On the extreme early morning of December 3, Japan time, TEPCO's Fukushima webcam showed indications of Beta and Gamma radiation impacting its Charge Coupled Device (CCD). The nature of these impacts was to produced fast pixel sized blips of light on the TEPCO webcam. Less than 12 hours after this incident at "at 1:05pm on December 3", and likely as quickly as was possible, TEPCO replaced the webcam and added "transparent camera covers". These covers are thick enough to cause a horizontal line reflection back into the camera.
The POTRBLOG team believes that the "transparent camera covers" are in actuality Nalgene beta radiation shields designed to prevent visual evidence of high beta radiation activity in the area, and to prevent the ingress of Alpa particles into the camera's CCD.
The shielding would not prevent Gamma ray interaction, however Gamma ray interaction with the CCD is less likely and produces a weaker effect when it does occur. Nor would the shield prevent Neutron damage to the CCD. Neutron damage to the CCD would be evidenced by black pixels on the CCD. Given TEPCO's rapid change out of the camera, there would have only been limited daylight hours available to ascertain/record the presence of such damage.
It is unfortunate that TEPCO has apparently taken such actions, as these nighttime visible radiation induced blips serve as a public early warning indicator of the severity of immediate radioactive discharge situation in Fukushima.
For a detail explanation on how radiation affects CCDs please see this article
Finally at Hat-tip to Majia's Blog for making us aware of the video that showed the radiation blips. We have embedded that video below.
Note that in In the past, were we have data available, such steam events have correlated with Neptunium 239 detections. Neptunium 239 and its parent Uranium 239 both rapidly and strongly eject Beta radiation. Our conjecture is that both Np-239, U-239, and/or possibly Y-90 (given the recent Strontium spill) may have caused the pixel sized flashes seen on the video below.
Below is a Fair-use image of the current web cam and TEPCO's explanation regarding its replacement status.
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