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ISO 7503, Measurement of Radioactivity –Measurement and Evaluation of Surface
Contamination Second Edition Issued January 15, 2016
Scott HayCabrera Services [email protected] 12, 2016
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ISO-7503First Edition – Evaluation of Surface Contamination
Second Edition – Measurement of radioactivity – Measurement and evaluation of surface contamination
ISO-7503-1 (1988)Part 1: Beta-emitters (maximum beta energy greater than 0.15 MeV) and alpha emitters, 15 pages
ISO-7503-1 (2016)Part 1: General principles, 34 pages
ISO-7503-2 (1988)Part 2: Tritium surface contamination, 7 pages
ISO-7503-2 (2016)Part 2: Test method using wipe-test samples, 18 pages
ISO-7503-3 (1996)Part 3: Isomeric transition and electron capture emitters, low-energy beta-emitters (EβMax < 0.15 MeV), 33 pages
ISO-7503-3 (2016)Part 3: Apparatus Calibration, 70 pages
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ISO-7503 Guidance• First Edition – focus on type of radiation and
energy• Second Edition – focus on type of
measurement• Measurements are simple, but interpretation
of results can be complicated
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References for the Second Edition• ISO 8769, Reference sources – Calibration of surface
contamination monitors – Alpha-, beta-, and photon-emitters
• ISO 11929, Determination of the characteristic limits (decision threshold, detection limit, and limit of the confidence interval for measurements of ionizing radiation – Fundamental and application
• ISO/IEC 17025, General Requirements for the competence of testing and calibration laboratories
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References for the Second Edition (cont.)
• ISO 9698, Water quality – Determination of tritium activity concentration – Liquid scintillation counting method
• ISO 18589-2, Measurement of radioactivity in the environment – Soil – Part 2: Guidance for the selection of the sampling strategy, sampling and pre-treatment of samples
• IEC 60325, Radiation protection instrumentation – Alpha, beta, and alpha/beta (beta energy > 60 keV) contamination meters and monitors
• No connection to ANSI 2540-1 or ANSI N323
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General Approach• Safety First
– Assume a significant dose rate, if the dose rate does not present a shielding issue or radiological hazard, then contamination can be addressed
• Clarifies the role of direct (Part 1) and indirect (Part 2) measurements
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Direct Measurements• Surface is readily accessible• Surface is reasonably clean• No interfering radiation (e.g., high
background)• Measure total contamination (fixed and
removable)
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Indirect Measurements• Surface is not readily accessible• Surface is reasonably clean• Interfering radiation fields present• Direct measurements not available (e.g.
tritium)• Cannot measure fixed contamination
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“There are many inherent shortcomings in both the direct measurement and indirect evaluation of surface contamination, so in
many cases the use of both methods in tandem may help to obtain results which best meet the needs of the evaluation.”
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Radionuclide Identification• Need to determine which nuclides are present to
accurately evaluate contamination if not previously known
• Onsite spectral analysis limited to photon emitters (50 keV to 1500 keV)
• Nuclide identifiers generally not appropriate for estimating contamination
• Alpha- and beta-emitting radionuclides typically require sample collection and laboratory analysis
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Monitoring Instruments• Selection – radiation type, energy, quantity• Instrument calibration
– Tests Before First Use (TBFU)– Not always available from manufacturer
• Periodic calibration (annual or semi-annual)• Function checks (daily, before and after use)
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Tests Before First Use• Light leakage• Response to radiation to be measured• Rejection of radiations not being measured
(primarily for alpha detectors)• Linearity of response over expected range of
activity• Uniformity of response over face of detector
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Efficiency Contour 100 cm2 Detector
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Instrument Efficiency Calibration• Similar to First Edition for single emission decay
schemes• Calibration source larger than detector• Appropriate radiation energies, especially for
beta and photon• Determine instrument efficiency• Determine P-factor (formerly surface efficiency)
inverse probability of particle emission
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Complex Decay Schemes• Most nuclides have complex decay schemes
– Multiple emissions– Multiple paths to ground state
• Need to account for all emissions• Determine effect of surface conditions on each
emission• Determine probability of detection of each
emission from a single decay
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Estimation of Instrument Response• Determine energy response of the instrument
– Instrument efficiencies for each emission energy• Model decay paths for radionuclide of interest• Determine overall instrument response
– Sum detection probabilities
• Process is complex and best performed by well-trained specialists
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Simplified Process• Assign emissions to energy regions• Alpha, 5400 to 5640 keV (Am-241)• Beta
– 40-70 keV (C-14), 70-140 keV (Tc-99), 140-400 keV(Cl-36), >400 keV (Sr-90/Y-90) [<40 keV H-3, Ni-63]
• Photon– 5-15 keV (Fe-55), 15-90 keV (I-129), 90 to 300 keV
(Co-57), >300 keV (Cs-137 and Co-60)
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Additional Guidance• Uncertainty• Reporting• Multiple radionuclides
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Recommendations• Buy it• Read it• Live it
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AcknowledgementsMichael S. Winters, CHP, Cabrera Services
Michael S. Plonski, Cabrera Services
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Questions?Scott Hay I Principal Health PhysicistCABRERA SERVICES INC. 2015 SAME SMALL BUSINESS AWARD RECIPIENTLAS VEGAS, NEVADA 89149P 702.645.9727 | C [email protected] | WWW.CABRERASERVICES.COM