Shielding of the earths magnetic field

Usually, the solid-angle factor Q00 is treated separately in this expression by introducing attenuation factors defined by 

This result states that the form of the angular correlation pattern measured with finite acceptance angles differs from that for a point-like detector only through attenuation factors which can be calculated for the given experimental set-up. 

The quantity which characterizes the shielding effect of /i-metal boxes is called the shielding factor S. It is defined by the ratio of outer to inner field strength (see Fig. 10.7), 

For a static magnetic field and a sphere with inner and outer diameters, D and D0, respectively, this shielding factor can be calculated giving [VAC75] 

When d is the thickness of /i-metal, with d D0, this result can be approximated as 

respectively, this shielding factor can be calculated giving [VAC75] 

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