tenthvalue

Tenth-value layer, abbreviated TVL, is a term used in radiological protection to describe the shielding effectiveness of a material against gamma and x-ray radiation. It is defined as the thickness of a given material required to reduce the radiation intensity by a factor of ten, corresponding to a 90 percent attenuation, for a specific radiation energy.

TVL is energy-dependent and material-dependent, so different photon energies and shielding materials have different TVL values. In practice, shielding designers consult published TVL tables or curves for common materials such as lead, concrete, or steel to determine the required thickness for a given protection level. The attenuation behavior is often represented by an approximate exponential relation, where the transmitted intensity I after a shielding thickness t is I = I0 × 10^(−t/TVL), with I0 the incident intensity.

From this relationship, the required thickness can be computed as t = TVL × log10(I0/I). TVL is related to, but distinct from, the half-value layer (HVL), which corresponds to a 50 percent reduction. For the same material and energy, the TVL is larger than the HVL because a tenfold reduction generally requires more shielding than a fivefold reduction.

Applications of TVL include the design of radiation shielding in medical radiography rooms, CT suites, radiotherapy vaults, nuclear power plants, and industrial radiography facilities. TVL values are a practical shorthand for assessing shielding needs, though real-world designs may account for mixed radiation fields and geometric considerations.