Swedish Radiation Protection Institute Research Articles

Assessment of Natural Radiation Exposure Due to 222Rn and External Radiation Sources: Case of the Far North, Cameroon.

This paper assesses public exposure to natural radioactivity from radon and external radiation sources in the Far North region, Cameroon, and studies the correlation between radon data obtained using several techniques. The RADTRAK, RadonEye, and Markus 10 detectors were used to measure radon concentrations in dwellings and soil, respectively. To understand radon variations in the study area, a correlation coefficient between radon in soil and in dwellings was determined. The ambient equivalent dose rate was measured using a RadEye PRD-ER, and the effective doses from internal and external radiation were determined. In soil, 20% of the measuring points had a concentration above 50 kBq m-3, the action value for radon exposure from soil according to Swedish Radiation Protection Institute regulations. After 90 d of measurement using RADTRAK, half of the concentrations in the dwellings were greater than or equal to 160 Bq m-3, which is above the WHO reference level of 100 Bq m-3. The ambient equivalent dose rate and the external and internal radiation effective dose were 0.08 μSv h-1, 0.6 mSv y-1, and 2.86 mSv y-1, respectively. These results reveal a strong correlation between the radioactivity level of a locality and its geological and mineralogical structure. Although these different results in general do not present a very high risk of radiological exposure for the public, it is nevertheless necessary that the rules of radiation protection are respected in order to reduce it.

Anomalous results with the widely used NRPB/SSI-type passive radon dosemeter

In an industrial hall, with large variations of radon concentration within minutes, simultaneous measurements were done with two types of passive radon detectors and an active radon measuring device. The widely used passive radon detector of the National Radiological Protection Board (NRPB) [Health Protection Agency (former NRPB) (HPA)]/Statens strålskyddsinstitut (Swedish Radiation Protection Institute) (SSI) type produced anomalous results, seemingly uncorrelated to the radon concentration which was in the order of hundreds of becquerels per metre, usually underestimating but occasionally overestimating. We tried to reproduce similar exposure characteristics in our laboratory, but failed to reproduce the anomalous readings. We suspected, but could not prove, that the anomalous results were due to the combination of high radon concentration gradients, with pressure-driven air exchange between the inside of the detector holder and the outside atmosphere. Moreover, this theory was at least partly contradicted when we drilled holes in the detector holder. Although of interest, this effect is not likely to have substantially influenced any radon surveys, given the unusual nature of the exposure that caused the effect.

Decommissioning of small nuclear waste buildings

A small-scale decommissioning concept was applied with staff from an earlier project with strong knowledge of radiation protection, minimized radiation doses and environmental pollution. The project was therefore initiated with less than 10 people involved using standard handheld equipment. The aim of the decommissioning project was to set free as much material as possible, i.e. remove waste from the regulatory control regime and also free the remaining structures and buildings for conventional demolition and subsequent reuse of the property. A final decommissioning plan was drafted together with a safety assessment covering the planned activities and abnormal events that may occur during decommissioning. Applications and contacts were made with five different authorities to obtain permits pursuant to national safety standards and requirements, including the areas of safety (Swedish Nuclear Power Inspectorate), radiation protection (Swedish Radiation Protection Institute), environmental protection (County Administrative Board), construction (Swedish Work Environment Authority) and building demolition (Municipality of Nykoping). Sufficient funds were available for decommissioning. Complete decommissioning will be concluded at the end of 2008 when all waste is taken care of. This is the fourth in a series of important decommissioning projects in Studsvik since the 1980s.

