Results of simultaneous radon and thoron measurements in 33 metropolitan areas of Canada

Indoor radon trends with building code change in two Canadian cities

Radon studies were conducted in two Canadian cities, in Halifax, Nova Scotia, and Winnipeg, Manitoba, to evaluate trends in indoor radon before and after the 2010 National Building Code of Canada was adopted into the legally binding provincial building codes in 2011. Participants were recruited in neighbourhoods characterized by newer housing developments. A postcard campaign in each city offered free radon testing to every house in the target areas, and free testing kits were mailed to study participants. Indoor radon measurements and house questionnaires were completed by 225 eligible participants in Halifax and 171 eligible participants in Winnipeg, using alpha-track radon detectors deployed for three months during the heating season in 2021-2022. Multivariate logistic regression analyses were conducted to evaluate the association between indoor radon and the period of construction, the area in contact with the ground, the number of storeys, the type of heating system, the water source, and the type of ventilation. These analyses were focussed on the detached study houses because the majority of the participants lived in a detached house, and significant associations were identified for the period of construction and the floor where the radon detector was located. An odds ratio of 1.91 (1.04-3.50) for the detached Halifax study houses built after 2011 was associated with having a higher than geometric mean radon concentration (p = 0.033), nearly double the likelihood. There was no evidence of significant change in the indoor radon after 2011 in the detached Winnipeg study houses. A lower likelihood - almost half - for measurement conducted on a main/upper floor compared to in the basement was associated with a radon concentration above the respective geometric mean for each city: an odds ratio of 0.48 (0.27-0.86) for the detached Halifax study houses (p = 0.012), and of 0.45 (0.32-0.64) for the detached Winnipeg study houses (p = 0.022). Radon is the second most important cause of lung cancer, after smoking, and the results of this study support strengthening the radon preventive measures required in new low-rise housing to reduce the associated lung cancer burden in Canada.

The BC Radon Data Repository (BCRDR) and BC Radon Map: Integrating disparate data sources for improved public health communication

SETTING

The potential for exposure to indoor radon varies dramatically across British Columbia (BC) due to varied geology. Individuals may struggle to understand their exposure risk and agencies may struggle to understand the value of population-level programs and policies to mitigate risk.

INTERVENTION

The BC Centre for Disease Control (BCCDC) established the BC Radon Data Repository (BCRDR) to facilitate radon research, public awareness, and action in the province. The BCRDR aggregates indoor radon measurements collected by government agencies, industry professionals and organizations, and research and advocacy groups. Participation was formalized with a data sharing agreement, which outlines how the BCCDC anonymizes and manages the shared data integrated into the BCRDR.

OUTCOMES

The BCRDR currently holds 38,733 measurements from 18 data contributors. The repository continues to grow with new measurements from existing contributors and the addition of new contributors. A prominent use of the BCRDR was to create the online, interactive BC Radon Map, which includes regional concentration summaries, risk interpretation messaging, and health promotion information. Anonymized BCRDR data are also available for external release upon request.

IMPLICATIONS

The BCCDC leverages existing radon measurement programs to create a large and integrated database with wide geographic coverage. The development and application of the BCRDR informs public health research and action beyond the BCCDC, and the repository can serve as a model for other regional or national initiatives.

Short-Term vs. Long-Term: A Critical Review of Indoor Radon Measurement Techniques

