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.     

Graft polymerization into the latent tracks of some perfluoropolymers films irradiated by heavy ions

The results of the graft polymerization of methacrylic acid into perfluoropolymers (the copolymer of tetrafluoroethylene with hexafluoropropylene, copolymer of tetrafluoroethylene with perfluoroallylether) irradiated with heavy ions (Kr, 430 MeV) are presented. It has been found that the graft polymer quantity depends upon the polymer nature and the ion fluence. The graft polymer amount and its penetration depth were measured by the weighting methods, the dye sorption and electron microscopy methods. The graft polymerization results in significant changes in the polymer volume and structure.     

Beam profile measurement with CR-39 track detector for low-energy ions

A CR-39 track detector was successfully used to measure the outline of thin low-energy ion beams. After the etching, the surface of the detector was examined with an observation system composed of a Normarski microscope, a CCD camera and a digital image processing computer. Beam images obtained with the system were in good agreement on the outline of the beam formed with a beam aperture. Also, the resolving power in the beam outline measurement was roughly explained from the consideration of the ion range and the etch-pit growth in the chemical etching for the CR-39 detector.     

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.     

Studies on the nuclear tracks in CR-39 plastics

A review was given for our recent studies on the latent tracks in CR-39 nuclear track detector. The radial size of track core has been determined through UV spectral measurements combined to the model of track overlapping and by AFM observations of slightly etched detectors. The track core radius was found to be about a few nano-meters and almost proportional to the cubic root of stopping power. As a control study, the etching properties of CR-39, irradiated by low-LET radiation, has been examined. The observed depth dependence and dose-rate dependence of the bulk etch rate of the irradiated CR-39 were explained that the damage formation process was governed by the reaction between the radiation induced radicals and the oxygen supplied from the air. This indicated that latent tracks in CR-39 are produced through local radiation induced oxidation process along the ion paths. Studies on vibration spectra, near-IR, FT-IR and Raman spectra, of CR-39 have also been carried out to estimate the chemical structure of the latent tracks. The creation of OH group in irradiated CR-39 has been confirmed.     

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.     

Measuring depths of sub-micron tracks in a CR-39 detector from replicas using Atomic Force Microscopy

One of the challenging tasks in the application of solid-state nuclear track detectors (SSNTDs) is the measurement of the depth of the tracks, in particular, the shallow ones resulting from short etching periods. In the present work, a method is proposed to prepare replicas of tracks from particles in the CR-39 SSNTDs and to measure their heights using atomic force microscopy (AFM). After irradiation, the detectors were etched in a 6.25 N aqueous solution of NaOH maintained at 70 °C. The etched detectors were immersed into a beaker of the replicating fluid, which was placed in a water bath under ultrasonic vibration and maintained at room temperature to facilitate the filling of the etched tracks with the replicating fluid. As an example of application, these results have been used to derive a V function for the CR-39 detectors used in the present study (for the specified etching conditions).     

Angular response of CR-39 to relativistic heavy ions and high-energy protons

Track etch detectors CR-39 irradiated with relativistic heavy ions (C, Ne, Si and Fe, ) and high-energy protons (35–230 MeV) were etched both chemically and electrochemically. To determine an angular dependence of response in detail (step 1), an arrangement of a single detector bent into a semi-cylindrical form was used. Experimental data were fitted by polynomic functions and the detection efficiencies for isotropic irradiation were calculated. Critical angles of registration were also determined for heavy ions. The possible influence of additional absorbers and radiators was also estimated.     

A new method for measuring tracks density in CR-39 detectors by compensating for overlapping tracks

CR-39 nuclear track detectors have been used as an efficient radon monitoring system. Exposing these detectors to radon would result in tracks where ever particles hit the surface of the detector. Natural radioactivity of alpha particles (radon concentration) is measured based on the count of these tracks on CR-39 detector. Counting these tracks by eye is not an easy task especially when the density of the tracks is high. Automated tracks counting systems are attractive solution for this problem. However, as the density of tracks increases the accuracy of these methods deteriorates. This is due to the fact that overlapped tracks are counted as one track during the segmentation process resulting in an underestimation of the real count of the tracks. This work proposes a new image processing based automated approach for tracks counting. This new automated approach solves the problem of counting overlapping tracks by approximating their number and then adjusting the final count of tracks by compensating for those uncounted tracks. The experimental results show that the proposed approach reduces the counting percentage error from 5.64% to 2.54% by solving the counting problem of the overlapped tracks.     

Response function of the plastic track detector CR-39

From available experimental data a general response function of CR-39 was derived, which has a linear and a supra-linear term with different temperature dependence. The factor of the supralinear term can be expressed in terms of the linear term which governs the response function in the low REL range. Therefore it is possible to establish the response function by means of alpha particles only.     

