Yields of formation and scissions at ether bonds along nuclear tracks in CR-39

Yields of CO₂ gas formation and the scissions at ether bonds have been determined along ion tracks in CR-39 plastics. Thin CR-39 films with thickness were irradiated by 130 MeV C-13 ions at 45 incidence up to , and then IR spectra were obtained without removing the samples from the vacuum chamber. The absorption band for CO₂ was observed clearly around , whose absorbance increased proportional to the fluence up to 3×10¹² ions/cm² and then saturated. Using a mole absorption coefficient for gaseous CO₂, the yield along the track was determined to be molecules/μm. This means that the G-value of CO₂ formation in CR-39 was about 3.6 molecules/100 eV. The scission yield of ether bonds was found to be 11,000 scissions/μm. This corresponds to a G-value of about 5.5 scissions/100 eV. These values suggest that the parts between the two carbonate ester bonds in each repeat unit of CR-39 can be segmented into two CO₂ and other small molecules along the nuclear tracks.     

Angular distribution measurements of Li(p,α)He reaction at 140 keV proton energy using nuclear track detectors

Angular distributions of a ⁶Li(p,α) ³He reaction were measured at six angles for 140 keV proton energy using nuclear track detectors (NTDs). The measurements were carried out over 60°–160° lab. angles in 20° increments using a scattering chamber of 80° beam line of the 350 kV accelerator. A semiconductor silicon surface barrier (SSB) detector was placed at +160° and was used as a monitor. The results have shown that the CR-39 detector has excellent capabilities to distinguish 1.4–2.7 MeV α+ ³He particles from the ⁶Li(p,α) ³He reaction and 8–9.4 MeV α-particles from the ⁷Li(p,α) ⁴He reaction through their track diameters. However, it was not possible to distinguish between the 2.3 MeV ³He ions and the 1.7 MeV ⁴He ions from the ⁶Li(p,α) ³He reaction from their track diameter measurements, but it was possible to differentiate between the two, from the darker contrast of the ³He particles caused by its deeper tracks as compared to those of ⁴He.     

Measurements of neutron yields and spatial distributions in U/Pb, Pb and Hg thick targets bombarded by 0.5 and 1.0 GeV protons

Measurements have been carried out on neutron yields and spatial distributions in U/Pb, Pb and Hg thick targets and the surrounding paraffin moderators bombarded by 0.533 and 1.0 GeV protons. CR-39 detectors were deployed on the surfaces of targets and moderators to record the neutrons produced in the targets. The measurements show that:

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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.     

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.     

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.      

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.     

On search and identification of tracks due to short-lived SHE nuclei in extraterrestrial crystals

The unique approach for search and unambiguous identification of short-lived (T_1/2=10³–10⁷ years) superheavy nuclei in cosmic-ray products of the recent nucleosynthesis in our Galaxy are discussed.It is based on: (a) the ability of non-conducting crystals to register and to store for many million years the tracks due to fast nuclei with atomic number Z20 (“fossil” tracks);(b) calibrations of the said crystals with accelerated heavy ions (20Z92) and on revealing the volume etchable track length (VETL) of the fast nuclei coming to rest inside crystals—both of fossil and “fresh” tracks—to determine the charge distribution of cosmic-ray nuclei tracks and(c) the so-called “four-zone” model of tracks in crystals (and also glasses) which provides not only the VETL track length dependence for 20Z92 nuclei but also demonstrates the regular annealing behavior of VETL of 20Z92 nuclei in a broad temperature interval.This approach was first applied in the early 1980s to investigate the “fossil” tracks due to 22Z92 cosmic-ray nuclei in olivine crystals from meteorites-pallasite Marjalahti and Eagle Station.The discovery of Th–U cosmic-ray nuclei tracks in 1980 was unambiguously confirmed by calibrations of the same crystals with ²³⁸U, ¹⁹⁷Au and ²⁰⁸Pb accelerated ions in the late 1980s. More than 1600 tracks due to cosmic-ray actinide nuclei were measured during the last two decades of the 20th century.Also, 11 anomalously long tracks (track length exceeds by a factor (1.6±0.1) the track length due to Th–U nuclei were measured. The detailed analysis shows that at least 5 of these tracks could not be attributed to the Th–U nuclei. It means that now we have a preliminary proof on the existence Z110 nuclei in cosmic-rays. The abundance is Z110/Th–U=(1–3)×10⁻³ in Z110 freshly formed cosmic-rays (time interval 10³–10⁷ years).The method proposed can provide the necessary and sufficient conditions for the discovery of Z110 nuclei in nature.     

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.     

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.     

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.     

The spatial distribution of thermal and epithermal neutrons in a graphite moderated spallation neutron field

The Gamma-3 assembly is located at the Joint Institute for Nuclear Research, Dubna, Russia. It consists of a cylindrical lead target (ø = 8 cm, L = 58.8 cm) surrounded by reactor grade graphite (110 × 110 × 60 cm). The target was irradiated with a beam of 1.6 GeV deuterons from the Nuclotron accelerator and CR-39 track detectors coupled to LR-115 2B film were used to measure the slow neutron distribution on the surface of the graphite. The detection efficiency of the CR-39 in the CR-39/LR-115 2B system was measured using a custom made calibration setup and found to be (1.12 ± 0.05) × 10⁻³ and (6.1 ± 1.2) × 10⁻⁴ tracks per neutron, for thermal and epithermal neutrons respectively, under the etching and counting procedures described in this work. The irradiation of the Gamma-3 was also simulated using MCNPX 2.7 Monte Carlo code and good agreement between the experimental and calculated track densities was found. This serves as a good validation for the computational models used to simulate spallation neutron production, transport and moderation.     

