Re: LF: Gamma spectroscopy (off topic)

[phl@netikka.fi]

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 <markusvester@aol.com>:

> 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 &lt;phl@netikka.fi&gt;
> An: rsgb_lf_group &lt;rsgb_lf_group@blacksheep.org&gt;
> 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