Modular Lead Shield for 2" detectors

How to build the perfect shield for your measurements? Discuss it here!
Sparky
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Joined: 01 Dec 2019, 13:58
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Re: Modular Lead Shield for 2" detectors

Post by Sparky » 24 Jun 2020, 08:06

I have seen a peak around 30 with all my Fiestaware and U glass spectrums and have racked my brain trying to figure out what it was. Now I know. Iodine x-rays.

Thanks!
Michael Loughlin

cicastol
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Re: Modular Lead Shield for 2" detectors

Post by cicastol » 26 Jun 2020, 02:19

Sparky wrote:
24 Jun 2020, 08:06
I have seen a peak around 30 with all my Fiestaware and U glass spectrums and have racked my brain trying to figure out what it was. Now I know. Iodine x-rays.

Thanks!
No, it isn't the iodine x-ray, normally, under 200keV in the photoelectric effect region, the Ka1 28.6 keV x-ray line of the Iodine escape the detector and is removed from a photopeak, this is a known effect called Iodine escape peak that happen with the NaI detectors.
Remember that below 100keV NaiTl are non linear and with really poor resolution , so looking in this region should be taken with a grain of salt.....

If you have an unknown 30 keV peak you should look at a photopeak at near 60 keV
Ciro

Sparky
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Joined: 01 Dec 2019, 13:58
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Re: Modular Lead Shield for 2" detectors

Post by Sparky » 26 Jun 2020, 08:00

Ciro,

Thanks much for the correction. I understand. Internal to the detector, it would have to be an escape peak. Uranium 238 has a Th234 photopeak at 63.3 that might be a candidate, although the difference would be about 34 and this looks more like 30-32. It lines up at about the same energy as the Ba Ka1 peak from Cs137.

My 38mm probe does pretty well down there for NaI. The attached spectrum show the KA1 lines for Ag and Cd, Am241 (the xrf exciter used) and the Am241 Compton backscatter peak at 48, all pretty much where they should be. The spectrum with the 48keV peak also has a peak at about 20 that I don't know what it is. Possibly an Iodine escape peak?
Attachments
Am241+Ag+Cd+Rum.png
Michael Loughlin

Mike S
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Joined: 25 Apr 2020, 10:24
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Re: Modular Lead Shield for 2" detectors

Post by Mike S » 26 Jun 2020, 16:57

cicastol wrote:
26 Jun 2020, 02:19

No, it isn't the iodine x-ray, normally, under 200keV in the photoelectric effect region, the Ka1 28.6 keV x-ray line of the Iodine escape the detector and is removed from a photopeak, this is a known effect called Iodine escape peak that happen with the NaI detectors.
Remember that below 100keV NaiTl are non linear and with really poor resolution , so looking in this region should be taken with a grain of salt.....

If you have an unknown 30 keV peak you should look at a photopeak at near 60 keV
Thank you. That makes sense. I'll have to study up on this a bit more.
Mike Sullivan
Central Coast of California, USA

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