Lessons learned from the surveillance: Measuring methods and monitoring strategies T. R. Beck, E. Ettenhuber Federal Office for Radiation Protection, Germany

Content — General Principles of Radiation Protection Monitoring — Natural Radiation at Workplaces: Present Status in Europe — Measuring Quantities and Assessment of Effective Dose — Monitoring Approaches

General Principles of Radiation Protection Monitoring Aims: — Verification of compliance with the limits specified for workers — Providing information for optimization of radiation protection and safety Requirements — Monitoring of workers (individual monitoring) should be made systema- tically and based on individual measurements — In cases within which individual measurements are impossible or in- adequate the individual monitoring should be based on an estimate arrived at either from individual measurements made on other exposed workers or from results of the workplace monitoring —

Number of Workers monitored due to Natural Radiation Natural Radiation at Workplaces: Present Status in Europe ESOREX www.esorex.cz Year Number of Workers monitored due to Natural Radiation 1996 6716 1998 5577 2000 6161

Natural Radiation at Workplaces: Present Status in Europe ESOREX www Natural Radiation at Workplaces: Present Status in Europe ESOREX www.esorex.cz Countries: AT, CZ, DE, NO, RO, SE, SI, UK In 2000 in Europe about 1100 workers were monitored due to natural radiation with individual doses of more than 5mSv a year.

Radon at Workplaces: Present Status in Europe EURADOS working group on „Harmonisation of Individual Monitoring in Europe“ — Action levels: Underground workplaces, industry, waterworks: 400 - 1000 Bq·m-3 Offices, schools, day-care homes: 200 - 500 Bq·m-3 — Monitoring strategies: In most countries both individual and workplace monitoring are authorized. — Measuring period: Finland: 2 months; Germany: 1 - 3 months — Instrumentation: Diffusion chambers using SSNTD Electrets Various electronic instruments for continuous and grab sampling In a few countries exposures to radon decay products are measured in mines. — Results published in: Lopez, M. A. et al: Workplace monitoring for exposures to radon and other natural sources in Europe: Integration of monitoring for internal and external exposures. Radiation Protection Dosimetry (2004), Vol. 112, No. 1, pp. 121-139

Radon at Workplaces: Present Status in Europe EURADOS working group on „Harmonisation of Individual Monitoring in Europe“ In Europe no workplaces with elevated exposures caused by thoron exist. Exposures caused by thoron or thoron decay products are completely disregarded in our further examination. No Thoron !

Measuring Quantities and Assessment of Effective Dose b- b- a short-lived Radon Decay Products The most important component of the dose comes not from the gas itself, but rather from ist short-lived decay products. Radon itself is an inert gas with a half-life of about 4 days and almost all the gas that is inhaled will be breathed out again. The decay products are isotopes of solid elements and will quickly attract to themselfes, molecules of water or other gases in the atmosphere and can eventually attach to aerosol particles. If inhaled, the decay products, whether attached to aerosol particles or „unattached“, will largely be deposited on the surface of the respiratory tract and, because of there short half-lives (less than half an hour) will decay there. Potential Alpha Energy: The total alpha energy emitted during the decay of a short-lived radon decay product along the decay chain up to Pb-210.

Measuring Quantities and Assessment of Effective Dose — The exposure of the lung caused by inhalation of short-lived radon decay products is the risk relevant quantity! — Doses to other organs (skin, eye, extremities) are not relevant. —

Measuring Quantities and Assessment of Effective Dose: Methods of Measurement Measurement of Exposure to Radon Decay Products Relation to dose direct measurement of the risk relevant quantity Quantity Potential Alpha Energy Exposure Instruments electronic with active air sampling Advantages/ Disadvantages direct relation to dose lower uncertainty of dose assessment high costs of instruments high expenditure of maintenance —

Measuring Quantities and Assessment of Effective Dose: Methods of Measurement Measurement of Exposure to Radon Relation to dose no direct; radon equilibrium factor is to be estimated Quantity Exposure to radon Instruments electronic and passive (e.g. diffusion chambers) Advantages/ Disadvantages passive instruments: cost-effectiveness, robust, and available in high quantities no direct relation to dose higher uncertainties of dose assessment —

