20 research outputs found
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 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 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
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 CCl 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 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 undergoes symmetry breaking driven by Jahn-Teller
distortion away from the initial tetrahedral structure (T) in 62 fs.
The resultant symmetry-broken covalently bonded form subsequently separates to
a noncovalently bound complex between CCl and Cl over 9010 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 and Cl.
The results for Jahn-Teller distortion to the symmetry-broken form of CCl
and formation of the Cl -- CCl 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