The BIPM and the International Reference System (SIR) for activity measurements

Bureau International des Poids et Mesures

The BIPM and the International Reference System (SIR) for

activity measurements

Bureau International des Poids et MesuresDecay Data Evaluation Project Workshop,

8th October 2012Laboratoire National de Métrologie et d’Essais, Paris

1


I. Presentation of the BIPM



2


Some relevant dates for the International System of Units (SI) (1/2)…

20 May 1875 : Establishement of the Metre Convention (Convention du Mètre); in 1899 the 1st CGPM sanctioned the international prototypes for the meter and the kilogram.

Prototypes of the kilogram and the metre

3


Some relevant dates for the International System of Units (SI) (2/2)…

1901 : Giorgi showed that it is possible to combine the mechanical units of this metre–kilogram–second system with the practical electric units to form a single coherent four-dimensional system by adding to the three base units, a fourth base unit of electrical nature, such as the ampere or the ohm, and rewriting the equations occurring in electro-magnetism in the so-called rationalized form.

1946 : the adoption of a four-dimensional system based on the metre, kilogram, second and ampere are endorsed by the CIPM.

1954 : The 10th CGPM approved the introduction of the ampere, the kelvin and the candela as base units.

1960 : The name International System of Units (SI) is given to the system by the 11th CGPM.

1971 : At the 14th CGPM the number of base units is brought to 7 by adding the mole (unit for amount of substance).

4


Metre Convention

An intergovernmental treaty which, inter alia, established the BIPM;

Affirmed international support for the International System of Units- the SI;

Created the General Conference of Weights and Measures which meets every 4 years and is responsible for all major decisions affecting the SI, the BIPM and links with other intergovernmental bodies etc;

BIPM is on an international territory at Sèvres with 76 staff ;

€12.5 M (2012) budget funded by 56 full Members States and 37 Associates of the General Conference of

of Weights and Measures.

5


BIPM’s Mission

THE ROLE OF THE BIPM IS WORLDWIDE UNFORMITY OF MEASUREMENT.

It achieves this through providing the necessary scientific and technical basis for such uniformity and by collaborating with other institutions and

organisations that have related missions.

6


BIPM’s political role

Working with Governments, National Metrology Institutes, and the accreditation community so as to maintain confidence in the world measurement system for science and trade;

To act on behalf of NMIs and Member States in dealings with international and intergovernmental bodies such as the World Trade Organisation, World Meteorological Organisation, World Health Organisation, the International Federation of Clinical Chemistry, International Laboratory Accreditation Co-operation, International Bureau for Legal Metrology etc;

Extend the geographical coverage of the Metre Convention amongst developing countries.

7


BIPM’s main technical roles

Maintain the kilogram - needed for the next 5/10 years until replaced, probably by Watt Balances or others means;

Disseminate Co-ordinated Universal Time based on weighted averages of clocks from many National Metrology Institutes;

Maintain unique world reference facilities e.g. SIR (ionizing radiation and isotopes), ozone spectrophotometers;

Maintain travelling standards to compare fixed national references e.g. Arrays of Josephson Junctions for the volt, Quantum Hall devices for the ohm, graphite calorimeter for dosimetry quantities etc;

Coordinate international comparisons and networks e.g. organic chemistry reference materials for laboratory medicine;

Promote traceable, accurate measurement for physical, engineering, chemical and medical measurements worldwide.

8


SCHEME OF EQUIVALENCE OF NATIONAL MEASUREMENT STANDARDS THROUGH KEY COMPARISONS

B I P Mand Consultative

Committee (CC) keycomparisonother

regional keycomparisons

APMPkey

comparisons

SIMEUROMET

keycomparisons

otherregional keycomparisons

250+ institutesparticipate in CC activities

More than 810 key comparisons havebeen identifiedBIPM

NMI participating in BIPM / CC key comparisonsNMI participating in BIPM / CC key comparisons and in regional key comparisonsNMI participating in regional key comparisonsNMI participating in neither BIPM / CC nor regional key comparisons but making bilateral comparisons

9


CIPM MRA (1/3)

In 1999 the CIPM developed an MRA between NMIs to address

technical barriers to trade caused by lack of traceability and

equivalence.

Complying with the MRA means that an NMI calibration certificate is

acceptable world-wide with a validated accuracy.

