Swift Heavy Ion Irradiation

Apatite fission-track analysis retraces the thermal histories of geological samples under ∼ 120°C but low numbers of confined tracks often lead to weak constraints on the modelling results. Ion irradiation and increasing etching time are effective means to increase the number of etched confined tracks. Our results support a linear dependence of the number of intersected tracks on the lengths and densities of both the ion and fission tracks. The effectiveness of ion irradiation also depends on the etched-track geometries, i.e. on the beam orientation and etching conditions. Knife-blade shaped ion tracks parallel to the apatite c-axis are more efficient than funnel-shaped tracks perpendicular to c but add to the angular bias in favour of high angles to c. The irradiation conditions do not affect the mean track length at a given angle to c. The number of confined tracks increases in linear proportion to etching time above a certain threshold, which we interpret as the time required to etch a track to measurable dimensions. Past this threshold, the rate of confined track revelation is rapid. The high rate of increase is itself a direct consequence of the fact that confined tracks are not measurable if etched for less than a certain minimum length of time. Etching time does not affect the angular bias but it does increase the mean track lengths at all angles. The average rate of increase of the fossil track lengths exceeds that of the induced tracks at the 2σ level. Under some conditions, ion irradiation leads to blocking of fission tracks and the development of "semi-tracks". The elliptical model of mean horizontal confined track length vs. angle to the c-axis in prismatic apatite sections is over-constrained with respect to the known symmetries and does not provide the best possible fit to the dataset. Some observations suggest a fundamental difference between fossil and induced tracks.

Ion beam assisted thermal depolymerisation of poly (methyl methacrylate) (PMMA) thin ®lms, 1 lm thick, has been studied in the temperature range RT ± 400°C using a 300 keV He beam at very low¯uence (`10 12 ions cm À2 ). The experiments have been performed using an in situ mass spectrometer in a 10 À7 torr vacuum chamber. A relevant methyl methacrylate monomer (MMA) evolution (mass signal m/z 100) at temperature (150°C) well below the polymer degradation temperature (360°C) has been detected during irradiation. These results have been compared with gas evolution during room temperature ion irradiation where volatile products dierent from monomer are known to be produced due to chain scission events. The low-temperature depolymerisation induced by ion irradiation performed on PMMA at temperature higher than T g (105°C) is promoted by the presence of beam-induced reactive species acting as initiators. Ó

Highly textured FeCo thin films have been prepared by pulsed laser deposition on Si(1 0 0) and MgO(1 0 0) single crystals. The influence of the microstructure on the magnetic properties has been studied using the magneto-optical Kerr effect and vibrating sample magnetometry. The in-plane coercivity of the films deposited on Si and MgO was 28 Oe and 12 Oe, respectively. A fourfold in-plane magnetic anisotropy has been observed for a film deposited on MgO(1 0 0), in contrast to the isotropic pattern of the film deposited on Si. The films have then been irradiated under an in-plane magnetic field of 104 Oe by 40-keV Ne-and 200-keV Xe-ions, at a fluence of 1 · 10 15 ions/ cm 2 . For Xe-ions, the film deposited on Si(1 0 0) developed a twofold magnetic anisotropy, while the film on MgO exhibited only slight changes of the fourfold anisotropy.

Assessment of the viability for different types of solar PV tracking technologies rely on the assessment of whether the annual production of the different tracking technologies is increased enough relative to a benchmark Fixed Tilt system to compensate for the higher installation and operational costs incurred by the tracking systems. To investigate this issue, we use the PVsyst software to simulate electricity production from three representative solar PV systems at Karnataka. In these simulations we use hourly solar irradiance, weather and surface albedo data, technical data relating to both module and inverter characteristics and impacts associated with module soiling and shading.

Using vibrating sample magnetometery (VSM) 50MeV Li3+ ion irradiation effects on magnetic properties of single crystals of SrGaxInyFe12−(x+ y) O19 (where x= 0, 5, 7, 9; y= 0, 0.8, 1.3, 1.0), are reported. The substitution of Ga and In in strontium hexaferrite crystals ...

