Search

Bacteria undergoing environmental effects is extremely interesting for structural, mechanistic, and evolutionary implications. Luminescent bacteria that have evolved in a specific ambient have developed particular responses and their behavior can give us new suggestions on the task and production of luciferina proteins. To analyze the UV interaction under controlled laboratory conditions, we used photoluminescent bacterial strains belonging to a new species evolutionarily close to Vibrio harveyi sampled from a coastal cave with a high radon content that generates ionizing radiation. The survival of the bacterial strains was analyzed, in the light and in the dark, following a variety of genotoxic treatments including UV radiation exposure. The strains were irradiated by a germicide lamp. The results demonstrated that most of the strains exhibited a low rate of survival after the UV exposure. After irradiation by visible light following the UV exposure, all strains showed a high capability of photoreactivation when grown. This capability was quite unexpected because these bacteria were sampled from a dark ambient without UV radiation. This leads us to hypothesize that the photoreactivation in these bacteria might have been evolved to repair DNA lesions also induced by different radiation sources other than UV (e.g., x-ray) and that the luminescent bacteria might use their own light emission to carry out the photoreactivation. The high capability of photoreactivation of these bacteria was also justified by the results of deconvolution. The deconvolution was applied to the emission spectra and it was able to show evidence of different light peaks. The presence of the visible peak could control the photolysis enzyme.

Laser ion sources offer the possibility to get ion beam utilizable to improve particle accelerators. Today many laboratories, as well as the LEAS, are employed to develop accelerators of the dimensions very contained to be installed in little laboratories and hospitals. Pulsed lasers at intensities of the order of 108 W/cm2 and of ns pulse duration interacting with solid matter in vacuum, plasma of high temperature and density is produced. The charge state distribution of the plasma generates high electric fields which accelerate ions along the normal to the target surface. The energy of emitted ions has a Maxwell Boltzmann distribution which depends on the ion charge state. To increase the ion energy, a post-acceleration system can be employed by means of high voltage power supplies of about 100 kV. The post acceleration system results a good method to obtain high ion currents by a not expensive system and the final ion beams find interesting applications in the field of the ion implantations, adrotherapy, scientific applications and industrial use. In this work we compare the electromagnetic and geometric properties, like the emittanza, of the beams delivered by a Cu and Y target. The characterization of the plasma was performed by a Faraday cup for the electromagnetic characteristics, whereas a pepper pot system for the geometrical ones. At 60 kV accelerating voltage and 5.5 mA output current the normalized beam emittance resulted of 0.22 π mm mrad for the Cu target, while under the same accelerating voltage but with 7.4 mA output current a lower normalized beam emittance value was reached for the Y target. It resulted of 0.14 π mm mrad. The brightness of the beams was of 114 and 378 mA( mm mrad)-2 for the Cu and Y target, respectively. When Ag targets were utilised, we implanted an AISI 420 stainless steel by a dose of 10x1015 inos/cm2. Besides, the laser ion sources have got very good properties to feed large machines.

In questo lavoro si presentano i risultati ottenuti impiantando ioni di Cu e Ag su polietilene Ultra High Molecular Weight Polyethylene. L'impiantazione è stata eseguita utilizzando la tecnica LIS (Laser Ion Source), con laser ad eccimeri KrF e utilizzando una doppia accelerazione ottendo 60 kV di accelerazione. La fluenza laser è stata di 2.2 J/cm2 corrispondente ad un flusso ionico di 1012 ions/cm2 . Test di antibattericità sono stati condotti utilizzando il ceppo Staphylococcus aureus. Esami preliminari dimostrano una diminuzione della proliferazione di batteri sui campioni trattati.

I fasci di ioni di alcune centinaia di kV di energia e di buona qualità geometrica sono oggi utilizzati in diversi settori applicativi per la modifica di materiali da drogaggio. Per generare sorgenti di ioni, un metodo moderno ed alternativo che viene presentato in questo lavoro è la tecnica dell'ablazione laser. L'acceleratore realizzato è un dispositivo compatto in grado di ottenere fasci ionici da laser plasma con energie sino a 160 keV per stato di carica. È stata condotta una caratterizzazione del fascio (energia, stato di carica, divergenza, emittanza, corrente) supportata dall'uso di un software di simulazione, Comsol Multiphysics.

Studies on Vibrio bacteria sampled from a coastal cave having an high radon content are presented. Most of the strains exhibited a low rate of survival after the UV exposure. All strains after UV and visible irradiation showed an high capability of photoreactivation. This capability was unexpected. We hypothesize that the photoreactivation might have been evolved to repair DNA lesions induced also by different radiations and that the luminescent bacteria might use their own light emission to carry out the photoreactivation. We assessed that the photoreactivation increased for some strains of about 42000 times.

