Search

The uncontrolled release of long-lived radioactive substances from nuclear accidents can contaminate inhabited land areas. The removal of topsoil is an important method for reducing future radiation exposure but can also generate a large amount of waste that needs safe disposal. To the best of our knowledge, previous studies have determined the optimal depth of topsoil removal but not the size of the area designated for this measure. For this purpose, this study performed Monte Carlo simulations of hypothetical 137Cs surface contamination on various ground areas in a typical northern European suburban area. The goal was to study the size of the areas needed and amount of waste generated to achieve a certain relative and absolute dose reduction. The results showed that removing the topsoil from areas larger than 3000 m2 around the houses in the study neighbourhood results in only marginal reduction in radiation exposure. If, on average, 5 cm of topsoil is removed over 3000 m2, then 150 m3 of waste would be generated. However, in this scenario adjacent properties benefit from each other's decontamination, leading to a smaller amount of waste for a given reduction in future radiation exposure per inhabitant of these dwellings. Additionally, it was shown that topsoil removal over limited areas has a higher impact on the absolute dose reduction at an observation point inside or outside the houses with higher initial dose. [ABSTRACT FROM AUTHOR]

Optically stimulated luminescence (OSL) signal properties of pellets from three types of NaCl (two household salts and one analytical grade salt) were investigated for their use in prospective dosimetry. Special attention was given to the OSL signal behaviour with time. The readout protocol was optimised in terms of preheat temperature, and the OSL signal yield of the NaCl pellet with time as well as the fading of the OSL signal with time was investigated. The effects of acute and chronic irradiations were compared. Irradiations and readout were performed using a Risø TL/OSL reader (TL/OSL-DA-15, DTU Nutech, Denmark). The optimal preheat temperature was determined to be 100 ºC, yielding OSL signals similar to a 1 h pause before OSL signal readout. There was no OSL signal fading observed as a function of time, but a decrease in the OSL signal yield of the NaCl pellets with time resulted in an apparent inverse fading when converting the OSL signal to an absorbed dose. For chronic radiation exposures of up to five weeks, the sensitivity of the NaCl pellets was found to be stable. The results of this study show that the use of NaCl pellets for prospective dosimetry is a promising, cost-effective, and accessible complement to commercially available alternatives for accurate absorbed dose determinations. [ABSTRACT FROM AUTHOR]

In this study the dosimetric properties of alumina (Al2O3) substrates found in resistors retrieved from mobile phones were investigated. Measurements of the decline of optically stimulated luminescence (OSL) generated following exposure of these substrates to ionising radiation showed that 16% of the signal could still be detected after 2 years (735 days). Further, the magnitude of the regenerative dose (calibration dose; Di) had no impact on the accuracy of dose estimates. Therefore, it is recommended that the Di be set as low as is practicable, so as to accelerate data retrieval. The critical dose, DCL, and dose limit of detection, DDL, taking into account the uncertainty in the dose–response relation as well as the uncertainty in the background signal, was estimated to be 7 and 13 mGy, respectively, 1 h after exposure. It is concluded that given the significant long-term component of fading, an absorbed dose of 0.5 Gy might still be detectable up to 6 years after the exposure. Thus, OSL from alumina substrates can be used for dosimetry for time periods far in excess of those previously thought. [ABSTRACT FROM AUTHOR]

The aim of this work was to determine how a latent optically stimulated luminescence (OSL) signal in irradiated household salt is preserved under various ambient conditions, from the time of exposure to the time of signal readout. The following parameters were examined: optical fading in fluorescent light and under darkroom conditions (red light), thermal stability of the OSL signal during storage in a light-tight container, optical fading in representative container types, and sensitization effects of the OSL signal in exposed household salt. Furthermore, the influence of grain mixing within the saltshaker or salt container was studied by determining the dose gradient within typical salt packages. Finally, the signal integrity of salt irradiated under field conditions in a village in Belarus contaminated by Chernobyl fallout was investigated. The results show that the OSL signal in household salt is preserved in large cardboard box containers, but not in white plastic salt containers or in small portion bags used in, e.g., fast food restaurants. Furthermore, the continuous wave blue OSL signal in household salt does not fade significantly during storage up to 140 days. On the contrary, the signal appears to slowly increase during storage ('inverse fading'). Field tests of two different salt containers (with and without black tape to block light) located in Belarussian households confirmed that the signal is preserved in white plastic salt containers when they are covered with extra light-shielding material. [ABSTRACT FROM AUTHOR]

