Half-value layer

Half-value layer (HVL) is the width of a material required to reduce the air kerma of an x-ray or gamma-ray to half its original value. This applies to narrow beam geometry only as broad-beam geometry will experience a large degree of scatter, which will underestimate the degree of attenuation

It is an indirect measure of photon energy or the hardness of a beam. HVL is measured in millimetres of aluminium. 

It is related to linear attenuation coefficient (μ) with following formula:

  • HVL = 0.693 / μ

Related articles

Share article

Article information

rID: 22271
Section: Physics
Tag: cases
Synonyms or Alternate Spellings:
  • HVL

Support Radiopaedia and see fewer ads

Updating… Please wait.

Alert accept

Error Unable to process the form. Check for errors and try again.

Alert accept Thank you for updating your details.