Ra226 spectrum from Scionix 35B57

[Conor Whyte]

So I have been following some advice to turn down the voltage on the GS-USB-PRO to 550V and up the gain in both Theremino MCA and PRA while using my Scionix 35B57 from iRad. The results speak for themselves. I see a tightening of the peaks as well as a huge improvement in linearity/ very little shifting with minor temperature variations. I also encounter far less noise in my spectrum.

I have always wanted to do an hour long run on my Radium watch hands since getting my new spectroscopy driver, so I am posting my first 1hr attempt. I took the data collected from PRA and imported it into Apple's iWork suite - numbers to create the graph.


I notice that the lowest energy peak was completely obscured in Theremino and kind of mashed together with the second Pb X-ray fluorescence peak @ 75KeV.
Is this tiny 11KeV peak just noise or is it the low energy Pb210 gamma showing? ( blank arrow) -- If it is indeed Pb210, why would Theremino MCA be mashing the spectrum together a the low end?


Please let me know what you think. Document is in .pdf format.

Ra226.pdf

[Conor Whyte]

I decided to post a .jpg file on here as well.
Again, this is data collected from PRA redone in numbers on MacOS..
The lower scale (KeV) is not necessarily accurate as it was created quickly.



Comments are appreciated! I am trying to refine my skills :)


This spectrum was taken without the use of a lead castle. I am working on trying to get the bits and pieces to build one but I am leaving next week to Seoul
so I have to leave this project for the new year. -- Looking for Cadmium sheet metal that doesn't cost an arm and a leg. I have a spectroscopy Pb castle design in mind similar to several commercial units I have seen.

Ra226.jpg

[Go-Figure]

Is this tiny 11KeV peak just noise or is it the low energy Pb210 gamma showing? ( blank arrow) -- If it is indeed Pb210, why would Theremino MCA be mashing the spectrum together a the low end?

Nice spectrum Conor!
I am aware of an x-ray from Uranium at 13.442 keV, but you don't get that from a Radium dial, because the starting point of the chain is Ra226, and it's unlikely to spot anyway.
There are also a number of x-rays between 10 and 12 keV, but honestly I never identified any of them in my spectra.
http://nucleardata.nuclear.lu.se/toi/Ga ... =10&Max=12

Massimo

[Conor Whyte]

Upon further investigation I am under the impression this may be one of a few low energy X-ray peaks common to Pb210. This peak is one of the more frequent intense peaks at the lower end (~8%) --- this being at 10.712KeV.. ---> Gamma for Pb210 is at 46.539KeV

Again, I'd love to get some gamma spec -vets to comment on this. I didn't realize that the Scionix 35B57 could venture down this low in energy.



I am really quite enjoying this kind of experimenting.

my next spectrum will be to try and identify trace Neptunium in an old 45year old ionization type smoke alarm. (Americium oxide coated gold foil)

[Sesselmann]

Conor,

Your spectrum looks great and your method is sound. Finding the best voltage for linearity is a good way to start. Occasionally you might come across a difficult probe and then there might be a problem with the voltage divider. A second check is to find the count rate plateau, this is a voltage range over which the count rate remains relatively constant. Hopefully both are in the same range.

Steven

[Conor Whyte]

I have tried a full voltage range from 750-500V. The best results occurring at 550V with a ~15x gain in PRA. Again, my results could be reproduced repeatedly with little upshifting of the spectrum from slight upward trending temperature variations.


Question: With the experimentation I have been doing, PRA seemed to be the winner in producing the cleaner spectrum whereas Theremino seemed to mash (distort) peaks together at lower energies... Anyone else also experience this behaviour?

Is there a way to fix Theremino...settings?

[Sparky]

Conner,

I think your spectrum looks fantastic. I have the same probe you are using. I can not get that low energy resolution and high energy range with my homemade pmt adapter (made from bubble gum and bailing wire) and Theremino, at least not at the same time. I can get low energy resolution with my set-up by increasing the voltage. This causes a pile-up on the high energy end that truncates that end of my spectrum. I generally bounce back and forth between 675V and 625V, depending on which end I am interested in. The red line in my attached spectrum is the high energy end pile-up I am referring to. I can do a little better than this with more careful volume and voltage adjustment, but I generally just live with it. Suggestions are very welcome.

Your peak labeled as 1001 keV is probably not Pa234m, because that is above Radium in the U238 decay chain. I believe it is another Bi214 Peak at 1133.7keV.
Your peak at 10 keV might be Zinc x-ray fluorescence from the phosphors used with Radium paint. 10 keV is pretty much at the limit of the probe because the housing attenuation.
I generally don't bother below 20 keV. It is just too difficult.

Sparky

[Conor Whyte]

I just had another look at the spectrum again, this time extracting a more accurate energy per division, still keeping 200KeV per separation. Spectrum now points to higher energies of Bi214 gamma instead of Pa234m which makes more sense (1133.7keV vs 1001.03KeV) . The lower energy peak is an x-ray of Pb210. This is now confirmed.