Nanoparticle formation in the, rf-sputtering grown, polycrystalline CeO 2 thin films is achieved by the swift heavy ion (SHI) irradiation. Crystal structure and phases present in the as-grown and irradiated thin films are investigated by the X-ray diffraction (XRD) measurements. Irradiation induced formation of spherically shaped nanostructures, on the film surface, is confirmed by the atomic force microscopy (AFM). The Raman spectra of the irradiated samples show increased line-width and peak position shifting in the Raman active mode (F 2g ) of CeO 2 , indicative of the nanocrystallization in the irradiated CeO 2 thin films. Formation of nanostructures in the irradiated samples is also briefly discussed in the light of ion energy and energy loss mechanisms.

Raman spectroscopy was used to investigate the structure of ion-irradiated α-SiC single crystals at room temperature and 400 • C. Irradiations induce a decrease of the Raman line intensities related to crystalline SiC, the appearance of several new Si-C vibration bands attributed to the breakdown of the Raman selection rules, and the formation of homonuclear bonds Si-Si and C-C within the SiC network. For low doses, the overall sp 3 bond structure and the chemical order may be almost completely conserved. By contrast, the amorphous state shows a strong randomization of the Si-Si, Si-C and C-C bonds. The relative Raman intensity decreases exponentially versus increasing dose due to the absorption of the irradiated layer. The total disorder follows a sigmoidal curve, which is well fitted by the direct impact/defect stimulated model. The chemical disorder expressed as the ratio of C-C bonds to Si-C bonds increases exponentially versus the dose. A clear correlation is established between the total disorder and the chemical disorder. The increase of temperature allows the stabilization of a disordered/distorted state and a limitation of damage accumulation owing to the enhancement of the dynamic annealing.

Ion irradiation of amorphous hydrogenated silicon carbide ®lms introduces additional disorder into the ®lms and leads to chemical modi®cations. These eects were monitored using Infrared, UV-visible optical and Raman spectroscopies. Samples were prepared by plasma enhanced chemical vapour deposition (PECVD), then irradiated with 300 keV Ar to¯uences ranging from 5 Â 10 13 to 1 Â 10 15 cm À2 . The hydrogen concentration was determined by elastic recoil detection analysis using 2.0 MeV He beam.

The phase transformations induced by electronic excitation (S e ) and ballistic processes (S n ) in Nd 2 Zr 2 O 7 pyrochlores irradiated with heavy ions in three domains of energy ($1 GeV, $100 MeV and a few MeV) were investigated by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. In the S e regime at high energy, results show that: (i) ion tracks are formed above a S e threshold of 12.5 keV nm À1 ; (ii) both pyrochlore ! anion-deficient fluorite phase transition and amorphization occur; (iii) total amorphization is always observed at the highest fluences; (iv) the internal structure (amount of amorphous phase vs. its anion-deficient fluorite counterpart) and the diameter of tracks depend on many parameters such as S e , the deposited energy density and the recrystallization rate. For irradiations performed with low-energy ions in the S n regime, only the anion-deficient fluorite phase is formed up to a dose of 40 dpa. Thus Nd 2 Zr 2 O 7 exhibits an unusual behaviour since this compound is amorphizable by S e and non-amorphizable by S n . Annealing of totally amorphized Nd 2 Zr 2 O 7 samples reveals strong differences in the recovery processes with other pyrochlore materials that are related to their different chemical compositions.

Inheritable chromosome aberrations (CA) are of concern because cytogenetic damage may trigger the carcinogenic process. Moreover, stability of radiation-induced CA is a prerequisite for meaningful biological dosimetry. CA inheritability arguably depends on the aberration structure, with symmetrical exchanges being favoured over asymmetrical rearrangements, but it is also affected by radiation quality. CA induced by low-LET protons and high-LET 12 C ions in G 0 peripheral blood lymphocytes were measured in first-, second-and third-generation by combined FISH/harlequin staining of metaphase as well as prematurely condensed interphase chromosomes 1 and 2. As expected, the frequency of non-transmissible (NT) aberrations declined through replication rounds. A radiation-induced arrest occurred prior to first post-irradiation mitosis that prevalently affected aberrant cells. Aberrant cells incurred cycle delays also at subsequent cycles following proton-irradiation but not 12 C ion-irradiation. As expected, the frequency of reciprocal translocations remained fairly stable while that of dicentrics was halved at each mitotic round. A significant fraction of complex-type exchanges was found in third-generation cells following both irradiations and appeared to be transmitted relatively more efficiently after protons than 12 C ions. A low but stably transmitted frequency of transmissible (T)-type insertions were detected after 12 C ions but not after low LET-irradiation. Our data support a differential ability by aberrant cells to progress through post-irradiation mitoses that is influenced by the aberration burden and radiation quality.

