Study of inhomogeneity in thickness of LR 115 detector with SEM and Form Talysurf

Long-term measurements of radon progeny concentrations using Solid-State nuclear tract detector are being actively explored. These measurements depend critically on the thickness of the removed layer during etching. Scanning electron microscope (SEM) observations have identified irregularities in etched LR 115 detectors, such as detachment of the active layer from the substrate and formation of air gaps in the substrate. After discarding these irregularities, by using “Form Talysurf” surface profile measurements, the thickness of the active layers for the LR 115 detector are found to be 11.8±0.2 and 5.0±0.4 μm before and after 2 h of etching, respectively. The coefficient of variation has thus risen from 1.7% to 8.0% on etching. The increased inhomogeneity is explained by the formation of track-like damages, which have been observed using Form Talysurf, SEM, optical microscope and atomic force microscope. With this relative large coefficient of variation, the thickness of the active layer in the LR 115 detector cannot be assumed to be homogeneous in general, and the associated uncertainties should be considered carefully when the detector is used for alpha spectroscopy.     

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.     

Effects of stirring on the bulk etch rate of CR-39 detector

It is well established that the bulk etch rates for solid state nuclear track detectors are affected by the concentration and the temperature of the etchant. Recently, we found that the bulk etch rate for the LR 115 detector to be affected by stirring during etching. In the present work, the effects of stirring on the bulk etch rate of the CR-39 detector is investigated. One set of sample was etched under continuous stirring by a magnetic stirrer at 70°C in a 6.25 N NaOH solution, while the other set of samples was etched without the magnetic stirrer. After etching, the bulk etch thickness was measured using Form Talysurf PGI (Taylor Hobson, Leicester, England). It was found that magnetic stirring did not affect the bulk etch of the CR-39 detector, which was in contrast to the results for the LR 115 detector.     

Determination of thorium and uranium contents in soil samples using SSNTD’s passive method

Thorium-to-uranium ratios have been determined in different soil samples using CR-39 and LR-115-II solid-state nuclear track detectors (SSNTDs). A calibration method based on determination of SSNTD registration sensitivity ratio for α-particles of thorium and uranium series has been developed. Thorium and uranium contents of the standard soil samples have been determined and compared with its known values. There is a good agreement between the results of this method and the values of standard samples. The method is simple, inexpensive, non-destructive and has a wide range of applications in environment, building materials and petroleum fields.     

The effect of etching solution composition on the response of an electrochemically etched CR-39 detector

Etching solutions of different compositions were applied at room temperature (22°C) for electrochemical etching. The background developed during electrochemical etching in a CR-39 track detector was investigated. Detectors irradiated with alphas of 5.49 MeV were measured also. It was found that the PEW solutions (potassiumhydroxid, ethylalcohol, water) showed good sensitivity. One of them (PEW_20/40 was applied for neutrons from a ²⁵²Cf source. The achieved registration sensitivity was about 10⁻⁵ spot/n after 3 hours of etching time.     

Use of chemical etching of CR-39 foils at elevated temperature for fast neutron personnel monitoring in India

CR-39 Solid State Nuclear Track Detecting foils (SSNTD), along with 1 mm thick polyethylene radiator, sealed in triple laminated pouches, are used for country wide Fast Neutron Personnel Monitoring in India. With the present system of processing by elevated temperature electrochemical etching (ETECE) and evaluation using automatic image analysis, only 16 foils are processed at a time and it is useful over the dose equivalent range 0.2 mSv to 10 mSv. It has been reported that, by processing CR-39 of good detection efficiency by chemical etching at elevated temperature, more numbers of foils can be processed simultaneously. In the present study, CR-39 foils from Pershore Moulding (UK) have been chemically etched using 7 N KOH under various conditions of temperature and etching durations and evaluated using high magnification microscope. The duration of chemical etching, has been optimized at a constant temperature of 60°C for chemical etching process. The characteristics of the chemically etched CR-39 foils are compared with the characteristics of the CR-39 foils processed by the existing system of ETECE and the detailed results are presented in the full text of the paper. It has been observed that by chemical etching process, the dose equivalent range of CR-39 foils can be extended above 60 mSv.      

