**4. Measurements**

Since the risk related quantities, *e.g.* effective dose, could not be measured, some measurable quantities need to be defined. These measurable quantities should then be an estimation of the risk related quantities. As an example of the use of data from field gamma spectrometry to estimate the radiation dose, some results from repeated measurements are presented.

#### **4.1 Measurable quantities**

The relations between the different categories of quantities, risk related and measurable, are shown in Figure 12. The physical quantities, such as the absorbed dose, can be used to calculate risk related quantities by the use of weighting factors (ICRP 1991; ICRP, 2007), but also by conversion coefficients (*e.g.* ICRP, 1996). Operational quantities are derived from the physical quantities through definitions given by the ICRU (ICRU 1993; ICRU, 2001), for photon as well as for neutron irradiation. These definitions utilises the so called ICRUsphere – a tissue equivalent sphere of 30 cm diameter – and the absorbed dose at different depths in the sphere. Furthermore, relations between risk related and measurable quantities can be found from data given by the ICRP (ICRP, 1996).

Environmental Dosimetry – Measurements and Calculations 193

When the effective dose is estimated by detectors worn by individuals, special attention ought to be given to how the detector is calibrated. In these measurements the detector is often a TL-dosimeter (Thermo Luminescence Dosimetry, TLD), which is commonly used for monitoring workers at hospitals or in the nuclear industry. These detectors are calibrated to show the personal dose equivalent and if the reading is to be used for estimation of effective dose, the relation between the reading and air kerma must be known. Thereafter the

We have made repeated field gamma measurements at 34 predetermined sites in western Sweden (Almgren & Isaksson, 2009) and the results are shown here to give an example of the use of these data to estimate the ambient dose equivalent. By a proper calibration of the field gamma detector, the amount of different radioactive elements in the ground can be determined. For the naturally occurring radionuclides with an assumed homogeneous depth distribution the inventory is given as Bq kg-1. However, for 137Cs a plane source is assumed and the activity given as Bq m-2. The latter is a common procedure when the depth distribution is unknown and the reported "equivalent surface deposition" (Finck, 1992) will underestimate the true inventory due to the absorption of photons in the ground. The quantity is, however, still a good measure of the photon fluence rate above the ground. Using published dose rate conversion factors and the relation between absorbed dose and ambient dose equivalent the field gamma measurements may be compared to intensimeter measurements made in connection to the field gamma measurements. Figure 14 shows the sum of the contribution to the ambient dose equivalent from the radionuclides in the uranium series, the thorium series and 40K, as well as the contribution from 137Cs. The figure also shows the results from intensimeter measurements, corrected for the contribution from cosmic radiation. Although a correction has been made to compensate for the fact that the intensimeter is calibrated for 137Cs (0.662 MeV), whereas the mean energy of the naturally

Fig. 14. Ambient dose equivalent rate at 34 reference sites shown as the sum of the contribution from the radionuclides in the uranium series, the thorium series and 40K, as well as the contribution from 137Cs. Also shown are the results from intensimeter measurements, corrected for the contribution from cosmic radiation and photon energy

effective dose can be estimated by the relations given above.

**4.2 Measurements in western Sweden** 

used in the calibration.

Fig. 12. Relations between the quantities of interest in radiation protection and measurements. Only one of the measurable and risk related quantities, respectively are shown in the figure; several other operational quantities are defined, which are used to monitor the radiation dose to individuals.

Instruments used for radiation protection purposes, *e.g.* intensimeters, are often calibrated to directly show a measurable quantity and guidelines for the calibration of those instruments have been issued by the IAEA (IAEA, 2000). Other types of detectors, *e.g.* high-purity germanium detectors (for determination of activity or fluence rate by field gamma spectrometry) or ionisation chambers (for determination of absorbed dose), can be used to measure a physical quantity. The relationship between detector response and the physical quantity of interest is then found by calibration.

Several measurable quantities have been defined for different purposes. Some are used to monitor personal exposure and others to monitor the radiation environment. The quantity of interest in environmental measurements is often the ambient dose equivalent, *H*\*(10), since it is an estimate of the effective dose. From Figure 13 it is obvious that an instrument calibrated to show ambient dose equivalent should never underestimate the effective dose. This may cause deviations if effective dose is estimated from field gamma spectrometry and compared to the reading of an intensimeter calibrated to show ambient dose equivalent.

Fig. 13. Effective dose and ambient dose equivalent per unit air kerma, respectively. Data from ICRP (1996).

