Track Formation Model Research Articles

GEANT4 modeling of alpha particles detection efficiency for polycarbonate SSNTD

In this paper, a simple model based on the GEANT4 simulation toolkit is presented to determine the detection efficiency of polycarbonate detectors. Different alpha energies obtained by traveling of 241Am source alpha particles through different air columns are considered. Experimental measurement are also carried out using two different solutions and electrochemical etching conditions. The thicknesses of the bulk and the electrochemical etching layers extracted from the etching process are assumed as the key parameters. When the vertical range of an alpha particle corresponding to a linear energy transfer above the threshold required for forming the tracks lies between the two above thicknesses, the model counts a track. Fitting the modeled and the experimental efficiencies in the energy range 0.2 to 5 MeV shows that the threshold for forming the tracks in polycarbonate is 240 keV μm−1. Finally, the linear energy transfer threshold as well as the model for track formation presented here can be utilized for future investigations on the polycarbonate detector.

Swift heavy ion-beam induced amorphization and recrystallization of yttrium iron garnet

Pure and (Ca and Si)-substituted yttrium iron garnet (Y3Fe5O12 or YIG) epitaxial layers and amorphous films on gadolinium gallium garnet (Gd3Ga5O12, or GGG) single crystal substrates were irradiated by 50 MeV 32Si and 50 MeV (or 60 MeV) 63Cu ions for electronic stopping powers larger than the threshold value (~4 MeV μm−1) for amorphous track formation in YIG crystals. Conductivity data of crystalline samples in a broad ion fluence range (1011–1016 cm−2) are modeled with a set of rate equations corresponding to the amorphization and recrystallization induced in ion tracks by electronic excitations. The data for amorphous layers confirm that a recrystallization process takes place above ~1014 cm−2. Cross sections for both processes deduced from this analysis are discussed in comparison to previous determinations with reference to the inelastic thermal-spike model of track formation. Micro-Raman spectroscopy was also used to follow the related structural modifications. Raman spectra show the progressive vanishing and randomization of crystal phonon modes in relation to the ion-induced damage. For crystalline samples irradiated at high fluences (⩾1014 cm−2), only two prominent broad bands remain like for amorphous films, thereby reflecting the phonon density of states of the disordered solid, regardless of samples and irradiation conditions. The main band peaked at ~660 cm−1 is assigned to vibration modes of randomized bonds in tetrahedral (FeO4) units.

Scanning force microscopy of 129Iodine surface impact structures in muscovite, zircon and apatite as proxies for damage of simulated fission fragments in solids

Abstract Using artificially created swift, heavy ions of 129 I with a typical fission-fragment mass and specific energies which are common during the spontaneous fission of 238 U, the response in minerals commonly used in geochronological dating such as muscovite, zircon and apatite, has been evaluated by the means of Atomic Force Microscopy (AFM). The surface impact structures form hillocks with greater diameters but smaller heights for low-energetic ions and smaller diameters but greater heights for high-energetic ions. The observed hillock widths range from 22 ± 2 nm for low-energetic ions to 17 ± 1 nm for the highest energy in mica. Furthermore, the dimensions formed in apatite for low and high-energy ions range from 53 ± 2 nm to 27 ± 2 nm and from 64 ± 3 nm to 28 ± 1 nm in zircon. With increasing 129 I particle energy hillock heights increase, but diameters decrease regardless of mineral orientation. The crystallographic orientation of apatite and zircon also seems to have no effect on hillock dimensions, which are identical for perpendicular and parallel to the c -axis oriented mineral grains. The results support the “Compound Spike” track formation model of Chadderton (2003) , which combines the Coulomb ion explosion model with a thermal spike model.

Three‐dimensional shapes and Fe contents of Stardust impact tracks: A track formation model and estimation of comet Wild 2 coma dust particle densities

Abstract– We investigated three‐dimensional structures of comet Wild 2 coma particle impact tracks using synchrotron radiation (SR) X‐ray microtomography at SPring‐8 to elucidate the nature of comet Wild 2 coma dust particles captured in aerogel by understanding the capture process. All tracks have a similar entrance morphology, indicating a common track formation process near the entrance by impact shock propagation irrespective of impactor materials. Distributions of elements along the tracks were simultaneously measured using SR‐XRF. Iron is distributed throughout the tracks, but it tends to concentrate in the terminal grains and at the bottoms of bulbs. Based on these results, we propose an impact track formation process. We estimate the densities of cometary dust particles based on the hypothesis that the kinetic energy of impacting dust particles is proportional to the track volume. The density of 148 cometary dust particles we investigated ranges from 0.80 to 5.96 g cm−3 with an average of 1.01 (±0.25) g cm−3. Moreover, we suggest that less fragile crystalline particles account for approximately 5 vol% (20 wt%) of impacting particles. This value of crystalline particles corresponds to that of chondrules and CAIs, which were transported from the inner region of the solar system to the outer comet‐forming region. Our results also suggest the presence of volatile components, such as organic material and perhaps ice, in some bulbous tracks (type‐C).

