Factors affecting the registration and counting of alpha tracks in solid state nuclear track detectors

In view of the fact that the radon progeny contribute the highest to the natural radiation dose to general populations, large scale and long-term measurements of radon and its progeny in the houses have been receiving considerable attention. Solid State Nuclear Track Detector (SSNTD) based systems, being the best suited for large scale passive monitoring, have been widely used for the radon gas (using a cup closed with a semi-permeable membrane) and to a limited extent, for the measurement of radon progeny (using bare mode in conjunction with the cup). These have been employed for radon mapping and indoor radon epidemiological studies with good results. In this technique, alpha tracks recorded on SSNTD films are converted to radon/thoron concentrations using corresponding conversion factors obtained from calibration experiments carried out in controlled environments. The detector response to alpha particles depends mainly on the registration efficiency of the alpha tracks on the detector films and the subsequent counting efficiency. While the former depends on the exposure design, the latter depends on the protocols followed for developing and counting of the tracks. The paper discusses on parameters like etchant temperature, stirring of the etchant and duration of etching and their influence on the etching rates on LR-115 films. Concept of break down thickness of the SSNTD film in spark counting technique is discussed with experimental results. Error estimates on measurement results as a function of background tracks of the films are also discussed in the paper.      

Designing polymers for nuclear track detection

This article describes our attempts since 1996 to systematically design and synthesize monomers and corresponding polymers for nuclear track detection. So far more than 15 homopolymers/copolymers have been prepared and tested by us for this purpose. Some of these polymers show better track detection characteristics vis-á-vis commercially available poly allyl diglycol carbonate (PADC) track detectors.      

Calibration of PM-355 nuclear track detectors; comparison of track diameter diagrams with track depth characteristics

The calibration diagrams, i.e. track diameters and track depths versus ion energy and etching time, as obtained for PM-355 track detector irradiated with He-ions are presented. The both detector characteristics are compared. The track etch rate is determined by two methods, as a function of the etch pit depth and the ion energy loss.     

Study of spatial structure and energy spectrum of ion beams by means of LR 115A and PM-355 nuclear track detectors

The paper reports on measurements of pulsed plasma-ion streams, as performed with the selected solid-state nuclear track detectors (SSNTD). The ion-beams were produced by an experimental device (RPI-IBIS) equipped with coaxial electrodes (each made of molybdenum rods) and a fast-acting gas valve. The device was operated at 30 kV/44 kJ, with puffing of pure hydrogen or deuterium. The spatial structure of the ion beams was studied with pinhole cameras equipped with replaceable detectors, and ion mass- and energy-spectra were measured with a Thomson spectrometer. To analyse low-energy ions (below the energy thresholds of LR 115A and PM-355 SSNTD) an additional accelerating system was applied. It was observed that ions of energy are emitted in bunches, and the ion flux amounts to at a distance of 30 cm from the electrodes outlet. Energy spectra of protons and deuterons ranged from about 30 keV to about 400 keV. The ion distributions, as recorded by means of the PM-355 and LR 115A detectors, are similar.     

Advantages of the use of solid-state nuclear track detectors in high-temperature plasma experiments

This paper reports on measurements performed with the use of SSNTDs at the PF-1000 Plasma-Focus facility in Warsaw and TEXTOR tokamak in Juelich. Fusion reaction protons were measured within the PF-1000 facility and TEXTOR tokamak.     

Ageing of AgCl/Cd nuclear track detectors monitored by luminescence spectroscopy

Abstract

Solid-state nuclear track detectors, made of Cd doped AgCl crystals, are commonly prepared by rolling into the form of thin foils. Subsequent long-term relaxation is however needed to obtain good quality tracks. The present communication shows for the first time that this detector “ageing” is reflected in lowtemperature (77 K) luminescence spectra. Maximum of the emission band shows a slow (lasting for ～ 100 hours) blue shift, the magnitude of which (as much as 25 nm) depends on the compression ratio caused by the rolling. The shift is believed to be due to the rearrangement of Cd⁺⁺ ions around freshly introduced dislocations. This finding opens the possibility of monitoring non-destructively the process of detector ageing and to determine the minimum time required for saturation.     

The atomic force microscope as a fine tool for nuclear track studies

Atomic force microscopy (AFM) is a relatively new tool in the study of materials used in the nuclear track methodology. The sensitivity to detect ionizing nuclear particles is strongly influenced by the surface roughness of the material used as detector. In this contribution a surface analysis of several commercial polycarbonates used as nuclear track detectors is presented.     

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.     