Intercomparative study of the detection characteristics of the CR-39 SSNTD for light ions: Present status of the besancon-dresden approaches

For the last few years, the Besançon and Dresden teams have been working in a parallel way on light ion (protons and alphas) registration characteristics for the CR-39 SSNTD. Even if the two groups use different approaches, the main part of both investigations concerns the study of the track etch rate (V_T) and the consequences of the obtained results, which have provided us with greater understanding of detection limits.

After recalling the methods used to determine the V_T from both teams, will show how fundamental datal related to the registration properties of the CR-39 detector can be extracted. Indeed, the knowledge of an analytical relation for the V_T enables the relationship between this velocity and the primary deposited energy to the examined with respect to the same spatial variable (the instantaneous depth of penetration (x) of the incoming particle). According to experimental uncertainties, the Bragg peak of the primary ionization coincides within a very close range with the maximum of the V_T. Moreover, if increasing the etching parameters (C, T) increases the maximum V_T value, these changes do not affect its position with respect to the instantaneous depth of penetration.

Taking into account the reduced etch rate, the Dresden team found that both protons and alphas exhibit the same behavior when this rate is plotted versus the primary energy deposition rate. As a consequence, the corresponding reduced etch rate is always identical no matter what type of particle deposits a given amount of energy (e.g. proton or alpha). The Besançon team has corroborated the results obtained by the Dresden group for alphas and have extended the study to various etching conditions. From these results, the sensitivity of the CR-39 SSNTD is obtained in terms of critical LET and leads to a very low energy threshold for alpha particles. We will see throughout this paper that the lower threshold does not seem to depend on the etching parameters.     

Experimental and Monte-Carlo studies of the spatial distribution of neutrons around extended Pb-spallation target

The spatial distribution of thermal and fast neutrons on the surface of a paraffin moderator surrounding a cylindrical lead target, irradiated with 1 GeV protons was studied. The lead target had 8 cm diameter and 20 cm length. The thickness of the paraffin around the target was 6 cm. The slow and fast neutron distributions were determined using LR 115 2B and CR-39 detectors via the ¹⁰B(n,) reaction and neutron induced nuclear recoils, respectively. The observed slow and fast neutron distributions on the surface of the paraffin were compared with Monte-Carlo simulations using the MCNPX-2.1.5 code.     

Comparison of responses of LR-115A, CR-39 and PM-355 track detectors to pulsed low-energy proton streams

The paper concerns applications of LR-115A, CR-39 and PM-355 solid-state nuclear-track detectors (SSNTDs) for investigation of pulsed fluxes of protons below 300 keV. The proton streams were generated by the RPI-IBIS device operated with hydrogen puffing [Baranowski et al. 2000. Studies of hydrogen discharges in RPI-type devices with different electrode configurations. Czech. J. Phys. 50 (Suppl. S3), 101–107]. To perform ion mass- and energy-analysis, a Thomson mass-spectrometer equipped with a special input system and exchangeable detectors was used. A quantitative analysis of proton tracks upon Thomson parabolas was performed by means of an optical microscope equipped with a CCD camera. It made possible to measure proton tracks and to determine their statistics. The paper presents proton energy spectra recorded with the selected detectors, and responses of these detectors to protons of energy from about 30 to 300 keV. The results are important for verification of detector characteristics and for measurements of protons at different experimental conditions.     

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.     

Influence of oxygen on the track etch rate along light ion trajectories in CR-39

The role of oxygen for stabilising radicals to form permanent damages in irradiated samples which are basically important for the etching process of track detectors has been studied. Samples of CR-39 were irradiated with 4 MeV -particles with a fluence of 30 000 particles per cm². The irradiations were performed in three different regimes:

• variation of out-gassing time in vacuum before irradiation;

• no out-gassing time but varied post-irradiation storage times in vacuum;

• variation of both storage times in vacuum before and after irradiation.

