Permanently magnetized high gradient magnetic air filters for the nuclear industry

This paper describes the structure and testing of two novel permanently magnetized magnetic filters for fine radioactive material. In the first filter the holes in the filter are left open as capture proceeds which means the pressure drop builds up only slowly. This filter is not suitable for composite particles which can be broken by mechanical forces. The second filter has been changed so as to strongly capture particles composed of fine particles weakly bound together which tend to break when captured. This uses a principle of assisted capture in which coarse particles aid the capture of the fine fragments. These filters have the following characteristics: (1) no external magnet is required; (2) no external power is required; (3) small in size and portable; (4) easily interchangeable; (5) can be cleaned without demagnetizing by using a magnetic fluid which matches the susceptibility of the captured particles.