Density evolution in formation of swift heavy ion tracks in insulators

Swift heavy ion irradiation leaves a latent ion track around the ion path in many materials. Here we report computational molecular dynamics (MD) simulation results on track formation in several insulating materials, quartz, amorphous silica (a-SiO 2), zinc oxide and diamond, concentrating especially in mass transport leading to density variations in the track volume during the initial stages of track formation. These details are largely unobservable in experiments due to the picosecond timescale and very local nature, and also in many computational models of track formation. Earlier a low-density core – high-density shell fine structure has been observed in latent tracks in amorphous silica, and here we study if other materials than silica show similar behavior. The results highlight the dynamical nature of track formation, that includes competing effects of heat and mass transport, rapid quenching of the heated area and recrystallization.

Time evolution and temperatures of hypervelocity impact‐generated tracks in aerogel

Abstract— Aerogel collectors have been used to capture cometary, interplanetary, and interstellar dust grains by NASA's Stardust mission, highlighting their importance as a scientific instrument. Due to the fragile and heterogeneous nature of cometary dust grains, their fragments are found along the walls of tracks that are formed during the capture process. These fragments appear to experience a wide range of thermal alteration and the causes of this variation are not well understood at a theoretical level as physical models of track formation are not well developed. Here, a general model of track formation that allows for the existence of partially and completely vaporized aerogel material in tracks is developed. It is shown that under certain conditions, this general track model reduces to the kinetic “snowplow” model that has previously been proposed. It is also shown, based on energetic considerations, that track formation is dominated by an expansion that is snowplow‐like in the later stages of track formation. The equation of motion for this snowplow‐like stage can be solved analytically, thus placing constraints on the amount of heating experienced by cometary dust fragments embedded in track walls. It is found that the heating of these fragments, for a given impact velocity, is expected to be greater for those embedded in larger tracks. Given the expected future use of aerogels for sample return missions, the results presented here imply that the choice of aerogel compositions can have a significant effect on the modification of samples captured and retrieved by these collectors.

On the long standing question of nuclear track etch induction time: Surface-cap model

Using a systematic set of experiments, nuclear track etch induction time measurements in a widely used CR-39 detector were completed for accessible track-forming particles (fission fragments, 5.2MeV alpha particles and 5.9MeV antiprotons). Results of the present work are compared with appropriately selected published results. The possibility of the use of etch induction time for charged particle identification is evaluated. Analysis of experimental results along with the use of well-established theoretical concepts yielded a model about delay in the start of chemical etching of nuclear tracks. The suggested model proposes the formation of a surface-cap (top segment) in each nuclear track consisting of chemically modified material with almost same or even higher resistance to chemical etching compared with bulk material of the track detector. Existing track formation models are reviewed very briefly, which provide one of the two bases of the proposed model. The other basis of the model is the general behavior of hot or energised material having a connection with an environment containing a number of species like ordinary air. Another reason for the delay in the start of etching is suggested as the absence of localization of etching atoms/molecules, which is present during etching at depth along the latent track.

Simulated weathering of dinosaur tracks and the implications for their characterization

Digital models of the tracks of bipedal theropod and ornithopod dinosaurs, and the quadrupedal tracks of a sauropod, were computationally eroded to investigate the effects of erosion on the shapes, sizes, and diagnostic details of fossil tracks. Narrow and (or) angular details, such as claw marks, interdigital ridges, and internal ridges, are removed early in erosion, creating the potential for misidentification of eroded theropod tracks as those of ornithopods. However, with the erosion models presented here, all tracks retain their basic shapes as indicated by the relative constancy of their interdigital angles and by the relative constancy of their footlength:footwidth ratios. Surface lengths of tracks did not increase significantly with erosion, so that dinosaurian hip height and speed estimates derived from trackways would not be greatly in error if based on eroded surface tracks. Synthetic undertracks from the surface tracks were also produced using information from published physical models of track formation. The differences between a weathered surface track and a freshly exposed, simulated undertrack are sufficient so that the two model tracks would not be confused. Large, rounded tracks are much better at retaining their characteristics than small, angular tracks, with the implication that large tracks may be over-represented in the fossil record, but they may be more reliably attributed to the appropriate trackmaker. This would bias estimates of dinosaur taxonomic diversity and body size ranges based on trackway evidence.

