In previous experiments at ILL we observed a gap in the magnetic excitation spectrum of the stripe-ordered superconductor (La,Nd)2-xSrxCuO4, x=0.12. We observed a spin gap of 1.5meV in the normal state, and an increased cap of 3.5meV in the superconducting state. We wish to determine the origins of this gap. To do this we propose to separate the different spin fluctuation components Sxx and Szz, to find out whether they follow the same energy dependence above and below the gap. The measurement makes use of the new LET spectrometer to obtain simultaneously detailed lineshape information at a number of incommensurate satellite peaks around (1/2,1/2,0)-type wavevectors over the full range of interest in energy. The measurement requires both high resolution and a wide dynamic range, features unique to LET.