[Aavso-photometry] cosmic rays - some progress

[Wolfgang Renz]

Hello Ben

Its interesting what you foud.

Did you also consider the 3 mm single-MgF2-coated 1/4 wave BK-7
CCD chaimber entrance window as the source ?

When you called Kodak, did you also ask them if its possible to remove
a permanent non-taped CCD cover slip glas without damaging the CCD
chip ?
I've heard thats this was done by some Genesis CCD guys with success
(even the Bayer mask of the KAF1601C !?), but could never locate a
description on how they did it as their user list died. Found just:
http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00BTqn&tag=

Removing the CCD cover slip glas would also help to reach a higher
NUV transmission, especially in the range below the Balmer jump
shortwards of 365 nm !
element \ transmission [nm]  275  300  325  350  375  400  425  450
KAF-3200 CCD QE        [%]     1    6   25   36   49   59   60   62
MAR chip cover slip    [%]   ( 0    0   35)  90   97   99   99   99
MgF2 BK-7 entrance win [%]   ( 0   45   83   91   93)  94   95   96
SBIG ST-10XME total    [%]   ( 0    0    4   30   44)  55   56   59
(values in brackets are well guessed from different sources)

SBIG sell their Kodak chip cameras just with a permanent CCD cover
slip glas. Their argument is that any dust thats located on the cover slip
glas would show up in the light and flat frames just as grey 'donuts'
(instead of as black 'rocks', due to the increased distance from the
chip) that should flat-field out pretty well. But FLI leaves this choice to
their customer:
http://www.fli-cam.com/FLIsupport/coverslip.htm
http://www.fli-cam.com/FLIsupport/camera_windows.htm

Clear skies
  Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany
Rz.BAV = WRe.vsnet = RWG.AAVSO



----- Original Message ----- 
From: "Ben Davies" <ben at davies.net>
To: <aavso-photometry at mira.aavso.org>
Sent: Tuesday, February 28, 2006 12:02 AM
Subject: [Aavso-photometry] cosmic rays - some progress


> 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> 
> 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