Our search for magnetic monopoles in lunar materials has been concluded with the exploration of an additional 11.5 kg of material returned by the Apollo 11, 12, and 14 missions, using a modified version of our electromagnetic detector. Again, no magnetic monopole was detected. Combining these results with the results of our previous experiment, we set an upper limit of 1.7×${10}^{-4\mathrm{}}$ monopoles/g for the density of isolated monopoles in the lunar surface and improve our upper limits set for the monopole flux in cosmic rays and for monopole pair-production cross section.

• Received 23 April 1973

DOI:https://doi.org/10.1103/PhysRevD.8.698