The BIPM and the International Reference System (SIR) for activity measurements
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Transcript of 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
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Bureau International des Poids et Mesures
I. Presentation of the BIPM
Bureau International des Poids et MesuresDecay Data Evaluation Project Workshop,
8th October 2012Laboratoire National de Métrologie et d’Essais, Paris
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Bureau International des Poids et Mesures
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
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Bureau International des Poids et Mesures
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).
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Bureau International des Poids et Mesures
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.
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Bureau International des Poids et Mesures
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.
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Bureau International des Poids et Mesures
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.
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Bureau International des Poids et Mesures
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.
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Bureau International des Poids et Mesures
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
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Bureau International des Poids et Mesures
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.
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Bureau International des Poids et Mesures
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
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Bureau International des Poids et Mesures
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:
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Bureau International des Poids et Mesures
BIPM current activities (1/3)
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Bureau International des Poids et Mesures
BIPM current activities (2/3)
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.
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Bureau International des Poids et Mesures
BIPM current activities (3/3)
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.
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II. 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
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Bureau International des Poids et Mesures
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
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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.
The International Reference System (SIR) for activity
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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.
The International Reference System (SIR) for activity
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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.
The International Reference System (SIR) for activity
measurements
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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
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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.
The International Reference System (SIR) for activity measurements
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3. International Reference System : Operating procedure
• 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.
The International Reference System (SIR) for activity
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3. International Reference System : Operating procedure
• 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.
The International Reference System (SIR) for activity measurements
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3. International Reference System : Operating procedure
• 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:
The International Reference System (SIR) for activity measurements
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3. International Reference System : Operating procedure
•
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.
The International Reference System (SIR) for activity measurements
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0RaRa f
s f
( )e
( )s
)
)
((
m
m rs
jt t
t tF I I
I IeAeA
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Bureau International des Poids et Mesures
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)
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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
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Bureau International des Poids et Mesures
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
The International Reference System (SIR) for activity measurements
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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
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Bureau International des Poids et Mesures
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)
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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
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Bureau International des Poids et Mesures
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
The International Reference System (SIR) for activity measurements
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KE E Ei i ii
rad1
n
i i iiip E E
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Bureau International des Poids et Mesures
3. International Reference System : SIR Efficiency Curve
• The detection efficiency becomes
or
with
The International Reference System (SIR) for activity measurements
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( )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
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Bureau International des Poids et Mesures
3. International Reference System : SIR Efficiency Curve
• 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
The International Reference System (SIR) for activity
measurements
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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
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Bureau International des Poids et Mesures
3. International Reference System : SIR Efficiency Curve
• 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
The International Reference System (SIR) for activity measurements
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5
1 e610 1
i
n
iiii f Ap EE
5
1,e610 1
i
n
i iii ifAf pE E
pE E
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Bureau International des Poids et Mesures
3. International Reference System : SIR Efficiency Curve
• 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
The International Reference System (SIR) for activity measurements
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5
, ,1,e6
10 1j j
ji
n
i iii if pEAf pE E
pE E b b b
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The International Reference System (SIR) for activity measurements
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The International Reference System (SIR) for activity measurements
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The International Reference System (SIR) for activity measurements
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The International Reference System (SIR) for activity measurements
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The International Reference System (SIR) for activity
measurements
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The International Reference System (SIR) for activity measurements
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Dimensions of the radium sources : L = 12 mmØ = 1,5 mm
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Bureau International des Poids et Mesures
The International Reference System (SIR) for activity measurements
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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
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The International Reference System (SIR) for activity measurements
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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
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Bureau International des Poids et Mesures
The International Reference System (SIR) for activity
measurements
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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 °/°°
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The International Reference System (SIR) for activity measurements
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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
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The International Reference System (SIR) for activity measurements
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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)
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The International Reference System (SIR) for activity measurements
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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
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Bureau International des Poids et Mesures
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 °/°°
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The International Reference System (SIR) for activity
measurements
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The International Reference System (SIR) for activity measurements
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The International Reference System (SIR) for activity measurements
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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 …..
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The International Reference System (SIR) for activity measurements
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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)
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The International Reference System (SIR) for activity measurements
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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
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The International Reference System (SIR) for activity measurements
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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
Bureau International des Poids et Mesures
The International Reference System (SIR) for activity measurements
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
Bureau International des Poids et Mesures
The BIPM and the International Reference System (SIR) for activity measurements
55
Thank you for your attention
55
Bureau International des Poids et Mesures
The BIPM and the International Reference System (SIR) for activity measurements
56