How Do PMT Mu Metal Shields Hold Up To Deformation?



The question is how well do mu metal shields work after they've been dropped, dented and completely deformed. Using a Hall probe and some old pmt mu metal shields we performed the following tests. Magnetic fields were measured with the Hall probe aligned vertically with the mu metal shields (the shields sitting as shown below). With this orientation the probe was nearly aligned with the Earth's magnetic field and read ~350 mGauss. Fields inside the shields were measured as nearly as possible to the centers of the shields.


Old Shield #1
Prior to any deformation -Magnetic Field = 11 mG
Hit with a hammer a few times -Magnetic Field = 13 mG
Hit with a hammer several times -Magnetic Field = 70 mG

Old Shield #2
Prior to any deformation -Magnetic Field = 3 mG
Dropped from ~3 feet -Magnetic Field = 6 mG
Hit with a hammer several times -Magnetic Field = 45 mG

Old Shield #3
Prior to any deformation-Magnetic Field = 5 mG
After denting one end -Magnetic Field = 13 mG
Hit with a hammer several times -Magnetic Field = 60 mG