In this work the real time evolution of luminescence properties of ion-irradiated polymer thin films was studied by means of ion beam induced luminescence (IBIL) measurements. The plastic scintillator NE102, a fluorinated polyimide and PMMA were irradiated by H þ (1.85 MeV), He þ (2.2 MeV) and N þ (1.2 MeV). The optical properties after irradiation were analysed with UV-Visible absorption, fluorescence spectroscopy and Fourier transform infrared spectroscopy (FT-IR), in order to correlate the IBIL measurements to the evolution of the optical and chemical properties of the matrix. Ó

The relationship between the electrical properties and structure evolution of single layer graphene was studied by gradually introducing the gallium ion irradiation. Raman spectrums show a structural transition from nano-crystalline graphene to amorphous carbon as escalating the degree of disorder of the graphene sample, which is in correspondence with the electrical transition from a Boltzmann diffusion transport to a carrier hopping transport. The results show a controllable method to tune the properties of graphene.

Zr-2.5 Nballoy is used as a pressure tube material in pressurized heavy water reactor (PHWR). It is one of the most critical component which decides the lifespan of the reactor. The in-reactor degrading phenomenon of prime concern is dimensional changes caused by irradiation induced creep and growth processes. The present study aims to understand the mechanism of irradiation damage by irradiating the alloy with heavy ion. Such type of irradiation study would facilitate larger damage of material in a shorter time. Zr-2.5Nb alloy samples were irradiated using 315 keV Ar9+ ion for different durations. The irradiation doses were varied in the range of 3.1X1015 to 4.17X1016 Ar9+/cm2. SRIM calculation was carried out to evaluate damage profile in the irradiated samples. Beam based Positron Annihilation Spectroscopy (PAS) technique was used for depth profiling to characterize defect distribution in the alloys. The no. of defects generated is seen to increase with the increase in the fluence.

We report here on changes in magnetism and microstructure when implanting, at 92 or 300 K, up to 5 Â 10 15 Au 26+ -ions cm À2 of 350 MeV into nat Fe(45 nm)/ 57 Fe(20 nm)/Si trilayers. This choice of ions and energy allowed to test the irradiation effects in the regime of pure electronic stopping. The samples were analysed before and after irradiation by Rutherford back-scattering spectroscopy, X-ray diffraction, conversion electron Mössbauer spectroscopy, and magneto-optical Kerr effect. Up to 1 Â 10 15 ions cm À2 , there was interface broadening at a mixing rate of Ds 2 /F = 55(5) nm 4 , followed by full Fe-Si inter-diffusion. The Mössbauer spectra revealed fractions of a-Fe and amorphous ferromagnetic and paramagnetic iron silicides, but no crystalline Fe-Si phase. The magnetic remanence in the as-deposited Fe-layer showed small components of uniaxial and four-fold magnetization. For increasing ion fluence, the component with four-fold symmetry grew at the expense of the uniaxial component. For the highest fluences, an isotropic magnetization was found. #

TRIFOL-TN, etc. at various low and high energies. A detailed study has been made taking into consideration different target and projectile combinations, e.g. heavy ion-light target, light ion-heavy target and light ion-light target. Overall the Ziegler et al. (The Stopping Power and Range of lons in Solids, Vol. I. Pergamon Press, New York, 1985) formulation (TRIM 95) provides the best agreement with the experimental results for all projectile and target combinations except the heavy ion-light target combination where it underestimates the stopping power data in the limited range of energy of the projectile. Mukherjee and Nayak (Nucl. Instrum. Meth. 159, 421, 1979) formulation totally fails at relativistic and low energies of the projectile, irrespective of the projectile-target combination. Northcliffe and Schilling (Atom. Data Nucl. Data Tables A7, 233, 1970) formulation does not show any particular trend. Benton and Henke (Nucl. Instrum. Meth. 67, 87, 1969) formulation gives good agreement between experimental and theoretical data within the range of experimental error. The present study has been undertaken in order to determine the best stopping power and range formulation for calibration of solid state nuclear track detectors.

