A reactor comprising an annular iron core constituting a closed magnetic path and a conductor wound on the annular core, said iron core being formed of particles of iron or an iron based magnetic material each covered with {HEAD ~ an insulative oxide film} which contains {TAIL ~ 0.3 to 0.8%} of oxygen by weight based on the particle 
contains
A reactor comprising an annular iron core constituting a closed magnetic path and a conductor wound on the annular core , said iron core being formed of particles of iron or an iron based magnetic material each covered with { HEAD ~ an insulative oxide film } which contains { TAIL ~ 0.3 to 0.8 % } of oxygen by weight based on the particle
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