Discovery of new etchants for CR-39 detector

After reporting the excellent etching properties of molten Ba(OH)2 8H2O as an etchant, we now report some more new and efficient etchants for CR-39 detector. CR-39 detectors were irradiated with fission fragments and alpha particles with a thin 252Cf source. The irradiated detectors were etched in a number of our newly introduced etching solutions as well as in conventionally used 6 M NaOH at 70 degrees C. The newly prepared etching solutions included NaOH/ethanol and NaOH/1-propanol. Processing conditions were optimized for these etchants. From fission and alpha track diameters, bulk etching velocity (VB), track etching velocity (VT), etching efficiency (eta) and their activation energies were determined and compared with that obtained for 6M NaOH at 70 degrees C.     

Structure effect in response function of CR-39 detector

The structure effect of CR-39 on the rate of its hydrolysing reaction was studied. It has been indicated that the sensitivity of any plastic detector is dependent on the its posibility to alkalai hydrolyse. It is known that polyesters and polycarbonates undergo decarboxylation under ionizing radiation so that would point to the carbonate group as the amplify induced radiation sensitive link. The structure effect would be one of the keys to develope the new, more sensitive nuclear track detectors.     

TEM investigations of heavy ion latent tracks

High resolution observations of GeS single crystals with a 400 keV transmission electron microscope (TEM) were carried out. The GeS was irradiated at the UNICAC with heavy ions at several MeV/u specific energy. The imaging of the tracks revealed relatively large amorphous cores of elliptical cross section, oriented with respect to the crystal lattice.     

Computer simulation of the processes in a CR-39 neutron detector

The application of CR-39 as a fast neutron dosimeter, based on counting elastic recoil nuclei tracks of H, C and O nuclei in a geometrically matched pair of detectors, was studied. A computer simulation of the processes during the exposure of a detector pair to neutrons is presented. The energy and spatial distribution of the recoil nuclei was calculated with the MCNP 4B program package. On the basis of this distribution, a Monte-Carlo procedure for the generation of latent tracks in the CR-39 detectors was run. Additionally, a procedure for calculation of the chemical track etching for revealing the visible track parameters was performed to obtain the detector response.     

用CR-39对空间重离子的鉴别模型

根据重离子在CR39中能量损失率公式,建立了一个鉴别空间重离子的数学模型LET=cZdRb.通过传能线密度与剩余射程之间的关系曲线,获得了该模型的系数.在实验中发现的CR39蚀刻率与离子有限传能线密度的关系VT=A·(REL)BE<350,被用来与该数学模型相关联,并得到一等式R=A0.0455Z3.18V–1T.最终,借助于标定实验得到了离子鉴别公式Z3.18=64541.08+2.53(dR/dV–1T).     

Calibration of CR-39 solid state nuclear track detector

Nowadays there are increasing uses of SSNTD on scientific works in Thailand. Currently we are using SSNTD as an important tool for confirming active fault zones in a province in which a new nuclear research reactor has been proposed to come up. Soil gas radon was measured by both active and passive methods. In the latter case CR-39 SSNTD was installed in a PVC tube of 50 cm long by 5 cm in diameter. The tubes were placed in 50-cm deep holes lining perpendicular to the faults’ trace for one week. In this paper we describe the method and the results on calibrating these detectors using a radon chamber and a NIST-traceable radium-226 standard source.      

Low-energy ion measurements by means of CR-39 nuclear track detectors

The paper presents an additional acceleration system, used to shift up an ion energy spectrum by 20 keV, and some examples of the ion parabolas registered by means of a Thomson-type spectrometer within the rod plasma injector (RPI-60) facility, designed for plasma physics and application studies. The use of the described acceleration system and CR-39 track detectors has enabled the registration of ions of energy above 20 keV to be performed. It made possible to measure the ion (e.g. deuteron) energy spectrum more exactly in the low-energy range, what is important for the determination of ion emission characteristics.     

Effects of low-LET radiations on CR-39 track detector

The effects of Co-60 gamma-rays and about 25-MeV pulsed electrons have been investigated on CR-39 plastic nuclear track detector. The bulk etch rate was measured as a function of the absorbed dose under three different irradiation conditions; gamma-ray exposure in air at the dose rate of 6 kGy/h, that in vacuum and electron shower in air at 126 kGy/h on average. It was found that the bulk etch rate (V) increased nearly exponentially with the dose (D); V=V₀exp(kD), and the characteristic parameter (k) was 35, 9 and 12 MGy⁻¹, respectively. It is considered that a lack of oxygen in damage formation processes could occur momentarily during a short electron pulse, just similarly to the vacuum effect of reduction in track etch rates in outgassed CR-39 plastic.     

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.