Track Etch Rate Research Articles

Many-hit model calculations for track etch rate in CR-39 SSNTD using confocal microscope data

The present work studied an important part of ion tracks: the Bragg peak region. Information about the microscopic nature of ion-energy dissipation based on zero-approximation in frame of the many-hit model of the track structure theory was studied. The detector response, Vt, was calculated in terms of Poisson’s distribution as a function of the ion’s linear energy transfer (LET). This approach can be considered to be a zero-approximation since LET is a special case of restricted energy losses with a cut off energy wcutoff=∞: LET=REL∞. Confocal microscopic data allows the visualising and analysing of the etched tracks one by one with high precision. A three-dimensional track image was observed and the track etch rate was measured. On the basis of χ2 analysis of the experimental track etch rate (square of the least deviation), with respect to that of the theoretical value, information about the energy transfer process can be obtained. Light ions of little MeV energy were slowed down in the CR-39 detector and the detectors responses close to the Bragg peak region were studied. It was shown that in the zero-approximation no one to one relation can be found between the primary linear energy transfer (LET) and the measured specific track etch rate. The statistical analysis can be split into two separate parts; before the Bragg peak (Bethe–Bloch) and after the Bragg peak (Thin Down). The two parts analysed reflect the separated domains where the etching rate increases or decreases, due to the different role of the delta-electrons in each of these domains. The main aim of this study is to develop a method for any ion describing Vt in this very sensitive Bragg region. This would allow ion identification at low velocities on the one hand, and on the other hand to have a better understanding of the physical processes involved during high velocity ion stopping.

Etched Single-Ion-Track Templates for Single Nanowire Synthesis

Polycarbonate membranes with one pore only are created by the track-etching technique. The shape and size of the pore are determined by the type of etchant as well as by the temperature and etching time. The dynamics of single-pore formation during etching is investigated to determine the breakthrough time and the track-etching rate. The pore is characterized by electrical conductivity measurements and scanning electron microscopy. This kind of template is employed for the electrochemical deposition of a single bismuth wire that is left in the polymer for further measurements of its electrical properties.

Role of UV light illumination and DMF soaking in production of PET ion track membranes

The pretreatment effects using UV light illumination and DMF soaking on bulk and track etching rates of PET films were investigated. The wavelength of illuminated UV light plays an important role in sensitizing track etching. Illumination with the light at wavelengths longer than 320 nm showed strong enhancement in the track etching rates without influence on the bulk etching rates, whereas light with the wavelengths lower than 320 nm causes large enhancement in both track and bulk etching rates even in the interior of the material. The track etching rate is found to be not constant along ion tracks, which is attributed to the inhomogeneous distribution of reactive chemical species induced during post-UV light illumination. Furthermore, the DMF soaking of PET after UV light illumination can enhance the etching sensitivity of the track by more than 100 times. The phenomenon is attributed to the high diffusion of organic solution along tracks after UV light illumination.

Calibration factors for LR-115 (type-II) based radon thoron discriminating dosimeter

Twin chamber solid state nuclear track detector based dosimeters are used for estimating radon ( 222 Rn) , thoron ( 220 Rn) gases and their progeny concentrations in air. These dosimeters employ two numbers of LR-115 (type II) detectors inside each of the two chambers for gas concentration estimations and a third detector is placed externally for progeny measurements. The tracks formed on the detector are etched under specific conditions and counted by spark counting techniques. A theoretical model has been developed to characterize the response of these detectors to alpha particles of different energies incident at different angles on the detector surfaces. This involves the estimation of the total time required for track formation that incorporates both bulk etch rates and the track etch rates. Using this information, the region of influence for the given geometry of the dosimeter is determined. The detectable tracks from this region of influence, computed by the model, are used to obtain the calibration factors (CFs). Results yielded the CF for each of the species in the bare mode exposure as 0.02 tr cm −2 per Bq d m −3 while those for 222 Rn and 220 Rn in the cup dosimeters were estimated as 0.023 and 0.018 tr cm −2 per Bq d m −3 , respectively. The CFs for the cup dosimeters were also determined experimentally in the laboratory by exposing the dosimeters to known concentrations of 222 Rn , 220 Rn and their progeny concentrations. These compared fairly well with the theoretically compounded values. This methodology will be useful in designing cup dosimeters with better efficiencies.

