  In this paper we present the measurement of the response of 50 $\mu$m thin
diamond detectors to 14 MeV neutrons. Such neutrons are produced in fusion
reactors and are of particular interest for ITER neutron diagnostics. Among
semiconductor detectors diamond has properties most appropriate for harsh
radiation and temperature conditions of a fusion reactor. However, 300-500
$\mu$m thick diamond detectors suffer significant radiation damage already at
neutron fluences of the order of $10^{14}$ n/cm$^2$. It is expected that a 50
$\mu$m thick diamond will withstand a fluence of $>10^{16}$ n/cm$^2$. We tested
two 50 $\mu$m thick single crystal CVD diamonds, stacked to form a "sandwich"
detector for coincidence measurements. The detector measured the conversion of
14 MeV neutrons, impinging on one diamond, into $\alpha$ particles which were
detected in the second diamond in coincidence with nuclear recoil. For
$^{12}C(n,\alpha)^{9}Be$ reaction the total energy deposited in the detector
gives access to the initial neutron energy value. The measured 14 MeV neutron
detection sensitivity through this reaction by a detector of effective area
3$\times$3 mm$^2$ was $5\times 10^{-7}$ counts cm$^2$/n. This value is in good
agreement with Geant4 simulations. The intrinsic energy resolution of the
detector was found to be 240 keV FWHM which adds only 10 % to ITER's 14 MeV
neutron energy spread.