The radiation tolerance of synthetic pyrochlore and defect fluorite compounds has been studied using ion irradiation. We show that the results can be quantified in terms of the critical temperature for amorphization, structural parameters, classical Pauling electronegativity difference, and disorder energies. Our results demonstrate that radiation tolerance is correlated with a change in the structure from pyrochlore to defect fluorite, a smaller unit cell dimension, and lower cation-anion disorder energy. Radiation tolerance is promoted by an increase in the Pauling cation-anion electronegativity difference or, in other words, an increase in the ionicity of the chemical bonds. A further analysis of the data indicates that, of the two possible cation sites in ideal pyrochlore, the smaller B-site cation appears to play the major role in bonding. This result is supported by ab initio calculations of the structure and bonding, showing a correlation between the Mulliken overlap populations of the B-site cation and the critical temperature. r

The effects of 150 MeV Ag ion irradiation on the molecular beam epitaxially grown In 0:1 Ga 0:9 As/GaAs samples have been studied using high resolution X-ray diffraction (HRXRD). Our earlier experiments suggest that the compressive strain will decrease due to ion beam mixing effects in an initially strained system. Similarly a tensile strain will be induced in an initially lattice matched system. These studies are being performed to explore the possibility of spatial bandgap tuning for the integration of optoelectronics circuits. Here we present a systematic study to understand the effects of ion fluence and the initial strain/layer thickness on the modification of strain. Strain measurements are performed using HRXRD by determining the angular shift in the layer peak position with respect to that of the substrate peak. Substrate peak broadens with ion fluence due to the implantation effects at the end of the ion range (13 lm). However, the thin InGaAs layer and the substrate region near to this layer will not be affected. It is shown that the Swift Heavy Ion induced mixing can alter the lattice strain at room temperature without loss of the quality of the structure.

In this paper we present the results of an experimental work aimed to study the formation of ''gate oxide damages" in patterned MOS capacitors during heavy ion irradiation. The samples under test are derived from 100 V power MOSFETs. The damages on these structures have the same nature of the corresponding MOSFET but can be much more easily characterized. The gate damages resulting from both 79 Br and 197 Au ion irradiations are presented for different test conditions.

The changes in thick ($300 lm) and thin (15 lm) Si p-i-n diode detectors that take place as a result of alpha particle and 63 Cu 5 ion irradiation have been studied by Deep Level Transient Spectroscopy (DLTS) and by monitoring the reverse-bias leakage currents. A linear increase in reverse-bias current with a-particle dose was observed that could be attributed to the formation of vacancy-associated defects (divacancy, A-and E-centres). Damage within the active layer of the device, characterised by the increase in leakage current per unit active volume, together with literature pion, proton and heavy ion data, exhibited a linear dependence on the energy deposited in nuclear processes over many orders of magnitude. Annealing at temperatures of 150°C for 4 h (vacuum bakeout) resulted in a reduction in leakage current and the size of the DLTS peaks became smaller. This temperature is much lower than expected for removal of divacancies, suggesting that recovery of the reverse bias current is mediated by other defect centres. Ó 1998 Elsevier Science B.V.

a b s t r a c t III-Nitrides have attracted much attention due to their versatile and wide range of applications, such as blue/UV light emitting diodes. Strained layer super lattices offer extra degree of freedom to alter the band gap of lattice-mismatched heterostructures. Swift heavy ion irradiation is a post-growth technique to alter the band gap of semiconductors, spatially. In the present study, strained AlGaN/GaN multi-quantum wells (MQWs) were grown on sapphire with insertion of AlN and GaN as buffer layers between substrate and epilayers. Such grown AlGaN/GaN MQWs, AlGaN/GaN heterostructures and GaN layers were irradiated with 200 MeV Au and 150 MeV Ag ions at a fluence of 5 Â 10 11 ions/cm 2 and 5 Â 10 12 ions/cm 2 respectively. As-grown and irradiated samples have been characterized by high resolution XRD, photoluminescence and RBS/channelling. Measured strain values show that strain increases upon irradiation and the luminescence properties are enhanced. RBS/channelling confirms the increase in strain values upon irradiation. In this paper we describe the effects of swift heavy ion irradiation on structural and optical properties.

