Knock-on electrons produced by muons of different energies have been investigated in lead and copper with a cloud chamber by coincidence and anticoincidence technique. The probability of their production in lead is (5.82 & 0.71)y0 per 1.27 cms P b and in copper (7.64 & 0.59)% per 1.27 oms Cu. Angles of emergent secondaries in P b follow a cos'.' 0 distribution and in Cu a COS* 0 distribution.
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