Experimental setup for studying the effects of alpha particles on zebrafish embryos

In the present work, we have studied the feasibility to use an experimental setup based on polyallyldiglycol-carbonate (PADC) films to study effects of alpha particles on dechorionated zebrafish embryos. Thin PADC films with a thickness of 16 μm were prepared from commercially available CR-39 films by chemical etching and used as support substrates for holding zebrafish embryos for alpha-particle irradiation. These films recorded alpha-particle hit positions, quantified the number and energy of alpha particles actually incident on the embryo cells, and thus enabled the calculation of the dose absorbed by the embryo cells. Irradiation was made at 4 h post fertilization (hpf) with absorbed doses up to 2.3 mGy. Images of the embryos at 48 hpf were examined for identification of morphologic abnormalities. The preliminary results showed that absorbed doses corresponding to the abnormally developed embryos ranged from 0.41 to 2.3 mGy, which was equivalent to 0.21-1.2 mGy in human.     

Long-term measurements of equilibrium factor with electrochemically etched CR-39 SSNTD

Recently, our group proposed a method (proxy equilibrium factor method) using a bare LR 115 detector for long-term monitoring of the equilibrium factor. Due to the presence of an upper alpha-particle energy threshold for track formation in the LR 115 detector, the partial sensitivities to ²²²Rn, ²¹⁸Po and ²¹⁴Po were the same, which made possible measurements of a proxy equilibrium factor F_p that was well correlated with the equilibrium factor. In the present work, the method is extended to CR-39 detectors which have better-controlled etching properties but do not have an upper energy threshold. An exposed bare CR-39 detector is first pre-etched in 6.25 N NaOH solution at 70 °C for 6 h, and then etched electrochemically in a 6.25 N NaOH solution with ac voltage of 400 V (peak to peak) and 5 kHz applied across the detectors for 1 h at room temperature. Under these conditions, for tracks corresponding to incident angles larger than or equal to 50°, the treeing efficiency is 0% and 100% for incident energies smaller than and larger than 4 MeV, respectively. A simple method is then proposed to obtain the total number of tracks formed below the upper energy threshold of 4 MeV, from which the proxy equilibrium factor method can apply.     

Bulk etch characteristics of colorless LR 115 SSNTD

The colorless LR 115 solid-state nuclear track detector (SSNTD) (from DOSIRAD) is based on cellulose nitrate and was first studied in view of its applicability in radiobiological experiments with alpha particles. In this paper, the bulk etch characteristics were studied. We first showed that the shape of the alpha-particle tracks are irregular with blurred contours under the optical microscope. This has made measurements of track diameters very difficult. The phenomenon was explained in terms of the roughness of the detectors. As a result, the common method used to determine the bulk etch rates through measurements of opening diameters of tracks is not valid. We then proposed the surface profilometry method for determination of the removed active-layer thickness during etching. The bulk etch rates with 2.5 N aqueous solution of NaOH as the etchant, with and without magnetic stirring were determined for etching temperatures of 40, 50 and 60 °C. The data supported the Arrhenius type equation. The corresponding activation energies were determined. Finally, relationships were derived between the residual active-layer thickness and the infrared transmittances at different wave numbers. The infrared transmittances were found useful in revealing the active-layer thickness of the colorless LR 115 SSNTD, the correlations being described by quadratic relationships.     

Nuclear track detection using thermoset polycarbonates derived from pentaerythritol

The paper describes the synthesis and performance of two polymers as nuclear track detectors, both having alpha sensitivity higher than that of the widely-used polymer CR-39. A homopolymer (PPETAC) from pentaerythritol tetrakis(allyl carbonate) (PETAC) monomer and its various copolymers with allyl diglycol carbonate (ADC) prepared by cast polymerization were successfully used as nuclear track detectors. The copolymer PETAC:ADC 4:6 weight percent shows maximum alpha sensitivity, almost double that of CR-39 under identical experimental conditions. This copolymer can reveal alpha particle tracks from ²³⁹Pu source in about 60 min and ²⁵²Cf fission fragment tracks by chemical etching in less than 30 min, compared to about 120 min and 45 min respectively, required by CR-39. The polymers can be conveniently etched using aqueous sodium hydroxide.     