The modification in the magnetic anisotropy introduced by swift heavy ion irradiation has been investigated. Ferromagnetic metallic glasses Fe78B13Si9 and Fe40Ni38Mo4B18 have been irradiated with 100 MeV 127I ions at different doses from 5×1012 to 7.5×1013 ions/cm2. Magnetic anisotropy has been studied by measuring the relative intensity ratio D23 of Mossbauer sextet. As received samples display orientation of the magnetic moments nearly parallel to the surface of the ribbon, which upon irradiation to a dose of 5×1012 ions/cm2 rotates to a nearly random orientation. At the dose of 7.5×1013 ions/cm2, the magnetic moments display completely random orientation.

This paper reports on the influence of ion irradiation on the magnetic properties of Co/ Ni multilayers with perpendicular magnetic anisotropy ͑PMA͒. This material is a very promising candidate for ultrahigh density spintronic applications since it exhibits high polarization and low damping parameters. We show that PMA can be tailored in a controlled way by using uniform He + ion irradiation or focused Ga + ion beam.

The three-dimensional magnetic structure and reversal mechanism of patterned Co/Pt multilayers, were imaged using complementary Lorentz transmission electron microscopy ͑in-plane component͒ and magnetic transmission x-ray microscopy ͑perpendicular magnetization͒. The Co/Pt films with perpendicular anisotropy were patterned by ion irradiation through a stencil mask to produce in-plane magnetization in the irradiated regions. The boundaries of the patterns, defined by the transition from out-of-plane to in-plane magnetization, were found to be determined by the stencil mask. The nucleation fields were substantially reduced to 50 Oe for the in-plane regions and 1 kOe for the perpendicular regions, comparing to 4.5 kOe for the as-grown film. The perpendicular reversals were found to always originate at the pattern boundaries.

Ge nanocrystals embedded in SiO 2 matrix have been synthesized by swift heavy ion irradiation of Ge implanted SiO 2 films. In the present study, 400 keV Ge + ions were implanted into SiO 2 films at dose of 3 Â 10 16 ions/cm 2 at room temperature. The as-implanted samples were irradiated with 150 MeV Ag 12+ ions with various fluences. Similarly 400 keV Ge + ions implanted into Silicon substrate at higher fluence at 573 K have been irradiated with 100 MeV Au 8+ ions at room temperature (RT). These samples were subsequently characterized by XRD and Raman to understand the re-crystallization behavior. The XRD results confirm the presence of Ge crystallites in the irradiated samples. Rutherford backscattering spectrometry (RBS) was used to quantify the concentration of Ge in the SiO 2 matrix. Variation in the nanocrystal size as a function of ion fluence is presented. The basic mechanism of ion beam induced re-crystallization has been discussed.

This paper reports on the influence of ion irradiation on the magnetic properties of Co/ Ni multilayers with perpendicular magnetic anisotropy ͑PMA͒. This material is a very promising candidate for ultrahigh density spintronic applications since it exhibits high polarization and low damping parameters. We show that PMA can be tailored in a controlled way by using uniform He + ion irradiation or focused Ga + ion beam.

Blisters on single-and polycrystalline tungsten surfaces formed by hydrogen and helium ion irradiation were investigated by grazing-incidence electron microscopy (GIEM) with an ultra-high-voltage transmission electron microscope. It was found that the blister skin thickness formed by D + irradiation of polycrystalline tungsten (PCW) was considerably larger than the calculated ion range of the implants; however, this skin thickness (or blister depth) is not related to the pre-existing grain boundaries in the PCW. Blister formation was also observed with GIEM for single crystal tungsten (SCW) irradiated with H + , D + , and He + . The critical ion fluence for blister formation in SCW is estimated to be $10 23 H + (D + )/m 2 for H(D) and $10 21 He + /m 2 for He. The size of the blisters and their skin structure depends on the irradiating conditions. Typical skin thickness was about 50-150 nm. Based on the assumption that gas particles (H 2 , D 2 , and He) accumulate within the blisters during H + , D + , and He + irradiation, the GIEM measurements provide a means to derive an estimate of the amount of gas so accumulated, by reproducing the observed blister shapes with finite element method (FEM) calculations. From the GIEM images and FEM calculations we have estimated the number of implanted ions being retained in the blisters, and compared these amounts with published retention measurements. A mechanism for the blister formation is proposed based on the present results.

