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Metrologia 2013, 50, Tech. Suppl. Series 06023
1/18
Activity measurements of the radionuclide 99m
Tc
for the CNEA, Argentina and the LNMRI/IRD, Brazil in the ongoing comparison
BIPM.RI(II)-K4.Tc-99m
C. Michotte1, M. Nonis
1, P. Arenillas
2, G. Cerutti
2, Carlos José da Silva
3, Paulo Alberto Lima
da Cruz3, Denise Simões Moreira
3, Akira Iwahara
3, José Ubiratan Delgado
3, Roberto Poledna
3,
Ronaldo Lins da Silva3, Antônio Eduardo de Oliveira
3, Régio dos Santos Gomes
3.
1
Bureau International des Poids et Mesures (BIPM), 2 Radioisotope Metrology Laboratory, Comisión Nacional de Energía Atómica (Argentina)
3 Laboratório Nacional de Metrologia das Radiações Ionizantes,
Instituto de Radioproteção e Dosimetria (Brazil).
Abstract
In 2012 and 2013, comparisons of activity measurements of 99m
Tc using the
Transfer Instrument of the International Reference System (SIRTI) took
place, respectively, at the Comisión Nacional de Energía Atómica (CNEA,
Argentina) and at the Laboratório Nacional de Metrologia das Radiações
Ionizantes, Instituto de Radioproteção e Dosimetria (LNMRI/IRD, Brazil).
Ampoules containing about 21 kBq (CNEA) and 66 kBq (LNMRI/IRD) of a 99m
Tc solution were measured in the SIRTI for more than two half-lives.
The comparison, identifier BIPM.RI(II)-K4.Tc-99m, is linked to the
BIPM.RI(II)-K1.Tc-99m comparison and the degrees of equivalence with
the key comparison reference value and between the present CNEA and
LNMRI/IRD results, the other K4 participants and the six participants in the
K1 comparison have been evaluated.
1. Introduction
Radionuclides are essential for nuclear medicine where very short-lived (much less than one
day) radionuclides are used, particularly for imaging. The use of nuclear medicine is
increasing with the accessibility of these radionuclides which are consequently of great
interest to the National Metrology Institutes (NMIs) in terms of the standardization and SI
traceability. However, sending ampoules of short-lived radioactive material to the Bureau
International des Poids et Mesures (BIPM) for measurement in the International Reference
System (SIR) [1] is only practicable for the NMIs that are based in Europe. Consequently, to
extend the utility of the SIR and enable other NMIs to participate, a transfer instrument
(SIRTI) has been developed at the BIPM with the support of the Consultative Committee for
Ionizing Radiation CCRI(II) Transfer Instrument Working Group [2].
The BIPM ongoing K4 comparison of activity measurements of 99m
Tc (half-life
T1/2 = 6.006 7 h; u = 0.001 h [3]) is based on the SIRTI, a well-type NaI(Tl) crystal calibrated
against the SIR, which is moved to each participating laboratory. The stability of the system is
Metrologia 2013, 50, Tech. Suppl. Series 06023
2/18
monitored using a 94
Nb reference source (T1/2 = 20 300 a; u = 1 600 a [4])1 from the Institute
for Reference Materials and Measurements (IRMM, Geel), which also contains the 93m
Nb
isotope. The 99m
Tc count rate above a low-energy threshold, defined by the
93mNb x-ray peak
at 16.6 keV, is measured relative to the 94
Nb count rate above the same threshold. Once the
threshold is set, a brass liner is placed in the well to suppress the 93m
Nb contribution to the 94
Nb stability measurements. It should be noted that the uncertainty associated with the 94
Nb
decay correction is negligible. The 99m
Tc SIR ampoule is placed in the detector well with the
brass liner to suppress the 99m
Tc x-ray peaks from the counts. No extrapolation to zero energy
is carried out as all the measurements are made with the same threshold setting. The live-time
technique using the MTR2 module from the Laboratoire National d’Essais – Laboratoire
National Henri Becquerel, France (LNE-LNHB) [5] is used to correct for dead-time losses,
taking into account the width of the oscillator pulses. The standard uncertainty associated with
the live-time correction, due to the effect of finite frequency of the oscillator, is negligible.
Similarly to the SIR, a SIRTI equivalent activity AE is deduced from the 99m
Tc and 94
Nb
counting results and the 99m
Tc activity measured by the NMI: AE corresponds to the inverse of
a detection efficiency, i.e. AE is the activity of the source measured by the participant divided
by the 99m
Tc count rate in the SIRTI expressed relatively to the 94
Nb count rate. The possible
presence of 99
Mo in the solution should be accounted for using -spectrometry measurements
carried out by the NMI.
