Diffraction filters based on polyimide and poly(ethylene naphthalate) track membranes

The problem of optical filters for soft x rays and extreme ultraviolet that provide a high degree of blocking ultraviolet and visible background radiations is considered. The subject of discussion is the filter based on a track membrane, a polymer film with micrometer and submicrometer pores, rather than the standard thin-film system. It is proposed that the membranes be made of poly(ethylene naphthalate) or polyimide, the UV absorption edge of which lies near the boundary of the visible range. The properties of poly(ethylene naphthalate) and polyimide membranes are contrasted with those of conventional porous poly(ethylene terephthalate) films, which are obtained by ion track etching. The spectral characteristics of poly(ethylene naphthalate) and polyimide films, as well as the formation of “track” pores when the specimens are successively treated by fast ions and chemicals, are studied. The basic parameters of the resulting porous structures are examined, and treatment conditions under which desired optical properties of the membranes are achieved are found. Filters based on poly(ethylene naphthalate) and polyimide track membranes may be applied in x-ray astronomy as constituents of detectors incorporated into solar telescopes and in experiments with the laboratory plasma.     

Effect of gamma irradiation on the structural,thermal and optical properties of Makrofol BL 2–4

Makrofol BL 2–4 is an extrusion film based on Makrolon polycarbonate. It comprises excellent die-cutting performance combined with high light transmission and moderate light scattering properties. It is a class of polymeric solid state nuclear track detectors which has many applications in various radiation detection fields. In the present work, Makrofol samples were irradiated using different gamma doses ranging from 10 to 350 kGy. The structural modifications in the gamma-irradiated Makrofol samples have been studied as a function of dose using different characterization techniques such as X-ray diffraction, intrinsic viscosity, Fourier transform infrared spectroscopy, thermogravimetric analysis, refractive index and color difference studies. The gamma irradiation in the dose range 20–200 kGy led to a more compact structure of Makrofol polymer, which resulted in an improvement in its thermal stability with an enhancement in its structural and optical properties.     

The effect of gamma irradiation on the activation energy of bulk and track etching in Lexan track detector

Various studies have been performed to determine the response of Lexan polymer to gamma irradiations. The track recording properties of certain polymers are changed under the influence of electromagnetic radiations and environmental conditions. In the present work, the effect of gamma irradiation on the activation energies of bulk and track etching in case of Lexan samples have been investigated. The attempt has also been made to study the influence of temperature on the bulk and track etch rates of gamma irradiated polymer. The studies reveal an increase in the bulk and track etches rates with gamma-dose. However, the activation energy associated with track and bulk etch rates at a given temperature and at a constant concentration decreases with gamma-dose.     

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.     

Assessment of integrated solar ultraviolet radiation by PM-355 detectors

The increase in environmental solar UV radiation due to depletion of ozone layer is a recent challenge to human health (skin cancer and eye effects) in countries having clear skies. Therefore, applying integrated, passive and inexpensive techniques to assess solar UV radiation is very much essential. Measurements of environmental solar UV radiation in Dhahran, Saudi Arabia area were carried out for a period of two months in the summer period in 1996 using two techniques in parallel namely: passive nuclear track detectors and active solar UV radiometers. Some of the nuclear track detectors were mounted in different conditions such as: under shadow band, on solar tracking mechanism following the solar rays. Others were mounted on perpendicular, tilted and horizontal surfaces in sunlight. All detectors were attached to a wooden background of the same thickness (0.5 cm) to eliminate interference of the heat effect of various support materials and have uniformity of the support materials. The assessment was carried out for different periods extending from two to nine weeks continuously. The investigated period covered the hottest months in Saudi Arabia (July and August) when the sky was clear of clouds. The results indicate linear correlation between alpha track diameters and the integrated exposure to solar UV as measured by the solar UV radiometer for all nuclear track detector positions and orientations. The highest slope has been observed for the detectors placed on solar tracking mechanism following the solar rays and the lowest from detectors oriented under the shadow band on horizontal position (measuring the diffused UV radiation only). The results show that most of the measured UV radiation (60%) were from the diffused UV radiation. The characteristics of the upper layer of the detectors are changed after chemical etching very quickly, with increase in the exposure time to UV solar radiation at certain orientation. The results encourage the use of nuclear track detectors for environmental and personal solar UV dosimetry on a large scale in Saudi Arabia and similar hot and clear-sky countries.     

Physical properties and device applications of graphene oxide

Graphene oxide (GO), the functionalized graphene with oxygenated groups (mainly epoxy and hydroxyl), has attracted resurgent interests in the past decade owing to its large surface area, superior physical and chemical properties, and easy composition with other materials via surface functional groups. Usually, GO is used as an important raw material for mass production of graphene via reduction. However, under different conditions, the coverage, types, and arrangements of oxygen-containing groups in GO can be varied, which give rise to excellent and controllable physical properties, such as tunable electronic and mechanical properties depending closely on oxidation degree, suppressed thermal conductivity, optical transparency and fluorescence, and nonlinear optical properties. Based on these outstanding properties, many electronic, optical, optoelectronic, and thermoelectric devices with high performance can be achieved on the basis of GO. Here we present a comprehensive review on recent progress of GO, focusing on the atomic structures, fundamental physical properties, and related device applications, including transparent and flexible conductors, field-effect transistors, electrical and optical sensors, fluorescence quenchers, optical limiters and absorbers, surface enhanced Raman scattering detectors, solar cells, light-emitting diodes, and thermal rectifiers.     

