RAD-07

Build-up factor

I = B I₀ e^{−μ x}. Broad-beam transmission with scatter build-up B ≥ 1.

Reading speed

AttenuationBuild-up

Governing equation

I=B I_0 e^{-\mu x}

where

I_0: Entrance (Gy/s)
B: Build-up (—)
\mu: Attenuation (1/cm)
x: Thickness (cm)
I: Transmitted (Gy/s)

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-07 — Build-up factor) is the form associated with Build-up. Working symbols: $I_0$ , $B$ , $\mu$ , $x$ $\rightarrow$ $I$ . B grows with μx and scatter angle. Taylor and geometric-progression fits tabulate B.

Purpose

Purpose: compute

I

from

I_0

B

\mu

x

in Radiation physics via

I=B I_0 e^{-\mu x}

I = B I₀ e^{−μ x}. Broad-beam transmission with scatter build-up B ≥ 1. 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

I_0 = 1.000\,\mathrm{Gy/s}

B = 2.500\,\mathrm{—}

\mu = 0.150\,\mathrm{1/cm}

x = 5.000\,\mathrm{cm}

, the governing relation

I=B I_0 e^{-\mu x}

yields

I = 1.1809\,\mathrm{Gy/s}

. A slab, a narrow exponential, a broader B-boosted beam. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Entrance I_01 Gy/sBuild-up B2.5 —Attenuation \mu0.15 1/cmThickness x5 cm

Outputs

Transmitted I1.1809 Gy/s

Reading speed

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Narration of this film

A slab, a narrow exponential, a broader B-boosted beam.

B grows with μx and scatter angle. Taylor and geometric-progression fits tabulate B.

Reading speed

Watch on YouTube