Solid State Phenomena Vol. 238

Abstract: Solid polymeric track detectors (SPTDs), due to their insensitivity to low LET radiations and integrating nature of signal registration, are found to be effective and convenient for neutron measurements, particularly in pulsed and mixed radiation fields such as in particle accelerator environments. This paper in addition to reviewing some of the existing methods of neutron spectrometry and dosimetry, explores new approaches on the use of SPTDs for neutron measurements, elaborates on the extended energy response and rapid etching techniques of SPTDs along with some new results. Microwave induced chemical etching (MICE) technique, recently introduced for rapid and efficient processing of track detectors is discussed in the paper.Contents of Paper

Abstract: Passive Solid State Nuclear Track Detectors (SSNTDs) have been employed successfully during the past two decades in space radiation studies due to their excellent physico-chemical properties. They are useful for charged particle detection in the linear energy transfer (LET) range above the threshold value of ~10 keV μm^-1. It was applicable for measurement of cosmic ray primary and secondary particles, including recoil nuclei, projectile and target fragments and secondary neutrons in past projects such as DOSMAP, BRADOS, ALTCRISS, Matroshka or recently in progress as SPD, DOSIS, as well as, in ground based experiment as Icchiban. The continuous development in the understanding of the track formation mechanism and improvement of detection techniques have resulted in the determination of the cosmic ray LET spectrum with less uncertainties and provided improved assessment of the dose burden of astronauts and helped to increase the effectiveness of radiation shielding of spaceships. Space dosimetry by nuclear track methodology stresses the advantages of passive systems for cosmic radiation field studies due to their robustness, compact dimensions, and complete independence from external power supply. SSNTDs cope also with requirement imposed by portable area monitoring or personal dose integrator to assess radiation risk of astronauts during intra or extra-vehicular activity. This review tries to provide a short summary about fundamentals and applications of space radiation studies using SSNTDs.Contents of Paper

Abstract: Leakages of hydrocarbon reservoirs often increase the radon concentration on the soil surface through distinct pathways; gas migration results in either prolific macro-seeps or micro-seeps. Soil gases, including radon, are recognized as potential tracers in geoscience. The surficial radiometric anomalies over hydrocarbon reservoirs provide the oil community with a complementary survey tool for oil exploration through the use of nuclear track methodology. The Solid State Nuclear Track Detector (SSNTD) is one of the recognized techniques to be employed advantageously in radon surveys for hydrocarbon exploration and occurrence of natural gas seeps. The nuclear track method provides information on the nature of radioactive gas sources, emanations from the soil and their transport pathways. Latent track etching conditions and their analysis are included.

Abstract: The article presents the most important results of radon research in Poland. Large-scale research, launched in this country in the early 1950s, was originally linked to using radon dissolved in groundwater in balneotherapy as well as to uranium ore exploration and mining. This early research focused on the area of the Sudetes and nowadays it is also south-western Poland where most radon research is being conducted. This is chiefly due to the geological structure of the Sudetes and the Fore-Sudetic block, which is propitious to radon accumulation in many environments. Radon research in Poland has been developing dynamically since the 1990s. A lot of research teams and centres have been formed, all of them using a variety of methods and advanced measurement equipment enabling research into radon occurrence in all geospheres and all spheres of human activity. The author presents the contribution of Polish science to broadening human knowledge of the geochemistry of radon, particularly of ²²²Rn isotope. The article also presents the ranges and mean values of ²²²Rn activity concentration measured in different environments in Poland including the atmospheric air, the air in buildings and underground hard-coal and copper mines, the cave air, the air in underground tourist sites and abandoned uranium mines, as well as soil air and groundwater.

Abstract: Solid State Nuclear Track Detectors (SSNTDs) have been widely used for time integrated radon measurements due to their cost effectiveness, portability and easy-to-use feature. In order to obtain a proper measurement of radon using SSNTDs, it is necessary to select a proper exposure mode. The various modes in which the SSNTDs can be exposed are: (i) bare mode, (ii) single cup mode, and (iii) twin cup mode. This paper addresses the merits and demerits of SSNTDs used in each type of mode of exposure for radon monitoring. The paper analyses the results of the conventional bare mode as well as the latest twin cup mode of SSNTDs. The paper also analyses the performance comparison of single entrance vis a vis double entrance type twin cup dosimeter. Design and features of the newly developed pinhole based single entrance twin cup dosimeter have been discussed. A protocol has been proposed for the selection of houses and deployment of the dosimeter. Some of the important findings from laboratory and field experiments of the new device have been presented.

