RAD-12

Photoelectric absorption

τ ∝ Z⁴ / E³. Photoelectric cross section sketch between edges.

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AttenuationPhotoelectric

Governing equation

\tau\propto Z^4/E^3

where

Z: Atomic number (—)
E: Photon energy (keV)
\tau_0: Prefactor at Z=1, 1 keV (b)
\tau: Photoelectric (b)

Lecture brief

Historical brief

Beer attenuation, Compton (1923), Klein–Nishina, Bragg–Gray cavity and KERMA are the transport of photons and charged particles in matter. The sheets compute fluence, kerma and stopping. This sheet (RAD-12 — Photoelectric absorption) is the form associated with Photoelectric. Working symbols: $Z$ , $E$ , $\tau_0$ $\rightarrow$ $\tau$ . Jumps at K, L edges. High-Z contrast in kV imaging is this Z⁴.

Purpose

Purpose: compute

\tau

from

Z

E

\tau_0

in Radiation physics via

\tau\propto Z^4/E^3

τ ∝ Z⁴ / E³. Photoelectric cross section sketch between edges. Use it when a real radiation physics question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

Z = 53.000\,\mathrm{—}

E = 40.000\,\mathrm{keV}

\tau_0 = 0.050\,\mathrm{b}

, the governing relation

\tau\propto Z^4/E^3

yields

\tau = 6.164\,\mathrm{b}

. A photon, a K-shell, a photoelectron. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Atomic number Z53 —Photon energy E40 keVPrefactor at Z=1, 1 keV \tau_00.05 b

Outputs

Photoelectric \tau6.164 b

Reading speed

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Narration of this film

A photon, a K-shell, a photoelectron.

Jumps at K, L edges. High-Z contrast in kV imaging is this Z⁴.

Reading speed

Watch on YouTube