Ion Track Diameters Research Articles

A Methodology for the Discrimination of Alpha Particles from Other Ions in Laser-Driven Proton-Boron Reactions Using CR-39 Detectors Coupled in a Thomson Parabola Spectrometer

Solid-state nuclear track detectors (CR-39 type) are frequently used for the detection of ions accelerated by laser-plasma interaction because they are sensitive to each single particle. To the present day, CR-39 detectors are the main diagnostics in experiments focused on laser-driven proton-boron (p11B) fusion reactions to detect alpha particles, which are the main products of such a nuclear reaction, and to reconstruct their energy distribution. However, the acceleration of multispecies ions in the laser-generated plasma makes this spectroscopic method complex and often does not allow to unambiguously discriminate the alpha particles generated from p11B fusion events from the laser-driven ions. In this experimental work, performed at the PALS laser facility (600 J, 300 ps, laser intensity 1016 W/cm2), CR-39 detectors were used as main detectors for the angular distribution of the produced alpha particles during a p11B fusion dedicated experimental campaign. Additionally, a CR-39 detector was set inside a Thomson Parabola (TP) spectrometer with the aim to calibrate the CR-39 response for low energetic laser-driven ions originating from the plasma in the given experimental conditions. The detected ion energies were ranging from hundreds of keV to a few MeV, and the ion track diameters were measured for etching times up to 9 hours. The goal of the test was the evaluation of the detectors’ ability to discriminate the alpha particles from the aforementioned ions. Within this study, the calibration curves for protons and silicon low energy ions are accomplished, the overlapping of the proton tracks and alpha particles is verified, and a methodology to avoid this problem is realized.

Comprehensive Understanding of Hillocks and Ion Tracks in Ceramics Irradiated with Swift Heavy Ions

Amorphizable ceramics (LiNbO3, ZrSiO4, and Gd3Ga5O12) were irradiated with 200 MeV Au ions at an oblique incidence angle, and the as-irradiated samples were observed by transmission electron microscopy (TEM). Ion tracks in amorphizable ceramics are confirmed to be homogenous along the ion paths. Magnified TEM images show the formation of bell-shaped hillocks. The ion track diameter and hillock diameter are similar for all the amorphizable ceramics, while there is a tendency for the hillocks to be slightly bigger than the ion tracks. For SrTiO3 (STO) and 0.5 wt% niobium-doped STO (Nb-STO), whose hillock formation has not been fully explored, 200 MeV Au ion irradiation and TEM observation were also performed. The ion track diameters in these materials are found to be markedly smaller than the hillock diameters. The ion tracks in these materials exhibit inhomogeneity, which is similar to that reported for non-amorphizable ceramics. On the other hand, the hillocks appear to be amorphous, and the amorphous feature is in contrast to the crystalline feature of hillocks observed in non-amorphizable ceramics. No marked difference is recognized between the nanostructures in STO and those in Nb-STO. The material dependence of the nanostructure formation is explained in terms of the intricate recrystallization process.

Hillocks created for amorphizable and non-amorphizable ceramics irradiated with swift heavy ions: TEM study

In a previous study, we found that hillocks (i.e. surface ion tracks) can be imaged using transmission electron microscopy (TEM) by irradiating thin CeO2 samples with swift heavy ions (SHI) at oblique incidence. In the present study, the same TEM method is applied to Y3Fe5O12 (YIG) and three fluorides (CaF2, SrF2 and BaF2) for observing hillocks. For YIG, which is one of the amorphizable materials, hillocks are found to have amorphous features consistent with amorphous features of ion tracks. For the fluorides, it is found that the hillocks do not exhibit amorphous features, and they are composed of nanocrystallites. Although hillocks for YIG and CaF2 exhibit different crystallographic features, hillock diameter agrees with the molten region diameter predicted by the thermal spike model for both materials. It is found that for YIG the hillock diameter is comparable to the ion track diameter, whereas for the fluorides it is always larger than the ion track diameter. The present result shows the existence of the velocity effect for ion track diameter in CaF2. It is also found that for fluorides both hillock and ion track diameters vary in the order of cation mass (i.e. CaF2 < SrF2 < BaF2). The above results of hillocks and ion tracks for SHI-irradiated fluorides can be consistently interpreted within the framework of the thermal spike model, if melting and successive recrystallization are assumed.

