Specific energies in cell nuclei from incorporated isotopes: computer calculations for plutonium-239

A model has been developed for calculating the amounts of energy deposited by incorporated isotopes in cell nuclei. For 239Pu, the assumption was made that one particle of 5.14-MeV energy is emitted per decay and that the mean range of the particle in water is 40 μm. The decaying nuclei are thought to be compiled into point sources delivering one decay per second. The distribution of the sources is uniform throughout the tissue. The specific activity Asub(s) is given by the number of sources per gram. The sources are located in the centres of spherical cells and cell nuclei of 10 and 8 μm diameter respectively. They emit homogeneously into the solid angle 4π. This is possible by adding up decays for a sufficiently long period of time. The minimum time considered sufficiently long is 5.236 min. This is equivalent to 100π particles or one particle average per μm2 of the cell surface. For the cells, a close-packed structure in tissue has been assumed. This gives √2 x 109 cells per gram. Specific energies z refer to the mass of the cell nuclei of 2.67 x 10-10 g. For an Asub(s) of 0.01 μCi/g, 350 nuclei receive the maximum z of 6.64 krads in 5.236 min. The number of exposed cell nuclei increases proportionally with Asub(s). The average value of z for exposed nuclei is 72.5 rads in 5.236 min and rises only for Asub(s) values higher than 53 μCi/g. (author)