Uncertainties of measurements in radiation protection

A. Steurer; C. Schmitzer; K. Gruen

doi:10.1515/kern-2003-0071

Article

Uncertainties of measurements in radiation protection

A. Steurer , C. Schmitzer and K. Gruen

Published/Copyright: March 11, 2022

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From the journal Kerntechnik Volume 68 Issue 4

Abstract

On September 1st, 2001, the Austrian standard OENORM S 5255-1 with the title “Uncertainties of measurements and limiting values in radiation protection – Part 1: Basics” was published. A part 2 of the standard with the subtitle “Assessment of measurements with regard to limiting values” was published on April 1st, 2002. Part 1 of the standard is a consequent application of the “Guide to the expression of uncertainty in measurement” (GUM) for measurements in radiation protection. It contains a summary of the most important definitions and mathematical methods, which are relevant for measurements in radiation protection. An important prerequisite is the standardisation of the coverage factor k = 1 for measurements in radiation protection. Finally, the use of the standard is demonstrated by a detailed example there (dose rate meter). First, the uncertainty of a dose rate meter is stated, using only information on tolerances available e. g. from instrument specifications. Additionally, the strategies to reduce the uncertainty and the necessary detailed knowledge of the dose rate meter are demonstrated. Part 2 of the standard gives a simple concept for interpretation of limits using the uncertainties calculated based on part 1 of the standard.

Abstract

In Österreich ist mit 01. 09. 2001 die ÖNORM S 5255–1 erschienen, welche den Titel ,,Messunsicherheiten und Grenzwerte im Strahlenschutz; Teil 1: Grundlagen“ trägt. Ein zweiter Teil der Norm mit dem Untertitel ,,Beurteilung von Messungen im Hinblick auf Grenzwerte“ erschien am 01. 04. 2002. Der Teil 1 der Norm ist eine konsequente Umsetzung des ,,Guide to the Expression of Uncertainty in Measurement“ (GUM) zur Anwendung bei Strahlenschutzmessungen. Er enthält eine Zusammenfassung der wichtigsten Begriffe und Rechenverfahren, soweit sie für Strahlenschutzmessungen relevant sind. Ein wichtiger Ansatz dabei ist, dass in dieser Norm für Messungen im Strahlenschutz der Erweiterungsfaktor k = 1 festgelegt wird. Schließlich wird anhand eines ausführlichen Beispiels (Ortsdosimeter) die Anwendung demonstriert. Dabei wird einerseits die Messunsicherheit eines Ortsdosimeters abgeschätzt, von welchem ausschließlich die Eichfehlergrenzen bekannt sind. Darüber hinaus wird präsentiert, mit welchen Strategien diese Messunsicherheit reduziert werden kann, und welche Kenntnisse über das Ortsdosimeter dafür die Voraussetzung sind. Der Teil 2 der Norm bietet ein einfaches Konzept zur Interpretation von Grenzwerten mit Berücksichtigung der gemäß Teil 1 der Norm ermittelten Messunsicherheiten.

Acknowledgement

The authors would like to thank the members of the working group FNA 088/AG 15 for good cooperation and the discussions which were very important for the successful development of the introduced OENORM-documents.

References

1 OEVE/OENORM EN ISO/IEC 17025: 2001-01-01: Allgemeine Anforderungen an die Kompetenz von Prüf- und Kalibrierlaboratorien (General Requirements for the Competence of Testing & Calibration Laboratories) (ISO/IEC 17025: 1999)Search in Google Scholar

2 EA-4-02: Expression of the Uncertainty of Measurement in Calibration (GUM), Europaen cooperation for Accreditation, December 1999Search in Google Scholar

3 OENORM S 5255-1:2001-09-01: Messunsicherheiten und Grenzwerte im Strahlenschutz; Teil 1: Grundlagen (Uncertainties of measurements and limiting values in radiation protection – Part 1: Basics)Search in Google Scholar

