Effetti biologici delle radiazioni ionizzanti: effetti non-targeted e loro implicazioni per la radioprotezione e la clinica

L'azione dlee radiazioni ionizzanti in sistemi biologici è generalmente spiegata invocando il coinvolgimento diretto o indiretto del DNA nucleare nell'interazione radiazione-cellula. In particolare, in accordo con questa descrizione, la radiazione incidente interagisce direttamente con il DNA nucleare attraverso le varie specie radicaliche originatesi dall'interazione della radiazione con l'acqua e il micro-ambiente del DNA stesso, dando luogo a una varietà di lesionialla struttura del DNA il cui successivo processamento determina l'espressione di una varietà di effetti biologici e quindi il destino finale della cellula irraggiata. recentemente si sono però accumulate evidenze sperimentali, principalmente in-vitro ma anche in vivo, che pongono in discussione la validità di questo approccio mostrando che, nel regime delle basse dosi di radiazione ionizzante, alcuni effetti biologicipossono essere indotti anche in cellule non direttamente interagenti con la radiazione incidente (effetti non-targeted). Tra questi si trovano l'ipersensibilità e la radioresistenza indotta; l'effetto bystander; l'instabilità genomica; la risposta adattiva. In questo lavoro di tesi si è dato maggiore enfasi allo studio della risposta adattiva in cellule umane (in vitro) esposte ai raggi γ e a ioni leggeri forniti da acceleratori di bassa energia.ope

Temporally Resolved Intensity Contouring (TRIC) for characterization of the absolute spatio-temporal intensity distribution of a relativistic, femtosecond laser pulse

Today's high-power laser systems are capable of reaching photon intensities up to $10^{22}$ W/cm^2, generating plasmas when interacting with material. The high intensity and ultrashort laser pulse duration (fs) make direct observation of plasma dynamics a challenging task. In the field of laser-plasma physics and especially for the acceleration of ions, the spatio-temporal intensity distribution is one of the most critical aspects. We describe a novel method based on a single-shot (i.e. single laser pulse) chirped probing scheme, taking nine sequential frames at framerates up to THz. This technique, to which we refer as temporally resolved intensity contouring (TRIC) enables single-shot measurement of laser-plasma dynamics. Using TRIC, we demonstrate the reconstruction of the complete spatio-temporal intensity distribution of a high-power laser pulse in the focal plane at full pulse energy with sub picosecond resolution.Comment: Daniel Haffa, Jianhui Bin and Martin Speicher are corresponding author

Femtosecond Symmetry Breaking and Coherent Relaxation of Methane Cations at the Carbon K-Edge

Understanding the relaxation pathways of photoexcited molecules is essential to gain atomistic level insight into photochemistry. Herein, we perform a time-resolved study of ultrafast molecular symmetry breaking via geometric relaxation (Jahn-Teller distortion) on the methane cation. Attosecond transient absorption spectroscopy with soft X-rays at the carbon K-edge reveals that the distortion occurs within $10\pm 2$ femtoseconds after few-femtosecond strong-field ionization of methane. The distortion activates coherent oscillations in the scissoring vibrational mode of the symmetry broken cation, which are detected in the X-ray signal. These oscillations are damped within $58\pm13$ femtoseconds, as vibrational coherence is lost with the energy redistributing into lower-frequency vibrational modes. This study completely reconstructs the molecular relaxation dynamics of this prototypical example and opens new avenues for exploring complex systems

Jahn-Teller Distortion and Dissociation of CCl4+_4^+ by Transient X-ray Spectroscopy Simultaneously at the Carbon K- and Chlorine L-Edge