Ion track diameter in fullerene C70 thin film using Raman active vibrational modes of C70 molecule

The effect of energy deposition in fullerene C70 (∼150 nm) thin film deposited by resistive heating method on glass, quartz and silicon substrates was investigated. The samples were irradiated with 90 MeV Ni ion beam at the fluences ranging from 1 × 1012 to 3 × 1013 ions/cm2. The pristine and Ni ion irradiated samples were examined for morphological and optical changes by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), UV–visible absorption spectroscopy and Raman spectroscopy. After ion irradiation, bigger grains are shown on surface as revealed by SEM analysis indicating the agglomeration of the smaller particles into bigger particles at the surface. UV–visible absorption studies reflect that the direct band gap of the film decreases with increase in ion fluence. At higher fluence, fullerene C70 is transformed into amorphous carbon (a-C) which is confirmed by Raman spectroscopy. The damage cross-section (σ) and radius of the damaged cylindrical zone (r) are approximated to be ∼1.72 × 10−13 cm2 and ∼2.3 nm, respectively using Raman active vibrational modes.

Defect accumulation in ThO2 irradiated with swift heavy ions

Polycrystalline ThO2 was irradiated with 2.2GeV Au ions and characterized by synchrotron X-ray diffraction, X-ray absorption spectroscopy, and Raman spectroscopy. The diffraction measurements indicated an increase in the unit cell parameter and the accumulation of heterogeneous microstrain with increasing ion fluence, both of which are consistent with a single-impact model of damage accumulation. An analytical fit of the data to a single-impact model yielded a saturation unit cell expansion of 0.049±0.002% and a saturation strain of 10.4±0.2%. Cross-section data determined from the model values yielded effective ion track diameters of 1.9±0.2nm and 3.2±0.3nm for the two modifications, respectively, indicating that the tracks consist of a core region in which swelling and strain have occurred and a defect-rich halo in which microstrain is present but the initial unit cell parameter has not changed significantly. The spectroscopic analysis revealed the presence of significant local structural distortion in the irradiated material, but no evidence of systematic modification to the electronic state or chemical environment of the cations. This indicates that swift heavy ion irradiation of ThO2 primarily produces simple point defects or defect agglomerates.

Elongation of gold nanoparticles by swift heavy ion irradiation: Surface plasmon resonance shift dependence on the electronic stopping power

Gold nanoparticles embedded in a silica matrix were irradiated with 2 to 40MeV Cu or Si ions at fluences ranging from 1×1013 to 4×1015 ions/cm2, and their deformation from spheres to prolate ellipsoids with major axis parallel to the ion beam was studied using P and S polarized light. For fixed ion energy, the longitudinal surface plasmon resonance (SPR) at 520nm is red-shifted with an increase of the ion fluence up to a certain value where it reaches a plateau indicating that a maximum aspect ratio is obtained. This saturation in the wavelength shift was found to depend on the ion energy and reaches a maximum of 40nm. The SPR shift was also used to measure the electronic stopping power dependent deformation rate and to deduce the electronic stopping power threshold of (1.9±1.3) keV/nm required for shape transformation of the embedded gold nanoparticles. Ion track diameters of 0.18 to 1.4nm were inferred from the fluence dependence of the SPR shift. Analysis by transmission electron microscopy shows that large (d>10nm) particles are more elongated than smaller ones. Our data are consistent with a mechanism of gold nanoparticle elongation requiring both the silica matrix and the nanoparticles to melt following the passage of the swift heavy ion and with elongation being due to the relief of stress in the gold nanoparticle which had built up as a consequence of the deformation of the surrounding silica matrix.

Structural properties of embedded Ge nanoparticles modified by swift heavy-ion irradiation