Radon epidemiology and nuclear track detectors: Methods, results and perspectives

An important achievement of nuclear track detectors is that they render it possible to measure a large number of radon concentrations. These are necessary for epidemiological studies aimed to estimate the lung cancer risk due to exposure to radon and its decay products in dwellings. Many case–control studies were conducted in the last 15 years in Europe, North America and China, in order to avoid the uncertainties associated with the risk extrapolation from epidemiological studies on miners exposed in underground mines. In this review paper, the main methodological issues of these studies are introduced: confounding factors, the impact of radon exposure uncertainties on the estimated risk, the retrospective assessment of radon exposure through the measurement of surface concentration on glass objects, the interaction between radon and smoking, statistical methods to analyze data and combine studies, etc. As regards the estimated risk of lung cancer, the main characteristics and results of each study are reported and discussed, together with the results of meta-analyses and, most importantly, of the three recently published analyses that pool 2 Chinese, 7 North American, and 13 European studies. Finally, some conclusions are given and a brief reference is made to ongoing studies.     

Measurement of radon and thoron concentration by using LR-115 type-II plastic track detectors in the environ of Brahmaputra Valley, Assam, India

Radon/thoron and their progeny concentrations were measured in different types of dwellings at different locations around industrial areas, cities and rural areas of Brahmaputra Valley of Assam by using LR-115 (type-II) plastic detector. Radon levels of different dwellings were analysed with reference to the nature of building materials, ventilation patterns and the types of underlying soil. The results were discussed under the light of exposure limits set by ICRP. The average concentrations of indoor radon and thoron varied from 39.5 to 215.2 Bqm⁻³ and 12.9 to 37.6 Bqm⁻³, respectively. The estimated inhalation dose due to radon, thoron and their daughter products in the study areas varied from 0.53 to 1.00 μSvh⁻¹.     

Measurement of indoor radon levels in Erbil capital by using solid state nuclear track detectors

Radon alpha activity concentration has been measured in 28 homes in the Erbil Capital-Iraqi Kurdistan region during the autumn season by using time-integrated passive radon dosimeters containing CR-39 solid state nuclear track detectors “SSNTDs”. The radon activity concentrations in these homes range from (10.33–90.34) with an average of . The average absorption effective dose equivalent for a person living in homes for which the investigation were done was found to be , obtained by using an equilibrium factor of 0.5 and an occupancy factor of 0.8. The average lung cancer cases per year per 10⁶ person was found to be 23±12.     

Comparison of responses of LR-115A, CR-39 and PM-355 track detectors to pulsed low-energy proton streams

The paper concerns applications of LR-115A, CR-39 and PM-355 solid-state nuclear-track detectors (SSNTDs) for investigation of pulsed fluxes of protons below 300 keV. The proton streams were generated by the RPI-IBIS device operated with hydrogen puffing [Baranowski et al. 2000. Studies of hydrogen discharges in RPI-type devices with different electrode configurations. Czech. J. Phys. 50 (Suppl. S3), 101–107]. To perform ion mass- and energy-analysis, a Thomson mass-spectrometer equipped with a special input system and exchangeable detectors was used. A quantitative analysis of proton tracks upon Thomson parabolas was performed by means of an optical microscope equipped with a CCD camera. It made possible to measure proton tracks and to determine their statistics. The paper presents proton energy spectra recorded with the selected detectors, and responses of these detectors to protons of energy from about 30 to 300 keV. The results are important for verification of detector characteristics and for measurements of protons at different experimental conditions.     

The applications of nuclear track detectors in transuranic contamination problems

Nuclear Track Methodology (NTM) is very well known for its possibilities in applications in a wide variety of fields. The appearance of the polycarbonate as alpha radiation detector material, established a very confident monitoring surface alpha contamination, soil and water alpha activity. The purpose of the study is to investigate the utility of the CR-39 (Allyl Diglycol Carbonate) in fast semi-quantitative transuranic contaminant evaluation, including the distribution in underground contaminated soils, hot spots and transuranic material accumulations.     

Annealing of heavy ion tracks in cellulose nitrate plastic track detectors

The effect of heat treatment on the latent tracks in cellulose nitrate plastic track detectors has been studied. The bulk etch rate increases with annealing temperature while the track diameters of different ions in cellulose nitrate decrease with increase in annealing time and temperature. Experimental results show that for heavier ions higher temperatures are needed for their complete erasure. The track length and track etch rate are decreased by the application of heat. Experiments reveal that annealing reduces track density. The vertical tracks are more stable than the oblique tracks and require higher temperature for their complete erasure.     

