Patent ID: 7176386

Claim:
A magnetically shielded container ( 1 ) having disposed in parallel opposed position on an axis (S) thereof magnetic field homogenizing pole shoes ( 10 . 1 , 10 . 2 ), having disposed about said pole shoes a magnetically shielding yoke ( 2 ), said-pole shoes and yoke enclosing a magnetic chamber ( 26 ), said container further comprising magnetic field sources ( 2 . 4 , 2 . 5 ) disposed about and radially distanced from said axis whereby there exists within said chamber substantially homogeneous magnetic field B o oriented in the direction of said axis and whereby there is a usable volume within said chamber where the ratio of the magnetic field gradient in the direction transverse to said axis to said magnetic field B o has a value of no more than 1.5×10 −3 /cm.