Radon is a known carcinogen, and the accurate assessment of indoor levels is essential for effective mitigation strategies. While long-term testing provides the most reliable data, short-term testing (STT) offers a quicker and more cost-effective alternative. This review evaluated the accuracy of STT in predicting annual radon averages and compared testing strategies in Europe (where long-term measurements are common) and the United States (where STT is prevalent). Twenty (20) studies were systematically identified through searches in scientific databases and the grey literature, focusing on STT accuracy and radon management. This review revealed several factors that influence the accuracy of STT. Most studies recommended a minimum four-day test for initial screening, but accuracy varied with radon levels. For low levels (<75 Bq/m3), a one-week STT achieved high confidence (>95%) in predicting annual averages. However, accuracy decreased for moderate levels (approximately 50% success rate), necessitating confirmation with longer testing periods (3 months). High radon levels made STT unsuitable due to significant fluctuations. Seasonality also played a role, with winter months providing a more representative picture of annual radon averages. STT was found to be a useful method for screening low-risk areas with low radon concentrations. However, its limitations were evident in moderate- and high-level scenarios. While a minimum of four days was recommended, longer testing periods (3 months or more) were crucial for achieving reliable results, particularly in areas with potential for elevated radon exposure. This review suggests the need for further research to explore the possibility of harmonizing radon testing protocols between Europe and the United States.

Assessment of thoron contribution to indoor radon exposure in Canada

From 2007 to 2013, simultaneous radon (²²²Rn) and thoron (²²⁰Rn) measurements were conducted in a total of 3534 residential homes in 34 metropolitan areas covering 71% of the Canadian population. While radon levels were above the detector's detection limit in almost all homes, thoron concentrations were measurable in only 1738 homes. When analysis was limited to homes where thoron concentrations exceeded the detection limit, a pooled analysis confirmed that thoron is log-normally distributed in the indoor environment, and the distribution was characterized by a population-weighted geometric mean of 13 Bq/m³ and a geometric standard deviation of 1.89. Thoron contribution to indoor radon dose varied widely, ranging from 1.3 to 32% geographically. This study indicated that on average, thoron contributes 4% of the radiation dose due to total indoor radon exposure (²²²Rn and ²²⁰Rn) in Canada.

The First Attempt to Reevaluate Radon and Thoron Exposure in Gansu Province Study Using Radon-Thoron Discriminating Measurement Technique

Although the epidemiological studies provide evidence for an increased risk of lung cancer risk associated with residential radon, an issue of radon-thoron discrimination remains to be solved. In this study, an updated evaluation of lung cancer risk among the residents in Gansu, China was performed where one of the major epidemiological studies on indoor radon demonstrated an increased risk of lung cancer. We analyzed data from a hospital-based case-control study that included 30 lung cancer cases and 39 controls with special attention to internal exposure assessment based on the discriminative measurement technique of radon isotopes. Results from the analyses showed non-significant increased lung cancer risks; odds ratios (ORs) adjusted for age, smoking, and total income were 0.35 (95% CI: 0.07–1.74) and 0.27 (95% CI: 0.04–1.74) for groups living in residences with indoor radon concentrations of 50–100 Bq m⁻³ and over 100 Bq m⁻³, respectively, compared with those with < 50 Bq m⁻³ indoor radon concentrations. Although the small sample size hampers the usefulness of present analyses, our study suggests that reevaluation of lung cancer risk associated with residential radon in the epidemiological studies will be required on the basis of precise exposure assessment.

A Summary of Residential Radon Surveys and the Influence of Housing Characteristics on Indoor Radon Levels in Canada

ABSTRACT

Based on community and nationwide radon surveys with long-term radon measurements in a total of 21,818 homes, radon distribution characteristics in Canada have been reassessed with the population-weighted arithmetic mean radon concentration of 82 Bq m-3, geometric mean radon concentration of 55 Bq m-3, and geometric standard deviation of 2.45. The major pathway for the influx of radon into Canadian homes is from the surrounding soil. Statistical analysis has shown that radon levels in houses with a basement are, on average, about twice the radon levels in houses without a basement, and houses with private wells also tend to have higher radon concentrations than houses with municipal water supply.