10


CIPM MRA (2/3)

Signed October 1999, by 38 NMIs and two international organisations; to date by 89 Institutes and three international organisations (IAEA, IRMM and WMO)

Covers ‘Metre Convention’ countries;

A new category of Associates to the General Conference on Weights and Measures (now 37) was created to involve other countries that were not (yet) full members;

Provides a data base covering the world’s NMIs and “designated institutes” that shows National capabilities and differences between National Standards – more than 25,000 CMC entries already;

www.bipm.org

11


CIPM MRA (3/3)

To have its calibration and measurement capabilities (CMCs) validated by others;

To take part in key comparisons that give confidence in day-to day measurements at the NMIs;

To implement and allow others to understand its quality/management systems.

TO MEET THE REQUIREMENTS OF THE MRA, AN NMI WILL NEED:

12


BIPM current activities (1/3)

13



MASS: maintain the kilogram; provide copies for Member States; agree better ways of measuring air density corrections and surface contamination;

TIME: TAI/UTC; two way time transfer and algorithms; collaborate with NMIs, GPS, Glonass and Galileo systems to harmonise world time. Issues of how to compare new cold atom and ion clocks- current time scales and satellite transfer methods are not good enough for air navigation requirements;

ELECTRICITY: meet NMI needs for travelling and reference standards in voltage, resistance and capacitance.

14



IONIZING RADIATION: x and γ reference chambers.WHO/IAEA dosimetry network; world reference system for radionuclides;

CHEMISTRY: reference network for atmospheric ozone monitors; new work in bio-analysis and organic chemistry with NMI “virtual” networks. MoU with WHO, WMO to set priorities;

KEY COMPARISON DATABASE: approved capabilities of the world’s NMIs;

METROLOGIA: editorial control of contracted out publication; JOINT COMMITTEES : ISO; ILAC; developing country work; laboratory

medicine; Regional Metrology Organisations; KNOWLEDGE TRANSFER : workshops; unique

calibrations/characterisations that do not duplicate NMI services; secondments/exchanges with NMIs; provide unique international experience for guest workers from NMIs;

NEW PROJECTS: Calculable Capacitor; Watt Balance.

15


II. The International Reference System (SIR) for activity

measurements



16


1. Recall of the Rôle of the BIPM :

• to establish and warrant the uniformity of the measurements carried out in NMIs,

• to contribute to the improvement of the precision of measurements every time it is feasible and required by the applications,

• to develop and use new measurement techniques,• maintain the perennial characteristics of measurements,• initiate the dissemination of units.

• These objectives should be met by all BIPM Departments and in particular by the Ionizing Radiation Department.

The International Reference System (SIR) for activity

measurements

17


2. Measurements of Radionuclides :

• In the field of the measurements of radionuclides this is achieved by a regular organization of international comparisons of activity concentration measurements : since its establishment at the BIPM in 1961 the ionizing

radiation department has organized 41 such comparisons, which represents an average of one comparison every 15 months.

• In the most recent comparisons the following radionuclides have been measured :

54Mn, 65Zn, 85Kr, 89Sr, 109Cd, 125I (2x), 133Ba,137Cs,152Eu,192Ir, 204Tl.


measurements

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2. Measurements of Radionuclides :

Most significant drawbacks :• international comparisons of activity measurements are :

– very demanding to implement,– time consuming, and – requiring important financial and personal ressources.

Consequently, international comparisons are:• not very frequent,• not accessible to all laboratories,• only a few radionuclides can be measured.


measurements

1919


3. International Reference System : Presentation

• For all these reasons the International Reference System was established in 1976.

Advantages :• simple to use (measurement in ionization chambers),• quick measurements,• stability [long–lived reference sources (Ra) are used],• precision of the results (about 0.1 %),• robustness of the results.


measurements

2020


3. International Reference System : Presentation

Drawbacks :• all g emitters are not measurable, e.g. when the radioactive

half-life is too short (less than a few days) or when the photons energy is too low,

• the measurements are relative, not absolute.

Since the CIPM Mutual Recognition Arrangement (CIPM MRA) has been signed the SIR has become the cornerstone of the process enabling the evaluation of the degrees of equivalence for all laboratories participating in comparisons of activity measurements in view of establishing their capabilities in calibrations and measurements (CMCs).

The International Reference System (SIR) for activity measurements

2121


3. International Reference System : Operating procedure

• The International System of Reference is based on two commercial re-entrant well-type ionization chambers filled with 2 MPa nitrogen.

• The two chambers are operated with a negative polarization voltage of - 500 V.

• The measurements rely on the principle of the Townsend balance with stepwise compensation.

• They consist of measuring precisely the time necessary to charge a capacitor of well-known capacitance to a precisely defined constant voltage.