Ions of different elements were generated by laser-induced-plasma and accelerated by a two adjacent cavities. Therefore, the ions were undergone a double acceleration imparting a maximum ion energy of 160 keV per charge state. We analyzed the extracted charge from a Cu target as a function of the accelerating voltage. At 60 kV of total accelerating voltage, the maximum current peak was of 5.3 mA. The ion flux resulted of 3.4x1011 ions/cm2. The normalized emittance measured by pepper pot method at 60 kV was of 0.22 π mm mrad. By this machine, biomedical materials as UHMWPE were implanted with carbon and titanium ions. At a total ion flux of 2x1015 ions/cm2 the polyethylene surface increased its micro hardness of about 3-hold measured by the scratch test. Considering the ion emission cone dimension, we estimated a total extracted charge per pulse of 200 nC.

In this work, we report on the characterization of pulsed soft X-rays emitted from laser-produced plasma by different targets. The measurements were performed in a vacuum stainless-steel chamber at 10-7 mbar .The plasma was generated by a pulsed KrF excimer laser of 248 nm laser wavelength, operating at single shot and having a pulses of 23 ns FWHM. The beam was focused on pure Si, Cu and Ta targets. The laser energies were 40, 80 and 120 mJ, concentrated onto a spot of about 0.01 cm2, with a resulting irradiance of 1.7, 3.5 and 5.2x108 Wcm-2. The utilized detector was a very sensitive Faraday cup which opportunely biased was able to record time resolved signals of X-rays and to estimate their energy. The found X-rays energy values were compared to the ion temperature of the target plasma fitting the time resolved ion current signals by the shifted Maxwell-Boltzmann velocity distribution.

We developed an ion accelerator with a double accelerating gap system supplied by two power generators of different polarity.-The ions were generated by laser ion source technique. The laser plasma induced by an excimer KrF laser, freely expanded before the action of accelerating fields. After the first gap action, the ions were again accelerated by a second gap. The total acceleration can imprint a maximum ion energy up to 160 keV per charge state. We analyzed the extracted charge from a Cu target as a function of the accelerating voltage at laser energy of 9, 11 and 17 mJ deposited on a spot of 0.005 cm2. The peak of current density was 3.9, 5.3 mA for the lower and medium laser energy at 60 kV. At the highest laser energy, the maximum output current was 11.7 mA with an accelerating voltage of 50 kV. The maximum ion dose was estimated to be of 1012 ions/cm2. Under the condition of 60 kV accelerating voltage and 5.3 mA output current the normalized emittance of the beam measured by pepper pot method was 0.22 π mm mrad.

In this work two different techniques to modify the polymeric surfaces are compared; Laser irradiation and ion implantation were performed on Ultra High Molecular Weight Polyethylene (UHMWPE) samples. The irradiation treatment was performed by using two different laser sources operating in the UV and IR range, applying many laser shots in air atmosphere on the polymer surface. Ion implantation was performed using a new LIS (Laser Ion Source) accelerator with an accelerating voltage of 40 kV. Contact angle, roughness and Fourier Transform Infra Red (FT-IR) measurements were performed on the samples before and after the two treatments in order to obtain information on the UHMWPE modification.

Generation of electromagnetic pulses of fast and high intensity is constantly in progress. The real time diagnostic of short current or voltage pulses is essential for good application with sophisticate and modern devices. Streak camera systems are able to detect sub ps pulses of particle or X-ray beams, but losing the possibility to use the beams during the detection. Besides, real time measurements of electromagnetic pulses offer a better control of the device functioning. Nowadays fast current or voltage pulses of sub ten picoseconds can be recorded in real time by means of modern fast digitizing oscilloscopes, but to get good results it is necessary to realize fast probes. Fast capacitive probes, which we will present in this work, are simple capacitors conceived like a transmission line. For this reason it is indispensable to construct them with electrodes of suitable dimensions and forms, e.g., i: the probe has to got a folded central electrode in order to present the internal skin dimensions close to external ones, ii: it has to got a particular configuration able to contain and to shield the integrating resistor avoiding electromagnetic irradiations. Such a probe is suitable for measuring fast voltage and current pulses propagating in coaxial structures of known characteristic impedance. Analysing the behaviour of the probe in a 50 Ω coaxial structure, the voltage amplification resulted to be of (3.6±0.1)x10-4 and as a consequence the current attenuation factor of 56±1 A/V. The rise time response was very interesting. It was less than 320 ps, which was limited by oscilloscope bandwave. In vacuum electrical devices the capacitor probe can measure potential values of the order of 100 kV.

Advanced high brightness photo-injectors require photo-cathodes with fast response time, long lifetime and relatively high quantum efficiency. Metallic cathodes could satisfy these proprieties and in order to control the emitting material and its surface we produced an yttrium thin film, prepared by PLD (Pulsed Laser Deposition).

