Track etching parameters for plastics

Abstract

A series of experiments was performed to study the effect of types of etchant, concentration of etchant, etchant temperature and other parameters on track development in cellulose nitrate, polycarbonate resin, cellulose triacetate, and cellulose acetate butyrate plastic. This work has led to a set of preferred etching conditions for each of these plastics. For example, although there were only slight differences in general etching rate when LiOH, KOH, and NaOH were used as track etchants for cellulose nitrate, the alpha particle registration sensitivity was greatest when NaOH was used. Also in cellulose nitrate the general etching rate and the particle registration sensitivity did not change significantly with increasing concentration for hydroxide solutions > 6 N. This was in marked contrast to other plastics which showed a strong concentration dependence.     

Response of triafol-TN plastic track detectors to238U-ions

Triafol-TN plastic detector foils have been irradiated with²³⁸U ions of energy 16.34 MeV/u and the tracks produced have been observed using the chemical etching technique. The bulk etch rate and track etch rate are determined under successive chemical etching. In our case, the validity of Arrhenius’s law is confirmed by the fact that the same value ofE _a obtained for these different concentrations, within experimental errors. The results show a linear correlation between the measured track etch rate along the track and the corresponding total energy loss rate and a threshold value of ～ 5.0 MeV/(mg/cm²) for track registration was obtained. The maximum etched track length of²³⁸U-ion in triafol-TN has been compared with the theoretically computed range.     

Tracks of 18·56 MeV/u 40Ar ions in Lexan polycarbonate detector

Latent damage tracks of energetic⁴⁰Ar ions (18·56 MeV/u) have been recorded in Lexan polycarbonate detector. Bulk and track-etch parameters are evaluated under successive chemical etching. Our results show a linear correlation between the measured track-etch rate along the track and the corresponding total energy-loss rate and predict a threshold value of 5·0 MeV mg⁻¹ cm² for track registration. Maximum etchable track lengths of⁴⁰Ar ions as a function of energies have also been measured and compared with three different sets of theoretical ranges.     

Neutron response study using poly allyl diglycol carbonate

The results of an experimental work aimed at improving the performance of the CR-39 nuclear track detector for neutron dosimetry applications are reported. A set of CR-39 plastic detectors was exposed to ²⁵²Cf neutron source, which has the emission rate of 0.68 × 10⁸ s⁻¹, and neutron dose equivalent rate 1 m apart from the source is equal to 3.8 mrem/h. The detection of fast neutrons performed with CR-39 detector foils, subsequent chemical etching and evaluation of the etched tracks by an automatic track counting system was studied. It is found that the track density increases with the increase of neutron dose and etching time. The track density in the detector is directly proportional to the neutron fluence producing the recoil tracks, provided the track density is in the countable range. This fact plays an important role in determining the equivalent dose in the field of neutron dosimetry. These results are compared with previous work. It is found that our results are in good agreement with their investigations.      

REGISTRATION OF LIGHT PARTICLES BY A CELLULOSE ACETATE SOLID STATE TRACK DETECTOR

In this paper, the recording energy range and efficiency of cellulose acetate trackdetector (made by Shanghai Film Works) to proton and deuteron registration were de-termined, and the upper limit of recording energy to α-particle registration was dete-rmined too The highest energies of α-particle, proton and deuteron registrated are11.7, 0.8 and 1.35 MeV respectively. At a certain removed layer thickness range, theefficiencies of vertical incident protons with energy 400--900 keV and deuterons withenergy 450--1350 keV registrated are all 100%. The model of restricted energy lossproposed by Benton was tested for the sensitive cellulose acetate track detector usingprotons, deuterons and alpha particles. It is shown that. the model may be applied tolight particle registrations. For these light particle registrations by the detector, thereis a functional relation between the etching rate ratios and ranges, thetefore, it maybe used to identify light particles.     

Electrochemical etching technique for neutron dosimetry

In the present work we have employed allyl diglycol carbonate (CR-39) and cellulose triacetate (CTA) plastic for detection of neutron recoil tracks without radiator. For CR-39, the results reveal that registration efficiency is a function of duration of chemical pre-etching and the best results are obtained with chemical pre-etching of 3 hours. It was also investigated that the ac field strength of 28 kV/cm having 2.5 kHz frequency was optimum for revelation of tracks. Interestingly the sensitivity is fluence dependent and it was constant up to a fluence of about 10⁸ n/cm². The sensitivity abruptly decreased with increased fluence. At optimum experimental conditions the minimum detection limit for CR-39 was found to be 0.47 mSv. For CTA, the tracks have been revealed by electrochemical etching (ECE) only and the minimum detection limit was found to be 0.85 mSv at optimum experimental parameters.      

The chemical etching of fission fragment tracks in natural fluorite

An experimental study of the mechanism for chemical etching of fission fragment tracks in the natural mineral fluorite is described. A systematic search showed that a 3:1 mixture by volume of sulphuric to hydrochloric acids was a most appropriate etchant. Experiments directed at determining the etching efficiency as a function of solvent temperature are also discussed. The preferential track etch ratioVt/Vg, the track length and the track density all depend upon the time and temperature of annealing.

It is variations of the fission track density in fluorite, with etching time and annealing temperature, which make possible an overall geophysical interpretation of annealing data for the mineral in terms of the paleoisotherm of its intrinsic fission track clock.

An interactive image analysis system INTIMAN, assembled for the swift and automatic readout of fission fragment track measurements, in both crystalline and non-crystalline materials, is described. Normal procedures for measuring and analyzing tracks are outlined.     

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.     

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.     