3D computation of the shape of etched tracks in CR-39 for oblique particle incidence and comparison with experimental results

Computation of the shape of etch pits needs to know the varying track etch rate along the particle trajectories. Experiments with alpha particles and 7 Li ions entering CR-39 detectors under different angles showed that this function is not affected by the inclination of the particle trajectory with respect to the normal on the detector surface. Track formation for oblique particle incidence can, therefore, be simulated using the track etch rates determined for perpendicular incidence. 3D computation of the track shape was performed applying a model recently described in literature. A special program has been written for computing the x, y, z coordinates of points on the etch pit walls. In addition, the etch pit profiles in sagittal sections as well as the contours of the etch pit openings on the detector surface have been determined experimentally. Computed and experimental results were in good agreement confirming the applicability of the 3D computational model in combination with the functions for the depth-dependent track etch rates determined experimentally.

Applicability of the multi-hit model to calculate the track etch rate in µm-scale in CR-39 detectors

An attempt was made to test the applicability of the multi-hit model in CR-39 SSNTD etched for a few micrometers. In this work the detector response (V t ) as a function of the particle restricted energy loss (REL) was determined from the well-known Poisson's distribution. The model can describe the function V t (REL) for a given ion through three registration parameters (ν, C, REL o ). The model was used to fit the experimental data of V t vs. REL that were quoted from the literature at different REL regions. A computer algorithm was developed to calculate, numerically, these parameters from the non-linear V t (REL) function. It was found that the multi-hit model can predict V t for a short as well as a long REL range in CR-39, within µm-scale, with good accuracy. The ν, C and REL o parameters that satisfy the best possible fit for such data have been obtained and their physical meaning was stated as well.

Computation of etched track profiles in CR-39 and comparison with experimental results for light ions of different kinds and energies

Computation of etched track profiles needs the knowledge of the variable track etch rates along the ion trajectories. Using the depth-dependent track etch rates experimentally determined for perpendicularly incident protons, deuterons and alpha particles as well as 7 Li , 11 B , 12 C , 14 N and 16 O ions of different energies simulations of the track development were performed. Two models of track etching were applied for that purpose recently published in literature. Although the models are based on the same physical fundamentals the results are slightly different. The reasons of the discrepancies were found by analysing the algorithms in detail. Comparison of the calculated track profiles with those determined experimentally from longitudinal sections of the etch pits showed good agreement for non-overetched as well as overetched tracks. The consistency of the whole experimental data set was checked by analysing the correlation of the track etch rates with geometric track parameters for all kinds of ions and etching times covered by the experiments.

Track etch rates along the trajectories of nitrogen and oxygen ions in CR-39

Experimental studies on track etch rates in CR-39 performed with protons, deuterons and alpha particles as well as 7 Li , 11 B and 12 C ions were extended to 14 N and 16 O ions. The results are compatible with the general systematics found for the dependence on the kind of ion and its initial energy. Analysing the etch rate ratios as function of the restricted energy loss (REL), the non-existence of a unique relationship has been confirmed. However, assuming a dependence of the etch rate ratio not only on REL, but also on the depth within the detector where a given REL value occurs, all experimental data could be adjusted. The experiments with 14 N and 16 O ions allow extension of the REL range studied up to about 14 000 MeV/ cm . The whole area relevant to neutron-induced charged particles generated within the CR-39 detectors is covered thereby. Having added the data for 14 N and 16 O ions, the array of curves for the etch rate ratio could be expanded up to 14 000 MeV/ cm without inconsistencies, demonstrating the compatibility of the new data set also quantitatively.

