Laser generation of proton beams for the production of short-lived positron emitting radioisotopes

Protons of energies up to 37 MeV have been generated when ultra-intense lasers (up to 10(20) W cm(-2)) interact with hydrogen containing solid targets. These protons can be used to induce nuclear reactions in secondary targets to produce P-emitting nuclei of relevance to the nuclear medicine community, namely C-11 and N-13 via (p, n) and (p, alpha) reactions. Activities of the order of 200 kBq have been measured from a single laser pulse interacting with a thin solid target. The possibility of using ultra-intense lasers to produce commercial amounts of short-lived positron emitting sources for positron emission tomography (PET) is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

Mono-energetic ion beam acceleration in solitary waves during relativistic transparency using high-contrast circularly polarized short-pulse laser and nanoscale targets

In recent experiments at the Trident laser facility, quasi-monoenergetic ion beams have been obtained from the interaction of an ultraintense, circularly polarized laser with a diamond-like carbon target of nm-scale thickness under conditions of ultrahigh laser pulse contrast. Kinetic simulations of this experiment under realistic laser and plasma conditions show that relativistic transparency occurs before significant radiation pressure acceleration and that the main ion acceleration occurs after the onset of relativistic transparency. Associated with this transition are a period of intense ion acceleration and the generation of a new class of ion solitons that naturally give rise to quasi-monoenergetic ion beams. An analytic theory has been derived for the properties of these solitons that reproduces the behavior observed in kinetic simulations and the experiments. © 2011 American Institute of Physics.

Investigations of DNA damage induction and repair resulting from cellular exposure to high dose-rate pulsed proton beams

Studies regarding the radiobiological effects of low dose radiation, microbeam irradiation services have been developed in the world and today laser acceleration of protons and heavy ions may be used in radiation therapy. The application of different facilities is essential for studying bystander effects and relating signalling phenomena in different cells or tissues. In particular the use of ion beams results advantageous in cancer radiotherapy compared to more commonly used X-rays, since the ability of ions in delivering lethal amount of doses into the target tumour avoiding or limiting damage to the contiguous healthy tissues. At the INFN-LNS in Catania, a multidisciplinary radiobiology group is strategically structured aimed to develop radiobiological research, finalised to therapeutic applications, compatible with the use of high dose laser-driven ion beams. The characteristic non-continuous dose rates with several orders of magnitude of laser-driven ion beams makes this facility very interesting in the cellular systems' response to ultra-high dose rates with non-conventional pulse time intervals cellular studies. Our group have projected to examine the effect of high dose laser-driven ion beams on two cellular types: foetal fibroblasts (normal control cells) and DU145 (prostate cancer cells), studying the modulation of some different bio-molecular parameters, in particular cell proliferation and viability, DNA damage, redox cellular status, morphological alterations of both the cytoskeleton components and some cell organelles and the possible presence of apoptotic or necrotic cell death. Our group performed preliminary experiments with high energy (60 MeV), dose rate of 10 Gy/min, doses of 1, 2, 3 Gy and LET 1 keV/µm on human foetal fibroblasts (control cells). We observed that cell viability was not influenced by the characteristics of the beam, the irradiation conditions or the analysis time. Conversely, DNA damage was present at time 0, immediately following irradiation in a dose-dependent manner. The analysis of repair capability showed that the cells irradiated with 1 and 2 Gy almost completely recovered from the damage, but not, however, 3 Gy treated cells in which DNA damage was not recovered. In addition, the results indicate the importance of the use of an appropriate control in radiobiological in vitro analysis.

Modeling target bulk heating resulting from ultra-intense short pulse laser irradiation of solid density targets

Isochoric heating of solid-density matter up to a few tens of eV is of interest for investigating astrophysical or inertial fusion scenarios. Such ultra-fast heating can be achieved via the energy deposition of short-pulse laser generated electrons. Here, we report on experimental measurements of this process by means of time-and space-resolved optical interferometry. Our results are found in reasonable agreement with a simple numerical model of fast electron-induced heating. (C) 2013 AIP Publishing LLC.