2222



• The collected current for the radionuclide i

Ii – If = CnU / ti

is compared to the current obtained for a Ra source (T1/2 = 1600(7) a)

IRa – If = CnU / tRa.

• The leakage current amounts typically to about 100 fA.


measurements

2323



• Five radium sources with increasing activity, in a geometrical progression of ratio 3 are available, with a total activity of 16.4 MBq.

• The radium source for the measurement is chosen so that

ti tRa.

• This set of radium sources enables to cover an activity range for the measured radionuclides from a few hundred kBq to a few hundred MBq.


2424



• Introducing the concept of equivalent activity, Ae, which is the radionuclide activity necessary to produce in the chamber a current equal to that produced by the radium source of the highest activity the ratio between the current produced by the radium source and that produced by the radionuclide can be written:


2525



•

with t0, reference time for the radium sources: 01-01-1976,tr, reference time for the sample from the laboratory,tm, measurement time at the BIPM, Fj, a constant, evaluated every year, to transform the measured current, obtained with the source of radium used to match the current of the sample, into the current which would have been produced by the highest–activity radium source.


26

0RaRa f

s f

( )e

( )s

)

)

((

m

m rs

jt t

t tF I I

I IeAeA

26


3. International Reference System : Corrections for Impurities • For every measured radionuclide, i, which emits g’s detected

in the chamber, the collected current has the expression

or, in the presence of several impurities

The International Reference System (SIR)

27

Ra 0

i

( )

( )

eRa f( )

i m r

m

i i

j

t t

t teAeA

IF I I

Ra 0

i

( )

1( )

1e

Ra f( )

i m r

m

n

n ii i

i j

t t

t t

IeAeA F I I

27


3. International Reference System : Corrections for Impurities

• If the contribution to the current due to the main radionuclide, rad, is separated from those due to the impurities, i, the expression becomes

or


28

rad f1 f

Ra fRa 0 Ra 0

rad

( ) ( )radrad

( ) ( )1 Ra f

e e( ) ( )

n

ii s

j

m r i m r

m m

i

ni

i j

t t t t

t t t tI I I I IF I I

e eA AF I Ie eA A

radrad

Ra 0i

rad

f

( )( )

rad e( )

1 rad ee

Ra f

1( )

m ri rad m r

m

sn

i

i j

t t t tt t

I IeA A A eA AeA F I I

28


3. International Reference System : Corrections for Impurities

• The equivalent activity of the main radionuclide can then be written

• As a consequence the correction due to the impurities can only be taken into account if the equivalent activities for the impurities are known.

The International Reference System (SIR)

29

rad

rad

radRa 0

( )( )Ra f e

e rad ( )1 rad ef

( )1

m r

i rad m r

mi

nj i

is

t tt t

t te F I I A A eA A A AI Ie

29


3. International Reference System : SIR Efficiency Curve

• The detection efficiency of the chamber for a given radionuclide can be written in function of the emission probabilities and of the energies of the radiations detected as

• Under the hypothesis that the detection efficiency varies monotonously with the energy as


30

KE E Ei i ii

rad1

n

i i iiip E E

30



• The detection efficiency becomes

or

with


31

( )1 i

ii

Ef KE

rad1 1

( )( ) 1 i

i ii

n n

i ii ii iK K i

EE E KEp pE EE

rad1

i

n

iiiK i fp EE

31



• The current produced in the ionization chamber by the sample has the expression

• As this current is proportional to the sample activity, the detection efficiency of the chamber is simply equal to


measurements

32

0Ra( ) ( )s f s Ra f s

e e( ) ( ) 1 1m rs m

jt t t t KI I A F I I AA Ae e

rad1 e

1i

n

iiiK Ki f A

p EE

32



• For convenience the constants K and K’ are so chosen that the energies are expressed in MeV and the activities in kBq; then the efficiency becomes

• Which leads, for the factor f, to the expression


33

5

1 e610 1

i

n

iiii f Ap EE

5

1,e610 1

i

n

i iii ifAf pE E

pE E

33



• Pure g emitters are relatively seldom. Generally the samples are decaying at the same time by b emission and the bremsstrahlung should also be taken into account. Therefore the general expression for the f factor becomes


