T. Otto,

1
Personal Dosimetry in a RIB Facility

• External Exposure
• Internal Exposure
• Biokinetic Models
• Dosimetry
• Threshold Measurements
• Particularities of a RIB facility
• Thomas Otto, CERN, TIS-RP

2
Dosimetry basic concept

• Absorbed dose
• together with suitable weighting or quality
  factors dose equivalent H
• radiation detriment is assumed to be proportional
  to dose equivalent in the low dose, low doserate
  regime
• dose equivalent H key quantity for radiological
  risk assessment

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External vs. Internal Exposure
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Effective Dose

• ICRP 60
• Risk-related quantityeffective Dose E
• Tissue weighting factors wT for 13 organs
  (tissues)
• Legal limits expressed in E
• E is one dose equivalent quantity

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Dosimetry of External Exposure

• Dose measurement
• Organs inaccessible for measurement
• Effective Dose cannot be measured directly
• Operational quantity Personal dose equivalent
  for protection purposes
• H gt E

• Measure H with calibrated dosimeter on
  representative part of body

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Personal Dosimeters

• Gamma/Beta
• mature technology
• TLD or OSL
• Neutrons
• Wide range of relevant energies
• Dosimeters only for partial energy range
• Albedo, Track-etch

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Internal Exposure

• Penetration of radioisotopes into the body
• inhalation via respiratory tract
• ingestion via Gastro-Intestinal tract
• by wounds
• description by biokinetic models

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Respiratory Tract Model

• Describe
• deposition in airways
• clearance into blood
• compartment model
• 1st order rate equations
• Particle size spectrum
• 1 um 51 deposition
• 5 um 82 deposition
• Clearance type
• Fast, Medium, Slow
• 10 min , 140 days, 20 years

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Dose Calculation

• Result of Calculations
• ICRP publications
• dose coefficients dose per activity
  (Sv/Bq)
• for workers and members of public
• for different particle sizes and clearance types
• for large range of isotopes

• Activity in target organs from biokinetic models
• Sum over 50 years
• all decays in one organ
• all organs
• Committed dose E(50)

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Dosimetry

• Dose measurement
• Organs inaccessible for measurement
• Effective Dose cannot be measured directly
• Calculation of dose from incorporated activity

• Need to estimate incorporated activity

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Incorporation Measurements

• Direct Measurement
• whole-body
• whole-body counters
• Anthropogammametry
• body part
• thyroid measurement
• for g-emitters

• Excretion Analysis
• urine
• feces
• chemical preparation
• nuclear counting techniques
• (AMS)
• for a/b-emitters

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Whole-Body Counters
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Excretion Analysis

• Relation of excreted activity to incorporated
  activity
• biokinetic models
• experiments on volunteers
• experience from accidents

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Excretion Analysis (2)

• Reference data for standard isotopes
• ICRP Publ. 78
• 3H, 59Fe
• 57,58,60Co
• 85,89,90Sr, 106Ru
• 125,129,131I
• 134,137Cs,
• 226,228Ra, 228,232Th
• 234,235,238U, 37Np
• 7 Transuranium isotopes

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Workplace Measurement

• Swiss Ordinance for Dosimetry
• documented measurement of aerosol concentration
  at workplace with threshold for full internal
  dosimetry
• thresholdE(50) ? 1 mSv
• Isotope-specific thresholds
• Guidance only for few isotopes
• Difficult Isotope discrimination

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Characteristics of a RIB facility

• Wide range of isotopes
• Prototype-like installation without large body of
  experience (as e.g. NPP)
• Experimental (vs. industrial) way of operation

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External Dosimetry in RIB Facility

• Full-body gamma dosimeters
• Electronic dosimeter upon access to activated
  area (front-end, separator, reactor, storage) for
  immediate dose control
• Extremity g/b dosimeters for specific work
• during operation, neutron dosimeter(type
  depending on driver reactor vs. accelerator)

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Workplace Monitoring in RIB Facility

• Regular checks for volatile contamination
• Activity-inair measurements
• Look for representative tracer nuclides and
  estimate total contamination from their
  concentration
• Identify such tracers
• Determine best measurement practice(Instrument
  sensitivities, sample preparation)

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Internal Dosimetry in RIB Facilities

• Periodic whole-body scans for gamma emitters are
  simple, low-cost and reassuring for emplyer and
  staff
• Periodicity has to be reviewed
• Extra-scans after incidents
• Excretion analysis needs identification of
  tracers and development of specific sample
  preparation/detection methods
• Use of automated equipment and personal
  protective equipment to raise threshold for
  real internal dosimetry

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Summary

• Personal dosimetry key element of radiological
  protection programme
• External vs. internal dosimetry
• Specific challenges of RIB-facilities
• non-standard character of installation
• range of isotopes
• Development work for implementation of full
  dosimetry programme is still necessary