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Sent: Sunday, January 19, 2020 11:19 AM
To: [email protected]
Subject: [XRF] Currency XRF Quiz

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Here’s Geo’s 1958 copper nickel in log space.? What do ?we have here?

Anyone?, anyone? Beuller?... Beuller?

Dud

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Since no one had a correct answer and undoubtedly the question will come up on any ?future final exams the answer is:

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First peak is the Si escape peak at 6.3 keV from Cu Ka at ?8.05 keV (8.05 Ka – 1.74 Si Ka)

The next 3 peaks are the characteristic X-rays from Ni Ka1 at 7.48, Cu Ka1 at 8.05, and Cu Kb1 at 8.9 keV

The next set ?of peaks (first clue) looks just like the Ni and Cu characteristic x-ray complex.? It does that because it’s the sum peaks of the Ni and Cu due to the high count rate (46% dead time remember) and high concentrations.

The first peak at 15.6 keV is the coincident sum peak of? 8.05 keV Cu and the 7.52 keV Ni

The second peak at 16.1 is the sum peak of the 8.05 Cu and 8.05 Cu

The third peak at 16.9 is the sum peak of the 8.05 Cu and the 8.9 Cu.

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Sum peaks are 2 photons arriving at the detector at the same time. That can be a Ka+Ka or Ka + Kb and a mix between high concentration elements as seen here. This can also be seen with coincident decay (i.e. Co-60) and in high concentration samples with a high count rate.. Keep the sample at a distance rather than close up (for an gamma spec sample not XRF). Keep your Dead time less than 10%.

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The escape peaks occur when the Si in the detector absorbs some of the energy from an x-ray and produces a peak (Si Ka) 1.74 keV below the element’s ?Ka or La . You’ll see this in the lower Z elements or at high concentration.

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Dud

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Here’s Geo’s 1958 copper nickel in log space.? What do ?we have here?

Anyone?, anyone? Beuller?... Beuller?

Dud

?