34

5

, ,1,e6

10 1j j

ji

n

i iii if pEAf pE E

pE E b b b

34



3535



3636



3737



3838



measurements

3939



40

Dimensions of the radium sources : L = 12 mmØ = 1,5 mm

40



41

Haute tension

Contrôle pas à pas Control

PC

Utilisateur

Référence de tension flottante isolée

Electromètre 642 KEITHLEY

Condensateurs de mesures Unité de contrôle BIPM

Equipement construit au BIPM

Equipement commercial Equipment

Chambre d’ionisation

SIR measurement set-up

Intégrateur R / C

41



42

226Radium 4 source ionization current with dV correction

106.4

106.5

106.6

106.7

106.8

106.9

107.0

107.1

avr-75 janv-78 oct-80 juil-83 mars-86 déc-88 sept-91 juin-94 mars-97 déc-99 sept-02 mai-05 févr-08 nov-10

Date of measurements

Val

ue (p

A)

Old SIR

Old SIR bis

Old SIR ter

New SIR currently in use

1 °/°°

Move of the SIR

42



measurements

43

SIR 226Ra source 5/4 ratio

3.13000

3.13200

3.13400

3.13600

3.13800

3.14000

3.14200

3.14400

avr-75 janv-78 oct-80 juil-83 mars-86 déc-88 sept-91 juin-94 mars-97 déc-99 sept-02 mai-05 févr-08 nov-10

Date of measurements

226 R

a 5/

4 ra

tio v

alue

5/4 ratio old SIR

5/4 ratio old SIR bis

5/4 ratio old SIR ter

New SIR currently in use

1 °/°°

43



44

1976 1980 1984 1988 1992 1996 2000 2004 2008105.5

106.0

106.5

107.0

Chamber no. 389 Chamber no. 488

Ioni

zatio

n cu

rren

t fro

m

the

226 R

a so

urce

no.

4 /

pA

1976 1980 1984 1988 1992 1996 2000 2004 2008-4

-2

0

2

4

Stability of 226Ra source no. 5 / no. 4

Year

Rel

. dev

iatio

nfro

m th

e m

ean

/ 10-4

44



45

520

525

530

535

540

545

550

555

560

565

570

575

580Registered SIR value

No 156Eu correction With 156Eu correction

equi

vale

nt a

ctiv

ity in

MB

qSIR result for 153Sm ampoule (T

1/2 = 46 h)

45



46

100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

I-12

5 C

e141 Gd-

153

Am

-241

Tl-2

01 B

a-13

3

Co-

57

I-12

3

Y

b-16

9

In-1

11H

g-20

3Ir

-192

I-13

1

Ru-

103

Cs-

134

Cs-

137

Nb-

95M

n-54

Sc-

46

Bi-2

07

F

e-59

Eu-

152

Y-8

8

Na-

24

Cd-

109

Sm

-153

Se-

75

M

o-99

Ce-

139 Ga-

67 Sn-

113

Sr-

85

Ho-

166m

Ag-

110m

Zn-

65 E

u-15

4

Sb-

124

Co-

60

Cr-

51

Tc-

99m

Res

pons

e of

the

SIR

IC

/ ph

oton

ene

rgy

(

a.u.

)

Photon energy / keV

46


BIPM.RI(II)-K1.I-131Degrees of equivalence for equivalent activity of 131I

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

NM

ISA

NM

IJ

LNE

-LN

HB

AN

STO

BA

RC

IRA

NIS

T

MK

EH

NP

L

LNM

RI

CIE

MA

T

PTB IFIN

KR

ISS

CM

I-IIR

BE

V

[Di =

(xi -

xR)]

/ (M

Bq)

-30

-20

-10

0

10

20

30

[Di /

xR)]

/ (kB

q / M

Bq)

Practical operation of the SIR

quality control andR a sources

SIR -T-04, 13

NMI findserror

SIR circular letter sentto the NM Is

(start of each year)SIR -M -01

Am poulessent d irect

to the B IPM

Reception and registration ofam poule

SIR-T-03, M-05

Collection from airport byauthorized personnel

SIR-T-02

Measurement in the SIRSIR-T-05, 13

im purityor

m easurem entproblem

Analys is of resultsSIR-T-07SIR-T-11

Production of Draft B report(KCW G)SIR-T-09

Publication of resultsin the KCDB

NMI resultsand uncerta inty

budget S IR -F-05/06

Im purity m easurem entS IR-T-06

Flow diagram for SIR Measurem ents in the BIPM ongoing key comparisons

NM I respondsusing B IPM/RI-

SIR-F-02

No furtheraction

NM I hasSIR

am poules

em ptyam poulessent to the

NMI

NO

SP LIT 4

Short halflife

YE S

YES

YES

NO

YES

YES

N O

NO

NO

Storage and ultim atedisposal of am poules

SIR-T-10

Storage withposs ible

rem easurem ent

YES

NO

YES

YES

Registration in the K CDBUpdate S IR database

SIR-T-08

Issue of SIR data sheet tothe NM I

NMI sendscom pleted

ADM -DO U-F-12

Agreem ent over datesand m ethod of

transportSIR-F-04

YES

NO

Adm inistrativearrangem ents

SIR-T-01

Transfer of am poulesSIR-T-12

NO

SIR 226Rad rapport 5/4

3,13000

3,13200

3,13400

3,13600

3,13800

3,14000

3,14200

3,14400

avr-75 janv-78 oct-80 juil-83 mars-86 déc-88 sept-91 juin-94 mars-97 déc-99 sept-02 mai-05 févr-08

