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Re: [Phys-l] Gamma-Gamma Coincidence



K-beta-2 x-rays become more than 100 keV at atomic number 87 (Fr), and K-alpha-1 x-rays become more than 100 keV at atomic number 93 (Np). The highest-energy x-ray listed in the table at the link given below is 156.2 keV for atomic number 104 (Rf).

The K-beta x-rays for these elements actually are not "weak." For Uranium atoms having a K vacancy, the x-ray will be one of the K-beta x-rays about 22% of the time, and therefore above 100 keV about 22% of the time. This percentage is typical for atoms near the end of the periodic table.

The energy difference between K-alpha and K-beta for thorium is high enough, and the K-beta is prevalent enough, that when we count the photons from a natural uranium sample we can "see" both thorium x-ray "peaks" in the spectrum obtained with our NaI detector. The detector cannot fully resolve the two (and of course both "lines" are really multiple lines), but we definitely see the K-beta multiplet as a bump on the high-energy side of the K-alpha multiplet.

Here is the link to a good table of x-ray energies and intensities...

http://ie.lbl.gov/atomic/x2.pdf


Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
1 University Drive
Bluffton, OH 45817
419.358.3270
edmiston@bluffton.edu


--------------------------------------------------
From: "Bernard Cleyet" <bernardcleyet@redshift.com>
Sent: Monday, March 29, 2010 2:06 AM
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Subject: Re: [Phys-l] Gamma-Gamma Coincidence

The K absorption edge of both Th and U is greater than 100keV. I suppose the emission at that energy is very weak.

The U Kb1 line is 111.3 keV.

http://www.epsci.ameslab.gov/etd/technologies/projects/xray/K-edge_final_report.pdf

bc thinks the 100 keV definition is rather arbitrary.