The protocol [6] for the BIPM.RI(II)-K4.Tc-99m comparison is available in the key
comparison database of the CIPM Mutual Recognition Arrangement [7]. Publications
concerning the details of the SIRTI and its calibration against the SIR are in preparation [8,
9].
2. Participants
As detailed in the protocol, participation in the BIPM.RI(II)-K4 comparisons mainly concerns
member states that are located geographically far from the BIPM and that have developed a
primary measurement method for the radionuclide of concern. However, at the time of the
comparison the National Metrology Institute (NMI) may decide for convenience to use a
secondary method, for example a calibrated ionization chamber. In this case, the traceability
of the calibration needs to be clearly identified.
The present comparison took place at the Radioisotope Metrology Laboratory, Comisión
Nacional de Energía Atómica (CNEA), Argentina, in November 2012 and at the Laboratório
Nacional de Metrologia das Radiações Ionizantes, Instituto de Radioproteção e Dosimetria
(LNMRI/IRD), Brazil, in July 2013. Through the calibration of the SIRTI against the SIR at
the BIPM, this K4 comparison is linked to the BIPM.RI(II)-K1.Tc-99m comparison and thus
degrees of equivalence between the CNEA, the LNMRI/IRD and all the K1 participants can
also be evaluated. Previous BIPM.RI(II)-K4.Tc-99m comparisons took place at the NIST,
KRISS, NMIJ and NIM [10 – 13].
1 Hereafter, the last digits of the standard uncertainties are given in parenthesis.
Metrologia 2013, 50, Tech. Suppl. Series 06023
3/18
3. The SIRTI at the CNEA
The reproducibility and stability of the SIRTI at the CNEA were checked by measuring the
count rate produced by the reference 94
Nb source No. 1, the threshold position (defined by the 93m
Nb x-ray peak), the background count rate, the frequency of the oscillator No. 1 for the
live-time correction and the room temperature as shown in Figure 1. The plots shown in the
Figure represent the differences from the values indicated in the figure caption, using the
appropriate units, as given, for each quantity measured.
Figure 1: Fluctuation of the SIRTI at the CNEA. Black squares:
94Nb No.1 count rate / s
–1
above 8480 s–1
; circle: threshold position / channel above 90 channels; stars: room
temperature / °C above 20 °C; open squares: background count rate / s–1
above
70 s–1
; triangles: frequency of the oscillator No.1 / Hz above 999 980 Hz.
The SIRTI was very stable during the comparison, except maybe a slight increase in the 94
Nb
count rate on the last day. The mean 94
Nb No. 1 count rate, corrected for live-time,
background and decay, measured at the CNEA is 8493.3 (9) s–1
which is in close agreement
with the mean since the set-up of the system in March 2007, 8493.34 (26) s–1
. The 94
Nb count
rate could not be checked at the BIPM after the comparison, because the SIRTI electronics
did not come back yet to the BIPM because of customs problems.
4. The SIRTI at the LNMRI/IRD
The electronics and reference 94
Nb source No. 1 of the SIRTI have been in Argentina since
the comparison which took place there in 2012. In consequence, a new counting system was
assembled using copies of the SIRTI electronic modules, new National Instrument scalers (to
replace the ORTEC 994 double scaler) and the reference 94
Nb source No. 3 available at the
BIPM. The core elements of the SIRTI, i.e. the NaI(Tl) detector and the brass liner, travelled
back from Argentina and were available for the comparison in Brazil. This new assembly was
10/11/2012 11/11/2012 12/11/2012 13/11/2012 14/11/2012
0
10
20
30
40
Nb-94 Background
Threshold Oscillator freq.
Temperature
Date
Metrologia 2013, 50, Tech. Suppl. Series 06023
4/18
validated at the BIPM by measuring the 94
Nb source No. 3 and comparing the results with
previous measurements of this source at the BIPM (see Figure 2).
Figure 2: Measurements of the reference 94
Nb source No. 3. The open diamond indicates the
measurement carried out with the copy of the SIRTI electronics before the
exportation to Brazil. The full line corresponds to the weighted mean of all data
(7633.3 (6) s–1
).
The reproducibility and stability of the SIRTI at the LNMRI/IRD were checked by measuring
the count rate produced by the reference 94
Nb source No. 3, the threshold position (defined by
the 93m
Nb x-ray peak), the background count rate, the frequency of the oscillator No. 4 for the
live-time correction and the room temperature as shown in Figure 3. The plots shown in the
Figure represent the differences from the values indicated in the figure caption, using the
appropriate units, as given, for each quantity measured.