General model for estimation of indoor radon concentration dynamics

A known relationship exists between high radon concentrations and lung cancer, and therefore, the indoor radon quantification is important, and it is beneficial to have a model to estimate indoor concentration. The work is focused on the development of an INDORAD (INDOor RAdon Dynamic) model for estimation of indoor radon dynamics, with time-dependent meteorological parameters and adjustable soil and building properties being considered. This model is based on a systemic approach, where the flows of material between compartments are considered, without a spatial resolution. This approach allowed to simplify the mathematical processing and enabled to consider together all known sources of indoor radon. The developed model was put in use in a laboratory building where soil constitutes major source of radon. The results (radon concentrations) from the model were compared to an existing data set from Saelices el Chico in a soil with high concentration of ²²⁶Ra. The outcome of the validation implies that INDORAD could predict radon concentrations satisfactorily. Suggestions for future updates of the model to improve indoor radon estimations are provided.

Evaluation of occupational radon exposure and comparison with residential radon exposure in Canada-a population-level assessment

Radon is a naturally occurring radioactive gas and presents everywhere on the Earth at varying concentration in workplaces and at homes. With Canadian labour statistics, time statistics and more than 7600 long-term radon measurements in workplaces, occupational radon exposure is evaluated for all 20 job categories based on North American Industry Classification System. Results are compared with residential radon exposure based on more than 22 000 long-term radon tests conducted in Canadian homes. The average annual effective dose due to radon exposure in workplaces is 0.21 mSv, which is lower than the average annual effective dose of 1.8 mSv from radon exposure at home by a factor of eight. Due to relatively higher radon concentration in residential homes and longer time spent indoors at home, exposure at home contributes to 90% of workers' total radon exposure (on average 1692 h in workplaces and 5852 h at homes). The analysis presented here is based on province-wide average radon exposures in various indoor and outdoor environments. Since the risk of developing lung cancer increases proportionally with increasing radon exposure, this evaluation indicates that on average reduction of radon levels in homes is very important and an effective way to reduce radon-induced lung cancers in Canada.

Measurement of Indoor Thoron Gas Concentrations Using a Radon-Thoron Discriminative Passive Type Monitor: Nationwide Survey in Japan

As part of a nationwide survey of thoron (220Rn) in Japan, the indoor 220Rn gas concentrations in 940 dwellings were measured throughout one year, from 1993 to 1996, using a passive type 222Rn-220Rn discriminative monitor. The monitor was placed in a bedroom or a living room in each house for four successive three-month periods. The mean annual indoor 220Rn concentration was estimated from the four measurements in each house. The arithmetic mean, the median and the geometric mean for indoor 220Rn concentrations in 899 dwellings were 20.1, 9.6 and 10.0 Bq m-3, respectively. The 220Rn concentrations exhibited a log-normal distribution. It was found that the 220Rn concentrations were dependent on the nature of the materials used for wall construction and also on the distance of measurement from the wall. Significant seasonal variations in the 220Rn concentration were not observed. It would seem that the nature of the wall material contributed to the increased indoor 220Rn concentrations.

Characteristics of Thoron (220Rn) and Its Progeny in the Indoor Environment

The present paper outlines characteristics of thoron and its progeny in the indoor environment. Since the half-life of thoron (220Rn) is very short (55.6 s), its behavior is quite different from the isotope radon (222Rn, half-life 3.8 days) in the environment. Analyses of radon and lung cancer risk have revealed a clearly positive relationship in epidemiological studies among miners and residents. However, there is no epidemiological evidence for thoron exposure causing lung cancer risk. In contrast to this, a dosimetric approach has been approved in the International Commission on Radiological Protection (ICRP) Publication 137, from which new dose conversion factors for radon and thoron progenies can be obtained. They are given as 16.8 and 107 nSv (Bq m-3 h)-1, respectively. It implies that even a small quantity of thoron progeny will induce higher radiation exposure compared to radon. Thus, an interest in thoron exposure is increasing among the relevant scientific communities. As measurement technologies for thoron and its progeny have been developed, they are now readily available. This paper reviews measurement technologies, activity levels, dosimetry and resulting doses. Although thoron has been underestimated in the past, recent findings have revealed that reassessment of risks due to radon exposure may need to take the presence of thoron and its progeny into account.

