A photometry method for measuring tracks density on SSNTDs

The purpose of this work is to determine alpha track density on solid state nuclear track detectors (SSNTDs) such as CR-39 efficiently with minimal time. Samples of CR-39 were irradiated with different doses from an alpha emitter. These samples were chemically etched and the tracks counted using an optical microscope. The intensity of the transmitted light (λ=400–1200 nm) through irradiated and etched CR-39 was measured using a photomultiplier. For all wavelengths used in this study, it is found that the transmittance of light decreases as irradiation time increases. In addition, the calibration factor was calculated from the relation between track density on CR-39 and light transmittance. The procedure appeared to be a good and fast technique for determining radon concentration in the environment and consequently dose reading.     

Empirical parameterization of CR-39 longitudinal track depth

In this work, new empirical equation describing the charged particles radiation track development against etching time and track longitudinal depth are presented. The equation involves four free fitting parameters. It is shown that this equation can reproduce tracks depth formed on the CR-39 by alpha particles at different energies and etching times. Parameters values obtained from experimental data can be used to predict etched track lengths at different energies and etching times. The empirical equation suggested is self consistent as far as reproducing all features of track depth development as a function of etching time and energy are concerned.     

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.     

On alpha particle spectroscopy based on the over-etched track length in PADC (CR-39 detector)

In the current work, alpha particle spectroscopy is investigated experimentally by utilizing the over-etched track lengths in the CR-39 detector. CR-39 samples were exposed perpendicularly to alpha particles emitted from ²⁴¹Am with an energy ranging from 0.5 to 5.5 MeV. CR-39 samples were etched in 6.25 N NaOH at (70±0.5)°C for different durations. The track diameter and track length were measured under an optical microscope. The results show that, the energy-over-etched track length calibration curve is monotonic, in other words, the over-etched track length is a monotonic function in alpha particle energy. On the other hand, the energy-diameter calibration curve is degenerated, i.e. alpha track diameter is non-monotonic function in alpha particle energy. These results suggest that the CR-39 detector could be used as a wide range alpha particles spectrometer using an energy-over-etched track length calibration curve.     

Efficient alpha particle detection by CR-39 applying 50 Hz-HV electrochemical etching method

Alpha particles can be detected by CR-39 by applying either chemical etching (CE), electrochemical etching (ECE), or combined pre-etching and ECE usually through a multi-step HF-HV ECE process at temperatures much higher than room temperature. By applying pre-etching, characteristics responses of fast-neutron-induced recoil tracks in CR-39 by HF-HV ECE versus KOH normality (N) have shown two high-sensitivity peaks around 5–6 and 15–16 N and a large-diameter peak with a minimum sensitivity around 10–11 N at 25°C. On the other hand, 50 Hz-HV ECE method recently advanced in our laboratory detects alpha particles with high efficiency and broad registration energy range with small ECE tracks in polycarbonate (PC) detectors. By taking advantage of the CR-39 sensitivity to alpha particles, efficacy of 50 Hz-HV ECE method and CR-39 exotic responses under different KOH normalities, detection characteristics of 0.8 MeV alpha particle tracks were studied in 500 μm CR-39 for different fluences, ECE duration and KOH normality. Alpha registration efficiency increased as ECE duration increased to 90 ± 2% after 6–8 h beyond which plateaus are reached. Alpha track density versus fluence is linear up to 10⁶ tracks cm⁻². The efficiency and mean track diameter versus alpha fluence up to 10⁶ alphas cm⁻² decrease as the fluence increases. Background track density and minimum detection limit are linear functions of ECE duration and increase as normality increases. The CR-39 processed for the first time in this study by 50 Hz-HV ECE method proved to provide a simple, efficient and practical alpha detection method at room temperature.     

