We report on particle detection experiments using aluminum superconducting transition edge sensors deposited on silicon wafers. The detectors consist of a 40 nm thick aluminum film patterned as a labyrinth with 299 lines. These films have Tc~1.35 K and Ic~8 µA at 1.30 K. New data have been obtained using a thin encapsulation 241Am alpha source (~1% FWHM source linewidth for 5.5 MeV) which allows a detailed study of these sensors. With a bias current of 1.2 µA at 1.33 K, 0.4 mV pulses 1.5 µs long are obtained for alpha particles incident directly on the aluminum film. The pulse height distributions are strongly peaked (~7% FWHM) and temperature dependent. In a second series of experiments, we have used the same alpha source to bombard the back of the silicon wafer (275 µm thick). With an alpha range of 25 µm, only the phonons generated by the alpha can produce the observed pulses in the aluminum film, demonstrating phonon mediated particle detection.