When the effective dose is estimated by detectors worn by individuals, special attention ought to be given to how the detector is calibrated. In these measurements the detector is often a TL-dosimeter (Thermo Luminescence Dosimetry, TLD), which is commonly used for monitoring workers at hospitals or in the nuclear industry. These detectors are calibrated to show the personal dose equivalent and if the reading is to be used for estimation of effective dose, the relation between the reading and air kerma must be known. Thereafter the effective dose can be estimated by the relations given above.

#### **4.2 Measurements in western Sweden**

192 Radioisotopes – Applications in Physical Sciences

Fig. 12. Relations between the quantities of interest in radiation protection and

reading of an intensimeter calibrated to show ambient dose equivalent.

monitor the radiation dose to individuals.

quantity of interest is then found by calibration.

from ICRP (1996).

measurements. Only one of the measurable and risk related quantities, respectively are shown in the figure; several other operational quantities are defined, which are used to

Instruments used for radiation protection purposes, *e.g.* intensimeters, are often calibrated to directly show a measurable quantity and guidelines for the calibration of those instruments have been issued by the IAEA (IAEA, 2000). Other types of detectors, *e.g.* high-purity germanium detectors (for determination of activity or fluence rate by field gamma spectrometry) or ionisation chambers (for determination of absorbed dose), can be used to measure a physical quantity. The relationship between detector response and the physical

Several measurable quantities have been defined for different purposes. Some are used to monitor personal exposure and others to monitor the radiation environment. The quantity of interest in environmental measurements is often the ambient dose equivalent, *H*\*(10), since it is an estimate of the effective dose. From Figure 13 it is obvious that an instrument calibrated to show ambient dose equivalent should never underestimate the effective dose. This may cause deviations if effective dose is estimated from field gamma spectrometry and compared to the

Fig. 13. Effective dose and ambient dose equivalent per unit air kerma, respectively. Data

We have made repeated field gamma measurements at 34 predetermined sites in western Sweden (Almgren & Isaksson, 2009) and the results are shown here to give an example of the use of these data to estimate the ambient dose equivalent. By a proper calibration of the field gamma detector, the amount of different radioactive elements in the ground can be determined. For the naturally occurring radionuclides with an assumed homogeneous depth distribution the inventory is given as Bq kg-1. However, for 137Cs a plane source is assumed and the activity given as Bq m-2. The latter is a common procedure when the depth distribution is unknown and the reported "equivalent surface deposition" (Finck, 1992) will underestimate the true inventory due to the absorption of photons in the ground. The quantity is, however, still a good measure of the photon fluence rate above the ground.

Using published dose rate conversion factors and the relation between absorbed dose and ambient dose equivalent the field gamma measurements may be compared to intensimeter measurements made in connection to the field gamma measurements. Figure 14 shows the sum of the contribution to the ambient dose equivalent from the radionuclides in the uranium series, the thorium series and 40K, as well as the contribution from 137Cs. The figure also shows the results from intensimeter measurements, corrected for the contribution from cosmic radiation. Although a correction has been made to compensate for the fact that the intensimeter is calibrated for 137Cs (0.662 MeV), whereas the mean energy of the naturally

Fig. 14. Ambient dose equivalent rate at 34 reference sites shown as the sum of the contribution from the radionuclides in the uranium series, the thorium series and 40K, as well as the contribution from 137Cs. Also shown are the results from intensimeter measurements, corrected for the contribution from cosmic radiation and photon energy used in the calibration.

Environmental Dosimetry – Measurements and Calculations 195

Clouvas, A.; Xanthos, S.; Antonopoulos-Domis, M. & Silva, J. (2000). Monte Carlo

Finck, R R. (1992). *High resolution field gamma spectrometry and its application to problems in* 

Golikov, V. ; Wallström, E. ; Wöhni, T. ; Tanaka, K. ; Endo, S. & Hoshi, M. (2007). Evaluation

International Commission on Radiation Units and Measurements (1993). *Quantities and* 

International Commission on Radiation Units and Measurements (1998). *Fundamental* 

International Commission on Radiation Units and Measurements (2001). *Determination of* 

International Commission on Radiological Protection (1977). *Recommendations of the* 

International Commission on Radiological Protection (1991). *1990 Recommendations of the* 

International Commission on Radiological Protection (1996). *Conversion coefficients for use in* 

International Commission on Radiological Protection (2007). *The 2007 Recommendations of the* 

International Atomic Energy Agency (2000). *Calibration of Radiation Protection Monitoring* 

Jacob, P.; Paretzke, H G.; Rosenbaum, H. & Zankl, M. (1988). Organ Doses from

Jacobi, W. (1975). The Concept of the Effective Dose - A Proposal for the Combination of

McParland, B J. (2010). *Nuclear medicine radiation dosimetry*, ISBN 978-1-84882-125-5,

Ninkovic, M M.; Raicevic, J J. & Adrovic, F. (2005). Air Kerma Rate Constants for Gamma

Shultis, J K & Faw, R E. (2000). *Radiation Shielding*, ISBN 0-89448-456-7, American Nuclear

Organ Doses, *Rad. and Environm. Biophys*. Vol.12, pp.101-109.