Registration temperature effect on sensitivity of CR-39(DOP) and SR-90 polymer track detectors

The samples of CR-39(DOP) and SR-90 polymer track detectors have been exposed to -particles from ²⁴¹Am source in an exposure unit. The temperature of the detectors during irradiation has been varied from −30°C to 70°C. These exposed samples have been etched in 6.25 N NaOH solution at 60°C for various etching times. The variation of sensitivity of these detectors as a function of registration temperature has been studied. It has been observed that at the fixed registration temperature, the sensitivity of SR-90 is more than CR-39(DOP) polymer track detector. However, the enhancement in sensitivity with the decrease in registration temperature is more pronounced in case of CR-39(DOP) than SR-90.     

Sensitization of polymeric track detectors with carbon dioxide

The effect of CO₂ on the sensitivity of polymeric track detectors was studied. It has been found that the sensitivity of SR-90 is dependent on the amount of CO₂ dissolved in the polymer at the time of etching. It has been also found that CR-39 can be sensitized to some extent with an aging in CO₂. Since the sensitization in CO₂ is possible even a long time after the irradiation, the mechanism of the latent track formation by CO₂ is quite different from that by O₂. This would be the key to achieve the long term stability of polymeric track detectors such as SR-90 and CR-39.     

Modifications in track registration response of PADC detector by energetic protons

It has been well established that different ionising radiations modify the track registration properties of dielectric solids. In an effort to study the response of Polyallyl diglycol carbonate (PADC Homalite) detector towards fission fragment, PADC detectors were exposed to 10⁴ Gy dose of 62 MeV protons and then one set of samples were exposed to fission fragments from a ²⁵²Cf source. Two of these detectors were containing a thin layer of Buckminsterfullerene (C₆₀). The study of the etched tracks by Leitz Optical Microscope reveals that the track diameters are enhanced by more than 70% in the proton irradiated zone as compared to that in the unirradiated zone. Scanning Electron Microscopy was performed after etching the sample in 6 N NaOH at 55°C for different etching times, to study the details of the surface modifications due to proton irradiation of PADC detectors with and without C₆₀ layer. Our observations revealed that the diameters and density of proton tracks have increased with etching time on the surface facing the fullerene layer as well as the other surface. However, a relatively more open structure of the etched surface containing C₆₀ as compared to the bare one may be an indication of the extra damage caused by the energy released upon the destruction of C₆₀ molecules by energetic protons.     

Anomalous cosmic ray carbon and oxygen tracks in CN-Kodak

For observation of low energy cosmic ray particles we used CN-Kodak nuclear track detectors on Cosmos satellites. In solar quiet periods during solar minima conditions the detectors registered anomalous cosmic rays (ACRs). The ACRs are characterized by flux enhancements of several elements and it is known that the carbon enhancement is small compared with that of oxygen. In all of our quiet-time exposures the relation between carbon and oxygen was extremely small (C/O 0.03). But in two quiet-time periods of 14.03.96–11.06.96 and of 15.12.97–14.04.98 we have identified many tracks as carbon in a L–R diagram. As a result the observed C/O ratio appears to be more than 0.5, whereas other experiments show no evidence of enhanced flux of carbon during these periods. The reason for the unexpected response of CN-Kodak is discussed.     

On the formation of heavy ion latent tracks in polymeric detectors

Three kinds of polymeric track detectors have been examined by ESR spectroscopy following heavy ion or energetic electron bombardment: (1) Typical nuclear track detectors: makrofol, kapton, terphane; (2) Polymers whose radiolysis under γ-rays or electron beams is well established: PMMA, PE, PP; (3) Polymers in which etchable tracks have not so far been observed e.g. teflon. The influence on the various ESR spectra of the radiation dose, of annealing or chemical etching treatments leads us to suggest that existence of heavy ion latent tracks might be correlated with the formation of “carbon-like” radicals such as produced in polymer pyrolysis.     

Electrical, structural and surface properties of fluorine doped tin oxide films

Fluorine (F) incorporated polycrystalline SnO₂ films have been deposited onto glass substrates by ultrasonic spray pyrolysis technique. To possess information about the electrical properties of all films, their electrical conductivities were investigated depending on the temperature, and their activation and trap energies were analyzed. The crystalline structure, surface properties and elemental analysis of the SnO₂ films were examined to determine the effect of the F element. After all investigations, it was concluded that each fluorine incorporation rate has a different and important effect on the physical properties, and SnO₂:F (3 at%) films were found to be the most promising sample for energy conversion devices, especially as conducting electrode in solar cells with its improved structural and electrical properties as compared to others.     

