1. International Atomic Energy Agency ASSESSMENT OF OCCUPATIONAL EXPOSURE DUE TO EXTERNAL RADIATION SOURCES AND INTAKES OF RADIONUCLIDES Dosimetric Quantities and Units

2. International Atomic Energy Agency Dosimetric Quantities and Units - Unit objectives The objective of this unit is to present the quantities used for radiation protection, their relationship, and appropriate units. The definitions of physical quantities, protection quantities, operational quantities and the appropriate conversion coefficients are reviewed. At the completion of this unit, the student should understand how the protection and operational quantities were defined, and how to use conversion coefficients to determine these quantities when calibrating radiation instruments.

3. International Atomic Energy Agency Dosimetric Quantities and Units - Unit Outline l Physical Quantities l Protection Quantities l Operational Quantities l Conversion Coefficients l Application of Conversion Coefficients l Reference Levels for Intake Monitoring

4. International Atomic Energy Agency Quantities for radiation measurement and dose assessment l Physical quantities - Directly measurable. l Protection quantities - Defined for dose limitation purposes, but not directly measurable. l Operational quantities - Measurable for demonstration of compliance with dose limits.

5. International Atomic Energy Agency Physical Quantities

6. International Atomic Energy Agency Physical quantities l Fluence l Exposure l Kerma l Absorbed dose

7. International Atomic Energy Agency Fluence,  The fluence, , is the quotient of dN by da, where dN is the number of particles incident on a sphere of cross section da, thus  = dN/da The unit of fluence is m -2

8. International Atomic Energy Agency Exposure, X where dQ is the absolute value of the total charge of ions produced in air when all the electrons liberated in air of mass dm are completely stopped in air. X is used to indicate the amount of ionization in air produced by x- or gamma-ray radiation. The SI unit of exposure is the coulomb per kilogram (C/kg).

9. International Atomic Energy Agency Exposure l The old, special unit of exposure is the röntgen (R). 1R = 2.58 x 10 -4 C kg -1 (exactly) Exposure, X, in units of C kg -1, is related to air kerma as follows: where W is the average energy to produce an ion pair, g is the fraction of secondary charged particles that is lost to bremsstrahlung radiation production and e is the electronic charge

10. International Atomic Energy Agency The quantity kerma, K, is defined as: K=dE tr /dm where dE tr is the sum of the initial kinetic energies of all charged ionizing particles liberated by uncharged ionizing particles in a material of mass dm. Kerma in air, K a, is used for radiation protection measurement purposes. The SI unit of kerma is the joule per kilogram (J/kg), termed gray (Gy). Kerma, K

11. International Atomic Energy Agency The absorbed dose, D, is defined as: where is the mean energy imparted by ionizing radiation to matter in a volume element and dm is the mass of matter in the volume element. The energy can be averaged over any defined volume, the average dose is the total energy imparted in the volume divided by the mass in the volume. The SI unit of absorbed dose is the joule per kilogram (J/kg), termed the gray (Gy) Absorbed dose, D

12. International Atomic Energy Agency Linear Energy Transfer Linear Energy Transfer (LET) where dE is the energy lost by a charged particle in traversing distance dl and  is an upper bound on the energy transferred in any single collision. The SI unit of LET is Jm -1

13. International Atomic Energy Agency Linear Energy Transfer l LET is a measure of how, as a function of distance, energy is transferred from radiation to the exposed matter l A high value of LET indicates that energy is deposited within a small distance l LET is a measure of the relative biological impact of a given radiation type l Alpha particles and recoil particles from neutron interactions have high LET values

14. International Atomic Energy Agency Protection Quantities

15. International Atomic Energy Agency Primary physical quantities are not used directly for dose limitation l The same dose levels of different radiations (i.e. photons and neutrons) do not have the same level of biological effect u Radiation weighting factor, w R (related to radiation quality) l Different body tissues have different biological sensitivities to the same radiation type and dose u Tissue weighting factor, w T

16. International Atomic Energy Agency ICRP has defined Protection Quantities for dose limitation l Equivalent dose Used for individual tissues or organs l Effective dose Used for the whole body