We present the diagnostic of a pulsed X-ray radiation utilizing as detector a very sensible and fast Faraday cup under a new approach. It allows to determine the X-ray energy and the dose. The plasma was generated by a pulsed KrF excimer laser focused on a Cu target by a convergent lens. The detector sensitivity was very high although the output laser energy was very low. With 30 mJ laser energy focused to an intensity of radiation on the target of 1.3 x108 W/cm2 a 140 eV X-ray photons were produced having a maximum energy of 1 keV. The plasma temperature was determined by the best fit of the modified Maxwell-Boltzmann equation which resulted of about 600 kK (57 eV). At higher laser energy, 102 mJ, a higher plasma temperature was reached, 970 kK (84 eV), as well as higher photon energy, 160 eV. Such a source is able for studying on living cells and on sequencing of DNA.

In this work the photoemission performance of rough and smooth cathodes is presented.

In the last years, the development of electrons sources able to satisfy the particles accelerator requests has stimulated the interest of many laboratories. In this sense, UV excimer laser sources are employed to investigate photocathodes even for high work function metals

A new LIS configuration was studied and realized in order to generate and accelerate ions of different elements. This ion source consisted of a laser-induced plasma from solid targets where the plume was made to expand before the action of the accelerating field. The accelerating field was reached by the application of two high voltage power supplies of different polarity. Therefore, the ions were undergone to double acceleration which can imprint a maximum ion energy up to 160keV per charge state. We analyzed the extracted charge from a Cu target as a function of the accelerating voltage at the laser fluence of 1.7 and 2.3 J/cm^2. At 60kV of total accelerating voltage and higher laser fluence, the maximum ion dose was of 10^12 ions/cm^2. Under this last conditions the maximum output current was 5 mA and the emittance measured by pepper pot method resulted of 0.22 π mm mrad. By this machine biomedical materials as UHMWPE were implanted with carbon and titanium ions. At doses of 6x10^15 ions/cm^2 the polyethylene surface increased its micro hardness of about 3-hold measured by the scratch test.

High intensity ion beams can be obtained by laser plasma or applying high electric fields or utilising large acceleration gaps. We get it developing a double acceleration gap system supplied by two power generators of different bias voltages. In this way we realized a new LIS accelerator configuration in order to produce and to accelerate ions of different elements. The LIS consists of a laser-induced plasma from solid targets, where the plume freely expands before the action of the accelerating fields. Our system provides ion beams of maximum energy up to 160 keV per charge state. We extracted charge from a Cu plasma as a function of the accelerating voltage at laser fluence values of 1.8, 2.2 and 3.4 J/cm 2 . At 60 kV of total accelerating voltage, the peak currents were 3.9 and 5.3 mA corresponding to 1.8 and 2.2 J/cm 2 laser fluences, respectively. At the highest laser fluence, the maximum output current was 11.7 mA with an accelerating voltage of 50 kV and a corresponding ion flux of 10 12 ions/cm 2 . Under the condition of 60 kV accelerating voltage and 5.3 mA output current (ion flux 3.4×10 11 ions/cm 2 ) the normalized emittance of the beam measured by pepper pot method resulted of 0.22π mm mrad. Under the condition of 160 kV accelerating voltage the ion flux was higher than 1.0×10 11 ions/cm 2 .

New photo-injector sources having fast response time, long lifetime and relatively high-quantum efficiency (QE) are very needed for many applications. Metallic cathodes are promising candidates to supply high-intensity and good quality electron beams. We carried out measurements utilising thin films and a smooth bulk made of yttrium (Y). The Y thin films were produced by pulsed laser deposition (PLD, using a XeCl excimer laser) in high vacuum. It was covered, in situ, by a gold film to avoid oxidation. The Y smooth bulk was mechanically processed in air. The laser used to get experimental values of photoemission was a KrF excimer laser of 5 eV photon energy and 23 ns pulse duration. The maximum accelerating voltage applied to the photodiode (the anode) was+25 kV. The measurements of photocurrent were performed at different laser energies. We found that the output current was depended on the cathode surface. The higher QE values were obtained for the smooth cathode. It provided a maximum output current of 8.4 A, at 25 kV and 12 mJ laser energy. The maximum QE was 7.0x(10)^-5.

In this work, the photoemission performance of rough and smooth cathodes is presented. The cathodes were made up of pure yttrium metal bulk. For evaluation of the photocathodes, a KrF excimer laser, operating at 248 nm wavelength, 5 eV photon energy and 23 ns full width at half maximum (FWHM) was used. The targets were tested in a vacuum photodiode cell at 10^(-7) mbar; they were irradiated at normal incidence and the anode-cathode distance was set to 5 mm. The measurements were performed after a series of electric breakdowns between anode and cathode, induced under high laser energy and high accelerating voltage. This operation was performed in order to restore/increase the surface roughness. For the rough cathode, the maximum output current was 10.5 A, reached at 25 kV and 12 mJ laser energy; the maximum quantum efficiency (QE) value was 1.3 x 10^(-4), whereas for the smooth cathode, the maximum output current was 8.4 A and the maximum QE value was 7.0 x 10^(-5), calculated in the same experimental conditions. The temporal behavior of photoemission from these cathodes was studied. Plasma production and Schottky effect played a fundamental role in this process.

