<a href="http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20693.pdf" class="externalURL" rel="nofollow" target="_blank">pnnl.gov/main/publications/ext…al_reports/PNNL-20693.pdf</a>
Cosmic Ray Interactions in Shielding Materials
A interesting behavior is revealed in the shielding behavior of low energy muons by high Z materials
A meter thick shield of iron and lead produces an increase in muons (0 to 20 MeV) passing through the high Z shield. See table 7 (Iron) and table 10(lead).
It looks to me like shielding does not materially effect low energy muons.
On page 85 is combined effect. It seems your increase claim is false (atleast cosmic muons)
When low energy / thermalized/stopped muons don't move further in their livetime (speak only cm scale).
It is true that in high energy (cosmic) muons (100Mev-10Gev) secondary radiation is higher in 10-20cm Fe/Pb shields.
But you must remember:
- they are cosmic muons, so lifetime near end when ground level
- it is broad spectrum, 10-20cm slow/stop 100- ~340Mev muons and secondary radiation appear.
There we suppose that max energy level is not 10Gev, however my GM tube test is blind for high energy muons, because lack of needed shielding material. But extra 40mm Pb decreased counts near BG level so IF energy spectrum was continous then generated muons <200Mev. But if there was some high energy spikes method was blind for them.
And if there was some pions etc. I have no idea how it behave. May tunnel outside shields easilly an do strange things.