Light scattering in the C57BL/6 mouse lens

To characterize inherent light scattering in the C57BL/6 mouse lens. Lenses from 20 6-week-old female C57BL/6 mice were extracted from freshly enucleated globes and microsurgically cleaned of remnants of the ciliary body. Lens light scattering was measured quantitatively with a light dissemination meter (LDM). Morphological properties of the mouse lenses were documented using grid- and dark-field illumination photography. Analysis of variance was performed to establish variance for animals, variance between left and right eyes and variance for measurements. Average inherent light scattering in the C57BL/6 mouse lens is 0.16 +/- 0.02 tEDC (transformed equivalent diazepam concentration). The mean size of a mouse lens at 6 weeks is 1.9 mm in diameter. Two lenses featured pre-existing cortical lens opacities. Variance for animals was assessed to be 7.9 10(- 4) tEDC(2), variance for measurements was 1.6 10(- 4) tEDC(2), and variance between left and right eyes was 8.8 10(- 4) tEDC(2). The tolerance limit for non-pathological light scattering was determined to 0.26 tEDC. No significant difference in light scattering between left and right mouse lenses was found. The minimum number of C57BL/6 mice required for detection of a 10% experimentally induced change in light scattering intensity was estimated to be 50 for independent group experiments and 25 for paired design experiments. The C57BL/6 mouse is a suitable animal in which to conduct experiments on light scattering or cataractogenesis with high precision at reasonable sample sizes. Before including C57BL/6 mice into a study on cataractogenesis, pre-existing lens opacities such as congenital cataract must be excluded.

INCREASED CANCER INCIDENCE IN NORTH SWEDEN-AN EARLY PROMOTING EFFECT CAUSED BY THE CHERNOBYL ACCIDENT

Introduction In Sweden the ground gamma radiation, due to uranium containing granite, contribute to the population's total radiation dose. After the Chemobyl nuclear power plant accident in 1986 as much as five percent of the released caesium-137 was deposited in Sweden, especially in the Northern part of the country. Our hypothesis was that this radiation caused increased cancer incidence, after adjustment by ground gamma radiation exposure. Methods The study base included the population of eight counties with the highest fallout after the Chernobyl accident, but also with unaffected areas in these counties serving as the reference. Each person 0–60 years of age living in the same parish at 31 December 1985 and 31 December 1987 were included in a cohort. With the coordinate of each person's dwelling from the National Land Survey of Sweden a total of 1 137 106 individuals could be given 1) ground gamma radiation exposure from the digital map of the Swedish Geological Agency and 2) caesium-137 exposure from a similar map created by Swedish Radiation Protection Institute. Accuracy of the dwelling coordinate was 100 metres and for the radiation exposures 200 metres as done by aeroplane measurements. Three time periods were analysed 1988–1991, 1992–1995 and 1988–1999. Results Population density, lung cancer incidence 1988–1999 and total cancer incidence 1986–1987 was risk factors for total cancer outcome in 1988–1999. Age adjusted ERR per 100 nGy/h for ground gamma radiation and total cancer incidence did not show any significant dose response measured, either in each three years time intervals or in the total period of 1988–1999. For caesium the ERR per 100 nGy/h (adjusted by population density, lung cancer incidence, total cancer incidence 1986–1987 and ground gamma radiation) was significant in 1988–1991 followed by a decline in risk 1992–1995 and then a slight but not complete return in risk. The ERR of 0.042 (95% CL 0.001;0.084) per 100 nGy/h for caesium exposure 1988–1999 is therefore dependent on the first three years increase, and to less extent by the following six years. Conclusion We have found an early effect of the Chernobyl fallout in Northern Sweden. However, even in the ERR of 0.101 per 100 nGy/h is relatively low in 1988–1991, it is stable in a stepwise regression, and therefore indicating a true effect. An interpretation of our results could be that the sudden exposure of ionizing radiation from Chernobyl might have acted as a late stage general promotor for cancer. Such an early effect can hitherto been overlooked in previous studies.

Depleted uranium in Kosovo: results of a survey by gamma spectrometry on soil samples.

