# Gamma radiation decay intensity (IAEA nuclide chart)

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• eneacasucci
In summary, the website lists the gamma radiation intensity for different nuclei, but the absolute intensity doesn't add up to 100%. I was wondering why and Google led me to understand that the intensity is related to the probability of emission.
eneacasucci
TL;DR Summary
Gamma radiation decay intensity in IAEA website, what does it represent.
I was looking at the gamma radiation data from IAEA's website:

(https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html)

and was confused by the absolute intensity listed in the page. I Googled it and it seems to be the probability of emission but why it doesn't add up to 100%?

For example Cs-137 https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html

I don't understand why, because for example the sum of the beta intensities is 100%:
I know about gamma intensity related to the attenuation in matter but this is another topic

Thank you so much for your help

Last edited:
The 0.662 KeV state of Ba137 decays 85% of the time only by gamma emission and decays by the internal conversion process the rest of the time.

eneacasucci
Some nucleai, like Co-60 decay by more than one gamma.

gleem said:
The 0.662 KeV state of Ba137 decays 85% of the time only by gamma emission and decays by the internal conversion process the rest of the time.
This would make sense and clarify the %, but how do you know it? I don't see this info in the website

Some nucleai, like Co-60 decay by more than one gamma.
Thank you for your answer. I know that there could be more than one gamma, but for Co-60 the main two gammas (1332 keV and 1173 keV) are related to different initial level. For Cs-137, considering the level 662 keV, if only 85% of times the nucleus decays to ground level emitting the related gamma, what happens the 15% of times (still starting from that level)?

eneacasucci said:
I don't see this info in the website

eneacasucci
eneacasucci said:
I know that there could be more than one gamma, but for Co-60 the main two gammas (1332 keV and 1173 keV) are related to different initial level
Huh?

They come from the Co-60 ground state, and you get two, not one or the other.

gleem said:
My fault, I wasn't considering the column of electrons and now I see them. My last question is: shouldn't these [%] (highlighted in yellow) make 100% (because it doesn't)?

(Excuse my ignorance, but what does the initials 'CE' mean (before the electron's shell)?

eneacasucci said:
My fault, I wasn't considering the column of electrons and now I see them. My last question is: shouldn't these [%] (highlighted in yellow) make 100% (because it doesn't)?
Keep in mind the percentages are the percentages of the radiation per decay. Cesium decays 5% of the time to the ground state of Ba which has no additional radiation processes. So only about 95% of the decays of Cs result in additional radiation so expect a gamma or an internal conversion electron 95% of the decays.

eneacasucci
I think I got it now.
The percentages match as it should be right?

Last edited:
I've tried to make the same reasoning applied to Co-60.
I considered level 1332. You can reach it with the beta decay
, and with gamma decays
. Also without considering the conversion electrons the tot probability to reach final level 1332 (99,9776%) is lower than the probability of decaying from that level (99,9826%)

I've also tried to download the excel file with the whole data but there is still this incongruency... so I'm doubting I didn't understand the concept

Did you take into account the uncertainties in the data especially the beta branching ratios?

gleem said:
Did you take into account the uncertainties in the data especially the beta branching ratios?
No I didn't, I don't know exactly how to deal with them. I just wanted to be sure that "my reasoning" (which would be the application of what you explained to me in the previous messages) was correct, and that the non-coincidence of numbers was due to something else

Play with the data and see how it affects your results. Increase the 1.332 Beta ratio 0.12 ±.03 to a value within the uncertainty for example.

I had the same question and found some information in this site:
https://www-nds.iaea.org/relnsd/vcharthtml/guide.html.
There it says:
Iγ(rel) Relative Intensity 100 is assigned to the most intense gamma from a given initial level, and other gammas relative intensities are referred to that.
So, my humble opinion in this case is, they do not have to add up to 100%, because the percentage here is just for comparison between any given intensity and the intensity of the “most intense” gamma, it would mean just how much smaller are those other gammas relative to the 100% highest intensity gamma. It would make more sense to relate them with a relative ratio than with percentage, which in most cases gives a balance of species out of a total.

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