High Energy Charged Particle Registration in CR-39 Polycarbonated Detector

Track etch rate characteristics of CR-39 plastic detector exposed to ²⁸Si ions of 670 MeV energy have been investigated. Experimental results were obtained in terms of frequency distribution of the track diameter, track density and bulk etching rate. A dependence of the mean track diameter on energy was found. The application of the radiation effect of heavy ions on CR-39 in the field of radiation detection and dosimetry are discussed. Results indicated that it is possible to produce etchable tracks of ²⁸Si in this energy range in CR-39. We also report the etching characteristics of these tracks in the CR-39 detector.     

Experimental study on the aging process of the LR 115 cellulose nitrate radon detector

An experimental determination of the aging process of cellulose nitrate detector material was based on the examination of special properties of the LR 115 solid state nuclear track detectors (SSNTDs) of various ages up to 18 years. The examined relevant parameters are the bulk etching rate v_b and the track etching rate v_t. These parameters are responsible for the appearance, the size and the registration efficiency of tracks of -particles from radon gas in the detector. To find a correlation between these material parameters and the detector sensitivity an experimental calibration of indoor room and outdoor soil detector devices based on LR 115 took place at the Umweltforschungszentrum Leipzig-Halle (Germany). To avoid routine calibration work in external radon exposure facilities a correction of the age dependent calibration factors with the material parameters measured in one's own laboratory was targeted. In this study a general age dependence, however, was not found. The following statements for practical applications can be made. (i) the bulk etching rate v_b for detectors of the same batch has a depth dependence and this dependence is constant over 2 years (LR 115 September 1994). (ii) detectors of different batches older than 5 years and stored at room temperature show an odd v_b behaviour when v_b is used for describing track shapes. (iii) the calibration factor of detectors of different batches that were stored at about +4°C is constant over 5 years (LR 115 September 1994 and February 1999, Table 2).

The conclusion is that LR 115 detectors not older than 5 years and stored in a refrigerator at about +4°C should be preferred for radon measurements. Furthermore these detectors should be recalibrated every year and the microscope work of this calibrations should be performed by the same person who performs the measurements.

In addition, a phenomenon related to fundamental track formation mechanisms was found, that the time straggling of the time t_through when vertical tracks penetrate the 12 μm thick detector layer is independent of the age of the detectors and the energy of the -particle at the detector surface.     

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.     

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.     

Informationen

Compared are some of the properties of the solid state track detectors (SSTD) on the basis of nitrogen-free cellulose derivatives (cellulose acetate, triacetate and acetobutyrate), cellulose nitrate (LR-115, CN-85) and a CR-39 track detector. The optimum composition of the cellulose acetobutyrate has been established which will ensure the best mechanical properties. A simple device has been used to measure the α detection effectiveness over the energy range from 0 to 1.2 MeV of the cellulose acetobutyrate detectors in an electric field or under UV radiation or after catalytic etching. The proton detection effectiveness of the CN-85 detector has been measured. Also presented are the track autoradiograms of the distribution of B, Li, N and ³He in silicon, silicon carbide and steel.     

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.     

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

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.     

Influence of external and internal conditions of detector sample treatment on the particle registration sensitivity of Solid State Nuclear Track Detectors of type CR-39

The sensitivity of charged particle registration with SSNTD is the most important parameter to decide about the applicability of those detectors in research, technology and environmental dosimetry. The sensitivity is strongly influenced by the treatment of detector samples before, during and after the exposure and the final evaluation process by chemical etching. Whereas changes in detection properties by external environmental influences are generally considered, the dependences on the etching conditions are ignored. Commonly the sensitivity is assumed to compensate variations in the etching conditions for track revealing. In the present work the validity of this hypothesis will be checked. In the frame of the existing database the sensitivity is not really independent on variations in etching temperatures and should be corrected for differences in the activation energies for stimulation of the bulk and track etching process. Differences in the concentration dependence may be of minor importance. Furthermore, the registration sensitivity depends on environmental conditions before, during and after the irradiation with particles under investigation. Such external parameters are the air pressure, the sample temperature and modification of bulk material by out-gassing in vacuum and exposure to γ-rays. However, the available database is insufficient and inaccurate to draw final conclusions on the detection properties of SSNTD under various external and internal conditions.     

Characteristic studies for fast detection of a wide energy range of alpha particles in polycarbonate detectors

Parametric investigations were carried out on electrochemical etching (ECE) process of Lexan polycarbonate (PC) detector. Outstanding experimental results showing the enlargement of the registration energy range of α-particle tracks of the PC and decrease of ECE time are presented in this paper.In the experiment, major parameters such as etching solution and ECE conditions are focused. Ethylene diamine is applied as an additional chemical agent to increase the bulk etching rate (V_B) which is maintained below a critical value . By using mixture of KOH, CH₃OH (methanol), NH₂(CH₂)₂NH₂ (ethylene diamine) and H₂O and applying interval-based ECE process in total duration of 70 min, expanded α-registration range of 0.5–4.7 MeV have been achieved, as well alpha track diameters decrease with increasing of alpha particle energy. In this process the density of background tracks also decreases comparably. In this paper, electric current is introduced as an effective ECE parameter for improving detection efficiency of low α-particles energy in the PC.     

Detection of energetic light charged particles by solid state nuclear track detectors

Experiments have been carried out to detect ₂ ³He particles and : rotons having energies up to 10 MeV/nucleon by using Kodak CA80-15, cellulose nitrate plastic track detector. Various etching conditions were tried in order to develop tracks for whole of the energy range considered. Detailed analysis seems to indicate that at high energies, the tracks are mainly produced by “secondaries” (elastically scattered nuclei of C, N, O and H, and other reaction products) while in the low energy region, the slowed down “primaries” play the dominant role. The prolonged etching factors of these detectors for different types of tracks have also been obtained and used to derive their average etchable ranges in the materials concerned.