Some more new etchants for CR-39 detector

Recently, several new etchants have been reported for CR-39 detector (Molten Ba(OH)2. 8H2O as an etchant for CR-39 detector, Radiat. Meas. 37 (2003) 205; Discovery of new etchants for CR-39 detector, Radiat. Meas. (2004)). We have made further progress in this direction and have unveiled two more new etchants which are reported in this article. CR-39 detectors were irradiated with fission fragments and alpha particles from a thin 252Cf disc source. The irradiated detectors were then etched in our newly introduced etching solutions as well as in conventionally used 6 M NaOH aqueous solution at 70 degrees C. The newly prepared etching solutions included NaOH dissolved in methanol and NaOH dissolved in methanol + water. Optimum values of NaOH concentration in methanol as well as in methanol + water were determined. Optimum etching temperatures were also determined for both the above-mentioned etchants. From fission and alpha track diameters, bulk etching rate (VB), track etching rate (VT) and etching efficiency (eta) were determined and compared with that obtained for 6 M NaOH at 70 degrees C. Both the newly introduced etchants were found more efficient than the conventionally used 6 M aqueous NaOH (64%) at 70 degrees C and have relatively much smaller etching time.     

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.     

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.     

Development of copolymer of CR-39 with high sensitivity to low let particles

Several types of copolymers of CR-39 were prepared to find its usefulness as a nuclear track detector of high sensitivity. Track responses of these copolymers were investigated by irradiating energetic ions from proton through Ar. The copolymer of CR-39 monomer with N-isopropylacrylamide (NIPAAm) shows higher sensitivity than that of pure CR-39 for low LET particles such as protons. Preliminary results are reported for the track responses of copolymers (CR-39/NIPAAm) with various contents of NIPAAm as well as the etching properties.     

CR-39核径迹探测器及其在核科学等研究领域中的应用

介绍了一种核径迹探测器ＣＲ－３９塑料的特性,这种探测器对逞电粒子非常灵敏,它还具有稳定、透明等特点,可记录ｐ、ａ粒子,裂变碎片和其他带电粒子,它是现有固体核径迹探测器中能量沉积密度探测阈最低的材料,介绍了ＣＲ－３９对带电粒子的响应,给出了各种带电粒子的ｖＴ对限定能量损失（ＲＥＬ）的响应曲线,利用ＣＲ－３９与转换屏的组合还可测定能量范围广的中子能谱,可作为方便的个人中子剂量计,介绍了ＣＲ－３９在研究     

Effect of Transferred Electronic Energy Density on Optical,Electrical and Structural Properties of Polyallyl-Diglycol Carbonate (CR-39) Polymer

Commercially available polyallyl-diglycol carbonate (CR-39) track detectors have attracted wide interest in many fields of science and technology. This is because of their low cost, relatively easy handling, and being more similar to human tissue than other passive detectors. After the Fukushima accident, there was a need to study the impact of the released alpha particles from radionuclides. In this study, CR-39 polymers were irradiated with α-particles with different linear energy transfers 11.11, 19.70, and 28.77 eV/Å, at fluences of 49,490/cm² and 2,482,763/cm². The modifications in the optical, electrical, and structural properties induced by the radiation were measured. The results showed that low values of transferred electronic energy density along the alpha particle tracks led to a slight increase in the optical band gap energy and a small reduction in the conductivity. The amorphous nature of the CR-39 samples was not affected by the changes of the transferred electronic energy density.     

Post-irradiation sensitization of CR-39 track detector in carbon dioxide atmosphere

The effect of post-irradiation treatment of CR-39 track detector in carbon dioxide atmosphere on the alpha particle registration sensitivity was investigated. Significant increase in etch rate ratio for 6.1 MeV ²⁵²Cf alpha particle was observed. The sensitization increasedboth as a function of trating time and as a function of carbon dioxide pressure in the treating vessel. Energy dependence of the sensitization was found to be small in the 2–9 MeV alpha particle energy interval. Fading of latent tracks after the sensitization process was slow in a one day period. Pre-irradiation treatment in carbon dioxide showed also some sensitization, though to a lesser extent than post-irradiation treatment. However, exposing CR-39 alpha particles in pure carbon dioxide atmosphere resulted in dramatic decrease in sensitivity. The role of dissolved oxygen and carbon dioxide in the primary latent track formation and in post-irradiation latent track transformation is discussed. Potential influence of the application of sensitization of CR-39 in radon, neutron and cosmic ray charged particle dosimetry is also discussed.     

