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Old 24-10-2015, 06:28 PM
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pmrid (Peter)
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Cosmic Ray/Muon hits on CCDs

I'm hoping someone out there knows something about this. I'm having a ' discussion ' with the manufacturer of one of my CCDs. I sent them some 10 and 20 minute dark subs showing what people keep telling me are cosmic ray hits. They are streaks of varying lengths and shapes in locations that vary from sub to sub. Those on the 20 minute subs are 3 or so times longer than those on 10 minute subs.

The manufacturer repeats the usual mantra aout cosmic rays being normal and insisting that the streaks on the longer subs are also not out of the ordinary.

But can anyone with actual knowledge comment on this. Cosmic rays/muons travel at 28.9 cm/ns gve or take a bit - measured at sea level ( according to a paper from RMIT). Thats aboutb1.07 billion km/hr. At that speed they would hit and pass through a CCD substrate in the minutest period of time. That being so, how dos that stack with the conventional wisdom from this manufacturer about long streaks correlatng with lnger exposures?

Can anyone add to or explain this?
Peter
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Old 24-10-2015, 09:40 PM
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Quote:
Originally Posted by pmrid View Post
I'm hoping someone out there knows something about this. I'm having a ' discussion ' with the manufacturer of one of my CCDs. I sent them some 10 and 20 minute dark subs showing what people keep telling me are cosmic ray hits. They are streaks of varying lengths and shapes in locations that vary from sub to sub. Those on the 20 minute subs are 3 or so times longer than those on 10 minute subs.

The manufacturer repeats the usual mantra aout cosmic rays being normal and insisting that the streaks on the longer subs are also not out of the ordinary.

But can anyone with actual knowledge comment on this. Cosmic rays/muons travel at 28.9 cm/ns gve or take a bit - measured at sea level ( according to a paper from RMIT). Thats aboutb1.07 billion km/hr. At that speed they would hit and pass through a CCD substrate in the minutest period of time. That being so, how dos that stack with the conventional wisdom from this manufacturer about long streaks correlatng with lnger exposures?

Can anyone add to or explain this?
Peter

They hit an atom & create a shower of particles.

I think it's more likely that such hits occur from natural background radioactivity
that exists in every substance.
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Old 24-10-2015, 10:11 PM
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Slawomir (Suavi)
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Hi Peter,

You might find this short paper interesting: http://www.jai.com/SiteCollectionDoc...CosmicRays.pdf

Conclusion: ship the camera not by airplane but by sea for any repairs and use it for imaging near the equator and at sea level

Regards
S.
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Old 25-10-2015, 12:38 AM
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pmrid (Peter)
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Quote:
Originally Posted by alpal View Post
They hit an atom & create a shower of particles.

I think it's more likely that such hits occur from natural background radioactivity
that exists in every substance.
But that does not support the suggested longer sub = longer streak argument does it?
Or am I missing something.
.
Peter
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Old 25-10-2015, 12:41 AM
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pmrid (Peter)
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Originally Posted by Slawomir View Post
Hi Peter,

You might find this short paper interesting: http://www.jai.com/SiteCollectionDoc...CosmicRays.pdf

Conclusion: ship the camera not by airplane but by sea for any repairs and use it for imaging near the equator and at sea level

Regards
S.
Thanks Slawomir. Interesting article. At airline heights, the chance of a hit over a 15 hour flight can reach 10% or so. But I get these things in every sub and in periods of minutes, not hours. And, other cameras operating at the same site and at the same time are not being affected.

I just can't accept the ray explanation, whatver the suggested source may be.

Peter
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Old 25-10-2015, 07:40 AM
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Quote:
Originally Posted by pmrid View Post
Thanks Slawomir. Interesting article. At airline heights, the chance of a hit over a 15 hour flight can reach 10% or so. But I get these things in every sub and in periods of minutes, not hours. And, other cameras operating at the same site and at the same time are not being affected.

I just can't accept the ray explanation, whatver the suggested source may be.

Peter
Hi Peter,

The 10% in the paper refers to a chance of a permanent change to a CCD due to cosmic radiation. Typically a CCD will get many more hits by fast moving particles during that time, originating both from the environment and space, resulting in bright pixels and temporary streaks on a CCD that disappear with the next sub.

A particle that hits a CCD face on (perpendicular to the surface of the CCD) will most likely result in one (or few) bright pixel(s) in a sub, while a particle that hits the CCD from a side (parallel to the surface of the CCD) will result in a streak.

CCD gets hit from all directions throughout an exposure, and although most particles hit the CCD approximately face on, a chance of being hit by particles moving across (not through) the CCD increases with time, thus longer subs should have a greater number of longer streaks.

Anyway, that's how I understand this phenomena
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Old 25-10-2015, 08:24 AM
cfranks (Charles)
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From my experience, longer subs just mean more CR hits, not longer streaks. From the sound of it, Peter's observations suggest some CCD's are more susceptible than others. My cameras are both QSI but have different CCD chips, the 540 showing few, if any, and the 683 showing plenty. With the proviso that I don't know much about CCD technology, I doubt that Cosmic Ray hits would do permanent damage as they happen 24/7 even when the camera is in the cupboard.
Interesting thread!
Charles
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Old 25-10-2015, 08:32 AM
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I've seen many interesting patterns on various sensors over the years from cosmic ray and or particle hits.

Further they can and do damage pixels on the CCD over time. A typical artifact is a hot pixel wil a charge spill below it, looking like a column defect.

All very normal for a sensor optimised to detect electrons (usually in the search for photons)
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Old 25-10-2015, 09:47 AM
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I feel that some manufacturers would take into consideration type of materials used in making the camera, while others might not. That's why IMO cameras from different manufacturers and with different sensors will show a varied response to fast particles. I think this paragraph explains it fairly clearly:

"One of the primary causes behind this phe- nomenon is natural radiation from Alpha particle sources. The major sources of Alpha particle emission have been found in the semiconductor material itself, as well as the materials used in packaging the die, and natural radia- tion from the ground (i.e. Radon.)"

And yes, CCDs do get gradually affected by such particles in a permanent way.
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Old 25-10-2015, 11:04 AM
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pmrid (Peter)
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Thanks guys. I appreciate the input and can see that what I'm experiencing is not unusual and I should obviously concentrate more on taking good quality calibration frames.

Peter
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