Relative height of radium peaks

[Jim Kovalchick]

I'm curious about what is wrong with the relative height of the "three bear" peaks in the goldilocks and three bear set in this radium spectrum. The middle peak of the triplet is too high relative to the other two. Am I seeing some kind of escape peak skew? I really wouldn't expect it at that energy. This spectrum was taken using a very old 5 inch by 2 inch NaI. I'm not worried about FWHM here. I'm just working on my electronics and sample setup.

Thanks

[Jim Kovalchick]

Also perhaps the issue is that the third peak is too shallow.

Any ideas?

[Jim Kovalchick]

I think I know what may be the issue. My sample was off center and close to the edge of the relatively large NaI crystal. This may skew the relative efficiency loss with higher energies. When I get a chance to test my theory, I will respond back.

[Jim Kovalchick]

I checked different sample geometry with no change to the relative peak heights. I changed out my detector with a simple 2 inch crystal and got the same relative shape. So it's either my electronics or the sample itself.

[Sesselmann]

Jim,

Just a shot in the dark, but could it be that your count rate is too high?

Would moving the source further away improver it?

Steven

[Jim Kovalchick]

Steven,
I thought of the count rate piece too. I moved the sample back three inches with no change in the relative height of the peaks though I did see less broadening of them. My next check will be a count of the sample using a completely different system and detector, but I expect to see the correct heights because they all come from the same isotope.

I also checked my background to see if there is any coincident contamination in the area of interest. There seems to be a very slight bend in the background curve near the second peak, but subtracting it did nothing.

[Jim Kovalchick]

Speaking of relative heights within radium spectra, I have wondered in the past if the relative height of the radium peak in comparison to the three lead 214 peaks speaks to the porosity of the radium. In other words, if the sample was free to leak a larger percentage of its radon, would one expect to see the relative height of radium peak be higher in comparison to the lead 214 peaks because equilibrium level is influenced by the radon removal by leakage? Does the shape of the sample itself influence this? In other words, granular or larger surface area shapes would have greater leakage and less equilibrium build up of daughters.

[Jim Kovalchick]

I stumbled into a "fix" for my question about the relative heights of the lead 214 peaks. I increased the number of channels my ADC was using to 16k and voila, the peaks look more in order. I have to ponder a bit why 2K did what it did. I will probably also try to find a lower resolution that looks good because 16k obviously takes so much more time.