17. International Atomic Energy Agency Equivalent dose, H T,R The absorbed dose in an organ or tissue multiplied by the relevant radiation weighting factor w R : H T,R = w R · D T,R where D T,R is the average absorbed dose in the organ or tissue T, and w R is the radiation weighting factor for radiation R. w R is related to LET

18. International Atomic Energy Agency Equivalent dose, H T When the radiation field is composed of different radiation types with different values of w R the equivalent dose is: H T = w R · D T,R The unit of equivalent dose is J/kg, termed the Sievert (Sv). R

19. International Atomic Energy Agency Radiation weighting factors, w R 1 Type and energy ranges Radiation weighting factor, w R 1 1 5 10 20 10 5 5 Photons, all energies Electrons and muons, all energies Neutrons, energy < 10 keV 10 keV to 100 keV 100 keV to 2 MeV > 2 MeV to 20 MeV > 20 MeV Protons, other than recoil protons, energy > 2 MeV Alpha particles, fission fragments, heavy nuclei 20 1)All values relate to the radiation incident on the body, or, for internal sources, emitted from the source.

20. International Atomic Energy Agency Neutron radiation weighting factors 30 25 20 15 10 5 0 wRwR Neutron energy - MeV 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 11010 2 ICRP Recommendation ICRP Approximation

21. International Atomic Energy Agency Effective dose, E T A summation of the tissue equivalent doses, each multiplied by the appropriate tissue weighting factor: E = w T ·H T where H T is the equivalent dose in tissue T and w T is the tissue weighting factor for tissue T. T

22. International Atomic Energy Agency Multipliers of the equivalent dose to an organ or tissue to account for the different sensitivities to the induction of stochastic effects of radiation. Tissue or organ w T Tissue or organw T Gonads0.20Bone marrow (red)0.12 Colon0.12Lung 0.12 Stomach0.12Bladder 0.05 Breast 0.05Liver 0.05 Oesophagus0.05Thyroid 0.05 Skin 0.01Bone surface 0.01 Remainder0.05TOTAL1.00 Tissue weighting factors

23. International Atomic Energy Agency Committed Effective Dose Internal exposure continues for some time after intake. Actual exposure duration depends on the radionuclide. The exposure is said to be “committed”. Assess the committed effective dose over a 50 year period.

24. International Atomic Energy Agency Operational quantity for internal dose assessment Intake - The activity of a radionuclide taken into the body To determine the committed effective dose from an estimated intake the dose coefficient for radionuclide j by ingestion, e(g) j,ing inhalation, e(g) j,inh

25. International Atomic Energy Agency Intake vs. Uptake Do not confuse intake with uptake! Uptake “The processes by which radionuclides enter the body fluids from the respiratory tract or gastrointestinal tract or through the skin, or the fraction of an intake that enters the body fluids by these processes.” (RS-G-1.2) It is the remaining uptake activity, or excreted that is measured through direct and indirect methods to establish intake

26. International Atomic Energy Agency Recommended dose limits Application OccupationalPublic Effective dose 1 20 mSv per year, averaged over defined periods of 5 years 1 mSv in a year Annual equivalent dose in the lens of the eye150 mSv15 mSv the skin500 mSv50 mSv the hands and feet500 mSv 1 The limits apply to the sum of doses from external exposure and the 50-year committed dose (to age 70 years for children) from intakes in the same period (see paragraph 143 of ICRP 60)

27. International Atomic Energy Agency Operational Quantities

28. International Atomic Energy Agency Protection Quantities can not be measured so, l Secondary or Operational Quantities are used for occupational monitoring l The ICRU* has defined 3 Operational Quantities for external monitoring: u Area Monitoring Ambient dose equivalent Directional dose equivalent u Individual Monitoring Personal dose equivalent * International Commission on Radiation Units and Measurements

29. International Atomic Energy Agency Operational Quantities have the body in mind l All 3 quantities are defined using tissue-like objects to simulate radiation interaction properties of tissue. l ICRU soft tissue substitute: l 10.1 % hydrogen l 11.1 % carbon l 2.6 % nitrogen l 76.2 % oxygen Area monitoring Individual monitoring

30. International Atomic Energy Agency Ambient dose equivalent, H*(d) H*(d) at a point in a radiation field, is the dose equivalent that would be produced by the corresponding aligned and expanded field in the ICRU sphere at a depth,d, on the radius opposing the direction of the aligned field. A depth, d = 10 mm is recommended for strongly penetrating radiation.