Emitters in Soil, *Health Physics*, Vol.78, No.3, pp.295-302.

*environmental biophysics*, Vol.46, pp.375-382.

Physics, Malmö, Sweden.

Bethesda, USA

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Publications, Bethesda, USA

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Springer-Verlag London, GB.

Society, La Grange Park, IL, USA.

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the ICRP l(3). Pergamon Press, Oxford.

*Instruments*, IAEA Safety Reports Series No.16.

Calculation of Dose Rate Conversion Factors for External Exposure to Photon

*environmental radiology*. Thesis. University of Lund, Department of Radiation

of conversion coefficients from measurable to risk quantities for external exposure over contaminated soil by use of physical human phantoms, *Radiation and* 

*Units in Radiation Protection Dosimetry,* ICRU Publications 51, ICRU Publications,

*Quantities and Units for Ionizing Radiation,* ICRU Publications 60 ,ICRU Publications,

*Operational Dose Equivalent Quantities for Neutrons,* ICRU Publications 66, ICRU

*International Commission on Radiologicul Protection*. ICRP Publication 26. Annuals of

*International Commission on Radiological Protection*. ICRP Publication 60. Ann. ICRP

*radiological protection against external radiation*. ICRP Publication 74. Ann. ICRP 26

*International Commission on Radiological Protection*, ICRP Publication 103, Ann. ICRP

Radionuclides on the Ground. Part I. Simple Time Dependencies, *Health Physics*.

Emitters used most often in Practice, *Radiation Protection Dosimetry*, Vol.115, No.1–

occurring radionuclides are slightly higher, a deviation between the results remains. One explanation may be that the measured area differs due to different angular sensitivity of the two measurements systems and that the correction of the intensimeter reading is insufficient. Still there is a good agreement between the two methods to estimate the ambient dose equivalent.

Figure 15 shows the contribution from each of the terms in the sum depicted in Figure 14. The main contributor to the ambient dose equivalent is 40K and the contribution from 137Cs is practically negligible in this area.

Fig. 15. Ambient dose equivalent rate at 34 reference sites from the radionuclides in the uranium series, the thorium series and 40K, as well as from 137Cs.

#### **5. Conclusion**

This chapter includes the basic relations for calculating the primary photon fluence rate from environmental sources of different shapes. Such calculations may be used for calibrating field equipment and also for estimating the exposure to people in the vicinity of the source. The chapter also dealt with practical environmental measurements and the importance to keep in mind the relation between effective dose and ambient dose equivalent. Measurements made by intensimeters tend to overestimate the effective dose due to the calibration requirements.

#### **6. References**


occurring radionuclides are slightly higher, a deviation between the results remains. One explanation may be that the measured area differs due to different angular sensitivity of the two measurements systems and that the correction of the intensimeter reading is insufficient. Still there is a good agreement between the two methods to estimate the

Figure 15 shows the contribution from each of the terms in the sum depicted in Figure 14. The main contributor to the ambient dose equivalent is 40K and the contribution from 137Cs

Fig. 15. Ambient dose equivalent rate at 34 reference sites from the radionuclides in the

This chapter includes the basic relations for calculating the primary photon fluence rate from environmental sources of different shapes. Such calculations may be used for calibrating field equipment and also for estimating the exposure to people in the vicinity of the source. The chapter also dealt with practical environmental measurements and the importance to keep in mind the relation between effective dose and ambient dose equivalent. Measurements made by intensimeters tend to overestimate the effective dose

Almgren, S. & Isaksson, M. (2009). Long-term investigation of anthropogenic and naturally

Attix, F H. (1991). *Introduction to radiological physics and radiation dosimetry*, ISBN 0471011460,

occurring radionuclides at reference sites in western Sweden, *Journal of* 

uranium series, the thorium series and 40K, as well as from 137Cs.

*Environmental Radioactivity*, Vol.100, pp.599-604.

Wiley-VCH Verlag GmbH, Germany.

ambient dose equivalent.

**5. Conclusion** 

**6. References** 

due to the calibration requirements.

is practically negligible in this area.


*Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata* 

When the Earth was formed, the crust and consequently the soil and water were conformed by a wide variety of chemical elements with different concentrations; being some of these radioactives. There are different activity levels of natural radionuclides, as those of the 238U and 232Th decay chains, 40K, 7Be and 14C, etc. along the planet [Cooper et al., 2003]. Among the 80 nuclides found in the environment, the more relevant concerning the radiobiological significance are 40K, and the nuclides belonging to the 238U and 232Th decay chains. The human activities can strongly modify the natural concentrations due to the presence of residues or accumulation of elements caused by the release of effluents to the environment. In the 60´s the nuclear power production and nuclear weapon testing discharge to the environment anthropogenic nuclides. In particular, the Southern Hemisphere was mainly polluted by the debris originated in the South Pacific and middle Atlantic nuclear weapon tests [UNSCEAR, 2008]. Along with the class of anthropogenic gamma emitter nuclides releases, the 137Cs is the most prominent isotope in the Earth crust originated by fission process. It is considered as one of the hazardous environmental contaminant due to the contribution to the external irradiation exposure and its incorporation to the human food

Regardless, both natural and man-made nuclides have radiobiological implication because they significantly contribute to human external radiation dose and to the internal dose by inhalation and ingestion [Cooper et al., 2003; UNSCEAR, 2008]. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has estimated that exposure to natural sources is approximately 98% of the total radiation dose (excluding medical exposure) [UNSCEAR, 2000; UNSCEAR, 2008]. The dose arising from natural nuclides varies worldwide depending upon factors such as height above sea level, the amount and type of radionuclides in the air, food and water, as well as the concentration of the natural nuclides in the soil and rocks, which in turn depend on the local geology of each

The information about the presence and migration anthropogenic radionuclides is crucial to fully understand the long-term behaviour in the environment, the uptake by flora and fauna including the human food chain, as well as potential contribution to groundwater. In consequence, before assessing the radiation dose to the population, a precise knowledge of the activity of a number of radionuclides is required [UNSCEAR, 2000;

**1. Introduction** 

chain [Singh et al., 2009].

region, etc.

María Luciana Montes and Judith Desimoni

 *Instituto de Física La Plata – CONICET,* 

*Argentina* 

United Nations Scientific Committee on the Effects of Atomic Radiation. (2008). *UNSCEAR 2008 Report to the General Assembly, with scientific annexes. Annex B.* **11** 

María Luciana Montes and Judith Desimoni

*Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata Instituto de Física La Plata – CONICET, Argentina* 

### **1. Introduction**

196 Radioisotopes – Applications in Physical Sciences

United Nations Scientific Committee on the Effects of Atomic Radiation. (2008). *UNSCEAR* 

When the Earth was formed, the crust and consequently the soil and water were conformed by a wide variety of chemical elements with different concentrations; being some of these radioactives. There are different activity levels of natural radionuclides, as those of the 238U and 232Th decay chains, 40K, 7Be and 14C, etc. along the planet [Cooper et al., 2003]. Among the 80 nuclides found in the environment, the more relevant concerning the radiobiological significance are 40K, and the nuclides belonging to the 238U and 232Th decay chains. The human activities can strongly modify the natural concentrations due to the presence of residues or accumulation of elements caused by the release of effluents to the environment. In the 60´s the nuclear power production and nuclear weapon testing discharge to the environment anthropogenic nuclides. In particular, the Southern Hemisphere was mainly polluted by the debris originated in the South Pacific and middle Atlantic nuclear weapon tests [UNSCEAR, 2008]. Along with the class of anthropogenic gamma emitter nuclides releases, the 137Cs is the most prominent isotope in the Earth crust originated by fission process. It is considered as one of the hazardous environmental contaminant due to the contribution to the external irradiation exposure and its incorporation to the human food chain [Singh et al., 2009].

Regardless, both natural and man-made nuclides have radiobiological implication because they significantly contribute to human external radiation dose and to the internal dose by inhalation and ingestion [Cooper et al., 2003; UNSCEAR, 2008]. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has estimated that exposure to natural sources is approximately 98% of the total radiation dose (excluding medical exposure) [UNSCEAR, 2000; UNSCEAR, 2008]. The dose arising from natural nuclides varies worldwide depending upon factors such as height above sea level, the amount and type of radionuclides in the air, food and water, as well as the concentration of the natural nuclides in the soil and rocks, which in turn depend on the local geology of each region, etc.