Although the threshold position slowly decreased over the comparison, the SIRTI 94
Nb count
rate remained quite stable. The room temperature and the frequency of the oscillator for the
live-time correction were very stable. The background level was more than twice the value
observed at the BIPM and is the highest observed to date.
The mean 94
Nb No. 3 count rate, corrected for live-time, background and decay, measured at
the LNMRI/IRD is 7632.6 (10) s–1
which is in close agreement with the mean since the set-up
of the system in March 2007, 7632.5 (5) s–1
. Finally, the 94
Nb count rate was checked on the
return of the SIRTI to the BIPM after the comparison, giving a slightly lower value of 7630.3
(8) s–1
. In consequence, a relative uncertainty of 4 × 10–4
was added in Table 4 to take into
account of a possible change of response of the SIRTI.
7626
7628
7630
7632
7634
7636
7638
7640
oct.-0
6
févr.
-08
juil.
-09
nov.-
10
avr.
-12
aoû
t-1
3
Co
rre
cte
d N
b-9
4 c
ou
nti
ng
ra
te / s
-1
date
Nb source No.3
Metrologia 2013, 50, Tech. Suppl. Series 06023
5/18
Figure 3: Fluctuation of the SIRTI at the LNMRI/IRD. Black squares: 94
Nb No.3 count rate
/ s–1
above 7600 s–1
; circle: threshold position / channel above 90 channels; stars:
room temperature / °C above 20 °C; open squares: background count rate / s–1
above 180 s–1
; triangles: frequency of the oscillator No.4 / Hz above 999 980 Hz.
5. The 99m
Tc solutions standardized at the CNEA and LNMRI/IRD
Details regarding the standardized solutions are shown in Table 1, including any impurities,
when present, as identified by the laboratory. At the CNEA, the density and volume of the
solution in the ampoule conformed to the K4 protocol requirements. Small drops (max. 2 mm
diameter) of solution were observed in the cylindrical part of the ampoule but this should have
a negligible effect on the SIRTI measurement. At the LNMRI/IRD the volume of the solution
in the ampoule was slightly higher than the K4 protocol requirements. In consequence, the
uncertainty contribution related to the ampoule filling height has been increased to 7 × 10–4
(see Table 4). Two relatively large drops of solution were observed in the ampoule neck but
could be removed by centrifugation of the ampoule.
Table 1: Characteristics of the 99m
Tc solutions
NMI Ampoule
number
Solvent
/ mol dm–3
Carrier
/ g g–1
Density at
20 °C
/ g cm–3
Mass
/ g
99Mo
impurity*
CNEA B H2O NaCl /
15.2
1 3.592 67 < 0.001
Volume = 3.592 67 cm3
LNMRI/IRD 91L13 HCl / 0.01 – 1.000 1 3.769 611
– Volume = 3.769 23 cm
3
* Ratio of the 99
Mo activity to the 99m
Tc activity at the reference date
03/07/2013 04/07/2013 05/07/2013 06/07/2013
0
10
20
30
40
50
Nb-94
Threshold
Temperature
Background
Oscillator freq.
Date
Metrologia 2013, 50, Tech. Suppl. Series 06023
6/18
At the CNEA, the 99m
Tc solution of the comparison should have been standardized by the
coincidence method. However, a failure of the preamplifier of the proportional counter made
this measurement impossible and the activity of the 99m
Tc solution was deduced from the
measurement with a HPGe -ray spectrometer and an overall dilution factor of 304.08 (12).
The HPGe efficiency at 140.5 keV was obtained by MCNP Monte-Carlo code, adjusted with
an experimental curve measured with 152
Eu and 57
Co sources. The 152
Eu point source is
traceable to the CNEA digital coincidence system 4(PC) (NaI). The 57
Co source is
traceable to the PTB.
At the LNMRI/IRD, the 99m
Tc activity was deduced from the measurement of the mother
solution in an IG11 ionization chamber (IC) and a dilution factor of 144.626 51. The
ionization chamber had been calibrated for 99m
Tc by the LNMRI/IRD one month prior to the
K4 comparison by 4β(LS)-(NaI) anticoincidence counting method [8].
The measurement results are summarized in Tables 2, 3a and 3b while the uncertainty budget
of the LNMRI/IRD primary measurement is given in appendix 2.
Table 2: The 99m
Tc standardization by the participants
NMI
Measurement
method
ACRONYM*
Activity
/ kBq
Standard
uncert.