Transport of laser accelerated proton beams and isochoric heating of matter

The acceleration of intense proton and ion beams by ultra-intense lasers has matured to a point where applications in basic research and technology are being developed. Crucial for harvesting the unmatched beam parameters driven by the relativistic electron sheath is the precise control of the beam. We report on recent experiments using the PHELIX laser at GSI, the VULCAN laser at RAL and the TRIDENT laser at LANL to control and use laser accelerated proton beams for applications in high energy density research. We demonstrate efficient collimation of the proton beam using high field pulsed solenoid magnets, a prerequisite to capture and transport the beam for applications. Furthermore we report on two campaigns to use intense, short proton bunches to isochorically heat solid targets up to the warm dense matter state. The temporal profile of the proton beam allows for rapid heating of the target, much faster than the hydrodynamic response time thereby creating a strongly coupled plasma at solid density. The target parameters are then probed by X-ray Thomson scattering (XRTS) to reveal the density and temperature of the heated volume. This combination of two powerful techniques developed during the past few years allows for the generation and investigation of macroscopic samples of matter in states present in giant planets or the interior of the earth.

A compact broadband ion beam focusing device based on laser-driven megagauss thermoelectric magnetic fields

Ultra-intense lasers can nowadays routinely accelerate kiloampere ion beams. These unique sources of particle beams could impact many societal (e.g., proton-therapy or fuel recycling) and fundamental (e.g., neutron probing) domains. However, this requires overcoming the beam angular divergence at the source. This has been attempted, either with large-scale conventional setups or with compact plasma techniques that however have the restriction of short (<1 mm) focusing distances or a chromatic behavior. Here, we show that exploiting laser-triggered, long-lasting (>50 ps), thermoelectric multi-megagauss surface magnetic (B)-fields, compact capturing, and focusing of a diverging laser-driven multi-MeV ion beam can be achieved over a wide range of ion energies in the limit of a 5° acceptance angle.

A laser driven pulsed X-ray backscatter technique for enhanced penetrative imaging

X-ray backscatter imaging can be used for a wide range of imaging applications, in particular for industrial inspection and portal security. Currently, the application of this imaging technique to the detection of landmines is limited due to the surrounding sand or soil strongly attenuating the 10s to 100s of keV X-rays required for backscatter imaging. Here, we introduce a new approach involving a 140 MeV short-pulse (< 100 fs) electron beam generated by laser wakefield acceleration to probe the sample, which produces Bremsstrahlung X-rays within the sample enabling greater depths to be imaged. A variety of detector and scintillator configurations are examined, with the best time response seen from an absorptive coated BaF₂ scintillator with a bandpass filter to remove the slow scintillation emission components. An X-ray backscatter image of an array of different density and atomic number items is demonstrated. The use of a compact laser wakefield accelerator to generate the electron source, combined with the rapid development of more compact, efficient and higher repetition rate high power laser systems will make this system feasible for applications in the field.

Plasma-based studies with intense X-ray and particle beam sources

The construction of short pulse (

Photodiodes array as potential diagnostic for measuring short bursts of K-alpha radiation from Ti targets irradiated with 45 fs laser pulses

We report on a study comparing absolute K-alpha yield from Ti foils measured with a calibrated system of an X-ray CCD coupled to a curved LiF Von-Hamos crystal spectrometer to the difference in the signals measured simultaneously with two similar photodiodes fitted with two different filters. Our data indicate that a combination of photodiodes with different filters could be developed into an alternative and inexpensive diagnostic for monitoring single shot pulsed emission in a narrow band of X-ray region.

Thin film capacitor cut from single crystals using focused ion beam milling

The focused ion beam microscope (FIB) has been used to fabricate thin parallel-sided ferroelectric capacitors from single crystals of BaTiO3 and SrTiO3. A series of nano-sized capacitors ranging in thickness from similar to660 nm to similar to300 nm were made. Cross-sectional high resolution transmission electron microscopy (HRTEM) revealed that during capacitor fabrication, the FIB rendered around 20 nm of dielectric at the electrode-dielectric interface amorphous, associated with local gallium impregnation. Such a region would act electrically in series with the single crystal and would presumably have a considerable negative influence on the dielectric properties. However, thermal annealing prior to gold electrodes deposition was found to fully recover the single crystal capacitors and homogenise the gallium profile. The dielectric testing of the STO ultra-thin single crystal capacitors was performed yielding a room temperature dielectric constant of similar to300, as is the case in bulk. Therefore, there was no evidence of a collapse in dielectric constant associated with thin film dimensions.