The presence of depleted uranium in the soil of former Yugoslavia after the 1999 conflict raised great public concern all over the world. The so-called Balkan-syndrome is often linked with depleted uranium contamination. An excellent compilation of data about DU and its possible impact on health and environment can be found in the 1999 UNEP report and publications from the Swedish Radiation Protection Institute. Unfortunately, very few systematic and reliable data on the possible depleted uranium concentrations were until now available. Some of these rare data are only available on the web, without adequate information about the experimental procedure used. To clarify the situation, a systematic survey was started in the summer of 2000 as a collaborative effort between Ghent University (Physics Laboratory) and the Belgian Ministry of Defense (Medical Service). From 50 sites selected all over Kosovo, 150 soil samples were measured in the laboratory with a high-resolution gamma-spectrometer. Some sites (14) were explicitly selected based on military information on the use of depleted uranium munitions in the vicinity. After careful analysis we can conclude that there is no indication of any depleted uranium contamination on these 50 sites with a minimal detectable activity of 15 Bq; this corresponds approximately to 1 mg depleted uranium in a typical sample (100-150 g).

Results of a simple intercomparison of natural radioactivity measurements using a ‘blue concrete’ sample

A simple intercomparison of natural radioactivity and radon emanation factor measurements co-ordinated by the Medical Physics Department of the University of Cantabria UC, Spain, has been carried out during 1998 in the framework of the EU Concerted Action ERRICCA (European Research into Radon in Construction Concerted Action). All the measurements have been made on a ‘blue concrete’ sample kindly donated by Dr G. Akerblom from the Swedish Radiation Protection Institute. In addition to UC, two other participant laboratories, STUK from Finland and ZVD from the Republic of Slovenia, have contributed to the development of the intercomparison exercise. Considering the uncertainties of the measurements, a good agreement between the results obtained by the three participating laboratories has been ascertained. However, in accordance with experimental results obtained by other authors, data reported by UC show a significant decrease of the radon emanation factor as moisture content of the sample decreases below 5% (per weight).

Experience from retrospective radon exposure estimations for individuals in a radon epidemiological study using solid-state nuclear track detectors

The relation between increased risk of lung cancer and exposure to indoor radon is assessed in epidemiological studies. Both the quality and reliability of smoking data and the radon exposure data are of primary importance. Contemporary measurement of radon concentration in the dwellings of individuals in a case-control study is traditionally used to assess past history of radon exposure. These assessments are somewhat unreliable since presently measured radon concentration might not be representative for a given location long ago. The measurement of long-lived decay products from 222Rn remaining indoors on hard surfaces, such as glass, makes it possible to assess the exposure to indoor radon. At the Swedish Radiation Protection Institute, a combination of two different solid-state nuclear track detectors has been developed to assess the 210Pb activity implanted in glass surfaces by measuring 210Po alpha activity. This detector (a RETRO detector) is used in the Swedish radon epidemiological case-control study of non-smokers with the aim to provide an alternative estimate of individual radon exposure and to evaluate the usefulness of RETRO measurements. A total of 576 different objects were found and 568 were measured. For 225 individuals, we measured two personal objects that had been in the same person's possession for more than 20 years. The standard deviation of the average radon concentration obtained from these two objects had a median value of 13 Bq/m 3 indicating a precision of exposure of approximately 20%. The correlation between 210Po surface activity measured earlier and the mean values of radon concentrations in a number of Swedish dwellings is used to estimate the historical, average radon concentration. This average correlation factor seems also to be valid for measurements in the non-smoker epidemiological study.

Measurements of Solar UVA, UVB and of Ozone: Estimates of Population UV Doses

The Swedish Radiation Protection Institute (SSI) has been involved for twenty years in measurements of ultraviolet radiation from artificial sources and from the sun, using spectral and broad-band instruments. Focus has shifted from artificial to natural ultraviolet radiation. Solar UVA, UVB and derived ozone column have been monitored with a filter instrument since 1989 at SSI in Stockholm. At present modern UV monitoring detectors complement the older instruments. Measurement results improve with newer instruments and techniques. Population UV doses are estimated roughly and need better assessment but may still require present or future improvements of UV measurements and monitoring as well as some refocussing to quantify and reduce overall exposure of the population.