The analysis of results of radon/thoron measurements performed with the use of nuclear track detectors

Radon has been identified as one of the most important hazards, causing lung cancer. The most important isotope of radon is²²²Rn (3.83 d), while thoron²²⁰Rn (55 s) is treated as the less important isotope due to its short half-life. The radon/thoron hazard for people is related to inhalation of their decay products, but usually, only measurements of radon gas are done in dwellings. For such a purpose nuclear track detectors are used in most of the cases. Since several years simultaneous measurements are done to estimate thoron contribution to indoor radon and thoron exposure with the use of track detectors, too. Typically, a set of two detectors are applied and thoron concentrations are calculated on the basis of discriminative calculations. Unfortunately, very often results of these surveys are not accurate due to underestimation of the lower limit of detection (LLD) for thoron in the presence of elevated radon concentrations. Therefore an analysis of thoron LLDs in relationship to radon concentrations is presented.

Statistical inferences from measured data on concentrations of naturally occurring radon, thoron, and decay products in Kumaun Himalayan belt

Regional averages of radon, thoron, and associated decay product concentration are reported to be higher than their respective global averages in recent studies conducted in Indian Himalayan belt. The present study explores another region in Indian Himalayan belt by conducting measurements of radon, thoron, and decay product's activity concentration in 92 dwellings of Bageshwar district. The year-long measurements were performed in all 3 seasons distinguishing dwellings as per their construction material. The average radon and thoron concentration for the study region was measured as 57 Bq/m³ and 66 Bq/m³, respectively. Analysis of the measured data in terms of seasonal effects and construction material led to well established inferences, i.e., higher concentration for mud houses and for winter season. In addition, the present study focuses on lesser probed statistical inferences. One of them is related to the appropriateness of frequency distribution function for the measured data and other dwells upon the correlation analysis of inter-related factors for high concentration cases. Three distribution functions (Lognormal, Weibull, and Gamma) were found to be following the trend of frequency distribution curve of the measured data. For mud houses in winter season, variations of radon/thoron concentration were attempted to correlate with mass/surface exhalation rate, emanation rate, and source term content. More than 80% of the dwellings of the study region were found to have gas and decay product's concentration levels, higher than the respective global average values. However, these values were mostly within the reference levels for residential environments. Nevertheless, this region requires further studies to pinpoint the causes for elevated levels and suggest simple remedial modifications if required.

Importance of Discriminative Measurement for Radon Isotopes and Its Utilization in the Environment and Lessons Learned from Using the RADUET Monitor

Radon (222Rn) and thoron (220Rn), sources of natural background radiation, have been the subjects of long-standing studies, including research into radon and thoron as major causes of lung cancer at domestic and international levels. In this regard, radon and thoron measurement studies have been widely conducted all over the world. Generally, the techniques used relate to passive nuclear track detectors. Some surveys have shown that passive monitors for radon are sensitive to thoron, and hence some measured results have probably overestimated radon concentrations. This study investigated radon and thoron measurements in domestic and international surveys using the passive radon-thoron discriminative monitor, commercially named RADUET. This paper attempts to provide an understanding of discriminative measurements of radon isotopes and to present an evidence-based roadmap.

Short-Term Measurement of Indoor Radon Concentration in Northern Croatia

(1) Background: Radon concentrations in the environment are generally very low. However, radon concentrations can be high indoors and can cause some serious health issues. The main source of indoor radon (homes, buildings and other residential objects) can be soil under the house, while other sources can be construction materials, groundwater and natural gas. Radon accumulates mainly in the lower levels of the buildings (especially low-ventilated underground levels and basements). (2) Methods: in this paper, we have measured the indoor radon concentrations at 15 locations in various objects (basements and ground floor/1st floor rooms) in the area of northern Croatia. (3) Results: the results show a higher concentration of radon in the basement area in comparison to values measured in the ground floor and first-floor rooms. The arithmetic mean (AM) and geometric mean (GM) of basement rooms were 70.9 ± 38.8 Bq/m3 and 61.2 ± 2.2 Bq/m3 compared to ground floor and first-floor rooms 42.5 ± 30.8 Bq/m3 and 32.8 ± 2.9 Bq/m3, respectively. (4) Conclusions: results obtained (AM and GM values) are within the maximal allowed values (300 Bq/m3) according to the Euroatom Directive. However, there are periods when maximum radon concentration exceeds 300 Bq/m3. Indoor radon concentrations vary with the occupancy of the rooms and it is evident that the ventilation has significant effect on the reduction of concentration.

