Discussion Category:  Scintillation Counters

Rubidium-86 in LS 3801--Thanks

Does anyone know the program detail for Rubidium-86 in LS 3801? Many thanks!

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lidoctor
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dpkleessr

It has been a LONG time since I have even seen an LS3801 but I would suggest the following: Start with a lower limit setting of 0 channels and set the upper limit to 1000 and perform a count on a sample of known activity in it to see the maximum activity of your sample. Since you know the amount of DPM activity in the sample, you can calculate the efficiency of the LS counter for Rubidium by the formula CPM/DPM= efficiency. Make sure that your known activity sample is prepared the exact same way that your normal samples are prepared. Then, I would start lowering the upper limit by about 100 channels at a time until you see approximately 99% of the maximum count rate. This will be the correct window setting for your sample based upon the amount of quench that is in your sample. You may have to change the upper limit setting in smaller increments in order to home in on the correct end point for the upper limit.

Don

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lidoctor

I appreciate your kindly information. One more question: how many channels do I select to count the rubidum-86: one or all three? Thank you again.

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dpkleessr

There are several ways to go about what I asked you to do.  You can just count in one channel or you can use all three channels to narrow in on your correct counting window.  I would start with channel one set to a window that is set at 800 for the upper limit.  Channel two should have the upper limit set to 900 and channel three should be set to wide open.  Remeber, only do CPM counting, make sure that the standard that you make up is identical to the samples you will be counting, and that you calibrate the counter before you start this process.  Then it is just a question of adjusting the upper limit settings until you get approximately 99% of the total counts in the wide open window.  The 1% spill over that I'm talking about is how Beckman established proper counting endpoints for any and all isotopes.  Good luck and take your time to get it correct and by time I would recommend at least 2 minute count times unless you have a very radioactively hot standard to count.  Then you count cut the counting time down to a minute.

Don

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dpkleessr

I actually found my original service manual and I believe that you are going to find that the best counting window is going to be an almost wide open window with an upper limit setting of around 990 channels. At least that's what my cheat sheet said so I would not spend too much time in doing what I previously said to do.

Don

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lidoctor

Thanks. Do I count 86-rubidium in three channels or just one channel for my real expreiment? Thank you again.

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