4 OENORM S 5237-2: 1998-11-01: Strahlenschutzdosimeter; Ortsdosimeter zur Messung der Umgebungs- und Richtungs-Äquivalentdosis bzw. -dosisleistung (Radiation protection dosimeters – Area dosimeters for the measurement of the ambient and directional dose equivalent resp. dose equivalent rate)Search in Google Scholar

5 OENORM S 5255-2: 2002-04-01: Messunsicherheiten und Grenzwerte im Strahlenschutz – Teil 2: Beurteilung von Messungen im Hinblick auf Grenzwerte (Uncertainties of measurements and limiting values in radiation protection – Part 2: Assessment of measurements with regard to limiting values)Search in Google Scholar

Appendix: Additional example

One measurement of dose rate of X-ray stray radiation with 150 kVp; indicated value: M = 4.5 μSv/h. Described are three cases:

(1) Calculation of the uncertainty of the result of one measurement of the dose rate with a dose rate meter with official certification.

– Using official certification tolerances according from the certification license

– Using maximum allowed deviation of response during variation of an influence quantity according to the certification license.

Result of the measurement:

H.=(4.50±1.51) μSv=h(k = 1) (see table).

(2) Reduction of the uncertainty using detailed data about the dose rate meter:

– Using real deviation of response for some influence quantities.

– No reduction according to direction of radiation incidence and electromagnetic influence (assumption: no information about these influence quantities).

Result of the measurement:

H.=(5.45±1.26) μSv=h (k = 1) (see table).

(3) Additional reduction of the uncertainty through calibration data:

– Using calibration factor and linearity (with f_max(k_L) for linearity) according to the certification license.

For a calibration factor of N¯=0.94±0.05 (k = 1) the uncertainty is reduced to 0.006163, with f_max(k_L) = 0.10. The uncertainty is reduced to 17.1 %. Result of the measurement: H.= (5:08 ± 0:87) μSv=h (k = 1)

Method	(1) Official certification			Value	(2) Official certification, additional data			Value
Indicated value	M¯	4.5	m_max = (16 - M)=100	0.004408	M¯	4.5	m_max = (16 - M)=100	0.004408
Calibration factor	N¯	1.0	ΔM_max=M = 0:30	0.030000	N¯	1.0	ΔM_max=M = 0:30	0.030000
Photon energy	k¯E	1.0	f_max(k_E) = 0.30	0.030000	k¯E	1.2	f(k_E) = 0.065	0.000978
Direction of radiation incidence	k¯R	1.0	f_max(k_R) = 0.20	0.013333	k¯R	1.0	f(k_R) = f_max(k_R) = 0.20	0.013333
Supply voltage	k¯U	1.0	f_max(k_U) = 0.10	0.003333	k¯U	1.0	f(k_U) = 0	0
Ambient temperature	k¯T	1.0	f_max(k_T) = 0.20	0.013333	k¯T	1.0	f(k_T) = 0.05	0.000833
Relative humidity	k¯W	1.0	f_max(k_W) = 0.20	0.013333	k¯W	1.0	f(k_W) = 0.03	0.000300
Air Pressure	k¯P	1.0	f_max(k_P) = 0.05	0.000833	k¯P	1.0	f(k_P) = 0.01	0.000033
Electromagnetic influence	k¯EM	1.0	f_max(k_EM) = 0.10	0.003333	k¯EM	1.0	f(k_EM) = f_max(k_EM) = 0.10	0.003333
Calculation	Product: 4.50		Sum:	0.111909	Product: 5.45		Summe:	0.053220
			Square root:	0.335			Square root:	0.231
Uncertainty	u c H . = 0.335 = U H . with k = 1 : 33 . 5 %				u c H . = 0.231 = U H . with k = 1: 23 .1 %
Result	H.=(4.50±1.51)μSv/h(k=1),U=±1.51μSv/h				H.=(5.40±1.25)μSv/h(k=1),U=±1.25μSv/h

Received: 2003-03-26

Published Online: 2022-03-11

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https://doi.org/10.1515/kern-2003-0071