RISK ASSESSMENT FOR RADON EXPOSURE IN VARIOUS INDOOR ENVIRONMENTS

Using data from a number of radon surveys, it was assessed that on average, radon progeny concentrations in Canadian homes are about three times higher than in school buildings, 4.7 times higher than in public buildings and indoor workplaces, and 12 times higher than in outdoor air. Canadian statistics show that most Canadians spend ~70% of their time indoors at home, 20% indoors away from home and 10% in outdoors. Due to relatively higher radon concentration in residential homes and longer time spent indoors at home, the exposure at home contributes to 90% of the radon-induced lung-cancer risk.

A cost effectiveness analysis of interventions to reduce residential radon exposure in Canada

The objective of this analysis is to estimate the incremental cost effectiveness ratios for the 2012 populations in Canada, each province/territory, and 17 census metropolitan areas, for practical radon mitigation scenarios to reduce residential radon exposures. Sixteen intervention scenarios compare radon mitigation implemented at differing rates in new and existing housing relative to preventive measures installed at construction, using three different radon mitigation thresholds. A period life-table analysis was conducted using data derived from two recent Canadian radon surveys, along with Canadian mortality and quality of life data. Analyses adopted a lifetime horizon and a discount rate of 1.5%. It is practical to reduce residential radon and associated lung cancer mortality in Canada, and the most cost effective scenario at each radon mitigation threshold is the combination of the activation of the preventive measures in new housing and mitigation of existing housing.

DOMESTIC RADON EXPOSURE AND CHILDHOOD LEUKAEMIA AND LYMPHOMA: A POPULATION-BASED STUDY IN CANADA

In this paper, we revisit the possibility, first raised using a data set collected in the 1970s, that there is a link between average radon concentrations and the incidence of childhood leukaemia and lymphoma in Canada. Following the launch of the National Radon Program in 2007, Health Canada completed a long-term radon survey in 33 census metropolitan areas (CMAs), which covers about 70% of the Canadian population. We used this data, together with leukaemia and lymphoma incidence rates among children (0-14 years of age) in the past decade (2006-15), and tried to link the city-level average radon concentrations to the leukaemia and lymphoma incidence rates in 33 major Canadian cities. Analyses were conducted for six subtypes (ALL, AML, CMD, HL, NHL and BL) of leukaemia and lymphoma. Estimated doses to red bone marrow from domestic radon exposure were low and we did not find any association between radon exposure at home and the increased risk for developing leukaemia among children under 15 years of age living in the CMAs. The results indicate a slight positive association for AML among 1-4 year males in CMAs of Peer Group C and NHL among 5-9 year females in CMAs of Peer Group A; however, these should be interpreted with caution owing to the crude exposure assessment and possibilities of other confounding factors.

A Comparative Study of Radon Levels in Federal Buildings and Residential Homes in Canada

Shortly after revision of the Canadian radon guideline from 800 to 200 Bq m, Health Canada established the Federal Building Testing Program in 2007 to demonstrate federal leadership in raising awareness about radon risk and the need for testing. By the end of 2017, more than 7,600 federal workplaces had been tested for radon. As is the case in all radon surveys, radon levels vary widely; federal building results ranged from below the detection limit to more than 2,500 Bq m in a few rooms of a few buildings. Weighted by the population of federal public servants across Canada, the average radon distribution in federal workplaces has a geometric mean of 22.0 Bq m with a geometric standard deviation of 2.3. The population-weighted arithmetic mean is 34.3 Bq m, significantly lower than the population-weighted average radon concentration of 72.9 Bq m in residential homes across Canada. On average, 2% of federal workplaces have radon concentrations above 200 Bq m, which is also significantly lower than the 7% of residential homes that tested above 200 Bq m. This comparative study demonstrated clearly that radon education and awareness in Canada should focus more on residential testing and remediation actions to effectively reduce the burden of radon-induced lung cancer.

