Track recording properties of soda glass detector for accelerated heavy ions

The etch pit diameters of soda glass detector samples exposed to ₅₄ ¹³² Xe-ions of different energies are measured for different etching times after etching the detector in a ‘new etchant’ free of the adverse effect of the etch product layer. The dependence of track diameter on the energy and on the energy loss, dE/dx of ₅₄ ¹³² Xe-ion in soda glass has been presented. The energy resolution of soda glass and the critical angle for etching of fission fragment tracks in glass detectors have also been determined. The maximum etched track length of ₅₄ ¹³² Xe-ion in soda glass has been compared with the theoretical range. The effects of different annealing conditions on bulk etch rate of glass detector and on diameters of ₅₄ ¹³² Xe-ion tracks have been presented. Experimental results show that there is a decrease in track etch rate, etching efficiency and etchable range of ₅₄ ¹³² Xe-ions with annealing. The annealing of oblique tracks shows that the vertical tracks are more stable than the oblique tracks.     

Critical etching parameters of mica, Lexan and cellulose acetate track detectors

Chemical etching characteristics of mica, Lexan and cellulose acetate have been studied for fission fragment tracks. Under suitable etching conditions a few critical etching parameters for these three track detectors have been determined. An empirical relationship between complete etching time and the etching temperature has been established.     

Micro‐Raman spectroscopy and SEM/EDX applied to improve the zircon fission track method used for dating geological formations

The zircon mineral is widely studied in geochronology. In the case of the fission track method (FTM), the age is determined by the density of fission tracks at the zircon surface, which can be observed with an optical microscope after an appropriate chemical treatment (etching). The etching must be isotropic at the zircon grain surface to be used in the FTM, which leads those zircon grains whose etching is anisotropic to be discarded. The only reason for this discarding is the nonuniform morphology of the surface grain seen by optical microscopy, that is, no further physicochemical analysis is performed. In this work, combining micro‐Raman and scanning electron microscopy (SEM) to study the etching anisotropy, it was shown that zircon grains that present at least one area at the surface where the density of fission track is uniform can be used in the FTM. The micro‐Raman showed characteristic spectra of the standard zircon sample either from the areas where there are tracks or from where there are not. The only difference found was in the Raman bandwidths, which were broader for the areas with higher density of fission tracks. This suggests simply a decrease in the relative percentage of the crystalline/amorphous phases at these areas. The SEM/energy dispersive spectrometry (EDX) showed that there were no significant differences in the principal chemical composition at the areas with and without fission tracks. Copyright © 2008 John Wiley & Sons, Ltd.     

Observations of fission-tracks in zircons by atomic force microscope

The fission-track (FT) method is a dating technique based on the observation of damage (tracks) by spontaneous fission of ²³⁸U left in a mineral. The date is calculated from the track density and the uranium concentration in the mineral. This is possible because the number of tracks is a function of uranium concentration and time since the start of track accumulation. Usually, the number of tracks is counted under an optical microscope after etching (chemical expansion of a track). However, as FT density per unit area rises, it becomes difficult to count the number of tracks. This is due to the fact that FTs overlap one another and are unable to be readily distinguished. This research examines the potential of atomic force microscope (AFM) for FT dating using zircons, which are likely to show higher FT density than other minerals due to their high U concentrations.To obtain an AFM image for a sample prepared for FT dating, removing the static electricity of the sample is essential to avoid an unexpected movement of the cantilever. A grain should be wider than about 30 μm to bring the cantilever on the mineral surface. Polishing with a fine grained compound is very important. There is not much difference in sharpness between images by AC mode (scanning with vibrating cantilever at a constant cycle) and Contact mode (scanning with the cantilever always in close contact with the surface). To confirm how tracks can be identified with the AFM, an AFM image was compared with an image obtained with the optical microscope. When change in the number of tracks and their shapes were observed through stepwise etching, the track expanded as the etching time increased. In addition, the etching rate was slower for large tracks than those for small tracks. This implied that the AFM can be used to observe etching of zircons with different degrees of nuclear fission damage. A track that could not be seen with the optical microscope due to insufficient etching could be observed by AFM methods, indicating the possibility of FT dating with high track densities using AFM after relatively short etching periods.     

Modeling the fission track etching process in apatite: Segmentation or crystallography influence

In this study, two factors which can influence fission track etching in apatite are considered: track segmentation (induced by thermal annealing) and variable radial etching speed (due to the reagent diffusion during the etching process).

During the latent track annealing, two distinguishable steps can be identified by measuring track lengths or diameters. A length reduction is firstly observed, followed by a segmentation process which leads to the emergence of disrupted regions (gaps).