Intercomparison of activity size distribution of thoron progeny and a mixture of radon and thoron progeny

The First International Intercomparison and Intercalibration Meeting for Thoron and its Progeny and Thoron/Radon Mixture was organized to compare techniques for determining concentrations and particle size distributions of 220 Rn and mixtures of 222 Rn and 220 Rn . The meeting was held at Elliot Lake, Canada, November 2–6, 1992. We have reported results of activity size distributions and measurements of unattached fractions of both thoron progeny and mixtures of thoron/radon. Four teams, including the US Bureau of Mines in cooperation with Canada Center for Mineral and Energy Technology, the US Environmental Measurement Laboratory (EML), the Lovelace Respiratory Research Institute, and the Swedish Radiation Protection Institute (SSI) participated in the intercomparison of activity size distributions. Each team had a different diffusion sampling system and counting protocol. Results for all four systems were in good agreement when thoron gas was used in the test chamber. However, in the case of thoron and radon gas mixtures, the agreement among the different sampling systems was not as good. One reason for the inconsistency of results was that the sensitivity of the systems was different. Calculation of size distribution for individual progeny ( 218 Po , 214 Pb , 214 Bi , 212 Pb , and 212 Bi ) requires sampling systems with improved sensitivity. Our results suggest those diffusion batteries with a minimum of four stages and more likely five stages are optimal. In addition, a system for continuously counting the total alpha particles, such as the EML system, or alpha spectrometry, such as the SSI system, is needed. Our results provide a relationship between the unattached fraction and condensation nucleus concentration over a wide range of particles from 300 to 16,000 cm −3. These findings are consistent with measurements obtained in indoor environments, mines, and underground caves, indicating that it is possible to establish a more universal relationship.

Second International Symposium on Ionising Radiation:`Environmental Protection Approaches for Nuclear Facilities', Ottawa, Canada, 10-14 May 1999

Second International Symposium on Ionising Radiation:`Environmental Protection Approaches for Nuclear Facilities', Ottawa, Canada, 10-14 May 1999

The calibration of the solid state nuclear track detector LR 115 for radon measurements

An experimental calibration of indoor room and outdoor soil detector devices which are based on LR 115 as sensitive element has taken place at the Swedish Radiation Protection Institute in Stockholm (Sweden) in 1994 and 1996, at the Physikalisch-Technischen Bundesanstalt in Braunschweig (Germany) in 1997 and at the Umweltforschungszentrum Leipzig-Halle (Germany) in 1997. Special properties of the used solid state nuclear track detector (SSNTD) material LR 115 ∗ have been measured to define the application of the experimental calibration.

222Rn Absorption in Plastic Holders for Alpha Track Detectors: A Source of Error

Experiments show that the plastic holder used for the Swedish Radiation Protection Institute's (SSI) alpha track detector absorbs 222 Rn (radon) and subsequently outgasses it slowly when stored in a lower radon concentration environment. This phenomenon is not unique to the plastic holder used at SSI. A discrepancy in the results found at an international intercomparison of radon detectors highlighted the problem. The observation implies that the practice of enclosing the detectors in plastic bags after exposure should be limited as it can lead to further etching of the detector and an overestimation of the intended measurement. This article describes a procedure for estimating the error that exposure caused by outgassing of radon from the detector housing would give under different exposure conditions. The calculated overexposure agrees with the observed one in the intercomparison. One conclusion is that film and plastic holders should be separated, especially after short-term exposures.

The use of tomography for dental implant planning.

