RAD-18

Linear energy transfer

LET_Δ = (dE/dl)_Δ. Restricted stopping, δ-rays below cutoff Δ kept local.

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DosimetryLET

Governing equation

\mathrm{LET}=dE/dl

$dl \in \left[0.05, 40\right]$

where

dE: Energy in cutoff (keV)
dl: Path (µm)
LET: LET (keV/µm)

The figure, part by part

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①

Governing law — red

\mathrm{LET}=dE/dl

$dl \in \left[0.05, 40\right]$

$dl = 0.05$ $LET = 400$

Along the curve

②

Domain of the variable — blue

dl_{\min} = 0.05,\quad dl_{\max} = 40

$dl \in \left[0.05, 40\right]$

$dl = 0.05$ $dl = 0.05$

Along the curve

③

Response curve — green

\mathrm{LET}=dE/dl

$dl \in \left[0.05, 40\right]$

$dl = 0.05$ $LET = 400$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}LET}{\mathrm{d}dl}

$dl \in \left[0.05, 40\right]$

$dl = 0.301$ $LET^{\prime} = -724$

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-18 — Linear energy transfer) is the form associated with LET. Working symbols: $dE$ , $dl$ $\rightarrow$ $LET$ . RBE rises with LET to ~100 keV/µm then falls (overkill). ICRP uses this for quality.

Purpose

Purpose: compute

LET

from

dE

dl

in Radiation physics via

\mathrm{LET}=dE/dl

LET_Δ = (dE/dl)_Δ. Restricted stopping, δ-rays below cutoff Δ kept local. 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

dE = 20.000\,\mathrm{keV}

dl = 1.000\,\mathrm{\mu m}

, the governing relation

\mathrm{LET}=dE/dl

yields

LET = 20.00\,\mathrm{keV/\mu m}

. A track, a dense core of ionisations. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Energy in cutoff dE20 keVPath dl1 µm

Outputs

LET LET20.00 keV/µm

Reading speed

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Narration of this film

A track, a dense core of ionisations.

RBE rises with LET to ~100 keV/µm then falls (overkill). ICRP uses this for quality.

Reading speed

Watch on YouTube