The stopping power of water, water vapour and aqueous tissue equivalent solution for alpha particles over the energy range 0.5-8 MeV

Experimental stopping power values are presented. The molecular stopping power of water is found to be significantly lower than that of water vapour at energies below 1.5 MeV and above 2.5 MeV. These results are compared with calculated stopping power values and discussed particularly with reference to the charge state of the alpha particle at various energies. The stopping power values for tissue equivalent liquid are found to be lower in general than calculated values or values obtained from tissue equivalent gases or solids except in the 2.5 to 3.25 MeV energy region. (author)