The effect of infrared radiation on etching characteristics of CR-39 plastic track recorder

The effect of infrared radiation on the etching characteristics of CR-39 plastic track recorder has been studied. CR-39, which is commonly employed in cosmic rays studies is found to be affected by IR radiations. The changes in the bulk etch rate, in the track etch rate and in etching efficiency due to infrared radiation exposure of CR-39 are discussed on the basis of scission and cross linking during infrared exposure.

Watching at the correlation between the specific track-etch rate and the primary physical parameters of the swift ion interaction with the CR-39

Analysis of etched nuclear tracks in CR-39 solid state nuclear track detectors has recently been made possible by the confocal microscope. This recent innovation has opened up some particularly interesting perspectives. The main originality of this microscopy technique is that it makes it possible to work on numerical, three-dimensional images of chemically etched nuclear tracks in the CR-39. We have studied the performances of this new approach for light ions (H, He, Li and C) with kinetic energies typically of the order of the MeV per nucleus. First, we determined the response functions of the CR-39 for these ions. We were then able to show that aside from decreasing the analysis time of traditional methods, the confocal microscope greatly increases the sensibility of the detection. The aim of this study was to find a correlation between the response functions and the primary physical parameters of the interaction between the ion and the material, such as the linear energy transfer (LET), the restricted energy transfer (REL ω0 ), the integrated radial dose or the rate of ionization. Although these parameters presented a strong resemblance to the experimental response functions (they are all “Bragg” curves), none of them were correlated to the response function in an unambiguous way.

Gamma effect on track properties of PADC detector

Effect of high gamma irradiation on track properties of PADC (Homalite) has been studied in the dose range of 10 1– 10 6 Gy . The properties like bulk-etch rates and track-etch rates of the detector are found to increase due to gamma exposure. Etching efficiency of the detector increases due to exposure and it is significant at the dose higher than 10 3 Gy . Another track property, the critical angle, is also influenced by gamma exposure and is found to decrease with increasing dose. In all cases it is observed that the post-gamma exposure has greater effect than the pre-gamma exposure. The experimental results are presented and discussed in details.

Molten Ba(OH) 2·8H 2O as an etchant for CR-39 detector

Systematic studies were carried out to discover/unveil a best etchant for CR-39, polymeric nuclear track detector. In this context, different concentrations of NaOH, KOH, LiOH and Ba(OH) 2·8H 2O were used at different temperatures. For these etchants, bulk-etching rate, track etching rate and efficiency of the CR-39 were determined using track diameter method. Activation energies for bulk and track etching processes as well as induction time of the etchants were also studied. The results obtained were compared with that of the 6 M NaOH at 70°C. Our study showed that molten Ba(OH) 2·8H 2O yields excellent etching properties with drastically reduced etching time and relatively higher efficiency.

Three-dimensional analytical determination of the track parameters: over-etched tracks

Three-dimensional analytical determinations of track parameters are extended to cases where the tracks are in the rounded and spherical phases of development. The equation for the track wall in three dimensions and the equation of contour line of the opening were derived for all types of tracks. The expression for the surface area of the track opening has also been found. The equations come up to the well-known expressions for minor and major axes for the special case of constant track etch rate.

Three-dimensional model of track growth: Comparison with other models

Here, we present a three-dimensional model of track growth in nuclear track detectors. The equation for the track wall in three dimensions and the equation of the contour line of the track opening have been derived for all types of tracks (i. e., tracks with sharp tips and tracks with rounded tips). The expression for the surface area of the track opening has also been found. The equations become the well-known expressions for minor and major axes for the special case of constant track etch rates. Computations of track parameters based on our model have been compared with the track growth models given by Somogyi and Szalay and the one given by Fews and Henshaw. Good agreements have been found among these three independent models.

