The pore opening process and its influence on conductivity measurements of irradiated polymer films by application of the electrochemical etching method

The technique of the electrochemical etching of irradiated polymer films is an useful method to investigate structures of the track cores.

The transversale etching rate as a function of the radius, derived from the time-dependence of the radius of the etching pore, can be interpreted as a corresponding magnitude of the degree of the damage within the track core.

In the case of polymer films irradiated by a high track density, the influence of the time distribution of the breakthroughs (pore opening process) of the etching microchannels on the conductivity changes during the etching process is to be discussed. First represented results lead to statements about the statistical nature of the pore opening process.     

Energy loss dependent transversal etching rates of heavy ion tracks in plastic

By the method of electrolytical etching track etching rates V_t and corresponding transversal track etching rates V_trans of single heavy ion tracks in thin Makrofol KG foils have been measured at ion energies from 10–480 MeV/u. Makrofol KG foils of 8 μm thickness were irradiated perpendicular to the surface with ⁷⁹Au and ⁵⁴Xe ions at specific energies with energy loss values of REL=(10–90) ^*10³ MeVcm²/g at GSI Darmstadt, Germany, and Lawrence Berkeley Lab., Cal., USA. Using the electrolytical etching method by measuring the resistance of the foil during the etching process (etching conditions: 6n NaOH, room temperature and controlled 50° C) the breakthrough time and track etching rates V_t, V_trans and V_m (bulk etching rate) were analysed. Response curves (V_t/V_m)-1 as a function of Restricted Energy Loss (REL), the maximum extension of the ion induced damage perpendicular to the ion path and the dimension of the ion track core depending on the deposited energy can be estimated.     

Design of a multifoil electrolytically controlled etching cell

Irradiating polymer films with heavy ions and subsequent electrolytically controlled etching (ECE) produces nuclear track filters with desired pore dimensions and pore density. During ECE, an electric field with low field strength and a frequency in the audio range is applied across the irradiated polymer film, which is immersed in the etching solution. An ECE cell for the simultaneous etching of three irradiated samples has been designed and developed. The average pore diameter and break-through time for tracks due to ²³⁸U(11.4 and 14 MeV/u) and ²⁰⁹Bi(13 MeV/u) ions in polycarbonate and polyethylene terepthalate have been measured.     

The pore opening process of etching polymer films irradiated by single and multiple heavy ions. The etching process in the range of the track core radius (10 nm)

The technique of electrochemical etching of irradiated polymer films is an useful method to investigate structures of the track cores. In the case of the investigation of multiple track foils, the mean effective radius corresponds to the average of all synchron etching pores. On the other hand, the etching cones of all tracks do not break through to conducting micro channels coincidentally. The statistical character of this pore opening (break through) process is still unexplained, although several effects concerning this topic have been observed in the past. Another computer program simulates by way of the Monte Carlo Method the etching process of an ensemble of tracks within a thin polymer film. The conductivity of the multiple track etching foil can be described by the convolution between the conductivity of a single pore and the time dependent breakthrough rate. By way of the Laplace Transforms the measurements of the multiple and single track etching polymer films can be deconvoluted and yield the statistical nature of the pore opening process.     

Submicroscopic analysis of tracks in mica

Tracks of 49 MeV ³⁵Cl ions in muscovite mica were analyzed by transmission electron microscopy up to 10 Å resolution applying the track replica method. The enlargement of the track diameter is measured as a function of etching time. The track shape evolution shows circular tracks for very short etching times. By increasing the etching time the tracks gradually become ovals. For longer etching times, tracks show the characteristic rhombic shape of the bulk region. A non monotonous decrease of the track velocity vs. radius is reported. Formation of a low velocity shell in the intermediate region between the central amorphous zone and the non-perturbed crystalline lattice is suggested.     

Latent track structure in polymers as observed by a highly sensitive electrolytical conductivity measurement

Abstract

First results of a new electrolytical conductivity cell are reported concerning the initial stage of the pore opening process during track etching in vitreous solids. On the basis of the soft mode (low-energy excitation) model for track etching, a distribution function for the number of perforated micropores as function of time is calculated by accounting for the radial etch rate as function of the effective pore radius.     

