Answer to Question #11009 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Shielding

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

Answer posted on 16 June 2014. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.