At present time, electron microscopy studies on fission tracks in apatite show profiles which lead to hypotheses of a variable radial etching speed versus depth. These variations can be interpreted in terms of acid diffusion along the track. Moreover, the existence of several bulk etching speeds related to crystallographic orientation is approached.

Taking into account these different points, a software program, integrating parameters as original track orientation and depth, number of gaps, etc., is developed in order to model the track profile evolution during the etching process. Comparison with experiments in Durango apatite (Mexico) are also undertaken.     

Funnel-type etched ion tracks in polymers

It is shown that conical track etching is a much more complicated process than generally assumed. The choice of the corresponding parameters (i.e. the ratios of concentrations and diffusion coefficients of both etchant (e.g. NaOH) and stopping solutions (e.g. HCl) and the etching temperature) determines the ratio of polymer dissolution to etchant penetration. The latter value controls the counterplay of diffusion, etching, ionic conductivity, field emission and capacitive effects, which is decisive for both the final track shapes and their electronic properties. The stages of track evolution during etching under different conditions are outlined in detail. Both transparent conical nanopores and “funnel-type” tracks can be obtained, the latter consisting of a shorter cone and a residual latent track. Depending on the internal structure of that latent track segment, such funnel-type tracks either allow smooth transmission of the rectified currents or they emit unipolar current spikes. Not only the study of electronic properties of single ion tracks, but also of a multitude of tracks makes sense. Depending on the applied parameters, the individual track properties may either just add up, or new effects may be found that emerge from the interaction of the tracks among each other. This is preferentially the case for spike-emitting tracks, where effects such as phase-locked spike synchronization can be found as described by neural network theory.     

Nuclear tracks in solids: registration physics and the compound spike

Observations of GeV heavy ion and MeV cluster-ion tracks in crystalline solids give us new insight into registration physics. Thermal and ion explosion spikes no longer compete; a ‘compound spike’ accounts for both. Ion explosion dominates for surface tracks (electronic sputtering). And there can also be transient plasma stopping in the bulk. For clusters there are ‘vicinage effects’—both electronic and nuclear—which can influence track dimensions and structure. Displacement cascades in large energetic clusters may lead to projectile “fission” and coherent flow into sub-tracks. The absence of tracks in certain targets, and their size/structure in others, leads to a model of projectile assisted prompt anneal (PAPA) in 10⁻¹¹s, either partial or complete, often by swift epitaxy, on elemental lattices (e.g. silicon) or on compound sublattices (e.g. fluorite). Phase transformations are important, but simple target amorphization is rare—the exception, not the rule. For many targets the thermal spike (macroscopic) fails, since ‘point’ defects (atomistic) characteristic of the target, their motion, and the electronic band structure, determine latent track detail. Circumstances in which the Bragg Rule of Additivity fails completely are revealed, and the kinetic threshold for constructive phase transitions in tracks described. This same track physics applies generally also to geothermometry—the opposite time extremum (10⁺¹¹s)—where annealing is due to defect assisted delayed anneal (DADA). Differences between etching rates of induced and spontaneous fission tracks can be explained. The geothermobarometric “Wendt/Vidal effect” (2002)—combined pressure, temperature and stress (with time) influences on fission track annealing (in e.g. apatite)—is briefly discussed.     

Damage morphology of Kr ion tracks in apatite: dependence on dE/dX

With the aim of characterizing damage along nuclear tracks in apatite, Durango fluoroapatite monocrystals were irradiated under a high fluence ⁸⁶Kr ion beam at the G.A.N.I.L. (Grand Accélérateur National d'Ions Lourds, Caen, France). The resulting irradiation damage was studied by associating CRBS spectrometry and chemical etching. By applying Poisson's law to the backscattering results, the nuclear track average effective radius R_e was calculated for different steps along the ion path. On the other hand, the chemical etching experiments allowed us to deduce three different damaging morphologies in correspondence to the R_e values. For the first time in apatite, it has been shown that a defect fragmentation produced along the ion paths may be detected by chemical etching. These results were also applied to fission tracks in order to quantify the damage rate and to describe the damage morphology evolution along fission fragment paths.     

Track shapes,etching characteristics and track density distribution on different planes of apatite

Abstract

Studies concerning track shapes, etching characteristics and track density due to spontaneous fission of uranium along various crystallographic planes of apatite are represented. The studies were carried out on large complete crystals as well as on small grains of apatite belonging to various geological origins. Three track types (hexagonal, pyramidal and needle type) have been identified along various crystallographic planes.     