31. International Atomic Energy Agency Expanded fields Field at point, P Expanded field PP P P 

32. International Atomic Energy Agency Expanded and aligned field P

33. International Atomic Energy Agency Directional dose equivalent, H′(d,  ) H′(d,  ) at a point in a radiation field, is the dose equivalent that would be produced by the corresponding expanded field in the ICRU sphere at depth d, on a radius in a specified direction, . A depth, d = 0.07 mm is recommended for weakly penetrating radiation.

34. International Atomic Energy Agency Personal dose equivalent, H P (d) l H P (d) is defined for both strongly and weakly penetrating radiations. l H P (d) is the dose equivalent in soft tissue below a specified point on the body at an appropriate depth d. l Depths of d = 10 mm for strongly penetrating radiation and d = 0.07 mm for weakly penetrating radiation are recommended.

35. International Atomic Energy Agency Conversion Coefficients

36. International Atomic Energy Agency Relationship of dosimetry quantities Primary physical quantities Fluence,  Kerma, K a Absorbed dose, D Protection quantities Operational quantities Ambient dose equivalent, H*(d) Directional dose equivalent, H'(d,  ) Personal dose equivalent, H P (d) Calculated using Q(L) and simple phantoms (sphere or slab) validated by measurements and calculations Compared by measurement and calculations (using w T, w R and anthropomorphic phantoms Monitored quantities: Instrument responses Related by calibration and calculation Calculated using w R, w T and anthropomorphic phantoms Organ absorbed dose, D T Organ equivalent dose, H T Effective dose, E

37. International Atomic Energy Agency Energy dependent dose conversion coefficients are used to establish the relationship between the Primary Physical Quantities, and the 1)Protection Quantities or 2)Operational Quantities For photons, the reference Primary Physical Quantity is Kerma, free in air, or "Air Kerma”, K a The conversion coefficients have units of Sv/Gy Dose Conversion Coefficients

38. International Atomic Energy Agency Conversion Coefficients for use in Radiological Protection against External Radiation Report of the Joint Task Group of the International Commission on Radiological Protection (ICRP) and the International Commission on Radiation Units and Measurements (ICRU)

39. International Atomic Energy Agency Joint Task Group was asked to provide: Fluence to Effective Dose calculations for a variety of radiations and energies for reference man and 15 year old, 5 year old, and 3 month old children Fluence to ambient dose equivalent, directional dose equivalent, individual dose equivalent (penetrating), and individual dose equivalent (superficial) calculations A detailed discussion of the relationship between the two sets of calculations

40. International Atomic Energy Agency Calculation of conversion coefficients for Effective Dose, E 1.Calculate D T for critical organs and tissues. 2.Use W R to calculate H T. 3. J.T.G. determined single set of H T values from published data. 4.Using proper tissue weighting convention, calculate E.

41. International Atomic Energy Agency Photon dose conversion coefficients for Effective Dose, E

42. International Atomic Energy Agency Neutron dose conversion coefficients for Effective Dose, E 10 3 10 2 10 1 Conversion coefficients - pSv cm -2 Neutron energy - MeV AP PA LAT ROT ISO 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 11010 2 10 3

43. International Atomic Energy Agency Photon dose conversion coefficients for E and H* Energy - keV 1010 2 10 3 10 4 10 1 10 -1 10 -2 10 -3 Conversion coefficients - Sv/Gy

44. International Atomic Energy Agency Neutron dose conversion coefficients for Ambient Dose Equivalent, H*(10) Neutron energy - MeV Conversion coefficients - pSv cm -2 10 3 10 2 10 1

