Answer to Question #11009 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I have seen the half-value layer (HVL) or tenth-value layer (TVL) data in many sources. However, I do not know if the value of a HVL or TVL was calculated with the given thickness of the shielding material factored in (as a distance from the source to the target). Do I need to consider the shielding material thickness in the shielding calculation or disregard it because it already accounted for in the given HVL or TVL?
The half-value layer (HVL) and the tenth value layer (TVL) of an attenuator do not change the distance between the source and the point of measurement, but are inserted between the two. For example, the source and the point of measurement may be two meters apart. The attenuating material would then be placed between them without moving either.
Bruce R. Thomadsen, CHP