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SCIENTIFIC ABSTRACT: We propose to perform deep imaging of the cores of clusters of galaxies at redshifts in the range 0.2 < z < 1.0 and which have already been observed at other wavelengths. The objective is to look for evidence of evolution in the general galactic population of clusters, for example in the frequency and luminosity of mergers, interactions and starbursts, by using mid and far IR colours and luminosities. We will perform imaging with ISOCAM in two wavebands (5-8.5 and 12-18 microns),and with PHOT-C in two other wavebands, 90 and 200 microns. With ISOCAM, we expect to detect the brightest cluster members, while with PHOT we will measure the integrated light of the cluster. Comparison with optical, radio and NIR data obtained by ground based observations will then provide a very large database for statistical studies, that will be a useful complement to the ISOCAM Deep Survey. OBSERVATION SUMMARY: All the ISOCAM observations will be performed in the microscanning mode. For z < 0.4 we will use displacements of 6 pixels of 6 arcsec; the area covered twice will be close to 5'x5'. We will spend up to 6000 sec per filter. We expect to reach S/N = 4 on sources of 0.05 mJy with LW2 and 0.2 mJy with LW3. For z > 0.4, we will use the same type of raster but with a PFOV of 3 arcsec. The area covered twice will be of 2.5'x2.5'. For z > 0.6 the displacements will be of only 4 pixels. Then, an area of 1'x1' will be covered 4 times, but the area observed is 4 times as large. Typical observing times per raster will be of 5 to 6000 sec, allowing to observe sources of 0.03 mJy with LW2 and 0.12 mJy with LW3, with S/N = 4. The axis of all the rasters will be aligned with the spacecraft axis. As a complement, all clusters will be observed with PHOT in the camera mode, using the chopper with a beam throw of 180". We will use C100 with the 90 micron filter, and C200 with the 200 micron filter. For z of order 0.2, we will perform a raster of 3x3 positions, displacing the array by steps of 1.5' in both directions, covering a field of 4.5'x4.5'. For higher z clusters, we will just take an image over a 3'x3' field of view. We intend to stay more than 10 min on the source with each filter, changing the position by 20" in the middle of the observation. In both channels, we expect to go beyond the confusion limit (> 1 mJy at 90 microns, and > 10 mJy at 200 microns), and aim to measure the integrated light from the cluster.