Following a radiological or nuclear emergency event, there is a need for quick and reliable dose estimations of potentially exposed people. In situations where dosimeters are not readily available, the dose estimations must be carried out using alternative methods. In the present study, the optically stimulated luminescence (OSL) properties of tooth enamel and different dental repair materials have been examined. Specimens of the materials were exposed to gamma and beta radiation in different types of liquid environments to mimic the actual irradiation situation in the mouth. Measurements were taken using a Risø TL/OSL reader, and irradiations were made using a Sr/Y source and a linear accelerator (6 MV photons). Results show that the OSL signal from tooth enamel decreases substantially when the enamel is kept in a wet environment. Thus, tooth enamel is not reliable for retrospective dose assessment without further studies of the phenomenon. Dental repair materials, on the other hand, do not exhibit the same effect when exposed to liquids. In addition, dose-response and fading measurements of the dental repair materials show promising results, making these materials highly interesting for retrospective dosimetry. The minimum detectable dose for the dental repair materials has been estimated to be 20-185 mGy. [ABSTRACT FROM AUTHOR]

This paper presents a study in which the specific activity of C in hair has been investigated as an easily determined bio-indicator of the integrated 14C exposure (over several months). The study includes 28 Swedish workers handling 14C-labelled compounds, or working in a 14C-enriched environment. Hair samples from personnel at a Swedish nuclear power plant showed very low levels of 14C contamination, if any. In contrast, personnel at the investigated research departments showed 14C levels in hair of up to 60% above the natural specific activity of 14C. Much higher levels, up to 80 times the natural specific activity of 14C, were found in hair from individuals working at a pharmaceutical research laboratory. This contamination was, however, not solely an internal contamination. There were indications that most of the 14C in the hair originated from airborne 14C-compounds, which were adsorbed onto the hair. The difficulties in removing this external 14C contamination prior to analysis are discussed, as are the possibilities of using accelerator mass spectrometry to analyse various types of samples for retrospective dose assessment. [ABSTRACT FROM AUTHOR]

The emissions of 137 Cs into the environment from the nuclear accidents in Chernobyl in 1986 and Fukushima in 2011 led to the need to decontaminate large areas to avert radiation doses to the population in the affected areas. To be able to perform cost-effective and sustainable remediation, knowledge is needed about how radiation doses can be minimized through optimized interventions such that the greatest possible reduction in radiation dose is obtained with the smallest possible negative impact on the area. Theoretical calculations have been performed to determine how radiation doses in single family houses in a typical Swedish residential suburb arise from a hypothetical 137 Cs deposition on the ground. The intention was to highlight how remediation of different parts of the surroundings affects the radiation dose to the residents in a particular property. A Monte Carlo model of the houses and the environment in a suburban area was set up to allow calculations of the dose contributions from different contaminated ground areas such as their own property, neighbouring properties, streets and surrounding recreational areas. Calculations were performed for eleven observation points inside different rooms of the house and one observation point in the garden outside the house, for four houses in the neighbourhood, and for two types of building construction material. The influence of the time spent in different rooms of the house and the contamination of areas surrounding the house was studied. The results show that in general the main dose contribution originates from their own property, but that a significant part (30–80%, depending on the observation point) can come from other areas, showing the importance of considering the surroundings in remediation actions. More detailed analysis of the results showed that the dose contribution from a source region is in general highly dependent on the position of windows in a brick house, whereas for a wooden house the distance to the source region is also of relevance. [ABSTRACT FROM AUTHOR]

In the remedial phase following an accidental radioactive release, it is important that soil decontamination measures are carried out on the areas that contribute most to the radiation dose. In this study, the newly developed concept of isodose lines was applied to the area around typical Swedish dwellings to identify these areas. The influence of the most common building materials in Sweden, wood and brick, and the importance of the positions of doors and windows on the isodose lines were demonstrated for specific positions inside the houses, as well as for the entire house, assuming the residents exhibit typical resident occupancy. Decontamination of the areas within certain isodose lines was shown to result in a greater dose reduction than decontaminating the same area of soil within a certain distance of the house. Furthermore, the impact of vertical migration of the radioactive contaminants in the soil on the isodose lines was studied, showing that the area enclosed by isodose lines decreases over time as the contaminants migrate deeper into the soil. The resulting isodose lines and their change over time are dominated by the downward movement of the contamination in the upper layer of soil. The impact of the variability in contamination on the final isodose lines and their dependence on building materials are demonstrated. [ABSTRACT FROM AUTHOR]