The charge collection performance of a diamond-graphite detector is reported. Buried graphite pillars with high aspect ratio were formed inside a single crystal synthetic diamond slab by using a femtosecond IR laser with 200 kHz of repetition rate. Grouped in two series and connected by graphite strips on the surface, eight independent 3D electrodes were used to collect the charge carriers generated by energy deposited in the detector. Collimated 90Sr,Y b-particles were used to test the charge collection in coincidence and self-triggering mode among pillars rows using different irradiation geometries. The charge collected by one pillar row saturates at 1.40±0.02 fC at ±0.67V/?m with electrons impinging orthogonally the rows demonstrating a high charge carrier collection efficiency.