Which Photon Buildup Model in Shielding is Most Reliable?

[GammaScanner]

Who do you believe?

I'm doing some shielding calcs for Cs-137 (662 KeV gamma) in stainless steel (Fe seems close enough) with ux (mfp) in the range of 5 to 15.

Shultis and Faw in Radiation Shielding (2000) treat Photon buildup pretty well.

Their coefficients for the Berger approximation agree pretty well with the tables in Martin's Physics for Radiation Protection. (2006) A lot better than the single and double term Taylor forms.

But Shultis and Faw say the Berger may be off by up to 45%. Glasstone and Sesonske (4th ed) say the Berger is more accurate than the Taylor.

Shultis and Faw say the Geometric Progression approximation is the cat's meow, but they don't treat it well enough for me to get a handle on it.

Is there a generally accepted table of buildup factors, or formula and coefficients, for photon buildup in shielding that most people use or accept as standard?

Is there a good description of the Geometric Progression Approximation available on the web somewhere?

For now I'm using the Berger approximation.

Thanks!

 

[daveb]

A lot of health physicists use tables from the Handbook of Health Physics and radiological Health edited by Shlein as a rough approximation, and then add an additional HVL or TVL (depending on what they're shielding) just to be sure. With a mfp between 5 and 15, the tables give a relatively lrge range of buidlup factor. For example, 5 mfp gives a buildup between 6.74 and 7.68. For 15 mfp, the factor is 27.5 to 35.1.