45. International Atomic Energy Agency Calibration quantities for individual monitoring l The value of H P (d) depends on the position of measurement on the body. l A water filled slab phantom, 30cm x 30cm x 15cm is recommended for calibrating dosimeters used to measure exposure to the whole body. l Conversion coefficients for calibrating dosimeters for whole body monitoring have been calculated using a slab of ICRU muscle substitute, 30cm x 30cm x 15cm, H slab (d)

46. International Atomic Energy Agency Photon dose conversion coefficients for E and H slab Conversion coefficients - Sv/Gy Photon energy - keV 1010 2 10 3 10 4 10 1 10 -1 10 -2 10 -3 E H slab (10)

47. International Atomic Energy Agency Neutron dose conversion coefficients 10 3 10 2 10 1 Conversion coefficients - pSv cm 2 Neutron energy - MeV 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 11010 2 10 3 E H*(10) H slab (10)

48. International Atomic Energy Agency H p conversion coefficients depend on angle Neutron energy - MeV Conversion coefficients - pSv cm 2 10 3 10 10 2 1 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 1 1010 2 neutrons W Angle of incidence, W 0° 15° 30° 45° 60° 75°

49. International Atomic Energy Agency Conversion coefficient angular dependence 1 1010 2 10 -1 10 -2 10 -3 10 -4 10 -5 10 -6 10 -7 10 -8 Neutron energy - MeV Relative Conversion Coefficients 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0° 15° 30° 60° 45° 75°

50. International Atomic Energy Agency Application of Conversion Coefficients

51. International Atomic Energy Agency Comparison of E and H P (10,  ) l Operational quantities should give a reasonable approximation to the protection quantities l Approximation quality can be determined by the ratio of conversion coefficients l For example, for 0.100 MeV photons, H p (10,0°)/K a = 1.811 Sv/Gy E/K a = 1.394 Sv/Gy (Task Group Report) l H p (10,0°)/E = 1.30 - a 30% overestimate

52. International Atomic Energy Agency Underestimation Overestimation E / H*(10), (ICRP 60) 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 110 1 10 2 2 1.5 1 0.5 0 H* as an indicator of E in AP geometry Protection Quantity / Operational Quantity Neutron energy (MeV)

53. International Atomic Energy Agency CONVERSION COEFFICIENTS FROM AIR KERMA TO IN AN ICRU SLAB AND ANGULAR DEPENDENCE FACTORS (PHOTONS)

54. International Atomic Energy Agency Conversion coefficients - An example l Assume a 100 keV (0.100 MeV) monoenergetic source l The air kerma rate at 2 meters is 1 mGy/h l A dosimeter is placed on a slab phantom at 2 m l The dosimeter is irradiated for 10 minutes l From the previous table, the conversion coefficient for 0.1 MeV photons is 1.811 Sv/Gy l H p (10,0°) = 10 -3 Gy/h  0.167 h  1.811 Sv/Gy = 0.301  10 -3 Sv = 0.301 mSv

55. International Atomic Energy Agency Conversion coefficients - An example l Now, replace the 100 keV source with a 1.0 MeV monoenergetic source l Keep the air kerma rate at 2 meters at 1 mGy/h l A dosimeter is placed on a slab phantom at 2 m l Again, irradiate the dosimeter for 10 minutes l The conversion coefficient for 1.0 MeV photons is 1.167 Sv/Gy [H p (10,0°)/K a )] l H p (10,0°) = 10 -3 Gy/h  0.167 h  1.167 Sv/Gy = 0.195  10 -3 Sv = 0.195 mSv

56. International Atomic Energy Agency Conversion coefficients - An example l Again, use the 100 keV source l Rotate the phantom to an angle of 60° with the source l All other conditions are the same l For 0.100 MeV, H p (10,60°)/H p (10,0°) = 0.834 l H p (10,0°) = 10 -3 Gy/h  0.167 h  1.811 Sv/Gy  0.834 = 0.251 mSv, compared with 0.301 mSv at 0° Source Phantom  =60° Dosimeter

57. International Atomic Energy Agency CONVERSION COEFFICIENTS FROM AIR KERMA FOR H p (10) AND H p (0.07) IN AN ICRU SLAB FOR ISO PHOTON REFERENCE RADIATIONS [a] F - fluorescent series; N - narrow spectrum series; S - radionuclide sources. Number denotes tube potential. [b] Numbers in brackets: Care needs to be taken as variations in energy distribution may have a substantial influence on the numerical values of the conversion coefficients.