Thermal spike model of track formation in YBa2Cu3O7−x

We consider a model based on the thermal spike concept for an explanation of latent track formation in YBa2Cu3O7−x single crystal. The model demonstrates some interesting peculiarities such as “electronic quenching” and the existence of bifurcation points. Arguments for why the energy spent on damage creation in the track should be equal to the melting heat and why the so-called “epitaxial regrowth” is impossible are given.

A modified REL track formation model and its application to registration of 1 GeV/n Au and U ions in polycarbonate

Identification of heavy ions recorded in track detectors requires the knowledge of the physical processes which take place in each of the three steps involved in ion registration: (i) energy deposition by the incident particle in the detector; (ii) track formation; and (iii) the identification method itself. The amount of energy deposited by the incident particle per unit path length ( d E / d x ) is usually calculated by means of the Bethe–Bloch formula, which is described in terms of the so-called close and distant collisions. The REL track formation model excludes the contribution of close collisions when calculating the fraction of d E / d x leading to track formation. The identification method relates REL to a measurable signal S in the detector, so that S = g ( REL ) h where g and h are parameters to be obtained from calibration. In this work, we present a modified REL model in which the energy deposited by close collisions may contribute partially to track formation. This contribution is accounted for by means of a new coefficient κ , introduced in the modified REL expression, which can take values between 0 and 1. We estimate the value of κ from measurements of tracks originated in polycarbonate detectors by incident Au and U ions of ∼ 1 GeV / n energy from accelerator. The results are consistent with a small contribution ( κ ∼ 0.3 ) of close collisions.

Track formation in germanium crystals irradiated with superhigh-energy ions

Damage production was studied in 710MeV Bi and 1.3GeV U ions irradiated single-crystalline germanium by means of transmission electron microscopy and selective chemical etching. The formation of discontinuous tracks was registered in the depth region of high electronic energy loss of the incident ions. The observed features of discontinuous track formation in Ge are described within the fluctuation model of track formation.

Nuclear track-formation models and the response of BP-1 detectors

The mechanism of nuclear track formation in solids is poorly understood, despite decades of experience with nuclear track-etch detectors. One of the roadblocks has been the lack of precision tests of track-formation models. Here we exploit the unparalleled resolution of a glass nuclear track-etch detector, BP-1, to test track-formation models. By the use of calibration beams, we have corrected all signals for fluctuations in detector response, eliminating a possible source of systematic error. Within this dataset we compared signals due to the same particle charge over a large range of Lorentz factor. We show from a variety of lines of evidence that the response of BP-1 is not a simple function of total energy loss nor of other quantities derived from total energy loss such as restricted energy loss. A generic feature of a large class of models is a significant relativistic rise, which we do not observe. We show that an empirical hybrid model fits the response of BP-1 detectors over a wide range of charge and energy.

Ionizing particles may create shockwaves

To find a model that describes the gas diffusion on irradiated polymers (Makrofol KG polycarbonate) the diffusion constants have been measured with argon as diffusion gas. The polymers were irradiated with uranium, gold and lead ions of about 10 MeV/u and ion fluences between 1×10 10 and 4×10 11 ions/ cm 2 . The ion irradiated probes show two quite different dependencies of the diffusion constant on the ion energy loss. These effects are strongly related to the fluence of the irradiation. In case of low ion fluences, the diffusion constant is up to 8 times higher than that of pristine material. In the probes with high ion fluences we observe a decrease of diffusion constant to half the value of the pristine material. To understand the dependence of the diffusion constant on ion fluences we apply a model of compacting. This model describes the compacting ability of shockwaves arising from latent tracks. A track formation model is suggested. When an ion penetrates the foil it creates shockwaves around its path. These shockwaves put compacting forces on earlier created latent tracks in the same foil.

