Questions for the "PlasmAge.py"

Allan_

Hi iolite,

I am confused for that the 208Pb/206Pb values and the uncertainty of isotope ratios when I export U-Pb data using "PlasmAge.py".

Is the value calculated by Cps(208Pb)/Cps(206Pb)? And is the value corrected by the standard?
I'm trying to using SRM 612 as standard, can the 208Pb/206Pb values of SRM 612 be used to access the 208Pb/206Pb of my samples?
Another question is that the uncertainty of isotope ratios when using "PlasmAge.py" is SD or SE?

Looking forward for your reply.

Joe

Allan_

Yes, it is just the background subtracted 208/206. No, not standard corrected.

If you want to standard correct the 208/206, you could add something like below after the imports:

rm_name = 'G_NIST612'

Pb208 = data.timeSeries('Pb208_CPS').data()
Pb206 = data.timeSeries('Pb206_CPS').data()
Raw86 = Pb208/Pb206
t = data.timeSeries('TotalBeam').time()

data.createTimeSeries('Pb208/Pb206', data.Intermediate, t, Raw86)

Spline86 = data.spline(rm_name, 'Pb208/Pb206').data()
RM86 = data.referenceMaterialData(rm_name)['208Pb/206Pb'].value()

Final86 = Raw86*RM86/Spline86

data.createTimeSeries('Final Pb208/Pb206', data.Output, t, Final86)

This would calculate a new channel called 'Final Pb208/Pb206' that uses the NIST612 208/206 spline and reference material data to correct the ratio. The 208/206 value will need to be specified for the RM as '208Pb/206Pb'. You would then need to modify the pb208_206 function to something like:

def pb208_206(selection):
    try:
        ratio = data.timeSeries('Final Pb208/Pb206').dataForSelection(selection)
        mean_ratio = np.nanmean(ratio)
        pct1se = 100*(np.nanstd(ratio)/np.sqrt(len(ratio)))/mean_ratio
        return (np.nanmean(ratio), pct1se)
    except Exception as e:
        print(e)
        return ('#N/A', '#N/A')

From a quick skim of the code it appears to be SE.

All the best,

Allan_

Joe Thank you very much. I used 208Pb_Cps/206Pb_Cps as the results to export, finding that the 208Pb/206Pb of SRM 610 is ca. 2.25, while the 208Pb/206Pb of SRM 612 is ca. 2.16. I wonder that if the 208Pb/206Pb values of SRM 610 are heterogeneous or not ? I know that maybe this question is not suitable to appear in iolite community forum. I'm just trying to find the answer. 😅

Allan_

Thank you very much!

Bence

I think at the level you're going for, they should be homogeneous enough (depending on your spot size etc, which will change your level of precision). If you look up these RMs on GeoReM you'll see that there is a range of values reported for 208/206, but this is more likely due to differences in analytical setups/approaches etc than heterogeneity in Pb isotopes. I would recommend checking out the sources cited there to get a feel for the range of values in any one experiment.

I think it's a good question for the forum 😃

Allan_

Bence Thanks for your replying !