Author Topic: PHA issues  (Read 7012 times)

neko

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Re: PHA issues
« Reply #15 on: October 19, 2018, 10:28:57 am »
I've got a good one for ya - here's two PHA scans, this time is the relative verification peaks for PET and LIF, but on the same spectrometer. PET looks a little weird but not obviously horrible, and then LIF has a nice little extra peak on the right side of the primary peak. It wasn't like this in the past, but we don't use LIF on that spectrometer very often (of our two LPET/LLIF spectrometers, this one is less sensitive for LIF than the other and vice versa for PET).

the PHA for Ca Ka/LPET is 1850/897 - not bad but a little low. The PHA for Fe Ka/LIF is 1849/400. The other LLIF crystal we have has a bias about 25 values higher.

I assume I need to adjust the gas flow again, ever so slightly.

Probeman

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Re: PHA issues
« Reply #16 on: October 20, 2018, 01:51:52 pm »
I've got a good one for ya - here's two PHA scans, this time is the relative verification peaks for PET and LIF, but on the same spectrometer. PET looks a little weird but not obviously horrible, and then LIF has a nice little extra peak on the right side of the primary peak. It wasn't like this in the past, but we don't use LIF on that spectrometer very often (of our two LPET/LLIF spectrometers, this one is less sensitive for LIF than the other and vice versa for PET).

the PHA for Ca Ka/LPET is 1850/897 - not bad but a little low. The PHA for Fe Ka/LIF is 1849/400. The other LLIF crystal we have has a bias about 25 values higher.

I assume I need to adjust the gas flow again, ever so slightly.

Hi Nick,
I don't know what causes the "shelf" on the high energy side of the PHA distribution, but I do see this sometimes on my scans, maybe at high currents and PET crystals, but I'm not sure.

Check the attached images on this post (login to see attachments):

https://probesoftware.com/smf/index.php?topic=217.msg6899#msg6899

and also here, earlier in this topic:

https://probesoftware.com/smf/index.php?topic=31.msg7167#msg7167

Does anyone know what causes this?
john
« Last Edit: October 20, 2018, 03:17:15 pm by Probeman »
The only stupid question is the one not asked!

Probeman

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Re: PHA issues
« Reply #17 on: October 23, 2018, 04:14:26 pm »
I accidentally left the valve on the P-10 gas cylinder I changed yesterday closed, so the system had no flow overnight. I have no idea if air could have entered the system but I suspect not as all my flow detectors terminate in separate oil filled "bubblers" (as per Cameca).

When I came in this morning and started tuning up with a student, we found the PHA distributions on the high pressure detectors looking like this:



The PHA distribution on the 1 atm detectors looked fine even though the count rates were extremely low:



I don't know if this explains the "shelf" that we sometimes see on some PHA distributions, but I thought it worth sharing.
john
« Last Edit: October 23, 2018, 05:01:15 pm by Probeman »
The only stupid question is the one not asked!