Stopping power of water for protons in the range 1--4 MeV.
The stopping power of liquid water was measured for the first time with 3.4 MeV protons with an innovative water target of thickness 50 $\mu$m. The experiment was performed at the 3MV Tandem Accelerator of Napoli University "Federico II". It provides stable proton beams up to 6 MeV. The result of the measured stopping power is in contrast with the major part of data in the literature, computed with the most used stopping power tools and database (NIST, SRIM/TRIM, LISE++). This measurement is of great interest, due to the importance of stopping power data in adrontherapy and the surprising lack of experimental data in the Bragg Peak region.