Studies of CR-39 etch rates

A series of chemical etching experiments have been carried out on CR-39 detectors irradiated with fission fragments of 252Cf to study the bulk and track etching characteristics. Experimental data has been analyzed to find out important track etch parameters. Both bulk and track etch rates are found to follow the Arrhenius equation which gives the variation of etch rate with temperature for a specific set of etching conditions. Activation energies for bulk and track etching have been determined by fitting Arrhenius equation to the experimental data. Other track etch parameters, e.g. critical angle of etching and track registration efficiency have also been determined using experimental data. Track etch parameters depend on properties of incident ion and etching conditions. Results describing the dependence of track etch parameters on etching conditions have been presented. These results are useful in the interpretation of track data.

Measurement of bulk etch rate of LR115 detector with atomic force microscopy

Equations for calculating track parameters have been proposed, which invariably involve the track etch rate V t and the bulk etch rate V b. The present study measured V b for the LR115 solid-state nuclear track detector using atomic force microscopy (AFM). The detectors were partially masked using rubber cement and then etched in 2.5 N NaOH solution at 60°C for time periods ranging from 5 to 40 min . The rubber cement was then peeled off and cross-sectional images of the LR115 detectors were obtained by AFM. V b has been found to have different values below and beyond the etching time of about 13.5 min , with the values of 0.0555 and 0.0875 μm min −1 , respectively. The increase in V b with the etching time can be explained by a diffusion-etch model, in which the additional damage of the detector material is due to those etchant ions diffused into the detector over time. Now that V b has been determined, this can be combined with the track etch rate V t to calculate track parameters.

Intrinsic efficiency of LR-115 in alpha particles detection: simulations and experiments

A numerical simulation is developed to characterize the response of the cellulose nitrate detector “LR-115 type II” to alpha particles of different incidence angles and energies. It permits to know whether an alpha particle at a given energy and direction is able to produce a visible etched track or not. For this purpose, a V t-variable track etch rate model is used. We have considered that the track etch rate is a function of the ionization rate and the defect created by delta rays along the alpha particle trajectory. Validation of the model is presented in the form of comparisons between theoretically computed values of the sensitive energy range and the track diameters and experimentally determined ones.

Dependence of the etch rate ratio on the energy loss of light ions in CR-39

Mathematical simulation of the etch pit evolution requires the knowledge of the relationship between the etch rate ratio and the restricted energy loss of charged particles. Whereas a unique correlation of both quantities independent of the kind of particle and its initial energy was found for protons, deuterons and alpha particles the results of the depth-dependent track etch rates for 7 Li , 11 B and 12 C ions indicated a different behaviour for heavier ions. A detailed analysis of the etch rate ratio in dependence on the restricted energy loss confirmed the existence of specific relationships for ions of different kind and initial energy. The spread of the corresponding curves is explained by the gradual increase of the track etch rate over a certain distance from the detector surface. The speed of this increase is the higher the lower the restricted energy loss is.

Studies of experimentally determined etch-rate ratios in CR-39 for ions of different kinds and energies

The ratio of track etch rate to bulk etch rate is correlated with the energy transfer of a penetrating ion. For quantifying this correlation the etch-rate ratio, V, in dependence on the restricted energy loss, REL, for ions of different kinds and energies was studied. The track etch rate was taken as depth-dependent function derived from track length measurements. A unique V(REL) relationship was found for all cases where the reduction of the track etch rate at the beginning of the etching process is of little influence. Etch-rate ratios determined after the common method of track diameter evaluation have been found to be systematically too low with the exception of the region near the detector surface.

Experimental determination of the critical angle for particle registration and comparison with model predictions

The generation of visible etched tracks by charged particles is only possible if the angle of incidence is lower than a critical angle θ c. This quantity has been calculated from the bulk etch rate and the track etch rate varying along the particle trajectory. The results for θ c can be described as a function of the initial particle energy and the etching time. Surprisingly, the energy dependence of θ c at a given etching time is characterised by splitting into two branches at higher particle energies. For example for the alpha-particle-induced tracks in CR-39, the theoretical findings were tested experimentally by measuring the etch pit axis and the detector efficiency as a function of the angle of incidence. This test confirmed the model prediction for the characteristic energy dependence of the critical angle.