The information about the presence and migration anthropogenic radionuclides is crucial to fully understand the long-term behaviour in the environment, the uptake by flora and fauna including the human food chain, as well as potential contribution to groundwater. In consequence, before assessing the radiation dose to the population, a precise knowledge of the activity of a number of radionuclides is required [UNSCEAR, 2000;

underground essays were the more numerous; however, the global environmental impact resulted small because the radioactive material remains in the essay area. On the contrary, the atmospheric ones delivered to the atmosphere huge amounts of radioactive detritus causing a big impact on the environment [UNSCEAR, 2008; Valkovic, 2000]. It is worth to mention that because of the atmospheric circulation, approximately the 82 % of the debris remain in the hemisphere of injection [UNSCEAR, 2008; Valkovic, 2000]. The relevant nuclides originate in the essays were 3H, 14C, 54Mn, 55Fe, 85Kr, 89Sr, 90Sr, 95Zr, 103Ru, 106Ru, 131I, 137Cs, 131Ce and 144Ce, among others [UNSCEAR, 1982]. Due to 90Sr and 137Cs are volatiles and have large half-life (28.6 years and 30.2 years, respectively) they are dispersed in the atmosphere, comprising the

When analyzing the total annual effective dose received by human from natural sources, the dose received by the cosmic ray, terrestrial exposure, ingestion and inhalation of long-lived natural radionuclides needs consideration. Each environmental matrix, e.g. soil, air and water, has several associated pathways. These three environmental media cannot be thought as isolated and so, nuclide transfers are produced from one to the other. The different pathways exposure routes are schematized in the Fig. 1. The importance of these paths depends upon the particular radionuclide or radionuclides present in each compartment. The starting point to evaluate the people doses is to determine the nuclide concentrations in the environmental matrixes [USNCEAR, 2000;

stratospheric global fallout, contributing to the residual background.

Fig. 1. Schematic terrestrial pathways of nuclide transfers and dose to humans.

Two kinds of surveys have been performed, some of them deal with the determination of nuclide activity concentrations in depth, while others only reported single values of surface activity concentrations. Argentina, Brazil and Chile are the most studied countries, while there are reported a few data of Venezuela and Uruguay. The location of the monitored places, type of survey and monitored nuclides are summarized in the Table 1. Regarding the natural nuclides in South America, the reports of UNSCEAR only account values of the activity concentration of the natural nuclide 40K for Argentina [UNSCEAR, 2000; UNSCEAR, 2008]. In San Luis Province, Argentina, two sites have been studied [Juri Ayub et al., 2008]. Recently, the first systematic studies to establish baseline activities for the naturally occurring radionuclides in unperturbed soils around La Plata city, Province of Buenos Aires, have been settled on samples taken from the surface down to a depth of 50 cm [Montes et al. 2010a, 2010b]. Moreover, in four superficial soils in the Ezeiza region, Argentina, the

UNSCEAR, 2008].

**3. Monitored regions and dataset** 

UNSCEAR, 2008]. The mobility of the radionuclide in the ecosystem involves a number of complex mechanisms [Velasco et al., 2006; IAEA, 2010; Salbu, 2009; Cooper et al., 2003; Sawhney, 1972; Cornell, 1993; Staunton et al. , 2002; Bellenguer et al., 2008], and their transfer through the environmental compartments implies multiple interactions between the biotic and abiotic components of the ecosystem, as well as human interferences like the use of fertilizer [Tomazini da Conceic & Bonotto, 2006] or the overexploitation of the natural resources. For the identification of these interactions it is necessary to develop and test predictive models describing the radionuclide fluxes from the environment to the man.

In South America, the soil resource is extensively used in agriculture, stockbreeding and for building materials. Baselines of natural and anthropogenic activity nuclides in several countries are not established ye, as well regulations concerning the natural and anthropogenic activity and chemical restrictions in freshwater and food accordingly to the local situations. These facts and the scattered of the activity dataset put in relevance the present review on nuclide activity determinations in soils of South America, that could be considered as the first attempt in this direction.

A systematic compilation of radionuclide activity data of soil of Argentina, Brazil, Chile, Venezuela and Uruguay are presented. Radionuclide activity data concern to the natural 40K, 238U, and 232Th and to the anthropogenic 137Cs nuclides. These different pieces of information are put together, the quality of the environmental compartments is provided and the impact on the population is evaluated throughout the exposure dose. The migration of 137Cs in soil is also analysed in the frame of different approaches [Kirchner, 1998; Schuller et al., 1997], and the transport parameters are discussed. Moreover, the caesium inventories are compared with the latitudinal UNSCEAR predictions [UNSCEAR 2000, UNSCEAR 2008].