Determination of alpha-particle track depths in CR-39 detector from their cross-sections and replica heights

A challenging task in the application of solid-state nuclear track detectors (SSNTDs) is the measurement of depths of the tracks. One approach involves breaking and polishing the side of SSNTDs to reveal the cross-sections of the tracks for direct measurements. Recently, surface profilometry was used to measure the heights of the replicas of alpha-particle tracks to give the track depths. In the present work, systematic comparisons among the track depths for alpha-particles with normal incidence and different incident energies were made for these two methods. After irradiation, the detectors were etched in a 6.25 N aqueous solution of NaOH at 70 °C. Both long etching time of 15 h (to produce spherical-phase tracks) and short etching time from 1 to 8 h (to produce sharp-phase tracks) were used. Good agreement was achieved between the two methods for spherical-phase tracks but not for sharp-phase tracks. It has been found that the surface profilometry method only works for replicas for spherical-phase tracks. Replicas for sharp-phase tracks are easier to collapse or deform, so the surface profilometry method may not give correct results.     

Feasibility study on the use of polyallyldiglycol-carbonate cell dishes in TUNEL assay for alpha particle radiobiological experiments

In the present work, we have studied the feasibility of a method based on polyallyldiglycol-carbonate (PADC) films to investigate the effects of alpha particles on HeLa cervix cancer cells. Thin PADC films with thickness of about 20 μm were prepared from commercially available CR-39 films by chemical etching to fabricate custom-made petri dishes for cell culture, which could accurately record alpha particle hit positions. A special method involving “base tracks” for aligning the images of cell nuclei and alpha particle hits has been proposed, so that alpha particle transversals of cell nuclei can be visually counted. Radiobiological experiments were carried out to induce DNA damages, with the TdT-mediated dUTP Nick-End Labeling (TUNEL) fluorescence method employed to detect DNA strand breaks. The staining results were investigated by flow cytometer. The preliminary results showed that more strand breaks occurred in cells hit by alpha particles with lower energies. Moreover, large TUNEL positive signals were obtained even with small percentages of cells irradiated and TUNEL signals were also obtained from non-targeted cells. These provided evidence for the bystander effect.     

Study of isotropic etching behavior of CR-39(DOP) polymer through ion tracks

The same sample of CR-39(DOP) polymeric foil has been exposed to ²⁰⁹Bi (11.4 MeV/u) ions at three different angles (30°, 45° and 60°) of incidence. The exposed sample has been etched chemically and various parameters of the etched tracks have been measured. The objective of the present study is to establish the isotropic etching behavior of CR-39(DOP) polymer.     

Determination of bulk etch rate for CR-39 nuclear track detectors using an X-ray fluorescence method

The thickness of a CR-39 detector is determined using an energy dispersive X-ray fluorescence (EDXRF) method of analysis. The method is based on exciting a suitable target and measuring the intensity of its fluorescence X-ray lines passing through the CR-39 sample in a fixed geometry. By properly selecting the target material, the method succeeds in assessing the thickness change of CR-39 detectors etched for different time intervals. The bulk etch rate (V_b) may thus be obtained, which is an important parameter for any solid state nuclear track detector. Application of the EDXRF method yielded a value of V_b = (2.01 ± 0.04) μm h⁻¹ for etching in a 6 N NaOH solution at 75 °C. This value agrees with the bulk etch rate of (1.90 ± 0.03) μm h⁻¹, obtained by the conventional mass-change method.     

国产CR-39塑料膜测量α粒子的研究

选用国产CR-39测量α粒子的实验研究结果表明:该材料经α标准源照射后,加以化学预蚀刻、电化学蚀刻,可得到清晰的树状径迹。在入射条件一致情况下,α粒子注量与产生的径迹密度呈线性关系。相对探测效率为20％。平均本底径迹为0.2个/mm~2。     

Charge resolution of CR-39 plastic nuclear track detectors for intermediate energy heavy ions

The charge resolution (δZ) for heavy ions (nuclear charge: Z < 40) of 0.1-1 GeV/n energy in CR-39 plastic nuclear track detector (PNTD) and its dependence on etching time, and on projectile Z and energy were investigated and optimized as part of an effort to make precise measurements of projectile charge-changing cross sections. Two types of CR-39 PNTD, HARZLAS TD-1 and BARYOTRAK, were exposed to heavy ion beams with seven values of Z behind thick targets to produce projectile fragments. Following chemical etching (7 N NaOH at 70 °C) for varying etch times, δZ of the projectiles was determined for each detector type. A strong dependence of δZ on the amount of bulk etch (B) was seen. It was also observed that δZ can be remarkably improved with longer etching time as a function of B^−1/2, in accordance with the trend seen in other types of track detector such as glass nuclear track detector. However, for B ? 60 μm (30 h etching), saturation occurs and there is no further improvement in δZ. Analysis of the correlations between projectile Z, energy, detector response, and fluctuation of the response make it possible to develop a model to predict the δZ for projectiles of given Z and energy. The predicted and measured values of δZ show good agreement within 10%. We conclude that 4 ? Z ? 30 at intermediate energy can be identified with good δZ in these detectors. The predictive model will be used in designing future cross section measurement experiments.     