The damage formation due to 593 MeV Au 30+ ion irradiation at room temperature in InP, GaP, GaAs and AlAs was investigated as a function of the ion fluence using RBS/C spectrometry. In InP an amorphous layer is formed at a nuclear energy deposition being by two orders of magnitude smaller than that required to render the material amorphous by elastic collisions. The observed behaviour is explained in terms of the thermal spike model in which it is assumed that above a critical value of the electronic energy deposition melting around the ion trajectories followed by fast cooling and re-solidification causes the formation of amorphous tracks. In GaP, GaAs and AlAs only a slight increase of the damage concentration with the ion fluence is registered, amorphisation is not reached up to ion fluences of 3 · 10 14 cm À2 . The damaging in these materials can be attributed to nuclear energy deposition, because in accordance with data published in literature the critical electronic energy deposition for track formation is not reached with 593 MeV Au 30+ ions.

In this paper we present the results of an experimental work aimed to study the formation of ''gate oxide damages" in patterned MOS capacitors during heavy ion irradiation. The samples under test are derived from 100 V power MOSFETs. The damages on these structures have the same nature of the corresponding MOSFET but can be much more easily characterized. The gate damages resulting from both 79 Br and 197 Au ion irradiations are presented for different test conditions.

Inheritable chromosome aberrations (CA) are of concern because cytogenetic damage may trigger the carcinogenic process. Moreover, stability of radiation-induced CA is a prerequisite for meaningful biological dosimetry. CA inheritability arguably depends on the aberration structure, with symmetrical exchanges being favoured over asymmetrical rearrangements, but it is also affected by radiation quality. CA induced by low-LET protons and high-LET 12 C ions in G 0 peripheral blood lymphocytes were measured in first-, second-and third-generation by combined FISH/harlequin staining of metaphase as well as prematurely condensed interphase chromosomes 1 and 2. As expected, the frequency of non-transmissible (NT) aberrations declined through replication rounds. A radiation-induced arrest occurred prior to first post-irradiation mitosis that prevalently affected aberrant cells. Aberrant cells incurred cycle delays also at subsequent cycles following proton-irradiation but not 12 C ion-irradiation. As expected, the frequency of reciprocal translocations remained fairly stable while that of dicentrics was halved at each mitotic round. A significant fraction of complex-type exchanges was found in third-generation cells following both irradiations and appeared to be transmitted relatively more efficiently after protons than 12 C ions. A low but stably transmitted frequency of transmissible (T)-type insertions were detected after 12 C ions but not after low LET-irradiation. Our data support a differential ability by aberrant cells to progress through post-irradiation mitoses that is influenced by the aberration burden and radiation quality.

We review the current status of the European fusion materials modelling programme. We describe recent findings and outline potential areas for future development. Large-scale density functional theory (DFT) calculations reveal the structure of the point defects in ␣-Fe, and highlight the crucial part played by magnetism. The calculations give accurate migration energies of point defects and the strength of their interaction with He atoms. Kinetic models based on DFT results reproduce the stages of radiation damage recovery in iron, and stages of He-desorption from pre-implanted iron. Experiments aimed at validating the models will be carried out in the future using a multi-beam ion irradiation facility chosen for its versatility and rapid feedback.

The damage and the residual stresses induced by 4 MeV Au ion irradiation in selected ceramic oxides (cubic zirconia and Gd 2 (Ti 2Àx Zr x )O 7 pyrochlores with x = 1 and 2) were investigated by X-ray diffraction. The variations of the lattice parameter and of residual stresses upon irradiation were shown to depend on the compound. The highest compressive stresses, linked to the largest swelling, were found in amorphizable Gd 2 TiZrO 7 . A two-step process was observed in damage, swelling and stress build-ups for non-amorphizable oxides (zirconia and Gd 2 Zr 2 O 7 ).