Date des mesures SIR

Vale

ur d

u ra

ppor

t

Rapport 5/4 present SIR

Rapport 5/4 present SIR bisRapport 5/4 present SIR terNext new SIR1 °/°°

47



measurements

4848



4949



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BIPM, F-92310 SEVRES Sheet no. 1

International Reference System for the Activity Measurement of Gamma -Ray Emitting Nuclides (SIR)

Radionuclide: 222Rn Total number of withdrawn results: Half life adopted: T½ = (3.8235 ± 0.0003) d _______________________________________________________________________________________________________________________________________________________ Data reported by laboratory Ionization-chamber measurements carried out at BIPM Activity Ae which would produce the same ion current as the Ra source Labora- Ampoule Method of Reference Activity Rel. uncert. Date Relative Ae Combined uncert. of Ae tory number standardization date at ref. Category uncertainty date A B Ae(r12 + r22 + r32)½ (kBq) (r1,%) (r2,%) (r3, %) (kBq) (kBq) _______________________________________________________________________________________________________________________________________________________ IRA-METAS 222Rn0301 4g NaI counting 2001-03-06 12.62 0.4 2001-03-09 0.372 9996 55 IRA-METAS M222Rn5A1 press. IC, calib. by 4g NaI counting 2003-01-22 368.16 0.041 0.483 2003-01-27 0.170 10 043 52 id., calib. by def. sol. ang. (Picolo) meth. “ 367.07 0.041 0.304 “ 0.170 10 013 35 PTB 2005-1394 NaI detec., calib. by def. sol. ang. -spec. 2005-05-23 1067 0.094 0.92 2005-05-26 0.068 9908 92 …..

50



51

BIPM.RI(II)-K1.F-18, 2001 CCRI(II)-K3.F-18 and 2001 APMP.RI(II)-K3.F-18 Degrees of equivalence for equivalent activity of 18F

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

IRA

LNE-L

NHBBEV

NPL

CIEMAT

PTB

ANSTOCMI

NIST

INER

[Di =

(xi -

xR)]

/ (M

Bq)

-65

-52

-39

-26

-13

0

13

26

39

52

65

[Di /

xR] /

(kBq

/ M

Bq)

51



52

BIPM.RI(II)-K1.Se-75 and 1992 CCRI(II)-K2.Se-75Degrees of equivalence for equivalent activity of 75Se

-3

-2

-1

0

1

2

3

IRA

LNE-LNHB

BARCBIPM

CMI-IIR

CNEANMISA

IFINKRISS

LNMRI

NIMNIST

NMIJNPL

NRCMKEH

PTB RCVNIIM

-72

-48

-24

0

24

48

72

[Di /

xR)]

/ (k

Bq

/ MB

q)

[Di =

(x i

- x

R)]

/ (M

Bq)

N.B. Right-hand scale gives approximate values only

52



53

BIPM.RI(II)-K1.I-123 and 1983 EUROMET.RI(II)-K2.I-123 Degrees of equivalence for equivalent activity of 123I

-6

-4

-2

0

2

4

6

IRMM LNE-LNHB IRA PTB NPL

[Di =

(xi -

xR)]

/ (M

Bq)

-6

-4

-2

0

2

4

6

[Di

/ xR)]

/ (kB

q / M

Bq)

N.B. The right-hand axis gives approximate relative values only

53



54

BIPM.RI(II)-K1.Sb-124 Degrees of equivalence for equivalent activity of 124Sb

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

MKEH VNIIM LNE-LNHB

[Di =

(xi

- xR)]

/ (M

Bq)

-50

-40

-30

-20

-10

0

10

20

30

40

50

[Di /

x R)]

/ [kB

q/M

Bq]

N.B. The right-hand axis gives approximate relative values only

54


The BIPM and the International Reference System (SIR) for activity measurements

55

Thank you for your attention

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The BIPM and the International Reference System (SIR) for activity measurements

56

The BIPM and the International Reference System (SIR) for activity measurements

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