  The $^{12}$C(n, 2n)$^{11}$C cross section was measured from just below
threshold to 26.5 MeV using the Pelletron accelerator at Ohio University.
Monoenergetic neutrons, produced via the $^3$H(d,n)$^4$He reaction, were
allowed to strike targets of polyethylene and graphite. Activation of both
targets was measured by counting positron annihilations resulting from the
$\beta^+$ decay of $^{11}$C. Annihilation gamma rays were detected, both in
coincidence and singly, using back-to-back NaI detectors. The incident neutron
flux was determined indirectly via $^{1}$H(n,p) protons elastically scattered
from the polyethylene target. Previous measurements fall into upper and lower
bands, the results of the present measurement are consistent with the upper
band.