58. International Atomic Energy Agency Reference Levels for Intake Monitoring

59. International Atomic Energy Agency Reference levels Reference levels are helpful in management of operations Expressed in terms of measured quantities or other quantities to which measured quantities can be related If exceeded, take specified action or decision Reference levels usually based on committed effective dose E(50) for radionuclide intake

60. International Atomic Energy Agency Intakes corresponding to Limits Given:  Exposure from a single radionuclide  Exposure by inhalation or ingestion  No external exposure  Relevant effective dose limit, L Intake I j,L corresponding to L is given by: where e(g) j is the relevant dose coefficient.

61. International Atomic Energy Agency Reference levels Appropriate dose limit fraction corresponding to each reference level should be established Take other sources of exposure into account Recording Levels and Investigation Levels relevant to internal contamination monitoring for occupational exposures.

62. International Atomic Energy Agency Recording level Defined as “a level of dose, exposure or intake specified by the regulatory authority at or above which values of dose, exposure or intake received by workers are to be entered in their individual exposure records” Example - RL for a radionuclide intake set to correspond to a committed effective dose of 1 mSv (0.001 Sv) from a year’s intakes

63. International Atomic Energy Agency Recording level For N monitoring periods per year, the recording level for intake of radionuclide j in a monitoring period would be given by:

64. International Atomic Energy Agency Investigation level Is “the value of a quantity such as effective dose, intake or contamination per unit area or volume at or above which an investigation should be conducted” Investigation level for radionuclide intake - A value of committed effective dose above which monitoring results justify further investigation Set by management, depends on programme objectives and type of investigation to be done

65. International Atomic Energy Agency Investigation level For routine monitoring, the investigation level for a radionuclide intake is set in relation to: u Type and frequency of monitoring u Expected level and variability of intakes Numerical value of the investigation level depends on conditions in the workplace Investigation level may be set for; u Individuals in a particular operation, or u Individuals within a workplace without reference to a particular operation

66. International Atomic Energy Agency Investigation level – An example Routine operation with routine monitoring IL set at a committed effective dose of 5 mSv (0.005 Sv) from a year’s intakes For N monitoring periods per year, the IL (in Bq) for the intake of any radionuclide j in any monitoring period is: where e(g) j is the dose coefficient for inhalation or ingestion

67. International Atomic Energy Agency Derived levels Measured quantities are radionuclide activities in the body or excreta samples It is convenient to establish reference levels for the measurement results themselves These are termed derived investigation levels (DILs) and derived recording levels (DRLs) Measurement results that imply radionuclide intakes or committed effective doses at the corresponding reference levels

68. International Atomic Energy Agency Derived levels Measurement result should always be maintained in the radiation monitoring records for the workplace and for the individual For worker exposure to external radiation or to multiple radionuclides, management may need to reduce the derived levels for individual radionuclides appropriately.

69. International Atomic Energy Agency Derived levels Derived investigation and recording levels are calculated separately for each radionuclide Specific to the radiochemical form in the workplace Are a function of time since intake For the previous examples,

70. International Atomic Energy Agency Derived Investigation and Recording Level Time elapsed between intake and bioassay (t 0 ) is usually set as 365/2N days, assuming that intake occurs at the mid-point of the monitoring period, then u Derived Investigation Level: u Derived Recording Level:

71. International Atomic Energy Agency Intake Fraction Intake fraction, m(t), The amount of material remaining or being excreted from the body at time, t, after intake divided by the intake quantity. The intake fraction depends on: the radionuclide, its chemical and physical form, the route of intake, time after intake

72. International Atomic Energy Agency Derived Air Concentration Derived air concentration (DAC) The concentration of airborne activity (in Bq/m 3 ) that would result in the limit on intake of I j,inh,L by a worker exposed continuously at that level for one year.