Utility gains from reductions in the modifiable burden of lung cancer attributable to residential radon in Canada

RESEARCH QUESTION

The objective of this analysis is to estimate the modifiable burden of disease according to the annual number of lung cancer deaths prevented and the associated period gain in quality-adjusted life years (QALYs) for the 2012 populations in Canada from reductions in residential radon exposures.

INTERVENTIONS

Two postulated interventions for residential radon mitigation in new construction are assessed, corresponding to a 50% reduction and an 85% reduction in radon nationally, in the provinces/territories, and in 17 census metropolitan areas in Canada.

METHODS

Data were derived from two recent Canadian radon surveys conducted by the Radiation Protection Bureau, Health Canada, along with Canadian mortality and quality of life data. Analyses adopted a lifetime horizon and a discount rate of 1.5%. A period life-table analysis was conducted using age- and sex-specific all-cause and lung cancer mortality rates, adjusted for smoking, and the BEIR VI exposure-age-concentration model for radon-attributable risk of lung cancer mortality.

RESULTS

A reduction in residential radon by 50% could prevent 681 lung cancer deaths, associated with a gain of 15,445 QALYs in the Canadian population at a discount rate of 1.5%; a reduction in radon by 85% could prevent 1263 lung cancer deaths, associated with a gain of 26,336 QALYs. On a per population basis, the Yukon was estimated to benefit most from radon mitigation.

CONCLUSION

The magnitude of QALY gains in Canada estimated under the two radon mitigation scenarios is appreciable but varies considerably across provinces due to variability in indoor radon concentrations and smoking rates.

A DISCUSSION ON DIFFERENT APPROACHES FOR ASSESSING LIFETIME RISKS OF RADON-INDUCED LUNG CANCER

Lifetime risks of radon induced lung cancer were assessed based on epidemiological approaches for Canadian, Swiss and Chinese populations, using the most recent vital statistic data and radon distribution characteristics available for each country. In the risk calculation, the North America residential radon risk model was used for the Canadian population, the European residential radon risk model for the Swiss population, the Chinese residential radon risk model for the Chinese population, and the EPA/BEIR-VI radon risk model for all three populations. The results were compared with the risk calculated from the International Commission on Radiological Protection (ICRP)'s exposure-to-risk conversion coefficients. In view of the fact that the ICRP coefficients were recommended for radiation protection of all populations, it was concluded that, generally speaking, lifetime absolute risks calculated with ICRP-recommended coefficients agree reasonably well with the range of radon induced lung cancer risk predicted by risk models derived from epidemiological pooling analyses.

CANADIAN POPULATION RISK OF RADON INDUCED LUNG CANCER-VARIATION RANGE ASSESSMENT BASED ON VARIOUS RADON RISK MODELS

To address public concerns regarding radon risk and variations in risk estimates based on various risk models available in the literature, lifetime lung cancer risks were calculated with five well-known risk models using more recent Canadian vital statistics (5-year averages from 2008 to 2012). Variations in population risk estimation among various models were assessed. The results showed that the Canadian population risk of radon induced lung cancer can vary from 5.0 to 17% for men and 5.1 to 18% for women based on different radon risk models. Averaged over the estimates from various risk models with better radon dosimetry, 13% of lung cancer deaths among Canadian males and 14% of lung cancer deaths among Canadian females were attributable to long-term indoor radon exposure.