To examine the use of tomography for dental implant planning. A questionnaire was sent to oral radiology clinics in Sweden and to implantology clinics in different parts of the world with questions on selection criteria and techniques for, and frequency of, pre-implant tomography. Differences between mean values were assessed by t-test. A new method developed by the Swedish Radiation Protection Institute was used to assess radiation absorbed dose from CT. Tomography was used by 93.4% of the clinics, but there was marked variation both between and within different clinical situations. It was performed in all cases by 21% and the majority used it for the evaluation of the maxilla, the posterior mandible and in single implant cases. Small clinics (< 100 patients per year) used tomography frequently and clinics in Sweden significantly more often than those in other countries. The majority had changed their policy recently, using tomography more often. CT was used by 73% of respondents, mainly the small clinics. The majority of the large clinics (> 500 patients per year) used conventional tomography. The mean absorbed dose for CT scanning protocols was 65 mGy. The variation within and between different makes of CT was considerable. There are large variations in frequency of use of both conventional and computed tomography for dental implant planning by different clinics who also vary in the indications for their choice. A substantial factor influencing the technique chosen was its availability rather than clinical need.

Sunbeds rival natural sun in population UV-dose among Swedish adolescents

Swedish Radiation Protection Institute, Department of Cancer Prevention, Karolinska Hospital, Stockholm, Sweden

Using SSNTDs in soil and indoors in two mediterranean locations for radon concentration measurements

In the frame of an European Project, measurements of radon in the soil and indoors have been carried out using Solid State Nuclear Track Detectors (SSNTD). Two of the involved laboratories Barcelona (Spain) and Montpellier (France) have the same climatic conditions and are geographically close. The Montpellier group uses an open-type dosimeter for soil measurements and an closed-type for indoor measurements, both based on LR-115 detector material, while Barcelona group uses a LR-115 based closed-type dosimeter for soil measurements and a Makrofol based closed-type for indoors. The dosimeters have been calibrated respectively in the SRPI (Swedish Radiation Protection Institute, Stockholm) and the ENEA (Ente per le Nuove Tecnologie, l'Energia e l'Ambiente, Roma) radon rooms and a description of the dosimeters (geometry, sensitivity, background and detection limit) is given. Some results of the soil and indoor radon concentration measurements in both regions are presented.

Truth or consequence--Bo Lindell's contribution to radiation protection.

Bo Lindell, former chairman and emeritus member of ICRP, former chairman of UNSCEAR, former Director General and emeritus worker of the Swedish RAdiation Protection Institute, is a phenomenon. His profound influence on radiation protection, and indeed on environmental protection and risk research in general, includes a profuse flow of scientific publications on all aspects of protection of man against harmful effects of radiation. In this context, perhaps his most important efforts hitherto are those relating to nuclear power. The concept of dose commitment, invented by Bo Lindell, is used worldwide to regulate emissions of radioactive substances, taking into account not only the often trivial dose to immediate bystanders, but the global effect over long time-frames. In the long run, his continuing personal influence on radiation protection as a branch of science and a kind of role model for other types of environmental protection may attain an even greater importance.

The Swedish Radon Programme: Thirteen Years of Experience and Suggestions for Future Strategy

Abstract The Swedish radon programme has been working for thirteen years. The municipalities and others have measured radon in 240,000 dwellings and other buildings, mostly schools and day nurseries. About 5.7% of the total of 4.04 million dwellings in Sweden have been measured. About 16% of the dwellings expected to have a higher radon concentration than the limit, 400 Bq.m-3, have been located: 40% of these have been mitigated. The Swedish Radiation Protection Institute has suggested a new ten year radon programme to the government. This was motivated by more reliable data on radon risks, Swedish studies finished in 1993, and the experience in the field.

Small, Simple but Useful: The SSI Approach to a Real-Time System for Decision Making Support

In case of a nuclear accident or a threat of a release, the Swedish Radiation Protection Institute (SSI) is responsible for advising and informing the Government, other authorities and the public. The Institute's experts are supported by a newly developed, small computerised system. Some of the criteria used when developing the system were: modest demand on computer power and money; simple technical support; easy to use in difficult situations (especially for staff with little training); fast response, especially in forecasting situations; commercially available software components if possible. Some components of the system are: a simple model for atmospheric dispersion and dose predictions; data bases including maps, nuclides, instruments and facilities to sort and handle measured values; on-line connection to nationwide system of automatic measuring stations; a number of data display facilities; and computer based handbooks. Most software for the system is written for the MS Windows environment.