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Hi Paul-Henrik,
wow, what a wealth of information and hints. That
will give me plenty to read, and I'll surely come up with more questions
thereafter.
Thanks a lot!
73, and have a good trip,
Markus (DF6NM)
Sent: Saturday, June 06, 2015 12:11 AM
Subject: Re: LF: Gamma spectroscopy (off topic)
Hello Markus, and others
interested.
Briefly, my PC / soundcard -based gamma spectroscopy
setup is as follows:
- Two self-constructed scintillation detector heads,
one using a
Russian/USSR 18 x 40 mm NaI(Tl) crystal coupled to a 25 mm
EMI 9111b
photomultiplier tube, and a refurbished 63 x 63 mm
Russian/USSR
NaI(Tl) crystal coupled to a 76 mm Photonis XP5312/SN1
photomultiplier
tube. The smaller probe is fitted with a dynode
voltage divider string
of approximately 60 Mohm total, and the larger
one has a 120 Mohm
string.
The pulse shaper / preamplifier is
the same one as in the Theremino
project, but the HV generator is made
from a CCFL PSU followed by a
three-stage cascade for a maximum
voltage of 1500 V. This is followed
by heavy but simple RC ripple
filtering. HV adjustment is by means of
a LM317 at the low voltage
input of the CCFL-module.
The signal derived from the photomultiplier
anode resistor is fed
trough a DC-blocking capacitor into the
Theremino pulse amp and from
there to MIC IN on either a "3D Sound"
USB audio card or the built-in
MIC input on the PC.
In the PC
there are a couple of freeware applications one can use, I
prefer
Theremino MCA and BeqMoni. Illy Sommer (Bionerd23) and Carl
Willis
that you have probably seen on YouTube both use a different
free
software that I have also tried, but found less handy to work
with
especially on the energy calibration side.
For Android there is an app
called "Atom Spectra", and for Apple iOS
products one can use "Geiger
Bot". I have tried both instead of a
normal PC with at least modest
success. Very handy if one wants to
measure in-situ instead of hauling
potential objects back home to the
"lab".
To increase the
signal to noise ratio further with the large detector
I will have to
invest in 100 kg of lead and have it cast in a suitable
container to
create a shielded well for the sample and the probe.
Using either probe I get
a total system resolution of 7 % at 662 keV (Cs-137).
To name a few
things I have done with my rig is:
- Determining if various glassware and
ceramics were coloured using
natural uranium (0.7% U-235) or depleted
uranium (0.2-0.3 % U-235)
- Finding out if slightly radioactive rocks I have
discovered in the
nature are radioactive due to containing thorium or
uranium
- Finding out that our neighbourhood probably got more Cs-137
fallout
in 1986 than our official averages show. Shows up in soil and
ashes
from local trees even without lead shielding. Hard to quantify
further.
- Making potash from the mentioned ashes concentrates Cs-137
even
further. I have a bag of the stuff that I can actually use when
doing
energy calibration of the setup.
Other handy calibration
tools are: Ionizing smoke detector (59 keV
from Am-241), Spark gap
tube (662 keV from Cs-137), thoriated lantern
mantle (many well
defined energies), radium watch or a radium doped
cold cathode
telephone tube (many well defined energies).
It is very simple to build
such a setup, since the software does most
of the hard work. Finding
good scintillation crystals and good
photomultipliers is perhaps the
hardest part. There is plenty for sale
on ebay, but it is often hit
and miss. I can provide some
recommendations off the
list.
Here is the Theremino documentation:
Adapter:
http://www.theremino.com/wp-content/uploads/2013/03/PmtAdapters_ENG.pdf
Software
links etc.: http://www.theremino.com/en/blog/gamma-spectrometry/
BeqMoni:
http://translate.google.com/translate?hl=en&sl=ja&tl=en&u=http%3A%2F%2Fblog.livedoor.jp%2Fkabuworkman-becqmoni%2F
or
try the download link provided by Karl in this forum thread:
http://www.gammaspectacular.com/index.php?route=forum/post&path=277
For
further reading you will have to visit Yahoo group "Gamma
Spectrometry". This is also a source for "good parts".
I hope
this off-topic provided some value.
Markus, I'm happy to discuss the
subject further per direct e-mail if
you have more questions. I will
be on a trip for a couple of weeks
starting Sunday so replying may
take a few days.
BR
Paul-Henrik,
OH1LSQ
Quoting Markus Vester <[email protected]>:
> Hi
Paul-Henrik,
>
> I'd be interested to learn more about your
soundcard gamma
> spectrometer, is there a description on the
web?
>
> The reason why I'm asking: I recently stumbled across
several rather
> enlightening videos from "bionerd23", the "Lady
who ate the
> Chernobyl apples". There's also one where she climbs
the huge
> transmit array of the former Duga-3 OTH-radar, also
known as "Steel
> Yard" or "The Woodpecker":
> http://forums.qrz.com/showthread.php?474249-Duga-3-The-Russian-Woodpecker-Antenna-Tour-and-Climb-Fall-2014
>
> 73, Markus (DF6NM)
>
> BTW Wouldn't mind having such an
decently-sized antenna in MY backyard ;-)
>
>
>
>
-----Ursprüngliche Mitteilung-----
> Von: phl
<[email protected]>
> An: rsgb_lf_group
<[email protected]>
> Verschickt: Fr, 5 Jun 2015
8:54 am
> Betreff: Re: LF: Re: USB stereo soundcard, CHEAP!?
> Have
a look at this specific product ("3D Sound" in transparent blue
> plastic
case), there are plenty sellers on the "bay" in DE:
>
> http://www.ebay.de/itm/USB-Soundkarte-Sound-Card-Audio-Adapter-5-1-Konverter-Skype-3D-Spiel-/111583623569?pt=LH_DefaultDomain_77&hash=item19fae6f991
>
>
>
I use exactly the same card for sound input from the NaI(Tl)
>
scintillator probe preamplifier in my gamma spectroscopy setup.
>
>
At least for that purpose it works as well or better than the built-in
>
audio interfaces I have tried. Key parameters in that application are
>
low noise, no extra "hidden" sound processing and good input waveform
>
reproduction.
>
>
>
> BR
>
> Paul-Henrik,
OH1LSQ
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