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.     

Investigations of heavy ion tracks in polyethylene naphthalate films

The heavy ion beam (with fluence 3x10⁸ ion/cm²) from a cyclotron has been used for irradiation of thin polyethylene naphthalate (PEN) films. Latent tracks in these polymeric films have been sensitized by UV radiation and then chemically etched in NaOH solution. The etching process parameters have been controlled by the electroconductivity method. After etching, parameters of samples have been examined by SEM and bubble point methods (Coulter® Porometer II instrument). Results have shown good quality of PEN track membranes with pore sizes in the range: 0.1 – 0.5 μm. The described procedure is known for thin polythylene terephthalate (PET) films. Taking into consideration that PEN films have got better mechanical, thermal, gas barrier as well as better chemical resistance properties in comparison with PET films, the possibility of application of such membranes is much wider.     

快重离子辐照金红石型TiO2的肿胀效应及化学蚀刻行为研究

二氧化钛（Titatium Dioxide,简称TiO₂）晶体在中能重离子辐照时表面会出现肿胀效应, 肿胀高度与入射离子的电子能损和辐照注量有关。 辐照后的TiO₂在一定条件下能够被氢氟酸溶液化学蚀刻,化学蚀刻的电子能损阈值为8.2keV/nm,未辐照TiO₂呈现几乎零蚀刻率。要达到饱和蚀刻深度,辐照离子的注量必须大于或等于1×1013ions/cm2。采用离子辐照的潜径迹理论分析研究了辐照损伤及对化学蚀刻的影响, 快重离子辐照结合化学蚀刻是制备TiO₂微结构的有效方法。 There appears volume swelling on the surface of the irradiated rutile TiO₂ crystal and the volume swelling is affected by the ion fluence and the electronic stopping power. To induce adequate irradiation damage for the chemical etching, the irradiation parameters must fulfill some requirement. There is minimum electronic stopping power for the chemical etching of the irradiated region in TiO₂ crystal, which is about 8. 2 keV/nm. If the ion fluence is below 1×1013ions/cm2, the saturated etching depth of the irradiated region in TiO₂crystal cannot be reached. The irradiation damage based on latent track formation frame and the theoretical linkage to the etching technique is investigated. It is hopeful to fabricate micro and nano scale structurce in rutile TiO₂ crystal by using the ion irradiation and chemical etching technique.      

Activation energy of etching for CR-39 as a function of linear energy transfer of the incident particles

In this work, we have studied the effect of the radiation damage caused by the incident particles on the activation energy of etching for CR-39 samples. The damage produced by the incident particle is expressed in terms of the linear energy transfer (LET). CR-39 samples from American Acrylic were irradiated to three different LET particles. These are N (LET₂₀₀ = 20 KeV/μm) as a light particle, Fe (LET₂₀₀ = 110 KeV/μm) as a medium particle and fission fragments (ff) from a ²⁵²Cf source as heavy particles. In general the bulk etch rate was calculated using the weight difference method and the track etch rate was determined using the track geometry at various temperatures (50–90 °C) and concentrations (4–9 N) of the NaOH etchant. The average activation energy F_b related to the bulk etch rate v_b was calculated from ln v_b vs. l/T. The average activation energy E_t related to the track etch rate v_t was estimated from ln v_t vs. l/T. It is shown that activation energy of etching is a constant value for CR-39 detector where E_t was found to be independent on the damage produced by the incident particle.     

Determination of the range of alpha particles in SSNTD by optical density method

A technique based on the optical density (D) measurement of the etched track is useful for charged particles spectroscopy using SSNTD. It was shown that the stopping power of alpha particles in CR-39 is proportional to D. We measured the optical density and derived an expression to estimate the range of alpha particles in CR-39 detector as a function of the bulk etching rate and etching time. The relation between the etching time, track parameters (depth, radius) and D for different alpha particles energy and etching conditions were studied. A relation describing D as a function of track size is proposed.     

