Decompositions and extremal type II codes over Z4

In precious work by Huffman and by Yorgov, a decomposition theory of self dual linear codes C over a finite field F-q is given when C has a permutation automorphism of prime order r relatively prime to q. We extend these results to linear codes over the Galois ring Z(4) and apply the theory to Z(4)-codes of length 24. In particular we obtain 42 inequivalent [24, 12] Z(4)-codes of minimum Euclidean weight 16 which lead to 42 constructions of the Leech lattice.