Aims. We study the physical properties of an active region (AR) jet in order to probe the mechanisms responsible for it. Methods. We report 2007 January 15/16 observations of a recurring jet situated on the west side of NOAA AR 10938. Multiwavelength data from all three instruments onboard Hinode were analysed. This paper focuses on one instance of a jet observed with the Hinode/EUV Imaging Spectrometer (EIS). Using EIS raster data we measured the temperatures, Doppler shifts, density, and

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... ng factor. Results. A strong blue-shifted component and an indication of a weak red-shifted component at the base of the jet was observed around Log T e = 6.2. The up-flow velocities exceeded 150 km s −1 . The jet component was seen over a range of temperatures between 5.4 and 6.4 in Log T e . Using Fe xii λ186 and λ195 line ratios, we measured densities above Log N e = 11 for the high-velocity up-flow component. We found that the density of the high-velocity up-flow increases with velocity. We estimate the filling factor in the jet upflow to be <0.03. With the Hinode/Solar Optical Telescope (SOT), we observed recurrent (quasi periodic) magnetic flux cancelations just before the recurrent jet emission was seen in images taken with the X-ray Telescope (XRT). Conclusions. The high-velocity up-flows, together with the density dependence on velocity, support an evaporation scenario for the acceleration of this jet. The high density and small filling factor, coupled with the high Doppler velocities are strongly suggestive of multiple small-scale magnetic reconnection events being responsible for the production of both EUV and X-ray jets.