[ RadSafe ] Tc-99m TVL for Concrete

[Aro, Jon]

Hi Radsafers, 
 
I am wondering is someone can give me the TVL for Tc-99m and concrete.
The value I have found through online searches is 66mm.  Calculations
using microshield indicate that this does not include buildup.
Including the buildup factors dramatically increases the TVL in concrete
to ~200 mm. 
 
I've also looked in Handbook of Health Physics & Radiological Health
(Shleien, B) to no avail.  Only the TVL for lead is listed. 
 
Any help would be appreciated. 

Thanks in advance,

Jon Aro
Associate RSO
The Ottawa Hospital