Etching Of Latent Tracks Research Articles

Impact of dicarboxystilbene impurities on the properties of swift heavy ion latent tracks in PET films

We present a new hypothesis and supporting experimental evidence about the essential role played by small impurities of dicarboxystilbene in the process of UV treatment of PET films irradiated with swift heavy ions (SHI). This treatment both forms highly selective membranes with permeability values comparable to natural ones (the track-UV technique) and sharply accelerates the etching of latent tracks in membrane production (the track-etching technique). We hypothesize (1) that these high permeability value is due to the presence of a molecular motor of an Archimedes screw type in the central part of the latent track formed by photoinduced trans-cis isomerization of dicarboxystilbene molecules that are anchored in helical conformations in the latent track; and (2) that the acceleration of etching rates is due to the preferential accumulation of phenanthrene-type molecules in the central part of the latent track due to the existence of a cyclization channel for photoexcited molecules of cis-dicarboxystilbene. In the presence of alkali solution, phenanthrene molecules release electrons which behave as strong anions in aqueous solution, catalyzing alkaline hydrolysis of PET molecules in the central part of the track. We present experimental observations of photoinduced changes in transmission light intensity after track-UV light treatment of both pristine and SHI irradiated PET films that confirm the presence of trans-cis isomerization of dicarboxystilbene molecules and show their contribution to the formation of new helical conformations in SHI irradiated PET films during the light treatment.

Fabrication of double conical PET nanochannel for molecular detection

Polymer nanochannels based on ion-track etching have attracted increasing interests for molecule detection using current blockage because of the easy control of nanochannel with precise geometry at 1 nm scale in recent years. In this work, polyethylene terephthalate (PET) membranes were irradiated with single ions of 2.15 GeV Kr and then the single latent ion track was developed to fabricate nanochannels of several nanometers for lambda-DNA detection. The ion-track etching with DC or AC provided reliable fabrication of double conical nanochannel with similar size of 48 kb λDNA with symmetrical ion transportation. Current blockage experiments demonstrated that the bi-conical PET nanochannel is sensitive for the translocation of 48 kb λDNA biomolecules with the mean translocation blockage factor Δi/i from 0.02 to 0.10 and the ability to differentiate the number of molecules. The nanochannel is more sensitive for biomolecule detection at lower KCl concentration. This investigation demonstrates that latent track etching of energetic heavy ions is a reliable approach in polymer nanochannel fabrication for biomolecule detection with accurate nanoscale control and low-cost mass production.

Structure and properties of poly(4-methylpentene-1) track-etched membranes

The influence of irradiation and the subsequent etching of latent tracks in poly(4-methylpentene-1) (PMP) films on the transport parameters of the resulting membranes has been studied. The films have been irradiated with accelerated Kr and Xe ions of 4.5 and 1.2 MeV/nucleon in energy at a fluence of 106–109 cm−2. It has been found that the irradiation followed by etching makes it possible to obtain an anisotropic membrane with a nonporous selective layer between two porous layers with tapered pores. The CH4, CO2, and He transport characteristics of the membranes have been examined. It has been shown that these modification methods can significantly increase the gas flux through the membrane. It is believed that the ion track etching procedure as applied to PMP can form the basis for fabricating membranes with a highly permeable, nonporous, gas-selective layer.

Etching of latent tracks in amorphous SiO2 and Si3N4: Simulation and experiment

The latent track formation in silicon dioxide (SiO2) and silicon nitride (Si3N4) irradiated with swift heavy ions (SHI) has been studied using computer simulation in the frame of the thermal spike model. We have calculated radii and lifetime of the molten regions, or the regions heated to the melting point, formed in SiO2 and Si3N4 along the ion trajectories for F, S, Cl, Ar, Kr and Xe ions in an energy range of (28–200) MeV. The radius of the molten region was chosen as a criterion for track “etchability” in the case of SiO2. The results of computer simulation have been compared with the experimental results of track etching in 4% aqueous solution of hydrofluoric acid (HF). The validity of the criterion taken for the creation of homogeneous “etchable” ion tracks in SiO2, namely, the formation of a molten region with radius larger than 3.0 nm [1] in the matrix along the ion trajectory, has been confirmed. It has been found that both the etched track depth and diameter increase with the fluence for the same type of ion species. Under our experimental conditions, for the case of Si3N4we failed to etch regular conical channels with uniform size distribution.

Peculiarities of latent track etching in SiO2/Si structures irradiated with Ar, Kr and Xe ions

The process of latent track etching in SiO2/Si structures irradiated with 40Ar (38MeV), 84Kr (59MeV) and 132Xe (133 and 200MeV) ions has been investigated. The experimental results of SiO2 etching in a hydrofluoric acid solution have been compared with the results of computer simulation based on the thermal spike model. It has been confirmed that the formation of a molten region along the swift ion trajectory with minimum radius of 3nm can serve as a theoretical criterion for the reproducible latent track etching tracks in SiO2.