Proton response of high sensitivity CR-39 copolymer

We studied the track response for the copolymer of CR-39 monomer with N-isopropylacrylamide (NIPAAm) as well as etching properties. It was found that copoly (CR-39/NIPAAm/Naugard 445) composed in wieght ratio of 99/1/0.01 is highly sensitive to low LET particles in the region below 10 keV/μm of LET and able to record normally incident particles of LET down to 1.5 keV/μm, recording protons up to the energy of 27 MeV. These results were compared with the responses for two types of CR-39 detectors containing a small quantity of antioxidant. The threshold energy proton registration is discussed.     

Track sensitivity and the surface roughness measurements of CR-39 with atomic force microscope

Atomic Force Microscope (AFM) has been applied to evaluate the surface roughness and the track sensitivity of CR-39 track detector. We experimentally confirmed the inverse correlation between the track sensitivity and the roughness of the detector surface after etching. The surface of CR-39 (CR-39 doped with antioxidant (HARZLAS (TD-1)) and copolymer of CR-39/NIPAAm (TNF-1)) with high sensitivity becomes rough by the etching, while the pure CR-39 (BARYOTRAK) with low sensitivity keeps its original surface clarity even for the long etching.     

Coded aperture imaging of alpha source spatial distribution

The Coded Aperture Imaging (CAI) technique has been applied with CR-39 nuclear track detectors to image alpha particle source spatial distributions. The experimental setup comprised: a ²²⁶Ra source of alpha particles, a laser-machined CAI mask, and CR-39 detectors, arranged inside a vacuum enclosure. Three different alpha particle source shapes were synthesized by using a linear translator to move the ²²⁶Ra source within the vacuum enclosure. The coded mask pattern used is based on a Singer Cyclic Difference Set, with 400 pixels and 57 open square holes (representing ρ = 1/7 = 14.3% open fraction). After etching of the CR-39 detectors, the area, circularity, mean optical density and positions of all candidate tracks were measured by an automated scanning system. Appropriate criteria were used to select alpha particle tracks, and a decoding algorithm applied to the (x, y) data produced the de-coded image of the source. Signal to Noise Ratio (SNR) values obtained for alpha particle CAI images were found to be substantially better than those for corresponding pinhole images, although the CAI-SNR values were below the predictions of theoretical formulae. Monte Carlo simulations of CAI and pinhole imaging were performed in order to validate the theoretical SNR formulae and also our CAI decoding algorithm. There was found to be good agreement between the theoretical formulae and SNR values obtained from simulations. Possible reasons for the lower SNR obtained for the experimental CAI study are discussed.     

Activation energy of etching for CR-39 as a function of linear energy transfer of the incident particles

In this work, we have studied the effect of the radiation damage caused by the incident particles on the activation energy of etching for CR-39 samples. The damage produced by the incident particle is expressed in terms of the linear energy transfer (LET). CR-39 samples from American Acrylic were irradiated to three different LET particles. These are N (LET₂₀₀ = 20 KeV/μm) as a light particle, Fe (LET₂₀₀ = 110 KeV/μm) as a medium particle and fission fragments (ff) from a ²⁵²Cf source as heavy particles. In general the bulk etch rate was calculated using the weight difference method and the track etch rate was determined using the track geometry at various temperatures (50–90 °C) and concentrations (4–9 N) of the NaOH etchant. The average activation energy F_b related to the bulk etch rate v_b was calculated from ln v_b vs. l/T. The average activation energy E_t related to the track etch rate v_t was estimated from ln v_t vs. l/T. It is shown that activation energy of etching is a constant value for CR-39 detector where E_t was found to be independent on the damage produced by the incident particle.     

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.      

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.     

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.     

Investigation of neutron emission from relativistic heavy ion interactions by nuclear tracks

Fast neutrons produced in 44 and 22 GeV ¹²C+Cu interactions have been recorded and analysed with a CR-39 detector stack. The irradiation of the CR-39 stack to fast neutrons was carried out at the accelerator Synchrophasotron, Joint Institute for Nuclear Research, Dubna, Russia. Areal and volume densities of tracks induced by fast neutrons in the CR-39 at different positions and for different etching time have been measured. The neutron production ratio of 44 GeV to 22 GeV ¹²C+Cu interactions has been obtained, which is 2.17 ± 0.30 by areal track density, or 2. 12±0.33 by step etch technique, or 2.03±0.34 by volume track density measurement. These results confirm that the production rate at 44 GeV ¹²C+Cu interactions is more than theoretical estimation.