The Watec Video CCD
The original Watec video CCD integrates the exposure in-camera, outputting the integrated image in real-time as a standard PAL video signal. It is ideal for monitoring samples in-beam on a simple TV monitor, but the images can also be digitised and saved on a computer.
This video camera is still available, but is being phased out in favour of the slim USB camera, which is entirely digital.
SONY CCD Device Structure
- B/W Sony ICX419ALL Interline CCD image sensor
- Optical size: Diagonal 8mm (nominal 1/2 inch sensor)
- Number of effective pixels: 752 (H) x 582 (V) approx. 440K
- Total number of pixels: 795 (H) x 596 (V) approx. 470K pixels
- Chip size: 7.40mm (H) x 5.95mm (V)
- Unit cell size: 8.6µm (H) x 8.3µm (V)
- High sensitivity, Low smear, High D range, High S/N
- High resolution and low dark current
Version-4 camera specifications
- LiF/ZnS neutron scintillator, green emission (~520nm)
- Rare-earth ultra-fast x-ray scintillator, green emission (~520nm)
- Front-surfaced Al/SiO2-mirror; optical flatness 2λ/25mm; reflectivity 94%
- Low light f1.0 lens (order of magnitude brighter than a normal camera)
- Ultra low light sensitivity (0.00001
lux at f1.0), S/N ratio: 52dB
- Exposure selected by hand-held remote controller on 3m or longer cable
- Fast shutter speed: exposures of 0.5, 1, 2, 4, 8, 16 msec
- On-board electronic frame integration system (Slow shutter speed)
- Slow shutter: integration over 1, 2, 4, 8, 16, 32, 64, 128, 256, unlimited frames
- Simultaneous output of composite video & Y/C signals
- Manual gain control (8-38dB) and Gamma correction (3 steps)
- Nominal image resolution ~100 microns (80x60mm compact camera)
- Nominal sensitivity 1 neutron/sec per 100 micron pixel (80x60mm compact camera)
- Reasonable Images with 10s exposures at 104.n.cm-2.sec-1
- Suitable for beams of 104 to 109 n.cm-2.s-1
(less than 103 n.cm-2.s-1 with cooling)
General Information and FAQs
- The camera sensitivity for a given neutron flux and exposure is inversely proportional to the square of the
largest side of the scintillator window.
- The camera thickness depends on the smallest side of the scintillator window.
- The compact camera weighs 525g; the 100mm camera weighs 1 Kg.
- The camera outputs PAL video, accepted by most frame grabbers.
- PAL video allows higher resolution and longer exposures than NTSC.
- The optional TFT display allows the image to be viewed without a computer.
- The included PC-interface is a high speed USB-2 frame grabber.
- The camera comes with a 12v DC regulated supply to EU or US specs.
- It should be possible to use the camera in a vacuum. You would need vacuum
connectors for the cables and a heat sink to dissipate 3 watts.
- Cameras use aluminium boxes and screws to reduce activation.
- The CCD unit, outside the beam, should be shielded from neutrons and x-rays.
- The scintillator will eventually be destroyed if left permanently in the beam (replacements are available).
- The light output will fall by 30% after an integrated flux of 1014.n.cm-2
(more than 100 days in a constant 107.n.cm-2.s-1 neutron beam).
- The scintillator will also detect X-rays and gammas, but we see these only as
isolated pixel flashes in the neutron beam.
- With long exposures a few noisy pixels will be seen, but can be eliminated
with the "salt and pepper" filter or the
optional Peltier cooler.
- With very long exposures (minutes) at maximum gain and gamma for very low fluxes
(<103 n.cm-2.s-1), a
diffuse noise patch may be seen in one corner of the image. This is low-level infra-red radiation
from the amplifiers at the edge of the CCD. A solution is to subtract a "dark field"
image obtained under the same conditions with the neutron beam off, or use the ImageJ Process/Subtract Background.
- Testing the camera without neutrons should show only a few isolated bright pixels for very long exposures (10+ sec).
If you remove the CCD unit and shine a light through the lens into the camera box, you can activate the whole scintillator,
which you can then see for some minutes after you replace the CCD unit.