Radon surveys in Brazil using CR-39

In this work results of two radon daughters survey in Brazil are presented and discussed. Some methodological problems concerning the first survey are pointed out which were corrected for the second survey in order to make a realistic long-term measurement of radon decay products in the air. The technique employed in both surveys was the alpha-spectroscopy using CR-39. The reliability of this technique as well as the results of the second survey are discussed, which indicate a poor correlation between radon and its decay products in the air at the researched dwellings.     

Alpha-particle calibration of CR-39 using a beehive collimator

A device to determine the detection efficiency of CR-39 for alpha particles is presented. A beehive collimator restricted the angle of incidence of alpha particles on a CR-39 sheet, such that the total number of alpha emitters could be determined. This makes it possible to obtain the critical angle of incidence, Θ_C, and the maximum angle of incidence resulting in round (diameter ratio <1.100) etch pits, Θ_max. In this work, these angles were determined for incidence energies around 7.5 MeV (more specifically 6.1 and 8.8 MeV).     

Techniques to investigate the characteristic of CR-39 detectors using Am---Be neutron source

Two techniques have been developed to investigate the characteristic of the sensitivity of CR-39 (polyallyldiglycol carbonate) track detector using Am---Be neutron source. The firstis to measure volume track density created by fast neutrons in CR-39 detectors. The second is to measure areal asymptotic track density on the surface of CR-39 sheets. Two types of CR-39—SY-2 CR-39 made in China and another made in USA were calibrated using the techniques. It shows that the two types of CR-39 detectors have nearly the same sensitivity to detect fast neutrons. The techniques developed in this work can be applied to calibration of other track detectors.     

Measurements of radon concentration in soil gas by CR-39 detectors

A miniature diffusion chamber with a 25 × 4 × 0.5 mm CR-39 track etch detector (Pershore Moulding Ltd.), mounted on the 1.1 m long pole has been developed for radon gas measurements at 1 meter depth in the soil. For chemically etched CR-39 (7h, 70°C NaOH) and automatic track analysis the lowest detection limit of the chamber was found to be 0.5 MBq h m⁻³ and the useful exposure range from 2 to 20 MBq h m⁻³. The typical exposure time in the soil is between 2 to 14 days. The chamber was tested against the active AlphaGUARD PQ-2000 (Genitron Instruments GmbH) probe. The test yielded consistent results for soils with typical values of permeability and which are not miniature with water. The pilot measurements of radon gas in soil conducted with the miniature diffusion chambers around 48 buildings in Kraków and Silesia regions yielded an average radon concentration of 13 kBq m⁻³. The chambers are to be applied to measure radon concentration in soil before constructing new houses in order to avoid high radon risk areas.     

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.     

General expression of the calibration curve for the CR-39 radon track detectors

The CR-39 detectors are widely used as passive radon dosimeters, as well as in physics laboratories or for industrial applications. For what concerns radon monitoring, the calibration curve which is usually adopted corresponds to a linear relation between the actual etched track density and the track density counted by an automatic acquisition system. This linear calibration provides very accurate radon exposure assessments in a restricted range of etched track density, however it neglects the effect of the tracks overlapping that becomes as relevant as the track density increases. In the present work the mathematical expression of the area covered by a set of uniformly distributed tracks is deduced. This result allows then to infer the probability that the system acquires the right track density, providing a general calibration curve for a solid state radon track detector. The process of track production and reading routine is also simulated adopting a Monte Carlo approach, showing that the obtained results are in agreement with the function proposed as calibration curve. Moreover, a linear dependence between the track average area and the rate parameter of the calibration curve has been observed. Finally a semi-empirical correlation based on the previous results is proposed.     

Experimental determination of CR-39 counting efficiency to α particles to design the holder of a new radon gas dosemeter

To design a new radon gas dosemeter, the knowledge of the SSNTD α counting efficiency is essential. It depends primarily on the energy and incidence angle into the detector, then on the etching conditions and finally on the track counting procedure. Therefore the elicited efficiency function represents all these factors. The detectors were exposed to α particles at different angles of incidence and energies, by using a ²⁴⁴Cm source; two alternative NaOH solution etching conditions were tested, 6.25 N 70°C at 6 and 12 h, respectively. The counting was performed with a light microscope, 267×, and with an automatic track analysis procedure. The critical incidence angle dependance on energy, in our standard condition (6 h), resulted θ_C(E)=380.0e^{(−0.286•(E−0.050))}(1−e^{(−0.186•(E−0.050))}), and it was used to design our new radon gas holder.     