SSNTD Techniques in Radon Surveys for Hydrocarbon Exploration and Occurrence of Natural Gas Seeps

Leakages of hydrocarbon reservoirs often increase the radon concentration on the soil surface through distinct pathways; gas migration results in either prolific macro-seeps or micro-seeps. Soil gases, including radon, are recognized as potential tracers in geoscience. The surficial radiometric anomalies over hydrocarbon reservoirs provide the oil community with a complementary survey tool for oil exploration through the use of nuclear track methodology. The Solid State Nuclear Track Detector (SSNTD) is one of the recognized techniques to be employed advantageously in radon surveys for hydrocarbon exploration and occurrence of natural gas seeps. The nuclear track method provides information on the nature of radioactive gas sources, emanations from the soil and their transport pathways. Latent track etching conditions and their analysis are included.

Swelling and structure of radiation induced near-surface damage in CR-39 and its chemical etching

Abstract Systematic measurements of swelling of CR-39 nuclear track detector (NTD) due to irradiation with fission fragments and alpha particles over a wide range of fluences from 252Cf are presented here. Precisely designed and optimized exposure and chemical etching experiments were employed to unfold the structure of radiation induced surface damage. Delays in the startup of the chemical etching of latent tracks in low radiation fluence detectors are measured and are found to contain important information about structure of the surface damage. Simple atomic scale pictures of radiation induced surface damage and its chemical etching are developed using measurements of radiation induced swelling of CR-39 detectors and nuclear track parameters. The computer code SRIM2010 was utilized for the calculations of basic features of latent tracks of fission fragments and alpha particles in CR-39. Another computer code TRACK_VISION was used to compute parameters of etched tracks. Computations and experimental findings in the paper coherently compose a realistic picture of radiation damage.

Radiation-Induced Nano-Explosions at the Solid Surface: Near Surface Radiation Damage in CR-39 Polymer

New measurements of fission fragment and alpha particle induced surface damage in the most sensitive and commonly used nuclear track detector CR-39 are presented here. Precisely designed and optimized exposure and chemical etching experiments are employed to unfold the structure of radiation induced surface damage (RISD). Delay in the startup of the chemical etching of latent tracks or surface radiation damage is measured and is found to contain important information about the structure of the surface damage. Simple atomic scale pictures of RISD and its chemical etching are developed in an empirical manner. Theoretical model and experimental findings coherently compose a realistic picture of early or femtosecond evolution of RISD.

Electrokinetic study of etching latent tracks of accelerated heavy ions in poly(ethylene terephthalate) and polyimide

The etching of latent tracks and pore formation in track membranes are studied. It is shown that the incorporation of K+ and Ba2+ ions into alkaline solutions accelerates the etching of poly(ethylene terephthalate) (PET) and latent tracks in it. The etching is accelerated due to a decrease in the negative surface charge of PET surface and the pores in track membranes. Isoelectric points are determined for PET and polyimide track membranes and it is established that they depend on pore diameter. As the pore diameter is enlarged from 30 to 70 nm, the magnitude of the negative surface charge rises seemingly due to the increase in the concentration of carboxyl groups on the pore surface. It is assumed that this effect is due to either a high mobility of carboxyl groups in a gel, which is formed on pore walls as a result of etching latent tracks, or a displacement of the slipping plane caused by a decrease in the thickness of the gel layer.

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.

Silica-based monolithic sensing plates for waveguide-mode sensors

We developed a monolithic sensing plate for a waveguide-mode sensor. The plate consists of a SiO(2) glass substrate and a thin silicon layer the surface of which is thermally oxidized to form a SiO(2) glass waveguide. We confirmed that the sensing plate is suitable for high-sensitivity detection of molecular adsorption at the waveguide surface. In addition, a significant enhancement of the sensitivity of the sensor was achieved by perforating the waveguide with holes with diameters of a few tens of nanometers by selective etching of latent tracks created by swift heavy-ion irradiation. Possible strategies for optimizing the plate are discussed.

Sensibilization of Chemical Etching of Poly(ethylene terephthalate) Films Irradiated with Accelerated Xenon Ions

Processes of the sensibilization of alkaline etching are studied for poly(ethylene terephthalate) films irradiated with xenon ions with an energy of 1 MeV per nucleon. The photosensibilization of alkaline etching of latent tracks in poly(ethylene terephthalate) is shown to be due to photooxidation processes involving molecular oxygen dissolved in the polymer. Oxygen is assumed to form molecular complexes with aromatic rings of the macromolecules and polyester degradation products; these complexes absorb in the near ultraviolet spectral range (λmax ≈ 310 nm) and initiate photooxidative degradation in poly(ethylene terephthalate) and in the substance of latent tracks. Ozone is shown to be an efficient sensibilizer of the chemical etching of the tracks. The photosensibilization and ozone sensibilization effects are greater in films irradiated with xenon ions, indicating a high selectivity of sensibilization processes in the latent tracks.

