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From:	geda AT psjt DOT org (Stephan =?utf-8?Q?B=C3=B6ttcher?=)
To:	John Doty <jpd AT noqsi DOT com>
Cc:	geda-user AT delorie DOT com
Subject:	Re: [geda-user] OT: ballooning
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	<s6nshidjnu0 DOT fsf AT blaulicht DOT brux>
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	<4733B1AC-D60F-42C6-A7AB-A3259D937A9B AT noqsi DOT com>
Date:	Wed, 05 Jul 2017 09:05:07 +0200
In-Reply-To:	<4733B1AC-D60F-42C6-A7AB-A3259D937A9B@noqsi.com> (John Doty's
	message of "Tue, 4 Jul 2017 19:22:18 -0600")
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John Doty <jpd AT noqsi DOT com> writes:

> On Jul 4, 2017, at 2:53 PM, Stephan Böttcher <geda AT psjt DOT org> wrote:
>
>>>> No, sorry.  What I have is for the RPi1.  I hope to launch it on a
>>>> balloon into the stratosphere next week:
>>>> 
>>>>  http://www.ieap.uni-kiel.de/et/people/stephan/rpirena/
>
> I used to do that stuff a long time ago. Last time was 1975, with a
> ton of gondola carrying NaI/CsI “phoswich” scintillation detectors for
> hard x-rays. We sent it up with a 1.5 million cubic meter “zero
> pressure” helium balloon.

One of our students build a phoswich detector with a plastic
scintillator inside and CsI outside, that flew on a Bexus mission.

  http://rexusbexus.net/
 
The CsI light yield was much higher than the plastic, and much slower.
The digital filters could easily distinguish hits in CsI form only
plastic hits.  The plasitc hits were 100% neutral particles, gamma and
neutrons.  The most difficult part was the PMT HV at 25km altitude.  She
blew multiple preamps the thermal vac testing, until the HV isolation
was ok.

>> That slope can be the tail of the noise or indeed some x-ray
>> background. It looks like the tail of the noise to me.
>
> Might also have some poorly collected charge. The outer edges of these
> diodes are usually not depleted: you’ll collect some charge from a
> track by diffusion, but you’ll lose some of it, too.

Right, these photodiodes do not have guard rings to provide sharp
edges of the sensitive volume.  All our custom made silicon detectors
have those. But there is still an edge.

>>  The light can be measured with the same kind of silicon
>> photodiodes.  The calibration is not as easy, since the light yield
>> depends on temperature and doping of the scintillator, on the shaping
>> time of the electronicsm and the resulting balistic deficit, which is
>> the light that comes to late to be integrated by the shapers.  The time
>> profile of the light emission depends on temperature as well.
>
> In the old days we used photomultipliers. At least with diodes you
> don’t have to worry about magnetic fields changing the gain!
>
> John Doty              Noqsi Aerospace, Ltd.
> http://www.noqsi.com/
> jpd AT noqsi DOT com


-- 
Stephan

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