The effect of gamma irradiation on the activation energy of bulk and track etching in Lexan track detector

Various studies have been performed to determine the response of Lexan polymer to gamma irradiations. The track recording properties of certain polymers are changed under the influence of electromagnetic radiations and environmental conditions. In the present work, the effect of gamma irradiation on the activation energies of bulk and track etching in case of Lexan samples have been investigated. The attempt has also been made to study the influence of temperature on the bulk and track etch rates of gamma irradiated polymer. The studies reveal an increase in the bulk and track etches rates with gamma-dose. However, the activation energy associated with track and bulk etch rates at a given temperature and at a constant concentration decreases with gamma-dose.     

Study of 18 40 Ar ion tracks in cellulose nitrate

Sample of cellulose nitrate (Russian) is exposed to ₁₈ ⁴⁰ Ar ions. The bulk etch rate has been studied at different etching temperatures and the activation energy for bulk etch rate has been calculated. The etched track lengths are measured for different etching times. The energy loss rate and range of ₁₈ ⁴⁰ Ar ions in CN(R) is also calculated. The critical threshold value for etchable track in CN(R) is determined by comparing the theoretical and experimental values of track length. The response curve of CN(R) is also presented.     

A comparative study of track registration response of makrofol-(KG, KL & N) polycarbonate to Ar ions

In the present work a comparative study of track registration response of ⁴⁰Ar ions in different types of Makrofol polycarbonates viz. Makrofol-KG, KL & N have been done. The etched track parameters viz. bulk etch rate, track etch rate, etch rate ratio, cone angle and etching efficiency were calculated. The variation of etching rates with temperature were found to be exponential and follow the Arrhenius equation. The values of activation energy for bulk and track etching were also calculated. Maximum etchable track length/range were also obtained and compared with the theoretical values obtained from computer program RANGE. From the results it is found that the polycarbonates having same chemical composition manufactured by different chemical processes have slightly different behavior.     

Measurement of the track etch rates along proton and alpha particle trajectories in CR-39 and calculation of the detection efficiency

Computation of the neutron response of CR-39 detectors needs to simulate the track formation by neutron induced charged particles taking into account the bulk etch rate and the track etch rate varying along the particle trajectories. The latter one was determined experimentally by track length measurement. The results allowed to derive the relationship between the track etch rate and the restricted energy loss of the charged particles. On this basis, the geometrical track parameters and track etch rates as well as the critical angle of particle incidence could be determined for protons and alpha particles in the energy range from 0.2 to 8.8 MeV. The energy dependence of the critical angle enabled to determine the detection efficiency for a charged particle of given energy and direction.     

Response of CR-39 to medium energy electron irradiation

The effect of 5-15 keV electron irradiation on the etch rate of CR-39 nuclear track detectors has been investigated for surface doses from 0.09 to 13.85 J/cm2. Even before etching, electrons produce a surface depression proportional to the surface dose raised to the power 0.78 +/- 0.01. Etch rate enhancement was observed in the surface region (about 4 micrometers deep) and was well approximated by a Gaussian function of depth. The depth and thickness of the etch rate enhancement increase with increasing electron energy, but are independent of dose. The maximum etch rate is proportional to the peak volumetric dose raised to the power of 1.45 +/- 0.06, independent of electron energy. No signs of a saturated response were found in the etch rate. This enhanced etching rate may significantly affect nuclear track identification in situations with an electron background.     

Study on response of CR-39 detector to light ions

The response of CR-39 detector has been obtained precisely for protons, deuterons, tritons, alpha-particles and lithiumions with energies of a few MeV/nucleon. The track etch rates were determined from the growth curves of pit radius and summarized as the response functions. The accuracy of this method is high enough to discriminate among hydrogen isotopes under a certain condition. The correlation between the response and LET with various cut-off energies has also been examined. It was found that LET is not an unique parameter describing the response function adequately for different ions by the same expression.     

The effect of post-exposure annealing on the track registeration characteristics of CR-39 nuclear track detectors

The effect of post exposure annealing on the track registeration characteristics of CR-39 (Pershore) Solid State Nuclear Track Detectors has been studied. The changes introduced in the bulk etch rates, track diameter, and the track density have been observed. The results indicate that the bulk etch rate of the detectors and the size of the tracks are considerably changed due to annealing. Variations in the track density are, however, not serious in the presently studied temperature range.     

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.     

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.     

On the response of LR-115 plastic track detector to 10 20 Ne-ion

The track etch rates of ₁₀ ²⁰ Ne-ion in cellulose nitrate (LR-115) have been measured for different temperatures and the activation energy is determined. The experimental results show that both the track etch rate and the normalized track etch rate depend on the energy loss as well as on etching temperature. The maximum etched track length of ₁₀ ²⁰ Ne-ion agrees with the theoretically computed range. The experimental results show that there is no sharp threshold, at least in CN(LR-115).     