73. International Atomic Energy Agency Example of DAC DAC = I j,inh,L / (2000 * 1.2) Assume airborne 137 Cs with a 5 μm AMAD. e(g) inh = 6.7 E-9 Sv/Bq Annual dose limit = 20 mSv = 0.02 Sv I j,inh,L = 0.02 / 6.7 E-9 = 3 E+6 Bq DAC = 3E+6/ (2000*1.2) = 1.3 E+3 Bq/m 3

74. International Atomic Energy Agency The measured airborne activity concentration, expressed as a fraction of the DAC, multiplied by the exposure time in hours gives an estimate of intake expressed in DAC·h. Example: 1 week at the 0.1 DAC would be 4 DAC·h, or an intake of 4/2400 = 0.002 I j,inh,L. 2400 DAC·h corresponds to an intake of I j,inh,L. Use of DAC·h

75. International Atomic Energy Agency References FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONAL LABOUR ORGANISATION, OECD NUCLEAR ENERGY AGENCY, PAN AMERICAN HEALTH ORGANIZATION, WORLD HEALTH ORGANIZATION, International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No. 115, IAEA, Vienna (1996). INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment of Occupational Exposure Due to External Sources of Radiation, Safety Guide RS-G-1.3 (1999). INTERNATIONAL ATOMIC ENERGY AGENCY, Calibration of Radiation Protection Monitoring Instruments, Safety Series No. 16 (2000). INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTS, Determination of Dose Equivalents Resulting from External Radiation Sources, Report No. 39, ICRU, Bethesda, MD (1985). INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTS, Determination of Dose Equivalents from External Radiation Sources - Part 2, Report No. 43, ICRU, Bethesda, MD (1988). INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTS, Determination of Operational Dose Equivalent Quantities for Neutrons, ICRU Report 66, [Journal of the ICRU Volume 1, No 3, 2001] (2002). INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTS, Measurement of Dose Equivalents Resulting from External Photon and Electron Radiations, Report No. 47, ICRU, Bethesda, MD (1992). INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTS, Quantities and Units in Radiation Protection Dosimetry, Report No. 51, ICRU, Bethesda, MD (1993).

76. International Atomic Energy Agency References INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION/ INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTS, Conversion Coefficients for Use in Radiological Protection Against External Radiation, ICRP Publication 74, Pergamon Press, London and New York (1997) or ICRU Publication 57, ICRU, 7910 Woodmont Ave., Bethesda, MD 20814 USA (1998). INTERNATIONAL ORGANIZATION FOR STANDARDIZATION, X and Gamma Reference Radiations for Calibrating Dose Meters and Dose Rate Meters and for Determining Their Response as a Function of Photon Energy ‑ Characteristics of the Radiations and their Methods of Production, ISO Standard 4037-1, Geneva (1995). INTERNATIONAL ORGANIZATION FOR STANDARDIZATION, Reference Photon Radiations - Dosimetry of X and Gamma Reference Radiations for Radiation Protection over the Energy Range from 8 keV to 1.3 MeV and from 4 MeV to 9 MeV, ISO/DIS 4037-2, Geneva (1995). INTERNATIONAL ORGANIZATION FOR STANDARDIZATION, Reference Photon Radiations ‑ Calibration of Area and Personnel Dosemeters and the Determination of their Response as a Function of Energy and Angle of Incidence, ISO/DIS 4037-3, Geneva (1995). NTERNATIONAL ATOMIC ENERGY AGENCY, Occupational Radiation Protection, Safety Guide No. RS-G-1.1, ISBN 92-0-102299-9 (1999). INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment of Occupational Exposure Due to Intakes of Radionuclides, Safety Guide No. RS-G-1.2, ISBN 92-0-101999-8 (1999). INTERNATIONAL ATOMIC ENERGY AGENCY, Indirect Methods for Assessing Intakes of Radionuclides Causing Occupational Exposure, Safety Guide, Safety Reports Series No. 18, ISBN 92-0-100600-4 (2002). INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Individual Monitoring for Internal Exposure of Workers: Replacement of ICRP Publication 54, ICRP Publication 78, Annals of the ICRP 27(3-4), Pergamon Press, Oxford (1997).