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.     

Modifications in track registration response of PADC detector by energetic protons

It has been well established that different ionising radiations modify the track registration properties of dielectric solids. In an effort to study the response of Polyallyl diglycol carbonate (PADC Homalite) detector towards fission fragment, PADC detectors were exposed to 10⁴ Gy dose of 62 MeV protons and then one set of samples were exposed to fission fragments from a ²⁵²Cf source. Two of these detectors were containing a thin layer of Buckminsterfullerene (C₆₀). The study of the etched tracks by Leitz Optical Microscope reveals that the track diameters are enhanced by more than 70% in the proton irradiated zone as compared to that in the unirradiated zone. Scanning Electron Microscopy was performed after etching the sample in 6 N NaOH at 55°C for different etching times, to study the details of the surface modifications due to proton irradiation of PADC detectors with and without C₆₀ layer. Our observations revealed that the diameters and density of proton tracks have increased with etching time on the surface facing the fullerene layer as well as the other surface. However, a relatively more open structure of the etched surface containing C₆₀ as compared to the bare one may be an indication of the extra damage caused by the energy released upon the destruction of C₆₀ molecules by energetic protons.     

Proton tracks and the formation of pores in poly[diethylene glycol bis-(allyl carbonate)

Modern dosimetry needs efficient detectors for registering light ions, especially light ions having energies of up to 10 MeV/amu. That is why this research pays attention to the development of materials for such a task. In this work, a CR-39 detector, which is the most efficient detector, was used. It was irradiated with low-energy protons. Using sensitive electrolytic etching and electron scanning microscopy, a complete analysis was carried out of the process of the formation of a pore starting from its opening to the final stage of its formation. The process of sequential track breakthroughs was observed. The data obtained on the shape of the pore and the parameters of its formation allow simulation of the process of etching. The etch rates and sensitivity of etching are determined. The influence of energy losses on the geometry of the pore is considered.     

Electrolytes in etching of latent tracks of heavy ions in polyethylene terephthalate

Previously unknown features of etching of polyethylene terephthalate, latent tracks of multiply charged accelerated ions in it, and track membrane pore formation are considered. It was found that K ions (in the form of KCl salt) in a KOH solution enhance etching of both initial polyethylene terephthalate and tracks. Ba²⁺ ions enhancing etching of initial polymer significantly inhibit etching of tracks. It is assumed that etching inhibition is associated with Ba²⁺ ion adsorption on track active centers. The features detected are used to fabricate track membranes with thin selective layer.     

Kinetic model for the relationship between mean diameter shortening and age reduction in glass samples

Fission tracks in glass samples are shortened when they experience thermal treatment. Consequently, the observable dimensions associated with track length also diminish. The dimension normally used to characterize track size is the mean diameter of the etched track at the surface, D. Another consequence of length shortening is the reduction of surface density, ρ, implying a reduction of the fission-track age. In this work, a kinetic model is developed to describe the relationship between fission-track mean diameter shortening and surface fission-track density reduction in glass samples, based on geometrical and etching hypotheses. The result is a two-parameter equation given by

(1)

in which h is the thickness of the layer removed during etching and n is a parameter related to the latent track geometry and etching reaction rate. The equation was compared with experimental data on Australite glass found in the literature and with fresh data on Macusanite glass presented in this work. The model fits the experimental curves quite well, showing that it describes the etching effects correctly (within its limitations). In addition, the model equation derived in this work can be very useful in age correction of partially annealed glass samples.     

Studies on the track formation mechanism of the heavy ions in CR-39

The bulk etch rate for two types of CR-39 detector was measured as a function of temperature and the activation energies of bulk etching was determined. Experimental values of track etch rate were derived directly from the function of the succesive measured track length vrs. etching time for ²⁰⁹Bi, ¹²⁹Xe and ²⁰Ne ions.

The maximum etchable length of 13 MeV/u ²⁰⁹Bi and 13.04 MeV/u ¹²⁹Xe ions have been measured at and below these energies. A comparison of the measured and calculated track length data is presented.     

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.