国产CR-39记录高注量的He++和H+的蚀刻特性

研究了国产ＳＹ－１型ＣＲ－３９记录加速器加速的高注量的Ｈｅ＾＋＋和Ｈ＾＋的蚀刻特性,对辐照过程中靶室内的环境本底做了观察实验。结果表明,在靶室内直接照射束斑位置以及远至４０ｍｍ处仍能记录到与束斑处相同的离子,而且在高注量离子的束斑区蚀刻后几乎辨不出径迹。进行了刻度实验,给出了ＣＲ－３９记录不同能量的Ｈｅ＾＋＋和Ｈ＾＋的径迹直径响应蚀刻曲线,对高注量束斑区蚀刻后注入新离子的实验表明记录特性不改变。     

On the long standing question of nuclear track etch induction time: Surface-cap model

Using a systematic set of experiments, nuclear track etch induction time measurements in a widely used CR-39 detector were completed for accessible track-forming particles (fission fragments, 5.2 MeV alpha particles and 5.9 MeV antiprotons). Results of the present work are compared with appropriately selected published results. The possibility of the use of etch induction time for charged particle identification is evaluated. Analysis of experimental results along with the use of well-established theoretical concepts yielded a model about delay in the start of chemical etching of nuclear tracks. The suggested model proposes the formation of a surface-cap (top segment) in each nuclear track consisting of chemically modified material with almost same or even higher resistance to chemical etching compared with bulk material of the track detector. Existing track formation models are reviewed very briefly, which provide one of the two bases of the proposed model. The other basis of the model is the general behavior of hot or energised material having a connection with an environment containing a number of species like ordinary air. Another reason for the delay in the start of etching is suggested as the absence of localization of etching atoms/molecules, which is present during etching at depth along the latent track.     

On the comparison of three methods of assessing beam quality for broad beam in vitro cell irradiation

The interaction of charged particles with living matter has recently attracted increasing interest in the field of biomedical applications such as hadron therapy, radioprotection and space radiation biology. Particle accelerators are particularly useful in this area.In vitro radiobiological studies with a broad beam configuration require beam homogeneity. The goal is to produce a dose distribution given to a cell population that is as close to uniform as possible.In this paper, we compare the results of three devices used to assess the beam quality for broad beam irradiation: a passivated implanted planar silicon (PIPS) particle detector, a position-sensitive solid state detector, which is camera-like, and a solid state nuclear track detector (CR39).The first device is a PIPS detector of 300 μm nominal depletion depth and an entrance window with a thickness of about 500 Å. It is collimated with a 0.5 mm aperture and mounted in air on an XY moving table as close as possible to the exit window of the beam line.The second device is a CMOS position-sensitive detector (technological process 0.6 μm AMS CUA), 112 × 112 pixels, with 153 × 153 μm² pixel size. It allows the user to rapidly obtain dose uniformity over a surface of 1 × 1 cm². During uniformity and dose rate assessment it is placed in air at the PIPS location.For both detectors, beam profile was obtained for various proton fluxes (from ∼5 × 10⁴ to 10⁶ particles cm⁻² s⁻¹). Preliminary tests were made with CR39 using 4 MeV He⁺⁺ ions.Results are analysed using Poisson distribution and cell hit probability.     

A fast method for the determination of the efficiency coefficient of bare CR-39 detector

A fast and simple method for the determination of the efficiency coefficient (η) of bare CR-39 detector is presented and discussed. The efficiency coefficient of bare CR-39 detector is then calculated by different ways and the obtained values are found to be comparable to each other. The average value of η of bare CR-39 is found to be 0.20 ± 0.01 tracks cm⁻² day⁻¹ per Bq m⁻³.     

