The multiscale physics of ion-beam cancer therapy
For more than ten years, ion-beam cancer therapy has been successfully used
clinically in Germany and Japan. Proton-beam therapy is performed in many
more centers around the globe. These therapies appear to be a more favorable
alternative to the conventional radiotherapy. Despite apparent experimental
and clinical successes, a comprehensive theoretical description of a
physical scenario is missing. One reason is that phenomena initiated by an
energetic ion incident on tissue happen on many scales in time, distance,
and energy. Our goal is to understand the physics of beam therapy on a
microscopic level and, while moving towards this goal, we developed a
multi-scale approach to understanding the physics related to ion/proton-beam
cancer therapy and the calculation of the probability of DNA damage as a
result of irradiation of tumors with energetic ions. This approach is
inclusive with respect to different scales, starting from the long scale,
defined by the ion stopping, followed by a smaller scale, defined by
secondary electrons and radicals, and ending with the shortest scale,
defined by interactions of secondaries with the DNA. We presented
calculations of the probabilities of single and double strand breaks of DNA,
suggested a way to further elaborate on such calculations, and also made
some estimates for glial cells exposed to radiation.
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CL10086
On the hunt for lost particles
The induced fission of compound nuclei has been investigated exhaustively for many decades but despite many years of experimental and theoretical effort our understanding of fission is still far from complete. The model description of fission point ranged from the early statistical models to the advanced dynamical descriptions. After many decades of intensive research in the field of fusion-fission reactions, various aspects of the problem still remain under debate and many theoretical methods have been developed to study dynamics of these reactions. There are several approaches to energy dissipation in heavy-ion fusion-fission reactions, but difference between particle multiplicity such as charged particles, gamma rays and neutrons in theoretical and experimental view as the main consequence of earlier investigation, show that statistical approach is not main way for definition of energy dissipation in heavy-ion reactions. In our project we find classical corrected neutron multiplicity in the base of dynamical approach in the frame work of asymmetric fission for a few typical systems and then we compare our results with experimental data. These constraints may reflect characteristic features of fusion-fission reactions.
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LW11113
Fractal magnetic domains discovered in the bulk of Nd2Fe14B
The structure and evolution of magnetic domains play a crucial role in
ferromagnetic materials by providing a link between the microscopic
magnetic structure and the macroscopic response to an external
magnetic field. Nevertheless, for the industrial strength
ferromagnet, Nd2Fe14B, the dimension, shape and arrangement of
magnetic domains are still under debate due to the lack of suitable
methods to study magnetic domain structures in the bulk. Using
small-angle neutron scattering, scientists at Ames Laboratory/Iowa
State University and the Institut Laue-Langevin have demonstrated that
the complex domain patterns at the surface, as revealed by
quantitative Kerr and Faraday microscopy, propagate into the bulk with
structural dimensions down to 6 nm, the domain wall size. Perhaps
most interesting is that the neutron scattering intensity follows a
power law with unusual exponents over one decade in length scale,
characterizing the magnetic domains as fractals with volume filling
boundaries. Below the spin-reorientation transition at 135 K, a
weakening in the magnetic anisotropy reduces the complexity of the
domain structure to a more regular arrangement and yields an anomalous
increase in the bulk magnetization. These observations open up a rich
experimental playground for studies of fractal structures in magnetic
systems with strong uniaxial anisotropy.
