[1] HVL can also be expressed in terms of air kerma rate (AKR), rather than intensity: the half-value layer is the thickness of specified material that, "attenuates the beam of radiation to an extent such that the AKR is reduced to one-half of its original value.
In this definition the contribution of all scattered radiation, other than any [...] present initially in the beam concerned, is deemed to be excluded.
Quarter-value layer is the amount of specified material that reduces the air kerma rate (or exposure rate, exposure, air kerma, etc...) to one fourth of the value obtained without any test filters.
The HVL of sound waves is determined by both the medium through which it travels, and the frequency of the beam.
The TVL is the average amount of material needed to absorb 90% of all radiation, i.e., to reduce it to a tenth of the original intensity.