Silica-embedded Ge nanoparticles (NPs) of different sizes irradiated with swift heavy ions (SHIs) at a given energy may reportedly elongate along the incident ion direction, perpendicular to it, or not at all. Here, for a given NP size distribution, we have investigated the SHI energy dependence of the elongation process. Higher-energy irradiation generally yielded elongation along the ion track (as previously observed), but for lower-energy irradiation, elongation both parallel and perpendicular to the ion direction was observed. We demonstrate that NP size and electronic energy loss together govern the elongation process, reinforcing the proposed model where elongation perpendicular to the ion direction is only expected for Ge NPs bigger than the mean ion track diameter in silica. Here, a wide fluence range is also probed, enabling us to follow in more detail the transition from spherical unirradiated Ge NPs to Ge NPs elongated either parallel or perpendicular to the ion beam. X-ray absorption spectroscopy (XAS) measurements are utilized for the quantification of crystalline, amorphous, and oxidized environments around Ge atoms. Combining such results with transmission electron microscopy (TEM) observations shows the Ge NPs are rendered amorphous prior to elongation, potentially via a melt-and-quench process. Thereafter, stronger electron-phonon coupling in amorphous Ge compared to crystalline Ge may potentially influence the elongation process. The Ge NP amorphization occurs at lower fluences for higher irradiation energies, indicating electronic energy loss---and not ballistic effects---governs the amorphization. Subsequent to amorphization and elongation, TEM and XAS results also show the NPs gradually intermix with SiO${}_{2}$ and dissolve within the matrix as the irradiation fluence increases. We discuss the impact of such results in the ion beam tailoring of Ge NPs for technological applications.

Role of Thermodynamics in the Shape Transformation of Embedded Metal Nanoparticles Induced by Swift Heavy-Ion Irradiation

Swift heavy-ion irradiation of elemental metal nanoparticles (NPs) embedded in amorphous SiO(2) induces a spherical to rodlike shape transformation with the direction of NP elongation aligned to that of the incident ion. Large, once-spherical NPs become progressively more rodlike while small NPs below a critical diameter do not elongate but dissolve in the matrix. We examine this shape transformation for ten metals under a common irradiation condition to achieve mechanistic insight into the transformation process. Subtle differences are apparent including the saturation of the elongated NP width at a minimum sustainable, metal-specific value. Elongated NPs of lesser width are unstable and subject to vaporization. Furthermore, we demonstrate the elongation process is governed by the formation of a molten ion-track in amorphous SiO(2) such that upon saturation the elongated NP width never exceeds the molten ion-track diameter.

Ion tracks in silica for engineering the embedded nanoparticles

Swift heavy ions have unique feature of creating ion tracks in insulators of dimension from a few nm to about 10 nm. This particular feature of the swift heavy ions is used to engineer the size and shape of the nanoparticles embedded in silica matrix. On the basis of several experiments, it is evidenced that the embedded nanoparticles either grow in size or reduce in size, if they are smaller than or comparable to the ion track size. The shape transformation from spherical to elongated along the beam direction occurs, when the nanoparticle size is larger than the ion track diameter in silica. The reduction, growth and elongation of Au nanoparticles embedded in silica matrix under swift heavy ion irradiation have been discussed in the frame work of thermal spike model.

Energy dependent saturation width of swift heavy ion shaped embedded Au nanoparticles

The transformation of Au nanoparticles (NPs) embedded in SiO2 from spherical to rod-like shapes induced by swift heavy ion irradiation has been studied. Irradiation was performed with A197u ions at energies between 54 and 185 MeV. Transmission electron microscopy and small angle x-ray scattering measurements reveal an energy dependent saturation width of the NP rods as well as a minimum size required for the NPs to elongate. The NP saturation width is correlated with the ion track diameter in the SiO2. NP melting and in-plane strain in the irradiated SiO2 are discussed as potential mechanisms for the observed deformation.

On the conflicting roles of ionizing radiation in ceramics

Ionizing radiation can produce competing effects in ceramic materials. It is well established that ionizing radiation can produce displacement damage via radiolysis in alkali halides and some other ceramics. At high stopping powers (electronic d E/d x>5–50 keV/nm, depending on the material), additional displacement damage via inelastic collision processes can also be created in the vicinity of the ion track (swift-heavy-ion displacement damage). On the other hand, ionizing radiation can promote the recovery of displacement damage in many ceramic insulators by enhancing the mobility of point defects (ionization-induced diffusion). Therefore, under different irradiation conditions (electronic stopping powers), ionizing radiation can lead to either a substantial enhancement or suppression of radiation resistance in ceramics. The microstructures of SiC, Al 2O 3, MgO, MgAl 2O 4, Si 3N 4 and AlN were examined by transmission electron microscopy (TEM) following irradiation with ion beams ranging from 1 MeV H + to 710 MeV Bi +. The oxides and Si 3N 4 were found to be susceptible to ionization-induced diffusion. In these materials, high fluxes of ionizing radiation produced coarsening of dislocation loops and cavities, and inhibited low-temperature amorphization. At high electronic stopping powers, displacement damage was produced in the ion tracks in the oxides and Si 3N 4 that could not be attributed to normal elastic collision processes. The amorphous ion track diameter in Si 3N 4 associated with 710 MeV Bi ion irradiation was 3.5 nm. AlN and SiC were resistant to swift-heavy-ion-track displacement damage up to electronic stopping powers of 34 keV/nm.