X-ray Transient Absorption Spectroscopy (XTAS) and theoretical calculations are used to study CCl$_4^+$ prepared by 800 nm strong-field ionization. XTAS simultaneously probes atoms at the carbon K-edge (280-300 eV) and chlorine L-edge (195-220 eV). Comparison of experiment to X-ray spectra computed by orbital-optimized density functional theory (OO-DFT) indicates that after ionization, CCl$_4^+$ undergoes symmetry breaking driven by Jahn-Teller distortion away from the initial tetrahedral structure (T$_d$) in 6$\pm$2 fs. The resultant symmetry-broken covalently bonded form subsequently separates to a noncovalently bound complex between CCl$_3^+$ and Cl over 90$\pm$10 fs, which is again predicted by theory. Finally, after more than 800 fs, L-edge signals for atomic Cl are observed, indicating dissociation to free CCl$_3^+$ and Cl. The results for Jahn-Teller distortion to the symmetry-broken form of CCl$_4^+$ and formation of the Cl -- CCl$_3^+$ complex characterize previously unobserved new species along the route to dissociation

I-BEAT: New ultrasonic method for single bunch measurement of ion energy distribution

The shape of a wave carries all information about the spatial and temporal structure of its source, given that the medium and its properties are known. Most modern imaging methods seek to utilize this nature of waves originating from Huygens' principle. We discuss the retrieval of the complete kinetic energy distribution from the acoustic trace that is recorded when a short ion bunch deposits its energy in water. This novel method, which we refer to as Ion-Bunch Energy Acoustic Tracing (I-BEAT), is a generalization of the ionoacoustic approach. Featuring compactness, simple operation, indestructibility and high dynamic ranges in energy and intensity, I-BEAT is a promising approach to meet the needs of petawatt-class laser-based ion accelerators. With its capability of completely monitoring a single, focused proton bunch with prompt readout it, is expected to have particular impact for experiments and applications using ultrashort ion bunches in high flux regimes. We demonstrate its functionality using it with two laser-driven ion sources for quantitative determination of the kinetic energy distribution of single, focused proton bunches.Comment: Paper: 17 Pages, 3 figures Supplementary Material 16 pages, 7 figure

I-BEAT: Ultrasonic method for online measurement of the energy distribution of a single ion bunch

The shape of a wave carries all information about the spatial and temporal structure of its source, given that the medium and its properties are known. Most modern imaging methods seek to utilize this nature of waves originating from Huygens' principle. We discuss the retrieval of the complete kinetic energy distribution from the acoustic trace that is recorded when a short ion bunch deposits its energy in water. This novel method, which we refer to as Ion-Bunch Energy Acoustic Tracing (I-BEAT), is a refinement of the ionoacoustic approach. With its capability of completely monitoring a single, focused proton bunch with prompt readout and high repetition rate, I-BEAT is a promising approach to meet future requirements of experiments and applications in the field of laser-based ion acceleration. We demonstrate its functionality at two laser-driven ion sources for quantitative online determination of the kinetic energy distribution in the focus of single proton bunches

Effetti biologici delle radiazioni ionizzanti: effetti non-targeted e loro implicazioni per la radioprotezione e la clinica

L'azione dlee radiazioni ionizzanti in sistemi biologici è generalmente spiegata invocando il coinvolgimento diretto o indiretto del DNA nucleare nell'interazione radiazione-cellula. In particolare, in accordo con questa descrizione, la radiazione incidente interagisce direttamente con il DNA nucleare attraverso le varie specie radicaliche originatesi dall'interazione della radiazione con l'acqua e il micro-ambiente del DNA stesso, dando luogo a una varietà di lesionialla struttura del DNA il cui successivo processamento determina l'espressione di una varietà di effetti biologici e quindi il destino finale della cellula irraggiata. recentemente si sono però accumulate evidenze sperimentali, principalmente in-vitro ma anche in vivo, che pongono in discussione la validità di questo approccio mostrando che, nel regime delle basse dosi di radiazione ionizzante, alcuni effetti biologicipossono essere indotti anche in cellule non direttamente interagenti con la radiazione incidente (effetti non-targeted). Tra questi si trovano l'ipersensibilità e la radioresistenza indotta; l'effetto bystander; l'instabilità genomica; la risposta adattiva. In questo lavoro di tesi si è dato maggiore enfasi allo studio della risposta adattiva in cellule umane (in vitro) esposte ai raggi γ e a ioni leggeri forniti da acceleratori di bassa energia