Radiation resistance of track etched membranes

Track etched membranes (TEMs) obtained by irradiation of polymer films with heavy ions and subsequent etching of latent tracks can be applied in many fields and among others in biomedicine as well. It is important to know radiation resistance of TEMs because of wide use of radiation sterilization in the case of biomedical devices. Tensile properties of TEMs made of PET and PC films with the thickness of 10 μm after electron irradiation at different doses are known from literature. Nowadays TEMs are being manufactured from thicker (20 μm) PET and PC films as well as polyethylene naphthalate (PEN) films are proposed for TEMs. It seems to be important to get data about radiation resistance of new kinds of TEMs. Samples of polymer films made of PET and PEN with the thickness of 19–25 μm and TEMs made of such materials have been irradiated using 10 MeV electron beam with doses up to 990 kGy. Tensile properties and SEM photographs of the samples after irradiation are given in the paper.

Etching of tracks of accelerated heavy ions in poly(ethylene terephthalate) and some physicochemical properties of track membranes

The features of etching of latent tracks of heavy ions in poly(ethylene terephthalate) up to pore formation were investigated. It was found that the etching process included the following stages: (1) electrolyte penetration into the pores due to capillary forces and removal of monomeric radiolysis products; (2) swelling of the cross-linked (due to secondary electrons) polymer areas around the tracks to give the gel layer; (3) removal of the gel layer and the formation of track membranes with a pore radius of 40–50 A. The radiation-chemical processes in polymers influence the physicochemical properties of the obtained membranes. The microrelief of the membrane surface was studied by atomic-force microscopy.

Study of pore formation during etching of latent tracks of accelerated heavy ions in poly(ethylene terephthalate) by atomic force microscopy

The process of transformation of latent tacks of accelerated heavy ions of poly(ethylene terephthalate) into pores and the formation of a porous structure of track membranes was studied by atomic force microscopy. It was shown that on initial etching, 10-nm high knolls with an average diameter of 800–1000 A are formed in place of tracks. Based on the knolls, through channels are formed, which emerge on the surface as conical cavities. It was shown that further etching gives first cylindrical channels of diameter 800–1000 A, which then undergo radial etching.

New technique for nondestructive examination of latent track etching

New technique for examination of latent track etching based on the transmission of charged particles is suggested and some of preliminary experimental results are presented proving the feasibility of the method.

Neutron dosimetry at low and high fluences with CR-39

In the Laboratory of Nuclear Microanalysis, we have developed two techniques for neutron dosimetry; the first for low fluence, the second for high fluence. These two techniques use a Solid State Nuclear Track Detector (SSNTD): the CR-39. The low fluence technique is based on the measurement of etched tracks resulting from a neutron-proton conversion. A Monte Carlo code performs a simulation of the (n,p) collision in the detector, and a numerical computer code of latent track etching allows the evaluation of the etched track parameters. The object of this is to obtain characteristics of a neutron fluence from the measured etched track parameters. When there is a high fluence and high doses, CR-39 is unsuited for optical microscopy analysis. This is because of track overlapping which makes it impossible to carry out counting and exploitation. We have therefore developed a new method permitting the reading of samples based on the measurement of the angular distribution of coherent light (HeNe laser) transmitted through the irradiated etched SSNTD. We present these two techniques and our initial results.

Discontinuous fission tracks in crystalline detectors

It is widely recognized that a key to the more complete exploitation of solid state nuclear track detectors lies in knowledge of the ways in which a particle is brought to rest, and how its energy is stored as lattice defects. One indirect way of looking at latent tracks — in an effort to bridge the micro/macro — has been small angle X-ray scattering, and the subsequent, multi-parameter model has spawned others for different solids. This work led to the so-called “gap model”, in which intermittent extended defects are separated by point defect rich regions. Latent intermittent fission fragment tracks were seen as long ago as 1962, using direct transmission electron microscopy (TEM). It is shown, in more detail, that the intermittency arises from periodic bursts of electronic energy loss along the particle trajectory, and that this makes it possible to measure the thickness of a crystal, using TEM, to an accuracy of one atomic (or molecular) layer. In other words anisotropy of the basic crystal lattice is responsible also for the latent track structure, as it is for the well-known angular variations in particle ranges evidenced in etched track polar plots, for which “channelling” and “quasi-channelling” are responsible. Simple probability theory, isotropic fragment emission, and the lattice structures of muscovite mica and molybdenite are used to predict the most probable extended defect length for at least an order of magnitude comparison with the X-ray work, since crystal orientations are not specified. Speculation is made on the consequences of this work for the etching of latent tracks.