Optical, chemical and thermal properties of the polymers can be modified by swift heavy ion (SHI) irradiation. Fifty microns thick films of Makrofol-N were irradiated with 70 MeV C5+ ions to the fluences of 107, 108 and 9.3 · 1011
and 9.3 · 1012 ions/cm2 from Pelle-
tron accelerator at Nuclear Science Centre, New Delhi, India. The characterization of the radiation
induced modifications has been car- ried out with FTIR, UV–Vis and differential scanning calorimetry
(DSC). No change has been observed at lower fluences of 107 and 108 ions/cm2. At higher fluences,
slight shift in the optical absorption edge towards the red end of the spectrum has been observed
with increase in fluence. FTIR and thermal data show changes at higher fluences.

Passage of heavy ions produces radiation-damage trails known as latent tracks in a variety of solid-state nuclear-track detectors (SSNTDs). These tracks are made visible in an optical microscope by a simple process known as chemical etching. It is a well-known fact that latent tracks are radiation damage trails in SSNTDs, which can be annealed by thermal heating. Modgil-
Virk formulation of single-activation-energy model of radiation damage annealing was proposed as
an empirical approach for explaining the thermal fading of nuclear tracks in SSNTDs. The
empirical formulation of this model is based on track annealing data collected from both isothermal and isochronal experiments performed on different types of SSNTDs using a variety of heavy ion beams and fission fragments. The main objective of this empirical model was to resolve some contradictions of variable activation energy derived by using Arrhenius plots to study annealing in
mineral SSNTDs. Some equivalent versions of the Modgil-Virk model have been proposed but the concept of single activation energy is vindicated in all empirical formulations. The model always yields a unique value of activation energy independent of the nature of the ion beam used and the degree of annealing. The anisotropy of the mineral SSNTDs is revealed by variation in activation energy along different crystal planes and even with different orientations of the ion beam on the same plane. Some recent experiments are a pointer to the successful exploitation of this model for future cosmic-rays studies using SSNTDs.

Fission track (FT) thermochornology is essentially based on empirical fits to annealing data of FTs revealed by chemical etching, because, until now, unetched, latent FTs could not be examined analytically at the atomic-scale. The major challenge to such an analysis has been the random orientation of FTs and their extremely small diameters. Here we use high-energy ions (2.2 GeV Au or 80 MeV Xe) to simulate FT formation along specific crystallographic orientations. By combining results from transmission electron microscopy (TEM) of single tracks and small-angle X‑ray scattering (SAXS) for millions of tracks, a precise picture of track morphology as a function of orientation is obtained. High-resolution analysis reveals that orientation affects the shape of tracks in apatite and zircon through the preferential creation of damage along directions with highest atomic density. However, track radius does not depend on orientation, contradicting previous reports. Independent of track orientation, track radii, as measured at each point along the entire length of 80 MeV Xe ion tracks in apatite, can be understood using the thermal spike model of Szenes. Thus, the well-known track annealing anisotropy of apatite is not due to track radius anisotropy. The combination of ion-irradiations with TEM and SAXS analysis provides a unique opportunity to understand and model track formation and annealing under various geologic conditions.

We report here on changes in magnetism and microstructure when implanting, at 92 or 300 K, up to 5 Â 10 15 Au 26+-ions cm À2 of 350 MeV into nat Fe(45 nm)/ 57 Fe(20 nm)/Si trilayers. This choice of ions and energy allowed to test the irradiation effects in the regime of pure electronic stopping. The samples were analysed before and after irradiation by Rutherford back-scattering spectroscopy, X-ray diffraction, conversion electron Mössbauer spectroscopy, and magneto-optical Kerr effect. Up to 1 Â 10 15 ions cm À2 , there was interface broadening at a mixing rate of Ds 2 /F = 55(5) nm 4 , followed by full Fe-Si inter-diffusion. The Mössbauer spectra revealed fractions of a-Fe and amorphous ferromagnetic and paramagnetic iron silicides, but no crystalline Fe-Si phase. The magnetic remanence in the as-deposited Fe-layer showed small components of uniaxial and four-fold magnetization. For increasing ion fluence, the component with four-fold symmetry grew at the expense of the uniaxial component. For the highest fluences, an isotropic magnetization was found.