Injection of metallic elements into an electron-beam ion trap using a Knudsen cell

A method of injecting metallic elements into an electron-beam ion trap (EBIT) is described. The method is advantageous over the conventional coaxial and pulsed injection methods in two ways: (a) complicated switching of injection and extraction beams can be avoided when extracting beams of highly charged ions from the EBIT and (b) a beam of stable intensity can be achieved. This method may be applicable to any metallic elements or metallic compounds that have vapor pressures of similar to 0.1 Pa at a temperature lower than 1900 degrees C. We have employed this method for the extraction of highly charged ions of Bi, Er, Fe, and Ho. (c) 2006 American Institute of Physics.

Effect of self-generated magnetic fields on fast-electron beam divergence in solid targets

The collimating effect of self-generated magnetic fields on fast-electron transport in solid aluminium targets irradiated by ultra-intense, picosecond laser pulses is investigated in this study. As the target thickness is varied in the range of 25 mu m to 1.4 mm, the maximum energies of protons accelerated from the rear surface are measured to infer changes in the fast-electron density and therefore the divergence of the fast-electron beam transported through the target. Purely ballistic spreading of the fast-electrons would result in a much faster decrease in the maximum proton energy with increasing target thickness than that measured. This implies that some degree of 'global' magnetic pinching of the fast-electrons occurs, particularly for thick (>400 mu m) targets. Numerical simulations of electron transport are in good agreement with the experimental data and show that the pinching effect of the magnetic field in thin targets is significantly reduced due to disruption of the field growth by refluxing fast-electrons.

Ultra-bright Optical Transients are Linked with Type Ic Supernovae

Recent searches by unbiased, wide-field surveys have uncovered a group of extremely luminous optical transients. The initial discoveries of SN 2005ap by the Texas Supernova Search and SCP-06F6 in a deep Hubble pencil beam survey were followed by the Palomar Transient Factory confirmation of host redshifts for other similar transients. The transients share the common properties of high optical luminosities (peak magnitudes similar to -21 to -23), blue colors, and a lack of H or He spectral features. The physical mechanism that produces the luminosity is uncertain, with suggestions ranging from jet-driven explosion to pulsational pair instability. Here, we report the most detailed photometric and spectral coverage of an ultra-bright transient (SN 2010gx) detected in the Pan-STARRS 1 sky survey. In common with other transients in this family, early-time spectra show a blue continuum and prominent broad absorption lines of O II. However, about 25 days after discovery, the spectra developed type Ic supernova features, showing the characteristic broad Fe II and Si II absorption lines. Detailed, post-maximum follow-up may show that all SN 2005ap and SCP-06F6 type transients are linked to supernovae Ic. This poses problems in understanding the physics of the explosions: there is no indication from late-time photometry that the luminosity is powered by Ni-56, the broad light curves suggest very large ejected masses, and the slow spectral evolution is quite different from typical Ic timescales. The nature of the progenitor stars and the origin of the luminosity are intriguing and open questions.

Use of a random phase plate as a KrF laser beam homogenizer for thin film deposition applications

Fabrication of devices based on thin film structures deposited using the pulsed laser deposition technique relies on reproducibility and control of deposition rates over substrate areas as large as possible. Here we present an application of the random phase plate technique to smooth and homogenize the intensity distribution of a KrF laser footprint on the surface of a target which is to be ablated. It is demonstrated that intensity distributions over millimeter-sized spots on the target can be made insensitive to the typical changes that occur in the near-field intensity distribution of the ultraviolet output from a KrF laser. (C) 1999 American Institute of Physics. [S0034-6748(99)02504-6].