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 membrane (mem) were considered. phi was computed as a function of the cell sizes and of the electron energy E. For a strictly intranuclear distribution, 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 absorbed fraction decreases when the energy increases and phi(nu) becomes less than 0.1 for E > or = 40 keV. For a cell membrane distribution, the absorbed fraction remains always less than 0.2. For very low energy electrons (E < 6 keV), phi(mem) = 0, due to the fact that the electron falls short to the nucleus target. The absorbed fraction is maximum for E ranging from 12 keV to 20 keV. For higher values of E, phi(mem) decreases when E increases. When considering a cytoplasmic distribution, the maximum absorbed fraction phi(cy) is obtained for E values ranging from 10 keV to 25 keV (phi(cy max) = 0.27). Dosimetric computations at the cellular level show that the absorbed fraction to the cell nucleus may have values ranging from 0 to 1, depending on the dimensions of the cell, the energy of the emitted electron and on the intracellular localization of the Auger emitter.