Low energy alpha particle spectroscopy using CR-39 detector

The possibility of using CR-39 to measure the depth profile of ¹⁰B in Si is analysed. The measuring technique exploits the ¹⁰B(n, )⁷Li nuclear reaction. For this reason the track parameters (size, optical properties) of low energy alpha-particles (<1.47 MeV) were studied. The results showed that an energy resolution of about 100 keV could be obtained by an appropriate selection of etching conditions. The profile of ¹⁰B in Si at a depth as small as 1 μm can be measured.     

Particularization of alpha contamination using CR-39 track detectors

Solid-state nuclear track detectors have found wide use in various domains of science and technology, e.g. in environmental experiments. The measurement of alpha activity on sources in an environment, such as air is not easy because of short penetration range of alpha particles. Furthermore, measurement of alpha activity by most gas ionization detectors suffers from high background induced by the accompanying gamma radiation. Solid state nuclear track detectors (SSNTDs) have been used successfully as detecting devices and as a passive system to detect alpha contamination on different surfaces. This work presents the response of CR-39 (for two types) to alpha particles from two sources, ²³⁸Pu with energy 5 MeV and ²⁴¹Am with energy 5.4 MeV. The methods of etching and counting are investigated, along with the achievable linearity, efficiency and reproducibility. The sensitivity to low activity and energy resolution are studied.      

Structure effect in response function of CR-39 detector

The structure effect of CR-39 on the rate of its hydrolysing reaction was studied. It has been indicated that the sensitivity of any plastic detector is dependent on the its posibility to alkalai hydrolyse. It is known that polyesters and polycarbonates undergo decarboxylation under ionizing radiation so that would point to the carbonate group as the amplify induced radiation sensitive link. The structure effect would be one of the keys to develope the new, more sensitive nuclear track detectors.     

Reduction of background in CR-39 SSNTD using chemical pre-etching methods

Presently, CR-39 Solid State Nuclear Track Detectors (SSNTD) is being used for Fast Neutron Personnel Monitoring in India. Individual detectors are cut manually from CR-39 sheets. Laser-cutting of the sheets will ensure precision and also save on the laborious efforts involved in sheet cutting. It was observed that there is a slight increase in background tracks due to laser-cutting. Studies were carried out on the effect of chemical pre-etching at higher temperatures in properties of CR-39 such as the background, sensitivity and minimum measurable dose. For this purpose a pre-etch step was included in the normal processing of the CR-39 foils in an elevated temperature electrochemical cell (ETECE cell) and the duration for pre-etch step at elevated temperature was optimized. Samples of CR-39 exposed to dose equivalents ranging from 1 mSv to 10 mSv using Am-Be neutron source were processed by both the methods, under normal processing using ECE cell and in the optimized chemical pre-etch followed by normal processing. The dose responses of CR-39 processed by both methods are compared in this paper.      

Measuring depths of sub-micron tracks in a CR-39 detector from replicas using Atomic Force Microscopy

One of the challenging tasks in the application of solid-state nuclear track detectors (SSNTDs) is the measurement of the depth of the tracks, in particular, the shallow ones resulting from short etching periods. In the present work, a method is proposed to prepare replicas of tracks from particles in the CR-39 SSNTDs and to measure their heights using atomic force microscopy (AFM). After irradiation, the detectors were etched in a 6.25 N aqueous solution of NaOH maintained at 70 °C. The etched detectors were immersed into a beaker of the replicating fluid, which was placed in a water bath under ultrasonic vibration and maintained at room temperature to facilitate the filling of the etched tracks with the replicating fluid. As an example of application, these results have been used to derive a V function for the CR-39 detectors used in the present study (for the specified etching conditions).     

