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4hv.org :: Forums :: Electromagnetic Radiation
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CMOS camera geiger hack

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Conundrum
Wed Sep 02 2009, 07:24AM Print View
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: People's Democratic Guernsey Republic
Posts: 3205
Hi all.

Update on my CMOS camera hack:- pyrolytic graphite works fine if split down, then sanded down to around 0.3mm thick.

I discovered that reducing the clock speed from 13.5 to 4 MHz increased the sensitivity by about a factor of three and allowed me to view individual particle interactions on my 'scope.

fwiw this is a B&Q camera, with the exposed chip surrounded with epoxy and a piece of PG installed about 1mm away from the chip.
The chip has damage that renders it unsuitable for use as a camera (large dead spots) that strangely enough doesen't show up on the geiger images.
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Proud Mary
Sun Sep 06 2009, 02:22AM
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4796
That's excellent Andre! You should write up a whole report about it in the projects section.

I expect the dead spots are not 'dead' but areas of reduced sensitivity, so that the higher detection efficiency of alphas is able to lift the signal above the noise floor to the point where it can be detected.

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Conundrum
Sun Mar 20 2011, 02:40PM
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: People's Democratic Guernsey Republic
Posts: 3205
Sounds about right.
Sadly the camera stopped working about a month later, I don't know why but suspect moisture damage to the chip.
Was a gradual failure, the output stopped generating video but I could still see the signals if I biased output at +V, then it stopped entirely a week later.

Memo to self, next time use UV cure glue as it fully encapsulates the delicate interconnects.

-A
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Adam Munich
Mon Mar 21 2011, 04:23AM
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: SF Bay, CA
Posts: 2225
I've tried this before actually with a webcam, and just so you know the radiation eventually causes more and more pixels to die until it's pretty much useless...
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Proud Mary
Mon Mar 21 2011, 09:59AM
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4796
A Google trawl for "CCD radiation damage" brings up a big hawl.

I found this one to be the most accessible to someone like me, who is unfamiliar with the field:

Radiation Damage in CCDs used as Particle Detectors
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