ABSORBED FRACTION TO THE CELL-NUCLEUS FOR LOW-ENERGY ELECTRONS

The absorbed fraction phi to the cell nucleus for low energy electrons (0.5 keV-50 keV) was evaluated, Distributions of radioactivity within either the nucleus (nu) and the cytoplasm (cy), or on the cell membra ne (mem) were considered, phi was computed as a function of the cell s izes and of the electron energy E. For a strictly intranuclear distrib ution, phi(nu) is close to 1 for very low energy values (E < 4 keV), i .e. the energy is totally absorbed in the cell nucleus itself, The abs orbed fraction decreases when the energy increases and phi(nu) becomes less than 0.1 for E greater than or equal to 40 keV. For a cell membr ane distribution, the absorbed fraction remains always less than 0.2, For very low energy electrons (E < 6 keV), phi(mem) = 0, due to the fa ct that the electron falls short to the nucleus target, The absorbed f raction is maximum for E ranging from 12 keV to 20 keV, For higher val ues of E, phi(mem) decreases when E increases, When considering a cyto plasmic distribution, the maximum absorbed fraction phi(cy) is obtaine d for E values ranging from 10 keV to 25 keV (phi(cy max) = 0.27). Dos imetric computations at the cellular level show that the absorbed frac tion to the cell nucleus may have values ranging from 0 to 1, dependin g on the dimensions of the cell, the energy of the emitted electron an d on the intracellular localization of the Auger emitter.