Re: shielding for Sr90 sealed source

[AndrewsJP@AOL.COM]

Bob.Westerdale@ametek.com wrote:


<<...The source vendor has advised me to shield the betas wherever possible, with 10-20 cm of acrylic,  but I'm troubled by the rather energetic scatter-  whose energy will be a continuum from approximately 2.3 Mev and down....    Our calculations say that about 2" of lead will bring this down to a couple of mR/hr, ... >>



Sounds to me like the vendor recommended 10 - 20 mm, or less than 1 inch of acrylic.  Then use some lead to reduce the lower energy bremstrahllung.  It doesn't take very much low z plastic material to do the attenuation of betas.  They do not penetrate in the same manner as gammas.  Do the calc.  Use the Rad Health Handbook.  I did and got about 0.35 inches from the graph of Penetration Ability of Beta Radiation for 2.3 MeV beta particles in my old 1970 copy of the book.  Note that most of these particles are much less energetic than 2.3 MeV.


This size shield is small enough to try without great expense.  Try it and see if it works.  (You could even use paraffin for the trial.)


John Andrews

Knoxville, Tennessee