Potential Alpha Energy Exposure PP Measuring Quantities and Assessment of Effective Dose: Calculation of the Effective Dose Effective Dose D = Conversion to Dose x Measurement of Exposure to Radon Decay Products Potential Alpha Energy Exposure PP

Potential Alpha Energy Exposure PP Measuring Quantities and Assessment of Effective Dose: Calculation of the Effective Dose Effective Dose D = Conversion to Dose x Measurement of Exposure to Radon Decay Products Potential Alpha Energy Exposure PP

Measuring Quantities and Assessment of Effective Dose: Dose Conversion Convention ICRP 65: An exposure to radon decay products of 1 mJ·h·m-3 is equivalent to an effective dose of 1.43 mSv for workers. 96/29/EURATOM: The conversion factor effective dose per unit potential alpha energy exposure is 1.4 mSv mJ·h·m-3 for radon at work. Conversion convention that based on equality of detriments, not on dosimetry.

Measuring Quantities and Assessment of Effective Dose: Dose Conversion Convention Note! Conversion convention based on epidemiological studies on miners to radon (ICRP 65). The dosimetric model (ICRP 66) is not used for dose assessment of workers and should be not adopted in legal regulations.

Potential Alpha Energy Exposure PP Measuring Quantities and Assessment of Effective Dose: Calculation of the Effective Dose 3.1 mSv MBq·h·m-3 ________ Effective Dose D Conversion to Dose x = Potential Alpha Energy Exposure PP Measurement of Exposure to Radon Decay Products = Transformation Coefficient 5.56 ·10-9 J·Bq-1 x Equilibrium Factor F = 0.4 Measurement of Exposure to Radon x Exposure to Radon PRn

Potential Alpha Energy Exposure PP Measuring Quantities and Assessment of Effective Dose: Calculation of the Effective Dose Effective Dose D = Conversion to Dose x Measurement of Exposure to Radon Decay Products Potential Alpha Energy Exposure PP = Transformation Coefficient 5.56 ·10-9 J·Bq-1 x Equilibrium Factor F = 0.4 Measurement of Exposure to Radon x Exposure to Radon PRn

Measuring Quantities and Assessment of Effective Dose: Variation of Equilibrium Factor Lognormal distribution: µLF = ln(0.4) L,F = 0.295 Variation of the equilibrium factor at a 95% confidence interval: 0.2 to 0.7 Distribution of the radon equilibrium factor in homes and at workplaces

Measuring Quantities and Assessment of Effective Dose: Accuracy of Dose Assessment using passive Instruments Accuracy Criteria for Radon Measurements: Near the Relevant Limit an Accuracy of 20% is required Overestimation not more than a Factor of 1.5 Uncertainty of dose assess-ment up to a factor of 2 !

Measuring Quantities and Assessment of Effective Dose: Accuracy of Dose Assessment using passive Instruments Results of the 2005 Intercomparison for Solid State Nuclear Track Detectors

Monitoring Approaches: Individual Monitoring Indication for Application Doses may represent a significant fraction of dose limits Workers with frequently changing workplaces or inhomogeneous exposure conditions

Monitoring Approaches: Workplace Monitoring Individual monitoring of a subset of the group Local instruments Indication for Application Workers with similar work patterns and exposure conditions Unlikely to receive doses approaching dose limits Detailed records of the duration spent at each work location

Conclusions Using passive radon instruments for monitoring of workers exposed to radon should be recommended. Passive instruments are cost-effective, robust, can be applied in different exposure conditions. Individual measurements are possible. Quality assurance and maintenance of the instruments are undertaken by a radon service. Employer has low expenditure in managing the monitoring.

Conclusions Under special circumstances the direct measurement of potential alpha energy exposure is recommended: Dose estimations give rise to doses approaching dose limits Information on the equilibrium factor are not available The mean equilibrium factor is lower or higher than defined values

Conclusions Generally individual monitoring and workplace monitoring may be used as synonymous alternatives. At special work patterns or exposure conditions one of the approaches is indicated.