用CR-39对空间重离子的鉴别模型

根据重离子在CR39中能量损失率公式,建立了一个鉴别空间重离子的数学模型LET=cZdRb.通过传能线密度与剩余射程之间的关系曲线,获得了该模型的系数.在实验中发现的CR39蚀刻率与离子有限传能线密度的关系VT=A·(REL)BE<350,被用来与该数学模型相关联,并得到一等式R=A0.0455Z3.18V–1T.最终,借助于标定实验得到了离子鉴别公式Z3.18=64541.08+2.53(dR/dV–1T).     

Computer simulation of the processes in a CR-39 neutron detector

The application of CR-39 as a fast neutron dosimeter, based on counting elastic recoil nuclei tracks of H, C and O nuclei in a geometrically matched pair of detectors, was studied. A computer simulation of the processes during the exposure of a detector pair to neutrons is presented. The energy and spatial distribution of the recoil nuclei was calculated with the MCNP 4B program package. On the basis of this distribution, a Monte-Carlo procedure for the generation of latent tracks in the CR-39 detectors was run. Additionally, a procedure for calculation of the chemical track etching for revealing the visible track parameters was performed to obtain the detector response.     

Estimation of the latent track size of CR-39 using atomic force microscope

As a frame work of the study for the latent track size measurement using atomic force microscope, we have measured the minute etch pits and the extremely small amount of bulk etch of CR-39 at the beginning of chemical etching, and obtained its growth curves in nanometer dimensions. The pieces of CR-39 were exposed to 6 MeV/nC and Fe ions with normal incidence angle and were etched in 70°C 7 N NaOH solution for 0.5,1,2,3,5 min. The diameters of latent track were estimated to be 17 nm for Fe ions and 8 nm for C ions, respectively. These values are comparable to the experimental data on the average ‘track core diameters’ that have been obtained by various experimental techniques.     

Comparison of SEM and optical analyses of DT neutron tracks in CR-39 detectors

A solid state nuclear track detector, CR-39, was exposed to DT neutrons. After etching, the resultant tracks were analyzed using both an optical microscope and a scanning electron microscope (SEM). In this communication, both methods of analyzing DT neutron tracks are discussed.     

Extension of alpha particles in CR-39-etched track depth model to heavier ions

In this paper, the previous modeling of protons and alpha particles tracks depth in CR-39 nuclear track detectors was extensively extended to describe tracks of heavier ions. These ions include deuteron, lithium, boron, carbon, nitrogen and oxygen. Based on a compilation of published experimental results related to these ions, a set of empirical fitted model parameters is obtained for each type of ion. The A dependence of these model parameters is obtained.     

Photoluminescence of irradiation induced defects on CR-39

A gamma-irradiated poly allyl diglycol carbonate solid state nuclear track detector is studied by means of photoluminescence. The irradiation is done using a ⁶⁰Co cell with a dose rate of 7.5 kGy/h. Photoluminescent radiation is recorded with excitation radiation of wavelength 346 nm. A broad luminescent band shows a possible dosemetric property for γ-radiation in the dose range 0.1–8.0 MGy. High-dose irradiation by γ-rays introduces donor and acceptor levels in the forbidden energy gap. The broad band may be attributed to the number of overlapping emissions caused by transitions between these acceptor and donor levels.     

Improvement of neutron detection efficiency with high sensitive CR-39 track detector

Two subjects have been studied for establishing an efficient detection technique applicable to neutrons with an energy higher than 20 MeV, for which personnel dosimetry becomes more important especially in space activities and radiation protection around high-energy accelerators.

A performance of a new sensitive detector, recently developed copolymer of CR-39 and N-isopropylacrylamide, was checked in a D–T neutron field. It was confirmed experimentally that its sensitivity was several times as high as a pure CR-39 in the radiator effect and more than twice in the total efficiency. In the other experiment, CR-39 samples were exposed to 65 MeV quasi-monoenergetic neutrons, and the registration characteristics have been investigated from a fundamental point of view. The particles recorded were divided into three groups of proton relatives, -particles and heavy ions by applying the growth curve method and the multi-step etching technique. The measured fractions were in good agreement with the values calculated by SSNERS code previously developed.