Modelling the length distribution of etched tracks taking into account fragmentation due to partial annealing

Fission track length measurements on apatite minerals are of great interest in thermo-chronology studies. RBS analyses on Durango apatites irradiated by Krypton ions have previously shown the progressive fragmentation of tracks by annealing. This study made for different irradiation energies corresponding to those of uranium fission fragments has been completed by TEM and AFM on etched tracks. In all cases, segmentation figures have been observed, that clearly necessitates to introduce fragmentation of latent tracks to model the length distribution of uranium etched fission tracks. This presentation concerns the case of a homogeneous population of tracks with partial amorphization. The next step will consist in considering multiple sub-populations with different segmentation rates. This algorithm is a new aspect to be included in our model, which already takes into account diffusion and crystallography in the track etching process.     

Etchability of Latent Fission Fragment Tracks in CR-39

We report the chemical etching behaviour of the CR-39 polymer detector exposed to fission fragments of 252Cf describing etchability of latent tracks, which are like nanocylinders. The fission fragment exposed detectors were etched in 1-7 N NaOH water solutions at temperatures 50-80℃ for 45 min in the case of track length and 180 min in the case of track diameter measurements. The reduced etch rate S （called here etchability） is determined using experimental results for all etching conditions and the etching conditions with the highest reduced etch are obtained. Physics and energetics of bulk and track etching are discussed. Possible effects causing spurious changes in determination of activation energy of etching are investigated.     

Fission fragment track etching modelling for the cellular localisation of Neptunium-237 nuclei in rat tissues

Heavy ion recording in dielectric isotropic detectors has a wide range of applications in uranium cartography or dating. In this study, solid state nuclear tracks detectors (SSNTDs) have been applied to localise neptunium-237, in vivo, by means of the neutron-induced fission cartography of neptunium-237 nuclei in organ sections. At the cellular level, a precise localisation can only be achieved with a good understanding of the etch pit evolution during the chemical etching process.

A tailor-made software for modelling the etching process has been developed to simulate the profile of an etched track produced by a neutron-induced fission fragment. This software is based on a model that considers the evolution of the track etching velocity along the damage trail in order to perfectly model the shape of the track.     

Fission studies of gold induced by (1665 MeV) π- using a CR-39 detector

The fission cross section and fission probability of ¹⁹⁷Au, induced by (1665 MeV) π^-, have been studied using CR-39 track detectors. A 4π-geometry was used to count track statistics. A beam of negative pions of 1665 MeV was produced at AGS of Brookhaven National Laboratory, USA, and allowed to fall normally on the stack. Two detectors from the stack were scanned for fission fragment tracks after etching in 6N NaOH at 70℃. The statistics of fission fragment tracks in both detectors were obtained. It was found that there was a marked asymmetry of registered tracks with respect to the forward and backward hemispheres. This asymmetry could be partly accounted for on the basis of momentum transfer to the struck nucleus. On the basis of counting statistics fission cross section was measured, and fission probability was determined by dividing the fission cross section with the reaction cross section. The fission cross-section and fission probability were compared with the computed values using the cascade-exciton model code CEM95.     

The effect of UV exposure on the track and bulk etching rates in different CR-39 plastics

It is observed that for both UK and Japanese CR-39 detectors the mean diameters of fission fragment and alpha tracks from a Cf-252 source become larger as a result of UV exposure; but in the case of ‘UV exposure last’ (i.e. Cf + UV) the diameters are larger than in the case of ‘UV exposure first’ (i.e. UV + Cf). The bulk and track etching rates undergo an increase with UV exposure for the two kids of CR-39.     

Response of cellulose nitrate track detectors to electron doses

In order to study alternative dose determination methods, the bulk etching velocity and the latent track annealing of LR 115 track detectors was studied during electron irradiation runs from a Pelletron accelerator. For this purpose alpha irradiated and blank detectors were exposed to increasing electron doses from 10.5 to 317.5 kGy. After the irradiation with electrons the detectors were etched under routine conditions, except for the etching time, that was varied for each electron dose in order to reach a fixed residual thickness. The variation of the bulk etching velocity as a function of each one of the electron doses supplied, was interpolated in order to obtain dosimetric response curves. The observed annealing effect on the latent tracks is discussed as a function of the total electron doses supplied and the temperature.     