Design and construct optimum dosimeter to detect airborne radon and thoron gas: Experimental study

Aim of this work is to design and select optimum dimension of a radon and thoron dosimeter within the measure optimum value of the calibration factor, using CR-39 Nuclear Track Detectors (NTDs). The results show that the best dimension to detect and measure real values of airborne radon and thoron concentrations is 6 cm and 7 cm for diameter and height, respectively. Calibration factors (K) for radon and thoron at this dimension were 2.68 ± 0.03 cm and 0.83 ± 0.01 cm, respectively, and these factors relatively depend on the detector efficiency. Therefore, the efficiency of CR-39NTDs to register alpha particles and their effects on the calibration factor estimated. It is found that the calibration factor increased exponentially with detector efficiency. Moreover, detector efficiency was equal to 80.3 ± 1.23% at the optimum dosimeter.     

The effects of intense gamma-irradiation on the alpha-particle response of silicon carbide semiconductor radiation detectors

Silicon Carbide (SiC) semiconductor radiation detectors are being developed for alpha-particle, X-ray and Gamma-ray, and fast-neutron energy spectrometry. SiC detectors have been operated at temperatures up to 306 °C and have also been found to be highly resistant to the radiation effects of fast-neutron and charged-particle bombardments. In the present work, the alpha-particle response of a SiC detector based on a Schottky diode design has been carefully monitored as a function of ¹³⁷Cs gamma-ray exposure. The changes in response have been found to be negligible for gamma exposures up to and including 5.4 MGy, and irradiations to higher doses are in progress.     

Study of change in the efficiency of CR-39 after storage for different product companies by using TRACK_TEST program

The main relation between efficiency of CR-39 nuclear track detector from different produced companies, critical angle for track revelation (θ_C) and bulk etch rate (V_B) have been stayed.Computer program TRACK_TEST was used for calculating track parameters and plotting profiles for etch pits in nuclear track materials.The results showed that for any application of CR-39 detector should be calibrated before used it. The detectors older than 3 years seemed to show odd behaviors of V_B with detector efficiency and the critical angle (θ_C).For age = 3 years the efficiency decreases exponentially for different alpha particle energy, and the bulk etch rate increases with decreasing age.This behavior may be important in applications of this detector; for example, the calibration factor for radon measurements should be established by taking into account the age of the detector.     

CR-39固体核径迹探测器观测方法

针对重离子辐射的CR - 39固体核径迹探测器中的微观径迹结构特点和剂量特征研究的必要步骤——探测器观测,从CR - 39中粒子潜径迹形成和发展出发,探讨了影响粒子径迹的因素,选取两种径迹观测方法——光学显微镜观测和电子显微镜观测进行对比分析.在此基础上进行了试验,用不同通量的100 MeV Si离子照射CR - 39...     

Designing experimental setup and procedures for studying alpha-particle-induced adaptive response in zebrafish embryos in vivo

The present work was devoted to designing the experimental setup and the associated procedures for alpha-particle-induced adaptive response in zebrafish embryos in vivo. Thin PADC films with a thickness of 16 μm were fabricated and employed as support substrates for holding dechorionated zebrafish embryos for alpha-particle irradiation from the bottom through the films. Embryos were collected within 15 min when the light photoperiod began, which were then incubated and dechorionated at 4 h post fertilization (hpf). They were then irradiated at 5 hpf by alpha particles using a planar ²⁴¹Am source with an activity of 0.1151 μCi for 24 s (priming dose), and subsequently at 10 hpf using the same source for 240 s (challenging dose). The levels of apoptosis in irradiated zebrafish embryos at 24 hpf were quantified through staining with the vital dye acridine orange, followed by counting the stained cells under a florescent microscope. The results revealed the presence of the adaptive response in zebrafish embryos in vivo, and demonstrated the feasibility of the adopted experimental setup and procedures.     

Development of Cell Chip Based on Track Detector for Examination of Biological Damage by Alpha Particles

A cell chip was developed for the examination of biological damage of cells irradiated by high-energy alpha particles. A CR-39 track detector was employed as a chip substrate to identify high-energy charged particles traversing target cells. Moreover, the patterning of a photopolymer layer spatially controlled the cellular adhesiveness on the chip substrate. HeLa cancer cells were cultured on a micropatterned photopolymer layer. In this way, all the cells on the chip were individually addressed through the block number in the photopolymer pattern. The biocompatibility of the cell chip was examined through a viability test with fluophor reagent and measurement of the cell proliferation rate. HeLa cancer cells on the chip were irradiated with alpha particles and stained with a fluorescent probe molecule for DNA damage detection. The CR-39 substrate was etched by means of an alkali solution during cell incubation. The HeLa cells and alpha tracks were successfully observed by microscopy at once. It was confirmed that fluorescent spots corresponding to DNA damage were located in the direction of the major axis of oval alpha tracks.