RAD-24

CPE dose–kerma link

D = K (1 − g) under charged-particle equilibrium. Radiative fraction g.

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DosimetryCPE

Governing equation

D=K(1-g)

$K \in \left[0.01, 20\right]$

where

K: KERMA (Gy)
g: Radiative fraction (—)
D: Dose under CPE (Gy)

The figure, part by part

Each numbered marker wears the color of its card. Hover a card to light the marker. Tap a marker to jump to that card. The slider walks a red point along the curve; Animate drawing traces it like a pen.

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①

Governing law — red

D=K(1-g)

$K \in \left[0.01, 20\right]$

$K = 0.01$ $D = 0.01$

Along the curve

②

Domain of the variable — blue

K_{\min} = 0.01,\quad K_{\max} = 20

$K \in \left[0.01, 20\right]$

$K = 0.01$ $K = 0.01$

Along the curve

③

Response curve — green

D=K(1-g)

$K \in \left[0.01, 20\right]$

$K = 0.01$ $D = 0.01$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}D}{\mathrm{d}K}

$K \in \left[0.01, 20\right]$

$K = 0.136$ $D^{\prime} = 0.997$

Along the curve

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-24 — CPE dose–kerma link) is the form associated with CPE. Working symbols: $K$ , $g$ $\rightarrow$ $D$ . g is a few percent in tissue at MV energies, tiny at kV. Transient CPE in build-up.

Purpose

Purpose: compute

D

from

K

g

in Radiation physics via

D=K(1-g)

D = K (1 − g) under charged-particle equilibrium. Radiative fraction g. 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

K = 2.000\,\mathrm{Gy}

g = 0.003\,\mathrm{—}

, the governing relation

D=K(1-g)

yields

D = 1.9940\,\mathrm{Gy}

. A kerma bar, a slightly smaller D. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

KERMA K2 GyRadiative fraction g0.003 —

Outputs

Dose under CPE D1.9940 Gy

Reading speed

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Narration of this film

A kerma bar, a slightly smaller D.

g is a few percent in tissue at MV energies, tiny at kV. Transient CPE in build-up.

Reading speed

Watch on YouTube