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Registered Member #118
Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72
During an experimental Lichtenberg run on June 7th, Andrew Seltzman, a physics grad student from the University of Wisconsin fabricated a small "cave" out of sheet lead, topping it with a piece of 1" thick LDPE. Inside the cave, he placed a Sony Cyber-Shot 3.2 MP camera, positioning it so that it could record video of various items being irradiated by the 3 to 5 MeV electron beam that we use to make Lichtenberg figures. The LDPE slowed down and stopped beam electrons without generating hard x-rays, and the sheet lead stopped lower energy scattered electrons. In the following video a large calcite rhomb and sphere of PMMA are irradiated along with some boxes of various thermoluminescent minerals. When the electron beam hits the calcite and PMMA, they both fluoresce brightly (yellow and blue-white respectively). The calcite then continues to glow with orange thermoluminescence, The sphere flashes shortly after being irradiated as it self-discharges. Speckles in the image and static in the audio are from scattered electrons and high energy photons impacting the camera's image sensor and audio circuitry. As the camera gets closer to the beam, these become "modulated" by the 100 Hz scanning frequency of the beam as at sweeps the 4 foot width of the cart. The camera sensors become overloaded as it passes under the beam, but it rapidly recovers, continuing to record. The camera survived this type of abuse for twelve separate passes at Mrad levels. However, the audio becomes progressively fainter after each pass. We thought that the radiation flux may have depolarized the camera's electret microphone, but full audio functionality came back after a few days of rest. Go figure... :^)
Following is an image of the same large (~4" x 4" x 2") calcite crystal surrounded by some smaller dogtooth calcite crystals. All are glowing from thermoluminescence after being irradiated with 5 MeV electrons. Traces of manganese are believed to be the "activator" for these particular crystals.
Finally, a couple of experimental 3D masked specimens done during the run. These have two interlinked charge layers - actual size of these is 6 x 6 x 3/4".
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Amazing. Wonder if they use these cameras at the "Hot Zone" ? I've had dead pixels on my cameras in less than an hour with moderate exposure, however this was with alpha particles which compared to electrons are like bowling balls.. (scuttles off to patent "Method of fabricating semiconductors at home using alpha source irradiation of silicon") Thanks to Jeri for inspiring me to look into homefabbing, turns out it doesen't always need nasty chemicals as you can also use a plasma arc at moderate pressure from a CCFL to prepare the silicon wafer.
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A "Cart's-eye view" of a 3-5 million volt electron beam - some footage from the "Rad-Cam"