Abstract: In this paper we present the preliminary results of a study of the radon and thoron (²²²Rn and ²²⁰Rn) and their progeny, concentration distribution inside the cellar as recorded by a 200×200 cm mesh of CR-39 bare detectors. The mesh comprised one hundred and sixty two 1.9×0.9 cm CR-39 (Lantrack^®) polycarbonate chips. The distribution of radon and thoron shows a complex pattern. Both sides of the mesh displayed a significant concentration gradient of radon and thoron levels, with a maximum near to the top and bottom of the detection grid, and minimum around the center. This spatially inhomogeneous distribution recorded by the detectors could be the result of the distance from the walls, gas kinematics, diffusion coefficient, room geometrical configuration, aerosol behaviors, and objects inside the room, among others. It suggests that the analysis of these complex distribution patterns may be applicable for the estimation and evaluation of indoor radon concentration levels, considering each particular location and characteristics of the place.

Abstract: The importance of measuring the decay products of ²²²Rn (radon) and ²²⁰Rn (Thoron) is being realized by researchers as these are the major inhalation dose givers to the general population. Basically the decay products are radioisotopes of Polonium, Bismuth and Lead, which are solid particles. Upon inhalation, these particles deposit in different parts of the respiratory tract, undergo radioactive decay and irradiate the nearby tissues. So, the study of the behavior of the decay products in indoor air is important for assessing the natural background radiation exposures received by general populations through the inhalation route. Although the inhalation doses are predominantly due to decay products yet it had been the usual practice to measure the gas concentration rather than the decay products because of the complexities involved in their detection. The most common method is to derive the progeny concentration from the measured gas concentration using an assumed equilibrium factor. While this is fairly justified for radon in view of the short-lived nature of the progeny as compared to the gas, this approach is beset with serious limitations in thoron-rich environments. However, the development of passive detection system for the decay products known as deposition-based Direct Radon and Thoron Progeny Sensors, has provided a solution to the long standing problem of measuring the time integrated decay product activity concentration. These deposition sensors are calibrated against active measurement techniques, and provide an easy to use method for passive and simultaneous time integrated decay product measurement. In addition, for multi-parametric study, the different modes of these passive sensors, like flow-mode and wire-mesh capped mode, are also used. These are further discussed in the manuscript.

Abstract: The present paper studies the indoor radon variations in two similar dwellings, one of them occupied and the other unoccupied, from the same residential building. In particular, the research study was carried out in two new dwellings in Madrid. Radon concentration and ambient parameters were measured three-hourly from 11 May to 12 December 2014. Solid state detectors, Radon Scout, were used for the radon monitoring. Simultaneously, two atmospheric variables were acquired from NOAA Air Research Laboratory. The results show that radon level is slightly higher in the unoccupied dwelling than in the other one. From the analysis developed in this study, it is found that a specific seasonal pattern exists in the indoor radon concentration. Besides, the anthropogenic influence is also analysed. Nearly periodical patterns could be observed in specific periods whether dwelling is occupied or not.

Abstract: Different measurements of equilibrium equivalent concentration of radon progeny (EEC_Rn) were obtained over a period of one year in indoor air of Physics Department at Minia University, located in the Upper Egypt. A method based on an alpha spectroscopy was used. Sartorius membrane filters (1.2 μm pore size, 25 mm diameter and its efficiency about 100%) were used as a collection media. Alpha activities were measured during and after air sampling by using surface barrier detector. EEC_Rn varied between 1.26 and 19 Bq m^-3 with an average value of 5.2 ± 0.46 Bq m^-3. Unattached fraction was determined using a single stainless steel-wire-mesh screen (50% penetration for 4 nm equivalent diameter). A mean unattached fraction (f_b) of 0.08 was obtained. Based on the obtained measured data values (f_b and EEC_Rn), dose conversion factors were compared to epidemiology based value of 4 mSv/WLM for indoor air.