In this work we report on the characterization of pulsed soft x-rays emitted from laser-produced plasma. The plasma was generated by a pulsed KrF excimer laser focused on pure Si, Cu and Ta targets by 40, 80 and 120 mJ laser energies. The utilized detector was a very sensitive Faraday cup which opportunely biased was able to record time-resolved signals of x-rays and to estimate their energy. The found x-rays energy values were compared with the ion temperature of the plasma obtained by fitting the time-resolved ion current signals with a shifted Maxwell-Boltzmann velocity distribution. The results showed that the laser-produced Ta plasma induced bunches of x-rays having in average the highest energy values and it was also characterized by ion temperature higher than the ones of the laser-produced Si and Cu plasmas.

X-ray radiation is generated by laser induced plasma also at very low laser fluence. In this work the diagnostic of a pulsed X-ray source utilizing as detector a very sensitive fast polarized Faraday cup is described. The plasma was generated by a pulsed KrF excimer laser focused on a pure copper target. The X-ray energy was studied at 30 and 102 mJ laser energy focused by a convergent lens of 15 cm focal length which provided an intensity of 1.3x108 and 4.5x108 Wcm-2, respectively. The maximum X-ray energy was approximately 1 keV for the both laser energies, whereas the energy peak value was of about 140 eV for the lower laser energy and about 160 eV for the higher. This behavior was compared with the calculation of plasma temperature performed by the Faraday cup at long time. The plasma temperature was determined by the best fit of the modified Maxwell-Boltzmann equation which resulted of about 600 kK (57 eV) and 970 kK (84 eV) for the lower and higher applied laser energy. Such a source is useful for studying on living cells and on sequencing of DNA.

In this work we present the experimental study and a theoretical approach of the photoemission of rough and smooth photocathodes. The cathode bulk was made of pure yttrium while its surface was morphologically modified. The cathode surface was irradiated by a KrF excimer at normal incidence with the anode-cathode distance set to 5mm. The measurements were performed after electric breakdowns between anode and cathode, induced under high laser energy and high accelerating voltage. This operation was made in order to increase the surface roughness. For the rough cathode the maximum output current was 10.5 A, reached at 25 kV and 12 mJ, with a maximum quantum efficiency value of 1.3×10-4. Instead, under the same experimental conditions the smooth cathode provided an output current of 8.4 A with a maximum quantum efficiency value of 7.0×10-5. We can conclude that in this process the plasma production and the Schottky effect play a fundamental role.

In this work, we present a new pulsed laser ablation technique to obtain energetic ion beams. The accelerator we made is a compact device able to extract and accelerate the ionic components of plasma up to 160 keV per charge state. It is composed by a generating chamber containing an expansion chamber used like first electrode. Next, a second electrode connected to ground and a third electrode connected to negative voltage are used. The third electrode is used also as Faraday cup. By the analysis of the ion signals we studied the plume parameters such as TOF accelerated signals, charge state, and divergence.

Plasmas induced by UV laser ablation have been studied and analysed using timeof- flight measurements. A KrF laser beam of 23 ns FWHM time duration was focused into Si and Nb targets with a moderate laser fluence of 2 J/cm2. A suitable theoretical expressions were derived for fitting the recorded ion current under the assumption of a “shifted” Maxwell- Boltzmann velocity distribution. The deconvolution of time resolved ion current signals, taking into account a multi-mode velocity distribution has revealed that the contribution of the different charge states of ions in the plasma induces electric field which accelerate the expanding plasma along the target normal.

In this work the experimental and simulation results of photoemission studies for photoelectrons are presented. The cathode used was a Zn disc having a work function of 4.33 eV. Two different excimer lasers were employed as energy source to apply the photoelectron process: XeCl (308 nm, 10 ns) and KrF (248nm, 23ns). Experimental parameters were the laser fluence (up to 70 mJ/cm2) and the anode-cathode voltage (up to 20 kV). The output current was detected by a resistive shunt having the same value of the characteristic impedance of the system. The best values of global quantum efficiency were approximately 5x10-6 for XeCl and 1x10-4 for KrF laser, while the peaks of the temporal quantum efficiency were 8x10-6 and 1.4x10-4, respectively. The higher efficiency for KrF is ascribed to higher photon energy and to Schottky effect. To enhance the Schottky effect, several electron-beam simulations using OPERA 3-D were carried out to analyze the influence of the geometrical characteristics of the diode.