Production of 239 Pu from a natural Uranium disk and "hot" rock using a   neutron howitzer
  A neutron howitzer was used to produce 239Np from the targets of natural U and a hot rock. An intrinsic Germanium detector enabled the observations of the gamma rays in the decay of 239Np and a determination of its half life of 2.3 days. This shows that 239Pu had been produced in both targets 
Joseph Steiner, Aaron Anderson and Michael De Marco