x2200 |
4144x2822 |
6248x4176 |
9576x6388 |
2048x2048 |
Image diag. mm |
8 (1/2") |
13 (1/1.2") |
17 (1.1") |
16 (1.1") |
16 (1") |
16 (1") |
17 (1.1") |
23 (4/3") |
28 (APS-C) |
43 (35mm) |
39 (square) |
Image area mm |
6.46x4.81 |
11.25x7.03 |
14.4x9.9 |
11.3x11.3 |
12.53x9.99 |
12.53x9.99 |
14.4x9.9 |
19.1x13 |
23.5x15.7 |
36 x 24 |
27.6x27.6 |
Pixel size µm |
8.6 x 8.3 |
5.86 x 5.86 |
9.0 x 9.0 |
3.76x3.76 |
4.54x4.54 |
4.54x4.54 |
4.5 x 4.5 |
4.6 x 4.6 |
3.76x3.76 |
3.75x3.75 |
13.5x13.5 |
Quantum effic |
~75% |
~80% |
~72% |
~80% |
~70% |
~70% |
~75% |
~90% |
~90% |
90% |
|
Fullwell e- |
~40,000 |
~30,000 |
~80,000 |
~50,000 |
~20,000 |
~20,000 |
~20,000 |
~66,000 |
~50,000 |
~50,000 |
100,000 |
Read noise e- |
10 |
7 |
5 |
3 |
5 |
6 |
3 |
1.2-7.3 |
1.0-3.3 |
1.5-3.5 |
2.9 |
Dark c. e-/pix/s |
<0.1@25°C |
~1.0@45°C |
~2.5@45°C |
0.001@-20°C |
0.0004@-10°C |
0.0004@-10°C |
0.03@-10°C |
0.002@-20°C |
0.003@0°C |
0.003@0°C |
.0004@-70°C |
Peltier Cooling |
uncooled |
uncooled |
uncooled |
Δ -35 °C or uncooled |
Δ -27 °C |
Δ -35 °C |
Δ -35 °C |
Δ -35 °C |
Δ -35 °C |
Δ -35 °C |
Δ -70 °C |
Max Frame Rate |
0.5 |
41 fps |
69 fps |
20 fps |
0.2 fps |
1 fps |
30 fps |
16 fps |
3.5 fps |
0.5 |
1 |
A/D Readout |
16-bits |
12-bits |
12-bits |
14-bits |
16-bits |
16-bits |
12-bits |
14-bits |
16-bits |
16-bits |
16-bits |
Binning h,v |
hardware |
software |
software |
hardware |
hardware |
hardware |
hardware |
hardware |
hardware |
hardware |
hardware |
Mount |
CS-mount |
C-mount |
C-mount |
C-or F-mount |
C-or F-mount |
C- or F-mount |
C- or F-mount |
M43-mount |
M43-mount |
F-mount |
F-mount |
Trigger signals |
Software |
Software |
Software |
Software |
Software |
Software/GPIO |
Software |
Software |
Software |
Software |
Software |
Interface |
USB 2.0 |
USB2/GigE |
USB3/GigE |
USB3 |
USB 2.0/GigE |
USB 2.0 |
USB 3.0/GigE |
USB 3.0 |
USB 3.0 |
USB 3.0 |
Andor |
Relative cost Detect+Lens |
1 |
1 |
1.5 |
1.7-2 |
4 |
6 |
5 |
3 |
5 |
9 |
50 |
The Andor ICON-L is shown for comparison. The collimation and quality of your neutron beam-line will usually be the limiting factor for neutron imaging, not the camera.
Choosing an Imaging Camera - More is not always Better
A Lens aperture of f/1.0 transmits x2 as much light as an aperture of f/1.4
The Optical path length depends on the required Field-Of-View (FOV), the lens focal length and the detector chip dimensions - see: Qioptiq.
The Overall efficiency depends on the ratio of the area of the FOV to the detector, so don't choose a FOV larger than necessary.
More pixels means smaller pixels that collect less light. Resolution will be limited by your beam collimation and scintillator thickness, not the detector.
Pixel area is proportional to light collection. Combining adjacent small pixels (binning) can be used to emulate large pixels.
Quantum Efficiency is just the conversion efficiency, and takes no account of the much more important pixel area.
Full Well Capacity is the number of electrons that can be stored in a pixel, and depends on the pixel area.
Read Noise is introduced simply by reading out the pixel charge, and is lower for CMOS than for CCD technology.
Dark Current is electron noise due to the temperature of the detector, and is lower for CCD than for CMOS technology. CCDs are better for long exposures (>60s).
Cooling reduces Dark Current, but with modern detectors little is gained below 0oC because of other noise sources, and long-term radiation damage.
Read Times are much shorter for CMOS than for CCD technology, where slow readout is favoured to reduce readout noise.
A/D readout determines the Dynamic Dange, and is much higher than the 8-bits (256) intensity levels seen by the human eye.
Binning increases the effective area of a pixel, and the light collected. Hardware binning increases the framerate.
Bright Lenses are designed with different camera mounts, and different detector-lens (flange) distances.
Trigger signals are used to synchronise exposures with sample rotation for tomography. Usually this can be accomplished with software.
The camera interface limits the frame rate: USB2 is slow, but long (10-20m) cables can be used. USB3 is faster, but with short (3-5m) cables.
The cost depends partly on the technology, but mainly on the market - how many are sold, and what the customer is willing to pay.