Neutron Absorber & Shield

[Joe Gayo]

Anthony,

Out of curiosity, where do you work?

Joe

[Dennis P Brown]

Interesting graph; those jumps - wonder if they are transitions to the next shell in energy?

[Rich Gorski]

Dennis,Yes. Those sudden jumps in the Mass atten coef are jumps to another quantum state. Known as "edge absorption" which most often occurs at the inner most electron shell (K shell). When the X-ray photon energy is just above the shell binding energy the greatest absorption occurs. The photon with energy just above the binding energy will have a greater chance of being absorbed and kicking an electron to another quantum state. The photon with energy just below the binding energy is unlikely to kick an electron to another quantum state. Thus the sudden jump in the coefficient just above the binding energy. So we can say the energy level at the jump corresponds to a transition energy. It appears that lead has several of these absorption edges over the range of energy shown.

Rich G.

[Rich Feldman]

Yes, what Rich said. in fact the threshold transitions are identified in the tabular source data, with two attenuation values at the same frequency.
The link above my chart is to the NIST page for lead.
M5, M4, M3, M2, M1 from 2.48 to 3.85 keV.
L3, L2, L1 from 13.0 to 15.9 keV
K at 88 keV.

The K transition for Al appears in our chart at 1.56 keV.
A different reference says "the K shell energy of carbon is only 0.28 keV."