  We studied the $^{12}$C(p,2p+n) reaction at beam momenta of 5.9, 8.0 and 9.0
GeV/c. For quasielastic (p,2p) events we reconstructed {\bf p_f} the momentum
of the knocked-out proton before the reaction; {\bf p_f} was then compared
(event-by-event) with {\bf p_n}, the measured, coincident neutron momentum. For
$|p_n|$ > k$_F$ = 0.220 GeV/c (the Fermi momentum) a strong back-to-back
directional correlation between {\bf p_f} and {\bf p_n} was observed,
indicative of short-range n-p correlations. From {\bf p_n} and {\bf p_f} we
constructed the distributions of c.m. and relative motion in the longitudinal
direction for correlated pairs. After correcting for detection efficiency, flux
attenuation and solid angle, we determined that 49 $\pm$ 13 % of events with
$|p_f|$ > k_F had directionally correlated neutrons with $|p_n|$ > k$_F$. Thus
short-range 2N correlations are a major source of high-momentum nucleons in
nuclei.
