[Aavso-photometry] cosmic rays - some progress

[Ben Davies]

As several of you pointed out, my images are showing a very high number 
of cosmic ray hits compared to the naturally occurring ambient flux. 
<http://ben.davies.net/cosmicrays2.htm> Worried that I might have a 
radioactive house, I went to two other locations and made more test dark 
images. One location was 4 miles away and the other 140 miles away. 
Happily, the results were similar to the one obtained at my house – 
around 7x ambient.

Since I needed to find a source somewhere, I began to look inside the 
ST-10. I called up SBIG and talked about it with them with them. They 
said that the issue had been addressed a few years ago and they were 
aware of no source that they were introducing.

I then called Kodak and learned that the glass window that is glued over 
the chip is Schott D263. A call to Schott and I learned that D263 glass 
contains 6.9% potassium, which is a source of beta particles and gamma 
rays. This makes my 6.9x ambient results consistent with results 
reported by NOAA. They had Schott BK7 glass containing 11% potassium 
producing hits at a 10x ambient rate. 
<http://snap.lbl.gov/ccdweb/ccdrad_talk_spie02.pdf> (page 32). and also: 
<http://www.ctio.noao.edu/pipermail/ccd-world/2001/000472.html> 
<%3Chttp://www.ctio.noao.edu/pipermail/ccd-world/2001/000472.html%3E> 
That whole thread is very interesting.

This of course does not demonstrate that the Kodak windows are 
contributing the excess radiation that I am finding, but it is 
suggestive. Someone with more resources than I have should make tests.

I wonder whether the potassium's 1.35 MEV electrons might also introduce 
spurious voltages into the registers or the analog-to-digital capacitor 
during readout?

Ben Davies