Further studies on sensitivity of a LR-115 based radon dosemeter

A radon dosemeter widely used in Italy and other countries has a cylindrically shaped diffusion cell and contains two LR-115 detectors covered by a thin film of absorber as an energy degrader. The sensitivity of this dosemeter was first studied by means of a simplified model for track formation in LR-115, based on three independent parameters ( E min , E max and the critical angle θ c). In this work the model, which is based on analytic and standard numerical methods, has been modified to take into account the actual functional dependence of LR-115 response on alpha particle energy and incidence angle. The new computed sensitivity has been compared with a new set of experimental data obtained with absorber thickness ranging from 6 to 53 μm .

Microstructure of Swift Heavy Ion Irradiated SiC, Si3N4 and AlN

ABSTRACTCross-section transmission electron microscopy was used to investigate the microstructure of single crystal silicon carbide and polycrystalline silicon nitride and aluminum nitride following room temperature irradiation with either 245 MeV Kr or 710 MeV Bi ions. The fluences ranged from 1×1012/cm2 (single track regime) to 1×1013/cm2. Ion track formation was observed in the Bi ion-irradiated Si3N4 specimen in regions where the electronic stopping power exceeded a critical value of ∼15 keV/nm (depths <24 μm). Ion track formation was not observed at any depth in 245 MeV Kr ion-irradiated Si3N4, in which the maximum electronic stopping power was 14.5 keV/nm. There was no evidence for track formation in either SiC or AlN irradiated with 710 MeV Bi ions, which indicates that the threshold electronic stopping power for track formation in these two ceramics is >34 keV/nm. The high resistance of SiC and AlN to track formation may be due to their high thermal conductivity, but further study is needed to quantitatively evaluate the suitability of the various track formation models.

Usage of a corrected Bethe–Bloch formula for charge identification of fast ions with Z⩾30 recorded in polycarbonate track detectors

The Bethe–Bloch formula is commonly used to calculate energy losses and ranges of charged massive (m≫me) particles when they penetrate into a given absorber. In order to make the formula applicable to ions of any charge and energy travelling inside any given material, several corrections must be introduced. To identify the charge of unknown ions employing SSNTDs, a track formation model, based on the energy deposition of the incident particles in the absorber, is needed. The Restricted Energy Loss (REL) model assumes that only the energy deposition due to distant collisions of the incident ion with the absorber atoms contributes effectively to track formation. In this work, the effect on the charge identification process of considering the corrections to the Bethe–Bloch formula is studied, as well as the possible effect of considering a contribution of the close collisions to the REL model. The identification procedure is applied to the Ultra Heavy cosmic ray ions recorded in the Ultra Heavy Cosmic Ray Experiment.

3-D Track Analysis Using a Confocal Laser Scanning Microscope

It is shown that a confocal laser scanning microscope can be used for 3-dimensional visualisation of chemically etched tracks in CR-39 if (a) the tracks are dyed with a fluorophor and (b) the tracks are viewed directly with an oil immersion objective. Two dyeing methods are described. This new method of track visualisation has potential applications in the development of track formation models and offers new possibilities for spectrometry and neutron capture radiography with nuclear track detectors. Currently available procedures for track analysis are briefly described and ideas regarding further developments are presented.

Model of track formation.

The developed theoretical model of track formation accounts for the influence of initial atomic displacements, momenta, and initial heating of atoms on the plastic deformation of solids near the trajectory of a penetrating fast heavy ion. These initial conditions result from the energy and momentum transfer from the excited electron subsystem to the ion one near the ion trajectory. The theoretical results obtained make it possible to investigate the dependencies of the anisotropic growth of amorphous alloys irradiated with high-energy heavy ions on the inelastic and elastic energy losses of the moving ion and on the irradiated temperature. A good agreement between these theoretical dependencies and existing experimental results was obtained.

Observations by X-ray diffraction of structural changes in mica irradiated by swift heavy ions

The descriptions of high-energy ion irradiation damage in mica by small-angle X-ray/neutron scattering and electron microscopy are used to support some models of track formation in dielectric solids. More recently heavy ion tracks in mica could be observed by atomic force microscopy and the dependence of the track radius on the particle energy loss is in contradiction with previous results. This discrepancy as well as the structural modifications (i.e. amorphization, dilatation, distortions) of ion-irradiated mica are discussed using the technique of wide-angle X-ray diffraction.

A transient thermodynamic model for track formation in amorphous metallic alloys

(1993). A transient thermodynamic model for track formation in amorphous metallic alloys. Radiation Effects and Defects in Solids: Vol. 126, No. 1-4, pp. 119-122.