We describe very accurate imaging of radio spectral index for the inner jets in three FRI radio galaxies .
Where the jets first brighten , there is a remarkably small dispersion around a spectral index of 0.62 .
This is also the region where bright X-ray emission is detected .
Further from the nucleus , the spectral index flattens slightly to 0.50 - 0.55 and X-ray emission , although still detectable , is fainter relative to the radio .
The brightest X-ray emission from the jets is therefore not associated with the flattest radio spectra , but rather with some particle-acceleration process whose characteristic energy index is 2.24.The change in spectral index occurs roughly where our relativistic jet models require rapid deceleration .
Flatter-spectrum edges can be seen where the jets are isolated from significant surrounding diffuse emission and we suggest that these are associated with shear .