RAD-13

Rayleigh scatter sketch

σ_R ∝ Z² / E². Coherent scatter, no energy loss.

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AttenuationRayleigh

Governing equation

\sigma_R\propto Z^2/E^2

where

Z: Atomic number (—)
E: Photon energy (keV)
\sigma_0: Prefactor (b)
\sigma_R: Rayleigh (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-13 — Rayleigh scatter sketch) is the form associated with Rayleigh. Working symbols: $Z$ , $E$ , $\sigma_0$ $\rightarrow$ $\sigma_R$ . Forward-peaked. Important at low energy and high Z, never a dose channel of its own.

Purpose

Purpose: compute

\sigma_R

from

Z

E

\sigma_0

in Radiation physics via

\sigma_R\propto Z^2/E^2

σ_R ∝ Z² / E². Coherent scatter, no energy loss. 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 = 20.000\,\mathrm{—}

E = 20.000\,\mathrm{keV}

\sigma_0 = 0.020\,\mathrm{b}

, the governing relation

\sigma_R\propto Z^2/E^2

yields

\sigma_R = 0.0200\,\mathrm{b}

. A cloud of bound electrons, a gentle scatter. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Atomic number Z20 —Photon energy E20 keVPrefactor \sigma_00.02 b

Outputs

Rayleigh \sigma_R0.0200 b

Reading speed

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Narration of this film

A cloud of bound electrons, a gentle scatter.

Forward-peaked. Important at low energy and high Z, never a dose channel of its own.

Reading speed

Watch on YouTube