COMPARATIVE STUDY OF RADON EXPOSURE IN CANADIAN HOMES AND URANIUM MINES-A DISCUSSION ON THE IMPORTANCE OF NATIONAL RADON PROGRAM

The history of lung cancer in uranium miners is well known for over hundreds of years when the disease was referred to as 'miner's disease' or 'mountain sickness'. Radon levels in uranium mines have decreased significantly over the past 30 years as a result of effective radiation protection measures at workplaces. For the most recent 10-year period, the average radon concentrations to underground and surface workers in Canadian uranium mines were 111 and 11 Bq m-3, respectively. Based on the recent radon survey carried out in roughly 14 000 homes in 121 health regions across Canada and the more recent radon and thoron survey in 33 Canadian cities and 4000 homes, the average radon concentration in Canadian homes is 77 Bq m-3. This study demonstrates that, nowadays, workers are exposed to radon in underground mines at a comparable radon level to what Canadians are exposed to at home. Since exposure to indoor radon is the main source of natural radiation exposure to the population, it is important for the National Radon Program to further increase radon awareness, and to encourage more Canadians to take appropriate actions to reduce radon exposure.

A study on the correlation between soil radon potential and average indoor radon potential in Canadian cities

Exposure to indoor radon is identified as the main source of natural radiation exposure to the population. Since radon in homes originates mainly from soil gas radon, it is of public interest to study the correlation between radon in soil and radon indoors in different geographic locations. From 2007 to 2010, a total of 1070 sites were surveyed for soil gas radon and soil permeability. Among the sites surveyed, 430 sites were in 14 cities where indoor radon information is available from residential radon and thoron surveys conducted in recent years. It is observed that indoor radon potential (percentage of homes above 200 Bq m^-3; range from 1.5% to 42%) correlates reasonably well with soil radon potential (SRP: an index proportional to soil gas radon concentration and soil permeability; average SRP ranged from 8 to 26). In five cities where in-situ soil permeability was measured at more than 20 sites, a strong correlation (R² = 0.68 for linear regression and R² = 0.81 for non-linear regression) was observed between indoor radon potential and soil radon potential. This summary report shows that soil gas radon measurement is a practical and useful predictor of indoor radon potential in a geographic area, and may be useful for making decisions around prioritizing activities to manage population exposure and future land-use planning.

TCAD simulation for alpha-particle spectroscopy using SIC Schottky diode

There is a growing requirement of alpha spectroscopy in the fields context of environmental radioactive contamination, nuclear waste management, site decommissioning and decontamination. Although silicon-based alpha-particle detection technology is mature, high leakage current, low displacement threshold and radiation hardness limits the operation of the detector in harsh environments. Silicon carbide (SiC) is considered to be excellent material for radiation detection application due to its high band gap, high displacement threshold and high thermal conductivity. In this report, an alpha-particle-induced electron-hole pair generation model for a reverse-biased n-type SiC Schottky diode has been proposed and verified using technology computer aided design (TCAD) simulations. First, the forward-biased I-V characteristics were studied to determine the diode ideality factor and compared with published experimental data. The ideality factor was found to be in the range of 1.4-1.7 for a corresponding temperature range of 300-500 K. Next, the energy-dependent, alpha-particle-induced EHP generation model parameters were optimised using transport of ions in matter (TRIM) simulation. Finally, the transient pulses generated due to alpha-particle bombardment were analysed for (1) different diode temperatures (300-500 K), (2) different incident alpha-particle energies (1-5 MeV), (3) different reverse bias voltages of the 4H-SiC-based Schottky diode (-50 to -250 V) and (4) different angles of incidence of the alpha particle (0°-70°).The above model can be extended to other (wide band-gap semiconductor) device technologies useful for radiation-sensing application.

An overview of radon research in Canada

Based on new scientific information and broad public consultation, the Government of Canada updated the guideline for exposure to indoor radon and launched a multi-year radon programme in 2007. Major achievements in radon research accomplished in the past 7 y are highlighted here.