Generally, the absence of dissolved oxygen in the irradiated sample results in a decreased detection sensitivity in comparison with the detection properties and track parameters of samples irradiated in air. To determine the sensitivity the depth dependence of the track etch rate v_T(x) along the particle trajectory has been measured. From the observation of the dependence of the decreasing sensitivity on the post-irradiation storage time in vacuum, a lifetime of free radicals of 30 min could be derived. The amount of permanent damages responsible for the etching mechanism is related to the concentration profile of back-diffused oxygen and the REL-dependent radical concentration. This confirms previous results that the detection sensitivity is not a simple function of REL but depends on both REL and x the stronger the deeper within the irradiated sample.     

Study on the chemical composition features of Longquan celadon excavated from the Chuzhou site of Huai'an City in Jiangsu Province by EDXRF

A mass of Longquan celadon shards were excavated from the Chuzhou site of Huai'an City in Jiangsu Province, China. These celadon shards were fired during the period of the Late Yuan Dynasty to the Tianshun era of the Ming Dynasty, as identified by archaeologists at Nanjing Museum. In order to research the chemical composition features of this ancient celadon porcelain, energy dispersive X-ray fluorescence (EDXRF) for non-destructive analysis was used to determine the chemical composition of the porcelain body and glaze in these shards. The results indicate that Ti and Fe in the body of Longquan celadon are characteristic elements which can distinguish porcelain produced during the Late Yuan Dynasty from those produced in the Ming Dynasties. The results of the principal component analysis (PCA) show that different body and glaze raw materials were used for the production of porcelain in different periods and the raw materials of the body and glaze are also different for various vessel shapes. The chemical compositions in the porcelain body of civilian ware are slightly different. The imperial and civilian Longquan celadon porcelains produced during the Hongwu era to the Tianshun era of the Ming Dynasty are distinguishable by the MnO, Fe₂O₃, Rb₂O and SrO content in their porcelain glaze.     

Computer studies of detection efficiency of fast-neutron spectrum based on PADC using the Monte Carlo method

A FORTRAN code for simulation of SSNTD detection efficiency is designed using the Monte Carlo method in this work. The theoretical basis for the fast-neutron spectrum measurement based on the assembly of PADC¹ detector+radiator+degrader is described. The main principle of this technique is that, the recoiled protons produced in the radiator by fast-neutrons can be slowed down in the degrader and only protons of energies within a limited range can be detected by PADC (proton energy within the PADC detection energy window). Therefore with a set of different-thickness degraders one can measure the fast-neutron spectrum. Studies show that the program can give reasonable results.     

Dose-rate effects on the bulk etch-rate of CR-39 track detector exposed to low-let radiations

The effect of gamma-rays and pulsed electrons has been investigated on the bulk etch rate of CR-39 detector at doses up to 100 kGy under various dose-rate between 0.0044 and 35.0 Gy/s. The bulk etch rate increased exponentially with the dose at every examined dose-rates. It was reveled to be strongly depend on the dose-rate: the bulk etch rate was decreased with increasing dose-rate at the same total dose. A primitive model was proposed to explain the dose-rate effect in which oxygen dissolved was assumed to dominate the damage formation process.     

The Bragg-peak studies in CR-39 SSNTD on the basis of many-hit model for track etch rates

Etching rates along tracks of protons and lithium ions with energies in the Bragg peak region were explored. The energy losses in this region, especially for protons of low energies, are of particular interest from the physical as well as biological points of view. The microscopic track etch rate, V_T, is studied using the many-hit model in its first approximation assuming that V_T is a function of the restricted energy loss (REL_ω). The ions multiple scattering and straggling effects on the average experimental V_T values are corrected by shifting the calculated REL_ω values along the track, until its maximum coincides with that of the V_T. The fitting of least square differences between calculated and experimental V_T values is used in order to determine the many-hit model registration parameters for the detector under investigation.     

