RAD-09

Half-value layer

HVL = ln 2 / μ. Thickness that halves a narrow beam.

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AttenuationHVL

Governing equation

\mathrm{HVL}=\ln 2/\mu

where

\mu: Linear attenuation (1/cm)
HVL: Half-value layer (cm)

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-09 — Half-value layer) is the form associated with HVL. Working symbols: $\mu$ $\rightarrow$ $HVL$ . n HVLs give 2^{−n}. Broad-beam HVL is larger because of scatter.

Purpose

Purpose: compute

HVL

from

\mu

in Radiation physics via

\mathrm{HVL}=\ln 2/\mu

HVL = ln 2 / μ. Thickness that halves a narrow beam. 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

\mu = 0.400\,\mathrm{1/cm}

, the governing relation

\mathrm{HVL}=\ln 2/\mu

yields

HVL = 1.733\,\mathrm{cm}

. Stacked slabs, a beam halved each time. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Linear attenuation \mu0.4 1/cm

Outputs

Half-value layer HVL1.733 cm

Reading speed

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Narration of this film

Stacked slabs, a beam halved each time.

n HVLs give 2^{−n}. Broad-beam HVL is larger because of scatter.

Reading speed

Watch on YouTube