Anisotropic etching of charged-particle tracks in crystals

It is well-known that highly-energetic heavily charged particles arising both from the fissioning of heavy elements and from cosmic and solar radiations leave tracks which have been found in glasses and crystal-line minerals recovered from lunar and meteoritic material. It has been shown that an appropriate analysis of these tracks can provide informationabout periods since solidification and the thermal and dynamic history of the specimen, as well as insight into the nature and temporal variation of the cosmic ray flux.^1-2 An understanding of the track registration characteristics of crystals is clearly an important pre-requisite to an appropriate interpretation of the natural tracks. ^3-6 This letter describes briefly some observations we have recently made on one particular aspect of this-the anisotropy in track distributions which seems to result from the inherently anisotropic structure of crystals. This effect seems so far to have received little attention.     

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.     

Thickness alterations of CR-39 plastic detectors due to the heating influence: Basic theory and experimental results

Heating experiments were conducted on CR-39 polymer/plastic detector samples at temperatures between 50 and 175 °C for various time intervals from 5 to 210 min to investigate the thermal behavior of detector material. Mass and thickness of un-heated and heated polymer samples were measured. Three distinct regimes have been observed showing different degrees of changes in thickness and mass of annealed samples. The percent change of thickness was considerably higher than the mass change during heating. Thermodynamic concepts are used to explain the experimentally observed heating regimes. Role of the difference between free energies of lateral and fold surfaces in detector thickening during heating is discussed. Scanning electron microscopy (SEM) was carried out on un-heated and heated CR-39 samples to examine the surface alterations due to heating. Results are useful for researchers who employ track detectors for radiation measurements in nuclear reactors and cosmic rays. They are also interesting for researchers in related fields, like fission track dating, which consider the thermal history of track recording materials. Our quantitative data and SEM imaging suggests that structural changes, especially surface changes in CR-39 polymer are very important and need to be explored carefully through joint SEM and the Atomic Force Microscopy (AFM).     

Advantage of PM-355 nuclear track detector in light-ion registration and high-temperature plasma diagnostics

Detailed calibration studies of selected types of SSNTDs have been performed at the SINS using monoenergetic light ions of energy within MeV range. These studies were motivated by the application of such detectors in the optimal way for plasma physics experiments. This paper shows track diameter evolutions versus particle energy and etching time. Some conclusions related to track registration phenomenon and detection properties of the investigated detectors, especially of the PM-355 type are also presented.     

Energy spectrum of 50-250 MeV/nucleon iron nuclei inside the MIR space craft

Stacks of CR-39 plastic nuclear track detectors were mounted inside the MIR spacecraft during the EUROMIR95 space mission for a period of 6 months. This long exposure time resulted in a large number of tracks of HZE-particles in the detector foils. All trajectories of stopping iron nuclei could be reconstructed by optimizing the etching conditions so that an automatic track measurement using image analysis techniques was possible. We found 185 stopping iron nuclei and used the énergy-range relation to calculate their energies at the stack surface. The measured spectrum of iron nuclei inside the MIR station is compared to results of model predictions considering the effect of the solar modulation for the mission period, the geomagnetic shielding effect for the MIR orbit and the shielding by material of the spacecraft walls and its instrumentation.     

The use of nuclear track detectors as an environmental solar ultraviolet radiation dosimeter

Investigation of using CR-39 nuclear track detectors as solar ultraviolet radiation (SUVR) dosimeter was studied. The nuclear track detectors were irradiated with Cf-252 (alpha and fission fragments) before exposure to sun light. The exposure of nuclear track detectors to SUVR were carried out under two different conditions (i) the detector was mounted on a solar tracker mechanism which always rotate towards the sun, and (ii) fixed on a horizontal surface. The measurements were performed for different periods extended from one to eight weeks continuously at Dhahran - Saudi Arabia. The period extended from the middle of July to middle of September: the hottest months in Saudi Arabia. The weekly integrated SUVR measured by Eppley sensor was ranged from 2400 W. h. m⁻² for one week up to 21000 W.h.m⁻² for eight weeks. The results indicate linear correlation between both the track diameters of alphas and fission fragments and the total exposure to SUVR. The results clearly demonstrate that it is possible to use the nuclear track detectors as an environmental and personal SUVR dosimeters.     

Comprehensive analysis of binary events in heavy ion reactions observed with dielectric track detectors

The dielectric track detectors are very efficient in registering the main fragments of a heavy ion reaction in the presence of lightly ionizing products and γ-radiations because of their threshold nature of registration and wide-angle acceptance. The binary events, revealed after chemical etching of these detectors, appear as the events having two correlated prongs in the body of the detector. The measurements of the geometrical parameters of these prongs provide the necessary data for subsequent kinematical analysis. We have made a thorough analysis of the two-pronged events in order to understand the physical mechanism of their production, using the track data from the reactions,