New limit set on cosmic-ray monopole flux by a large-area superconducting magnetic-induction detector

A search for cosmic-ray magnetic monopoles has been conducted using a fully coincident superconducting induction detector consisting of six independent high-order gradiometer coils forming the surfaces of a rectangular parallelepiped. The detector had an effective area for isotropic flux averaged over 4π sr of 1.0 ${\mathrm{m}}^2$. Data have been collected from October 1986 to January 1989 with an accumulated live time of 13 410 h. No monopole candidate events were seen, setting a new lower monopole flux limit for induction detectors of 3.8×${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{s}}^{\mathrm{-}1}$ ${\mathrm{sr}}^{\mathrm{-}1}$ at the 90% confidence level.