Gamma spectrum of a Polonium/Beryllium neutron source

[stamasd]

I wanted to see what (if any) my 4mCi Po/Be source emits. Here is the result below. Done with a 2.5inch NaI(Tl) crystal, count time 5 minutes. Background is subtracted. X-axis channel number, Y-axis counts. Calibrating against a 137-Cs with same probe and same tube bias and counting parameters, the 3 peaks I'm seeing result at approximate energies of 11.7, 83.3 and 847keV.

The test was done in a small lead castle of 1.5cm thickness, lined with 0.7mm copper on the inside.

A quick check online hasn't given practically any results for a gamma spectrum of this type of source.

[Sesselmann]

Those low energy peaks look like they could be the x-rays from Po-210
http://nucleardata.nuclear.lu.se/toi/nu ... iZA=840210

Not sure what's happening at the 750 keV mark, the Po210 gamma has very low intensity, I would be surprised if it made a bug peak like that.

Steven

[stamasd]

I forgot to mention, the numbers on the X axis are not keV but channels in my software. The most energetic peak (based on calibration with a 137Cs source) is at 847keV, not 750.
It could be that my calibration is off and it's in fact the 803.1keV described there - the one that occurs 0.00121%.
If you look at the counts (on the Y axis) that peak is only 80 tall, in 5 minutes from a source of 4mCi. I would call that low intensity. :)

[MaxGaspa]

With so few details of your source it is difficult to help you but:

For sure Po210 is not responsible of the gamma emission. The gamma yield of Po210 is very very low (that's why it was used to kill people....)

A peak at about 835 keV can be observed in a PoBe neutron sources. The Po210 is created using Bi209 exposed to a thermal neutron flux in a nuclear reactor. The resulting Bi210 decays into Po210. Impurities in Bi starting material can create other isotopes during the neutron irradiation phase. For example Fe54 has a fast neutron reaction to produce Mn54 that has a 835 keV emission. Usually Po210 is purified from the starting material but with no details of your Po210 source it is difficult to make an educated guess.

How did you get the PoBe source? Is it a DIY source?

[stamasd]

I think I posted my source before in a thread here. Anyway it's a "static eliminator" device that I'm leasing from NRD

[broken link removed - Steven]

I filled the window of the device with 1mm thick beryllium chips.

[MaxGaspa]

I didn't observe your source before now. But that kind of sources are prepared using pure Po210 in a laminated structure. My guess is that the hypothesis of observing the peak at 800 keV due to Mn54 is very unlikely. The used Po210 is chemically purified.

So we should come back to the gamma emission (804 keV) from Po210 and compute a reasonable estimation.

You source has 4 milliCurie of Po210 of activity equal to 148 MBq. The probability of gamma emission

(from R. W. H ayward , D. D. Hoppes , and W. B. Mann - Branching Ratio in the Decay of Polonium-210 - Journal of Research of the National Bureau of Standards Vol. 54, No .1, January 1955 )

is 1.22 +/- 0.06 10^-5.

So the gamma activity is 1.81 kBq. If the source was measured very close to the NaI crystal we can estimate a geometry factor of 0.3-0.4.

Unfortunately to estimate the full peak efficiency further details are needed and you don't provide the total count of the peak. But as a guess I would say that the low counts in your spectrum at 800 keV may be compatible with the gamma emission activity of your source.

Even if the gamma emission probability is very low the source activity is high (148 MBq) and the resulting gamma emission activity can be detected if your NaI is very close to the source.

P.S:

I'm always surprised that such sources are available to the public so easily. Even if the source is safe, stupid people can do stupid thing with it. I'm sure is not your case but there are so many un-educated people around....

[stamasd]

The source was at 10cm from the detector. That is because this particular experiment was done as part of a series of tests I did, the full details of which was posted on another board http://www.fusor.net/board/viewtopic.php?f=13&t=11994 . Essentially I needed enough space between the source and detector to add increasing thicknesses of lead (I switched detectors in the course of things too, the other detector used was a 3-inch BC412 scintillator, and the scope of the experiment was to determine the suitability of the BC412 to detect fast neutrons).

I'm attaching below the full data from the experiment - the raw output from my detection system for the background counts and the counts with source for the NaI detector. Also a spreadsheet I used to subtract the background and do the graphing. In the calculations I cut off the forst 10 channels which were below 50mV which is the cutoff I used, and contain only artifact due to the integration algorithm.

The relevant file for each of the counts is spectrum.txt which is CSV, with the format: "channel number, counts". There are 1000 channels, each 5mV wide. For the Nai/PoBe part of the experiment there was no lead added between the PoBe source and the probe.

In the series "NaITl-5min-PoBe-openPbcastle" if you look at the spectrum.png file you will see 2 curves. The red one is background, the green one is with the PoBe source.

[Sesselmann]

Carl Willis did a few experiments with a Po210 source like that. Some stuff here on his blog if you scroll down a bit.

https://carlwillis.wordpress.com/category/projects/

[stamasd]

Carl Willis' blog is what inspires me to do a lot of my experiments. I'm currently working on copper, indium and antimony activation. :)

(not too great results so far; my detector is quite large and sensitive, but I don't have yet a good enough shield so background is a problem - I'm working on upgrading that)

[Sesselmann]

I would love to have a play with one of those Po210 sources. http://www.amstat.com/esd-ionizer/nucle ... a-ionizer/

I am really curious as to what would happen if one suspended one of these on an insulator in the centre of a hollow vacuum chamber. The alpha particles are emitted at more than 5 Mev. so in a vacuum chamber they would carry positive charge to the chamber walls where the particle would recover it's electrons.

Within a very short time the nuclespot should become negatively charged no?

Obviously something would have to give before it reached -5 million volts, but what?

Could it power a fusor?

Sounds like too much fun.