A novel method for detecting and counting overlapping tracks in SSNTD by image processing techniques

Overlapping object detection and counting is a challenge in image processing. A new method for detecting and counting overlapping circles is presented in this paper. This method is based on pattern recognition and feature extraction using “neighborhood values“ in an object image by implementation of image processing techniques. The junction points are detected by assignment of a value for each pixel in an image. As is shown, the neighborhood values for junction points are larger than the values for other points. This distinction of neighborhood values is the main feature which can be utilized to identify the junction points and to count the overlapping tracks. This method can be used for recognizing and counting charged particle tracks, blood cells and also cancer cells. The method is called “Track Counting based on Neighborhood Values” and is symbolized by “TCNV”.     

Effects of radiations on the characteristics of alpha and fission tracks in CR-39 detectors

Abstract

The effects of neutron, gamma and alpha radiations on the alpha and fission fragment tracks registration and revelation properties of CR-39 detectors (CR-39 and CR-39(DOP) were studied. It was found that the ratio of the bulk etch rate of irradiated to unirradiated (V_G(irr.)/V_G(unirr.) detectors is linearly dependent on dose. An exponential decrease in fission track densities with increase in neutron fluence was observed. The ratio of V_G(irr.)/V_G(unirr.) was found to be high in CR-39 than that in CR-39(DOP) exposed to the same reactor neutron fluence. The decrease in fission track densities with increase in neutron fluence was observed to be faster in CR-39 than in CR-39(DOP). This indicates that doping with dioctyl phthalate improves the radiation resistance of CR-39 detectors. It was observed that in detectors exposed to an alpha flux of the order of 9.36 × 10⁶ / cm², the fission track density was reduced by 11% and thereafter it remained constant. The results also indicate that thermal neutron fluence up to 7.01 ×10¹¹ neutrons/cm² does not affect the alpha and fission track densities. I.R. spectra were also studied to find out the nature of chemical changes produced by these radiations on CR-39.     

根据干涉条纹测量未知光源的波长

根据干涉叠加原理研究非单色光的干涉现象,对不同谱线宽度的光波干涉及相干长度进行对比分析,研究了双中心波长准单色光干涉光强的变化规律,以双黄汞灯为光源,按照理论分析的结果进行未知波长测量实验,得出了一定条件下测量未知波长的实验方法,实验结果与理论分析相符.     

Projectile fragment emission in the fragmentation of 56Fe on C,Al and CH2 targets at 471 A MeV

The emission angle and the transverse momentum distributions of projectile fragments produced in the fragmentation of 56Fe on CHs, C and A1 targets at 471 A MeV are measured. It is found that for the same target, the average value and width of the angular distribution decrease with an increase of the projectile fragment charge; for the same projectile fragment, the average value of the distribution increases and the width of the distribution decreases with increasing the target charge number. The transverse momentum distribution of a projectile fragment can be explained by a single Gaussian distribution and the averaged transverse momentum per nucleon decreases with the increase of the charge of projectile fragment. The cumulated squared transverse momentum distribution of a projectile fragment can be explained well by a single Rayleigh distribution. The temperature parameter of the emission source of the projectile fragment, calculated from the cumulated squared transverse momentum distribution, decreases with the increase of the size of the projectile fragment.     

A new measurement method of coatings thickness based on lock-in thermography

Coatings have been widely used in modern industry and it plays an important role. Coatings thickness is directly related to the performance of the functional coatings, therefore, rapid and accurate coatings thickness inspection has great significance. Existing coatings thickness measurement method is difficult to achieve fast and accurate on-site non-destructive coatings inspection due to cost, accuracy, destruction during inspection and other reasons. This paper starts from the introduction of the principle of lock-in thermography, and then performs an in-depth study on the application of lock-in thermography in coatings inspection through numerical modeling and analysis. The numerical analysis helps explore the relationship between coatings thickness and phase, and the relationship lays the foundation for accurate calculation of coatings thickness. The author sets up a lock-in thermography inspection system and uses thermal barrier coatings specimens to conduct an experiment. The specimen coatings thickness is measured and calibrated to verify the quantitative inspection. Experiment results show that the lock-in thermography method can perform fast coatings inspection and the inspection accuracy is about 95%. Therefore, the method can meet the field testing requirements for engineering projects.