Swift heavy ion-based materials science research at NSC

Effects of large electronic excitation in different types of materials, viz. metals, semiconductors, superconductors, polymers and organic crystals are being investigated using the swift heavy ions (SHI) of energies from 10 to 270 MeV available from 15 UD NSC Pelletron. Defect production in semiconductors, structural strain on electronic transport properties of materials having colossal magneto resistance (CMR), flux pinning in high T c superconductors (HTS), desorption of hydrogen from polymers, ion beam mixing in metal/Si interface and optical waveguide formation are some of our research activities. Resistivity and 1/ f noise measurements from room temperature down to 77 K are used for the studies of SHI-induced defects into the materials. Quadrupole mass spectrometer (QMS) in the materials science beam line is used for the studies of radiolysis of polymers induced by SHI. For polymers, ion track diameters have been estimated by on-line monitoring of the loss of hydrogen (using ERD and QMS) during ion irradiation. An ultra high vacuum scanning tunneling microscope (UHV STM) is being installed at the materials science beam line to study the individual damage created by SHI on the solid surfaces. A three-axes goniometer has been installed for RBS-channeling studies of various materials. Experimental facilities and the research work carried out at Nuclear Science Centre are briefed.

Track formation and dislocation loop interaction in spinel irradiated with swift heavy ions

The microstructure of polycrystalline stoichiometric magnesium aluminate spinel (MgAl 2O 4) has been examined by cross-section electron microscopy following 430 MeV Kr + or 614 MeV Xe + ion irradiation near room temperature up to a fluence of 1.1 × 10 16 ions/m 2. In addition, the microstructure was examined for two spinel specimens which had been preirradiated with either 2 MeV Al + ions or 3.6 MeV Fe + ions and subsequently irradiated with 430 MeV Kr + ions. The Al + and Fe + preirradiated specimens contained a high density (10 21–10 23 m −3) of interstitial dislocation loops with diameters between 5 and 30 nm prior to the swift heavy ion irradiation. Near-continuous latent ion tracks were observed in all of the specimens irradiated with swift heavy ions. The swift heavy ions also appeared to efficiently destroy pre-existing dislocation loops with diameters <5 nm, whereas larger loops remained intact following the swift heavy ion irradiation. The swift heavy ions caused structural disordering of the octahedral cautions, but did not appear to produce amorphous cores in the ion tracks. The disordered ion track diameters were ∼2.0 and ∼2.6 nm for the 430 MeV Kr and 614 MeV Xe ion irradiations, respectively.

Heavy ion track diameters in mica studied with scanning force microscope

In the present study, the scanning force microscope (SFM) was employed to measure the heavy ion track diameters in mica and was operated in the lateral-force mode with different loading forces. The mica samples were irradiated with Se, Au, Pb and Zn ions with a kinetic energy of 11.4 MeV/u at the UNILAC of GSI. The measured average track diameter increased slowly with increasing loading force between the SFM tip and sample. The experimental data pointed out that the track diameter versus loading force could be fitted by a linear function both for Se and Au ion species and the slopes of the fitted lines were nearly the same. By extrapolating to zero loading force, the intrinsic diameters of the ion tracks were obtained. A possible mechanism for the observations was discussed.

Ion track diameters in mica studied with scanning force microscopy

Aiming at a detailed study of morphology and size of heavy-ion tracks in mica, thin samples were irradiated with several heavy-ion species at the universal linear accelerator UNILAC of GSI. The latent ion tracks were investigated in air with a scanning force microscope (SFM) operated in the lateral-force mode. The track cross sections appear as areas of increased friction. The diameters of individual latent tracks were extracted by registering lateral-force line profiles of the amorphous track cross sections embedded in the undisturbed crystalline mica lattice. Averaged track-diameter values were determined by fitting the diameter distributions with Gaussian curves. We observed an increase of the track diameters with increasing electronic energy loss. The results are compared with earlier data from small-angle scattering and from topographic SFM measurements.