Home Forums Iolite User Forum Dwell times

This topic contains 2 replies, has 2 voices, and was last updated by  Tanya Ewing 3 weeks, 2 days ago.

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  • #13996

    Tanya Ewing
    Participant

    Hi there,

    I’ve just discovered that I entered the wrong dwell times for a dataset I spent some time processing (dwell times for all isotopes are too short by a factor of 5). I am using Iolite (version 3.65, with Igor Pro 7.08 on a Windows computer) to process U–Pb geochronology data with the VizualageUcomPbine DRS. My input data are FIN2 files with data in CPS.

    I corrected the dwell times and re-crunched the data, but there seemed to be no change in the results on channels such as 207Pb_CPS (which I thought was a good candidate to be affected by the dwell times), so I wasn’t sure if it had really updated the dwell times.

    It’s not clear to me what the dwell times are actually being used for, and whether it in fact matters that I got them so drastically wrong. Can anyone tell me if this error will have made a difference to the results I get? And if so, is there any way to correct the dwell times in the existing file and recrunch, to avoid starting the whole lengthy process again from the import step?

    Any insight would be much appreciated!

    Best regards
    Tanya Ewing

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  • #14000

    Dr Bence Paul
    Keymaster

    Hi Tanya,

    Dwell times are used in iolite just to calculate the Pettke Limits of Detection. If you’re not doing trace elements and calculating this value, changing the dwell times of an existing dataset will have no effect.

    The main considerations with dwell times occurs during measurement. If your dwell times are too short, you will have insufficient counts and therefore lower precision. If your dwell times are too long, you’ll lose time resolution and start to get aliasing affects. However, by the time it gets to iolite, your counts are set and so changing the dwell time in iolite has no effect (iolite reads the counts in the raw data files).

    I hope this clarifies things. If not, please feel free to reply to this post.

    Cheers,
    Bence

    #14001

    Tanya Ewing
    Participant

    Hi Bence,

    Thanks so much for your speedy reply, which is very helpful! And good news that I do not need to redo my data processing.

    I have actually recently experimented with using different dwell times for U–Pb measurements, which has given me a strong appreciation for just how important they can be for the quality of the final result, as you point out.

    Cheers,
    Tanya

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