Archived - Attenuated Gamma Spectra

[Frank Sanns]

Note** Archived due to its relevance for Gamma spectro folks in the forums. Clean and concise with interesting results, well explained. RH


Now that I am finally back in town, I am trying to pack in some experiments before classes start again. One of the questions on the site was relating to the gamma spectra of a neutron activated fusor. Would the spectra be shifted downward by attenuation through the fusor shell?

The photo below show the spectra for radium. The top scan is a normal spectrum and the bottom is a spectrum through a piece of ~6 mm lead (longer aquisition time). As you can see, the peaks for the most part still exist especially the biggest area peaks. They remain at exactly the same energy because there is a probability that a photon will go right through the lead unimpeaded (no energy loss). For those photons that do interact with the lead, well they loose some of their energy and they contribute to random energies that fill the spaces below thier respective peaks and raise the overall floor of the spectrum.

Frank S.

[Carl Willis]

Hi Frank,

It's great to see that MCA working. Congrats on a healthy unit.

If your experience parallels mine, you won't get any sleep for the next couple nights because of all the stuff you can do with it!

-Carl

[Richard Hull]

The careful eye will note the definite peak at the 512kv region on that second spectrum. Pair production and the resultant 512kv gammas are there as some tiny fraction of Ra226 and its daughters have gammas over 1.2mev and those puppies tend to pair produce while interacting with matter. It is only way a hot gamma can pair produce. (interact with real matter).

I did my old shielding experiment way back in aught-two and my full report is in the files forum here. The pair peak occured at a specific lead thickness. Cool stuff.

viewtopic.php?f=19&t=7942#p57346


Carl is right, you'll go nuts with your gamma-spec as I did over 5 years ago.

Richard Hull

[Frank Sanns]

Nice work Richard. I did not know that existed. There is so much info on this site I think I shall never get to it all. Oh well, it is always fun doing it for the first time yourself. It did get me the confidence to identify the same peaks under my foundation. The high counts are from radon daughters filtered through a bunch of concrete and dirt becasue the peaks are there but are muffled almost down into the noise. Good thing my under slab fan takes all of those critters out before I have to breath them!

Frank S.