Study of the etching characteristics of -mixed NaOH solution

In the present paper the effect of the presence of Na₂CO₃ on the etching characteristics of NaOH has been presented quantitatively. Six CR-39 detectors were etched at 50, 60 and in 6 M NaOH solutions containing 0%, 1%, 2%, 3%, 4% and 5% concentration of Na₂CO₃. Etching was performed in 22 steps of 5–10 min starting from 15 min up to 210 min. These detectors were previously exposed to ²⁵²Cf source. Lengths of 35 randomly selected fission fragment tracks were measured after each etching time interval. Similarly, diameters of 25 randomly selected fission fragments having 90 incidence angle were also measured as mentioned above. Track etch rate, bulk etch rate, etching efficiency and activation energies of both track as well as bulk etching have been determined.     

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.     

Contribution of Radon Daughters Plated-Out in a Cylindrical Device by Track-Technique

CR-39 plastic nuclear track detector is used to measure the fraction of alpha-particle tracks due to radon daughters activities plated-out on the internal walls of a cylindrical-shaped plastic can. Radium chloride solution is used as a radon source, the exposure time is ranged from 4 hours to 3 days. To assess the percentage of plate-out effect on CR-39 nuclear track detector, two different methods were used. In one experiment, a few circular parallel pairs of CR-39 sheets were hanged in the can device. In the other experiment, the estimation of the plate-out effect has been performed, after exposure to the radon source, by detecting tracks with a second unexposed sheet placed in close contact to the exposed wall and detectors. In the two methods, it was found that the chemically etched tracks related to plated-out activities contribute about 50% of the measured alpha-particles tracks.

Der CR-39 Plast-Kernspurdetektor wurde zur Messung des Anteils an Spuren von Alphateilchen verwendet, die sich von den Radon-Tochterprodukten ergeben und auf den Innenwänden eines zylindrisch gestalteten Plastbehälters abgeschieden haben. Als Radonquelle wurde eine Radiumchlorid-Lösung verwendet und die Expositionszeiten lagen zwischen 4 Stunden und 3 Tagen. Um den Anteil des Abscheidungseffektes in einem CR-39 Spurdetektor zu bestimmen, wurden zwei unterschiedliche Methoden angewendet. In dent einen Versuch wurden einige zylindrische Parallelpaare von CR-39 Folien in den Behälter gehängt. In dent anderen Versuch wurde der Abscheidungseffekt in der Weise ermittelt, daβ nach der Exposition auf die Radonquelle mit einer zweiten nichtexponierten Folie die Spuren bestimmt wurden. Die nichtexponierte Folie war dabei in einem engen Kontakt zur exponierten Wand und den Detektoren. Durch beide Methoden wurde gefunden, daβ die chemiseh geätzten Spuren, die auf die Abscheidimgsaktivitäten züruckgeführt werden können, einen ungefahren Anteil von 50% an den gemessenen Alphateilchenspuren ausmachen.     

Hot particles in industrial waste and mining tailings

Industrial waste was studied concerning its radioactive pollution. Using known properties of the solid state nuclear track detector CR-39 we found among a high concentration of more or less homogeneously distributed single α-tracks discrete spots of very high enrichments of α-particles created by so called hot particles. We will report about the α-activity, the concentration of hot particles and about their ability to be air borne.     

Study of nuclear tracks on different polycarbonate foils and their feasibility for use in personnel monitoring

CR-39 (PADC) a Solid State Nuclear Track Detector., is used as a routine personnel monitor. 1800 workers are being monitored quarterly for fast neutron using CR-39 foils. These foils procured from Pershore Mouldings, UK are very expensive and indigenous development will make the foils cost effective. The aim of this paper is to find a suitable alternative to the imported CR-39 foils for use in personnel monitoring. The foils from three different manufacturers have been compared with the CR-39 foils from Pershore Moulding, UK, presently in use. Out of the three, only sample no 1 is promising. It has a background and sensitivity comparable with CR-39 presently used. The sample 2 is CR-39 being developed in India, has a relatively high background and poor sensitivity. Efforts are being made to improve the quality of this sample. The sample 3 was a poly carbonate from local manufacturer which produced very few tracks and the standard deviation of track counts was very large and hence not useful for Personnel Monitoring.      

Characteristic studies for fast detection of a wide energy range of alpha particles in polycarbonate detectors

Parametric investigations were carried out on electrochemical etching (ECE) process of Lexan polycarbonate (PC) detector. Outstanding experimental results showing the enlargement of the registration energy range of α-particle tracks of the PC and decrease of ECE time are presented in this paper.In the experiment, major parameters such as etching solution and ECE conditions are focused. Ethylene diamine is applied as an additional chemical agent to increase the bulk etching rate (V_B) which is maintained below a critical value . By using mixture of KOH, CH₃OH (methanol), NH₂(CH₂)₂NH₂ (ethylene diamine) and H₂O and applying interval-based ECE process in total duration of 70 min, expanded α-registration range of 0.5–4.7 MeV have been achieved, as well alpha track diameters decrease with increasing of alpha particle energy. In this process the density of background tracks also decreases comparably. In this paper, electric current is introduced as an effective ECE parameter for improving detection efficiency of low α-particles energy in the PC.     

Thermal annealing of proton tracks with energies of 4 and 6 MeV in CR-39 polymer detectors

In this paper, we study the thermal annealing of proton tracks of 4 and 6 MeV at temperatures ranging from 150 to 240°C in CR-39 polymer detectors. A special experimental set-up for irradiating the detectors was arranged to obtain adequate proton beams from the Cyclotron CV-28 at IPEN/SP, Brazil. We report experimental data on track densities, track diameters, and activation energies based on current annealing models for the annealing of proton tracks in the energy range investigated. A value of (0.20±0.02)eV was determined as the mean activation energy of the annealing process in CR-39 detectors.     

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.