The light transmission method of automated track scanning

An empirical method of automated track scanning is described. This new method is based on the measurement of light transmission (LT) through solid state track recorders (SSTR). Fission fragment tracks in mica SSTR are used to demonstrate the utility of this method. Data analysis reveals that the LT method is equivalent to a point sampling method at the approximately 2% (1σ) uncertainty level of the calibration data. The total (1σ) uncertainty of the LT method decreases with increasing fission density from approximately 5% at a fission density of 4.0E + 06 fissions/cm² down to approximately 2.5% at a fission density of 1.2E + 07 fissions/cm². The current stage of development permits only a qualitative comparison of the LT and point sampling methods. Recommendations to refine the LT method are advanced with emphasis on processing procedures for mica SSTR.     

Track revelation and optical properties of pentaerythritol tetrakis (allyl carbonate) plastic for application as nuclear track detector: effects of gamma radiations

The etching conditions of an indigenously prepared thin film of pentaerythritol tetrakis(allyl carbonate) (PETAC) were standardised for the use as a nuclear track detector. The optimum etching times in 6?N NaOH at 70°C for the appearance of fission and alpha tracks recorded in this detector from a ²⁵²Cf solid source were found to be 30 min and 1.50?h, respectively. The experimentally determined values for the bulk and track-etch rates for this detector in 6?N NaOH at 70°C were found to be 1.7?±?0.1 and 88.4?±?10.7?µm/h, respectively. From these results, the important track etching properties such as the critical angle of etching, the sensitivity and the fission track registration efficiency were calculated and compared with the commercially available detectors. The activation energy value for bulk etching calculated by applying Arrhenius equation to the bulk etch rates of the detector determined at different etching temperatures was found to be 0.86?±?0.02?eV. This compares very well with the value of about 1.0?eV reported for most commonly used track detectors. The effects of gamma irradiation on this new detector in the dose range of 200–1000?kGy have also been studied using bulk etch rate technique. The activation energy values for bulk etching calculated from bulk etch rates measurements at different temperatures were found to decrease with the increase in gamma dose indicating scission of the detector due to gamma irradiation. The optical band gap of this detector was also determined using UV–visible spectrometry and the value was found to be 4.37?±?0.05?eV.     

On methodical problems in estimating geological temperature and time from measurements of fission tracks in apatite

The results of apatite fission-track modelling are only as accurate as the method, and depend on the assumption that the processes involved in the annealing of fossil tracks over geological times are the same as those responsible for the annealing of induced fission tracks in laboratory experiments. This has hitherto been assumed rather than demonstrated. The present critical discussion identifies a number of methodical problems from an examination of the available data on age standards, borehole samples and samples studied in the framework of geological investigations. These problems are related to low- (<60°C) and high-temperature (>60°C) annealing on a geological timescale and to the procedures used for calculating temperature–time paths from the fission-track data. It is concluded that it is not established that the relationship between track length and track density and the appearance of unetchable gaps, observed in laboratory annealing experiments on induced tracks, can be extrapolated to the annealing of fossil tracks on a geological timescale. This in turn casts doubt on the central principle of equivalent time.

That such uncertainties still exist is in no small part due to an insufficient understanding of the formation, structure and properties of fission tracks at the atomic scale and to a lack of attention to the details of track revelation. The methodical implications of discrepancies between fission track results and the independent geological evidence are rarely considered. This presents a strong case for the re-involvement of track physicists in fundamental fission track research.     

The influence of etching parameters on the sensitivity of plastics

Abstract

It seems that the critical rate of primary ionization for track registration must also depend on the etching conditions. Simple experimental methods are presented to show a possible change in registration sensitivity as a function of the chemical parameters. It was proved, from investigations of α-particle tracks, that the sensitivity of a cellulose acetate detector can considerably depend on the concentration and type of etching reagent. Quantitative data are given on the ratio of the rate of chemical etching along the track and on the detector surface as a function of concentration of NaOH solution for tracks of fission fragments registered in plastics of cellulose acetate, polycarbonate and polyethylene-terephthalate.     

Annealing of 54 132 Xe-ion tracks in Lexan and Makrofol plastic track detectors

Samples of Lexan and Makrofol-E polycarbonate plastic track detectors were exposed to 1·1 MeV/N ₅₄ ¹³² Xe-ions to investigate the thermal track fading properties of these plastics. The experimental results show that there is no effect of annealing on the bulk etch rate while the track etch rate decreases with annealing. The track diameter decreases with increase in annealing time and temperature. It is also observed that the track density is reduced as a result of annealing. The experiments reveal that the track lengths are, in general, decreased by the application of heat and that the oblique tracks are less stable than the vertical tracks. The decrease in diameter of ₅₄ ¹³² Xe-ion tracks in Makrofol-E due to heat treatment is faster than that of ₅₄ ¹³² Xe-ion tracks in Lexan.