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Project B.2.4

Femtosecond time-resolved radiation biology

Femtosecond radiation biology will rely on ultrafast pulses of high-energy charged particles provided by LION in CALA. We will address the physical processes occurring immediately after ion impact in biological matter as they occur in ion-beam radiation therapy of cancer patients. Pioneering work in experiment and theory is planned on a broad range of excitation mechanisms. So far, the physical processes occurring on pre-chemical scales (< 1 ps) after ion impact have been inaccessible. The new field of ultrafast radiation biology explores primary processes like radical generation for an improved understanding of the subsequent biological processes. Special phenomena are expected when ion tracks overlap leading to a combined nonlinear interaction of two or more radicals with the biological matter.

The project capitalises on the ultrashort duration of ion pulses produced by LION and their femtosecond synchronism with ultrashort NIR, VIS, UV laser pulses, which serve as a probe in the first phase of the project. In the second phase, probing will be implemented with LUX’s ultrafast X-ray pulses providing direct images of structural (chemical) changes of the irradiated molecules.

Laser-accelerated ion pulses currently exhibit an energy distribution ranging up to 10-20 MeV. Typically, 106 – 107 ions / MeV•msr are produced within the several 10 fs of the laser pulse. Due to time of flight an ion bunch with 10 MeV / u energy and 1% spread will broaden to 100 ps after one meter. A comparable ion-bunch duration is achievable at the Tandem accelerator where first tests of ion-pump, optical / IR probe will be performed. With laser acceleration, however, the shorter pulses required for the investigations of this project can be generated by the reduction of the distance between ion generation and ion application and by energy filtering.

The manipulation of the ion phase space by a second acceleration stage appears particularly rewarding. The challenge will be the low repetition rate and the presently rather large fluctuations of the beam parameters, which will be met by single shot probing. Basic techniques such as Fourier domain interferometry and time-resolved absorption spectroscopy using a set of probing pulses need to be developed or adapted. Prior to their application to biologically relevant samples these techniques can be tested at primary targets and will yield new information on the ion generation process.