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Plasmon excitation and subsequent isomerization dynamics in naphthalene and azulene under fast proton interaction
摘要： The interaction of fast protons (velocity between 1.41 and 2.4 a.u.) with naphthalene and azulene is investigated as a model of an ion-polycyclic aromatic hydrocarbon interaction system. Production of various intact and fragment ions in coincidence with electron emission, electron transfer to projectile, or both is analyzed. The two targets being isomers, the rather obvious similarity in the fundamental ion-molecule collision energetics is quantitatively verified. The fast isomerization processes of cationic azulene are observed to be influencing its further dissociation channels such as C2H2 and H eliminations. A first ever attempt is presented here wherein single plasmon excitation in conjunction with isomerization dynamics is reported. Evidence from dication evaporation energetics is used to invoke the double plasmon excitation model. A model based on the multiplasmon resonance explains the observed proton velocity dependence of double to single ionization cross sections. Moreover an attempt is made to reinforce the proposition of double plasmon excitation by explaining the observed suppression of neutral H loss from dications as opposed to monocations.
关键词： double plasmon excitation,isomerization dynamics,naphthalene,azulene,ion-polycyclic aromatic hydrocarbon interaction,plasmon excitation,fast protons
更新于2025-09-23 15:21:01
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Effect of Temperature on the Characteristics of 4H-SiC UV Photodetectors
摘要： The influence exerted by the carrier concentration in the range (1–50) × 1014 cm–3 in n-4H-SiC chemical-vapor deposited (CVD) epitaxial layers on the spectral characteristics of UV photodetectors with Cr Schottky barriers in the range of 200–400 nm is revealed and explained in terms of the photoconductivity theory. Schottky barriers with a Cr film thickness of 20 nm and diameter of 8 mm are formed by thermal evaporation in vacuum through masks. A noticeable effect of the carrier concentration in the CVD epitaxial layers on the spectral characteristics of photodetectors upon heating to 200°C is also observed and accounted for by a difference between the generation-recombination processes. The irradiation of photodetectors with 15-MeV protons at a fluence of 4 × 1012 cm–2 and a temperature of 200°C leads to an increase in the quantum efficiency as compared to samples irradiated in similar modes at 25°C. This is indicative of an increase in the radiation hardness and service life of 4H-SiC devices at elevated temperatures.
关键词： irradiation,quantum efficiency,protons,silicon carbide,fluence
更新于2025-09-19 17:13:59
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Shaping of a laser-accelerated proton beam for radiobiology applications via genetic algorithm
摘要： Laser-accelerated protons have a great potential for innovative experiments in radiation biology due to the sub-picosecond pulse duration and high dose rate achievable. However, the broad angular divergence makes them not optimal for applications with stringent requirements on dose homogeneity and total flux at the irradiated target. The strategy otherwise adopted to increase the homogeneity is to increase the distance between the source and the irradiation plane or to spread the beam with flat scattering systems or through the transport system itself. Such methods considerably reduce the proton flux and are not optimal for laser-accelerated protons. In this paper we demonstrate the use of a Genetic Algorithm (GA) to design an optimal non-flat scattering system to shape the beam and efficiently flatten the transversal dose distribution at the irradiated target. The system is placed in the magnetic transport system to take advantage of the presence of chromatic focusing elements to further mix the proton trajectories. The effect of a flat scattering system placed after the transport system is also presented for comparison. The general structure of the GA and its application to the shaping of a laser-accelerated proton beam are presented, as well as its application to the optimisation of dose distribution in a water target in air.
关键词： Genetic algorithm,Beam shaping,Laser-driven protons,Monte Carlo simulations,Dose optimisation
更新于2025-09-16 10:30:52
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Diamond detector with laser-formed buried graphitic electrodes: micron-scale mapping of stress and charge collection efficiency
摘要： The paper reports the micron-scale investigation of an all-carbon detector based on synthetic single crystal CVD-diamond having an array of cylindrical graphitic buried-contacts, about 20 μm in diameter each, connected at the front side by superficial graphitic strips. To induce diamond-to-graphite transformation on both detector surface and bulk volume, direct-laser-writing technique was used. Laser-treatment parameters and cell shape have been chosen to minimize the overlapping of laser-induced stressed volumes. Optical microscopy with crossed polarizers highlighted the presence of an optical anisotropy of the treated material surrounding the embedded graphitized columns, and non-uniform stress in the buried zones being confirmed with a confocal Raman spectroscopy mapping. Dark current-voltage characterization highlights the presence of a field-assisted detrapping transport mainly related to highly-stresses regions surrounding buried columns, as well as superficial graphitized strips edges, where electric field strength is more intense, too. Notwithstanding the strain and electronic-active defects, the detector demonstrated a good charge collection produced by 3.0 and 4.5 MeV protons impinging the diamond, as well as those generated by MeV β-particles emitted by 90Sr source. Indeed, the mapping of charge collection efficiency with Ion Beam Induced Charge technique displayed that only a few micrometers thick radial region surrounding graphitic electrodes has a reduced efficiency, while most of the device volume preserves good detection properties with a charge collection efficiency around 90% at 60 V of biasing. Moreover, a charge collection efficiency of 96% was estimated under MeV electrons irradiation, indicating the good detection activity along the buried columns depth.
关键词： β-particles,3D detectors,graphitic pillars,IBIC,sc-CVD diamond,protons
更新于2025-09-11 14:15:04