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Shielding Half Value Layer Calculator

Work out shielding half value layer instantly with clear inputs, formula shown and shareable results.

About Shielding Half Value Layer Calculator

Shielding follows exponential attenuation, I = I0 exp(-mu.x), so the half-value layer is ln2/mu. With mu = 0.7 per cm the HVL is 0.99 cm, and 5 cm of shield is just over five HVLs, cutting the beam to 3% - an attenuation factor of 33. Exponential decay means there is no thickness that stops radiation completely.

Formulas

Exponential attenuation

I = I0 exp(-mu x)

Half-value layer

HVL = ln2 / mu

Worked example

With the default values below, Shielding Half Value Layer Calculator returns Half-Value Layer of 0.9902. Change any input above and every figure here is recalculated in your browser.

Inputs used

Linear attenuation coefficientminimum 0 1/cm
0.7 1/cm
Shield thicknessminimum 0 cm
5 cm

Results

Half-Value Layer
0.9902 cm
Radiation Transmitted
3.0197%
Attenuation Factor
33.12
Half-Value Layers Of Shielding
5.049

Step by step

  1. 1Values used
  2. 2Exponential attenuation
  3. 3Half-value layer
  4. 4Half-Value Layer= 0.9902 cm
  5. 5Radiation Transmitted= 3.0197
  6. 6Attenuation Factor= 33.12
  7. 7Half-Value Layers Of Shielding= 5.049

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why can radiation never be fully stopped?

Because attenuation is exponential - each layer removes a fixed fraction, not a fixed amount. Practical shielding aims for an acceptable dose rate, not zero.

What is lead's half-value layer for typical gamma rays?

About 12 mm for cobalt-60 gammas at 1.25 MeV, and only 0.1 mm for diagnostic X-rays, which is why thin lead aprons work.

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