Annealing of heavy ion tracks in cellulose nitrate plastic track detectors

The effect of heat treatment on the latent tracks in cellulose nitrate plastic track detectors has been studied. The bulk etch rate increases with annealing temperature while the track diameters of different ions in cellulose nitrate decrease with increase in annealing time and temperature. Experimental results show that for heavier ions higher temperatures are needed for their complete erasure. The track length and track etch rate are decreased by the application of heat. Experiments reveal that annealing reduces track density. The vertical tracks are more stable than the oblique tracks and require higher temperature for their complete erasure.     

Simulation of the track growth and determining the track parameters

We have found the equation of the etch pit wall in solid state nuclear track detectors, as follows:

where: x is the distance along a track from the point where the particle entered the detector; V(x) is the ratio of the track etch rate to the bulk etch rate; C is the integration constant that can be determined from particle penetration depth, and y is the normal distance from the particle trajectory to the etch pit wall. The equation is derived assuming the increasing track etch rate V_t along the particle trajectory.

The above equation can be used for the simulation of the track growth and calculating the major and the minor axis of the etch pit opening. The corresponding computer program was set up. The input parameters of this program are: alpha particle energy, incidence angle and removed layer: the output are track parameters. The results obtained by this method are compared with another approach given by Somogyi and Szalay (1973) and reasonably good agreement is found.     

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.     

Calibration of CR-39 with atomic force microscope for the measurement of short range tracks from proton-induced target fragmentation reactions

We studied the track response of CR-39 plastic nuclear track detectors (PNTD) for low (<6 MeV/n) and high (>100 MeV/n) energy heavy ions using the atomic force microscope (AFM). CR-39 PNTD was exposed to several heavy ion beams of different energy at HIMAC (Heavy Ion Medical Accelerator in Chiba). For AFM measurement, the amount of bulk etch was controlled to be ∼2 μm in order to avoid etching away of short range tracks. The response data obtained by AFM for ∼2 μm bulk etch was in good agreement with data obtained by the conventional optical microscope analysis for larger bulk etch. The response data from low energy beams (stopping near the surface) was also consistent with the data from high energy beams (penetrating the detector) as a function of REL (restricted energy loss) with the δ-ray cut off energy of ω₀ = 200 eV. We experimentally verified that REL (ω₀ = 200 eV) gives a universal function for wide energy range in CR-39 PNTD. This work has been done as part of a basic study in the measurement of secondary short range tracks produced by target fragmentation reactions in proton cancer therapy fields.     

CR-39 and Lexan calibrated as low-LET radiation dosimeter, for three Mexican irradiation facilities

An experimental calibration of two common nuclear track detectors, CR-39 and Lexan, for gamma and electrons radiation, was performed using various irradiation facilities. The dose response was obtained as a function of two parameters, the bulk etch rate and the UV absorbance for a wide dose range from 10 to 1000 kGy. The bulk etch rate sensitivity, for gamma and electrons, in CR-39 detector is higher than for Lexan detector. Lexan has a well-defined UV absorbance spectrum, but presents saturation for doses higher than 500 kGy, the same saturation characteristic is observed for the corresponding bulk etch rate response. For electron and gamma radiation, CR-39 shows a good response for doses from 10 kGy up to 1000 kGy, where data fit well an exponential curve for electrons and a lineal curve for gamma radiation.     

Studies on the variation of the track etch rate along alpha particle trajectories in CR-39

At the beginning of the etching process a constant track etch rate can be assumed. In deeper detector layers, however, the etch rate varies drastically along the particle trajectories. Consequently, the indirect determination of the track etch rate by measuring the etch pit diameters on the detector surface does not yield correct results. Therefore, a method for the direct measurement of the track etch rate as a function of the depth within the detector was developed. Applying this method, the relationship between the track etch rate and the energy loss in CR-39/PATRAS could be derived.     

Calibration study on the triton response of CR-39 track detector

Triton response of the CR-39 track detector has been studied at energy ranges below 2.7 MeV. Triton irradiation was made both on the top and the well polished side surface of the CR-39 sample sheets, using ⁶Li(n,t)⁴He reaction in a thermal neutron field. At large residual ranges more than 10 μm, fine results of etch rate ratio were obtained by analysing the growth curves of etch-pit radius on the top surface. But the response at near the track end-point could not be obtained well in this method, as a result of the missing track effect. Clearly resolved response at short residual ranges was attained by means of the shape analysis of the etch-pit profile observed on the side surface.     

Calibration of different plastic track detectors using accelerated heavy ions

Measurements of the dependence of track etch rate on the energy-loss of different ions have been presented. In this method, ₁₈ ⁴⁰ Ar, ₁₀ ²² Ne, ₈ ¹⁶ O and ₆ ¹² C-ions of different energies are used as energetic heavy ions for track formation in the detectors. The bulk etch rate and track etch rate are measured for different temperatures and hence the activation energies are determined. The variation ofV =V _t /V _b along the trajectory of the track has been shown for different temperatures. The maximum etched track length is compared with the theoretical range as well as with the range reported earlier. The experimental results indicate the absence of a well-defined threshold in the plastics studied.     

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.