Measurement of the energy spectra of fission fragments using nuclear track detectors and digital image processing

Energy spectra of fission fragments were determined using a Nuclear Track Methodology (NTM) supported by digital image analysis and numerical data processing using a standard personal computer. The analysis of a californium (²⁵²Cf) spectrum with this approach shows improvement compared with the values reported previously using the standard procedure, in terms of resolution and accuracy. This new method adds full automation to the technical advantages and cost effectiveness of an NTM.     

In vivo boron-11 MRI and MRS using (B24H22S2)4- in the rat.

In vivo boron-11 magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) were performed on a rat that had been infused with a potential boron neutron capture therapy agent, Na₄B₂₄H₂₂S₂, using methods for detecting nuclei with a short T₂ relaxation time. MRI and MRS were also performed on a euthanized rat that had been similarly infused in vivo. Boron-11 spectral intensities decreased in the living rat over a 25-h period. The results demonstrate the capability of MRI and MRS to noninvasively monitor the distribution and excretion of boron agents in vivo.     

New results from exposures of CR-39 nuclear track detectors

Six stacks of nuclear track detectors were exposed in December 1994 to ²⁰⁷Pb⁸²⁺ ions of 158 A GeV at the CERN-SPS. Each stack was made of CR39 sheets placed after a target. The CR39 was manufactured by the Intercast Europe Co. of Parma (Italy). The exposures were carried out at normal incidence to an average density of 400 ions/cm². The main purpose of the exposures was the calibration of the CR39 nuclear track detector used in a large area detector to search for magnetic monopoles (experiment MACRO at the Gran Sasso Laboratory). We compare the response of CR39 of different production batches in different etching conditions. The results indicate no relevant aging effect for the CR39 made more than 5 years ago. The first result of a “long period” investigation of possible fading effects for the CR39 is also presented.     

Radon exhalation studies in building materials using solid-state nuclear track detectors

Indoor radon has been recognized as one of the health hazards for mankind. Building materials constitute the second most important source of radon in dwellings. The common building materials used in the construction of dwellings are studied for radon exhalation rate. The ‘Can’ technique using LR-115 type-II solid-state nuclear track detector has been used for these measurements. The radon exhalation rate in these samples varies from 4.75 m Bq m⁻² h⁻¹ (0.14 m Bq kg⁻¹ h⁻¹) for limestone to 506.76 m Bq m⁻² h⁻¹ (15.24 m Bq kg⁻¹ h⁻¹) for soil.     

Supervised nuclear track detection of CR-39 detectors by cellular automata

In this paper, cellular automata are used to detect the nuclear tracks in the track images captured from the surface of CR-39 detectors. Parameters of the automaton as the states, neighborhood, rules and quality parameters are defined optimally for the track image data set under analysis. The presented method is a supervised computational algorithm which comprises a rule definition phase as the learning procedure. Parameter optimization is also performed to adapt the algorithm to the data set used.     

Long-term measurements of radon progeny concentrations with solid-state nuclear track detectors

In this paper, we review existing methods for long-term measurements of radon decay products with solid-state nuclear track detectors. We then propose a method to determine the equilibrium factor using the bare LR 115 detector. The partial sensitivities p_i of the LR 115 detector to and its α-emitting short-lived progeny, and , were investigated. We determined the distributions of lengths of major and minor axes of the perforated α-tracks in the LR 115 detector produced by , and through Monte Carlo simulations. The track parameters were first calculated using a track development model with a published V function, and by assuming a removed active layer of . The distributions determined for different α-emitters were found to be completely overlapping with one another. This implied equality of partial sensitivities for radon and its progeny.Equality of partial sensitivities makes convenient measurements of a proxy equilibrium factor F_p possible which is defined in the present work as (f₁+f₃) and is equal to the ratio between the sum of concentrations of the two α-emitting radon progeny to the concentration of radon gas . In particular, we have found F_p=(ρ/ρ_itC₀)-1, where ρ (track/m²) is the total track density on the detector, (for the V function mentioned above and for a removed active layer of ), t is the exposure time and C₀ (Bq/m³) is the concentration of . If C₀ is known (e.g., from a separate measurement), we can obtain F_p. The proxy equilibrium factor F_p is also found to be well correlated with the equilibrium factor between radon gas and its progeny through the Jacobi room model. This leads to a novel method for long-term determination of the equilibrium factor.Experimental irradiation of LR 115 detectors to known concentrations as well as known equilibrium factors were carried out to verify the present method. The relationship between ρ_i and the removed layer was then derived for the V function specifically determined for the LR 115 detectors we were using for the experiments. The actual removed layers for individual detectors after etching were measured accurately using surface profilometry. A curve showing the relationship between the removed layer and the track diameter of normally incident 3 MeV α-particles is also provided for other researchers, who do not have access to surface profilometry, to use the present technique conveniently.