/ kBq
Reference
date YYYY-MM-DD
Half-life
used by the
NMI / h
CNEA HPGe efficiency
curve #
UA-GH-GR-00-00-00 20.81 0.28
2012-11-12
16:00 UTC 6.0067 (10)
LNMRI/IRD
IC calibrated 4P-IC-GR-00-00-00
in June 2013 by
4β(LS)-(NaI)
anti-coinc. 4P-LS-CE-NA-GR-AC
65.79 0.72 2013-07-04
12:00 UTC 6.0067 (10)
* See appendix 1 #
obtained using Monte-Carlo simulations and, 152
Eu and 57
Co sources traceable to the CNEA
coincidence system (4P-PC-BP-NA-GR-DC) and the PTB respectively (see text).
Table 3a: The CNEA uncertainty budget for the activity measurement of ampoule B
(November 2012)
Uncertainty contributions due to
Evaluation
method
Relative standard
uncertainties 104
Counting statistics A 80
Weighing B 35
Efficiency B 100
Relative combined standard uncertainty 130
Metrologia 2013, 50, Tech. Suppl. Series 06023
7/18
Table 3b: The LNMRI/IRD uncertainty budget for the activity measurement of ampoule
91L13 (July 2013)
Uncertainty contributions due to
Evaluation
method
Relative standard
uncertainties 104
Counting statistics A 9
Weighing B 5
Background B 15
Counting time B 5
Decay correction of 99m
Tc B 0.4
Calibration factor of IC (see appendix 2) B 98
IC stability with 226
Ra source B 12
Relative combined standard uncertainty 110
6. The 99m
Tc measurements in the SIRTI at the CNEA and the LNMRI/IRD
The maximum count rate corrected for live-time in the NaI(Tl) was 9390 s–1
and 18 160 s–1
at
the CNEA and the LNMRI/IRD respectively, which conform with the limit of 20 000 s–1
set
in the protocol [6]. In addition a relative standard uncertainty of 2 × 10–4
and 4 × 10–4
was
added to take account of a possible drift in the SIRTI at a high count rate [9], for the CNEA
and the LNMRI/IRD respectively. The time of each TI measurement was obtained from the
synchronization of the laptop with the official time, transmitted by telephone, in Argentina
and with a time server, in Brazil.
In principle, the live-time correction should be modified to take into account the decaying
count rate [15]. In the present experiments, the duration of the measurements made at high
rate has been limited to 1000 s so that the relative effect of decay on the live-time correction
is less than one part in 104.
The 99m
Tc measurement results are shown in Figures 4a and 4b. The reduced chi-squared
value evaluated for these series of measurements is 1.1 and 0.90 for CNEA and LNMRI/IRD
respectively, showing that the data are consistent. For the LNMRI/IRD, the results in the last
two hours of measurement seem slightly higher and are sensitive to the background count
rate. However, these measurements have a larger statistical uncertainty and have negligible
influence on the final result which is the weighted mean of all results.
The uncertainty budgets for the SIRTI measurements of the 99m
Tc ampoule are given in
Table 4a and 4b. Further details are given in reference [9].
Metrologia 2013, 50, Tech. Suppl. Series 06023
8/18
Figure 4a: The 99m
Tc measurement results in the SIRTI at the CNEA. The 99m
Tc measurement
uncertainty and the 94
Nb mean count rate uncertainty, which are both constant over
all the measurements, are not included in the uncertainty bars shown on the graph.
Figure 4b: As for Figure 4a, but for the LNMRI/IRD.
13.13
13.14
13.15
13.16
13.17
13.18
13.19
0 5 10 15 20 25
AE
/ kB
q
Time from reference date / h
12.695
12.700
12.705
12.710
12.715
12.720
12.725
12.730
12.735
12.740
5 10 15 20 25
AE
/ kB
q
Time from reference date / h
Metrologia 2013, 50, Tech. Suppl. Series 06023
9/18
Table 4a: Uncertainty budget for the SIRTI measurement at the CNEA
Uncertainty contributions
due to Comments
Evaluation
method
Relative
standard
uncertainties
104
99mTc measurement ratio
including live-time,
background , decay
corrections
Standard uncertainty of the weighted mean of
37 measurements, taking into account the
correlation due to the 99m
Tc half-life A 2.1
Nb reference source
measurements Weighted standard deviation of 4 series, each
series consisting of 10 measurements A 0.8
Long-term stability of
the SIRTI Weighted standard deviation of 56 series,
each series consisting of 10 measurements A 0.3
Effect of decay on the
live-time correction Maximum measurement duration evaluated
from [16] B < 1
SIRTI drift at high count
rate Mean possible drift over all
99mTc
measurements at the LNMRI/IRD. B 2
Ampoule dimensions From the IRMM report [17] and sensitivity
coefficients from Monte-Carlo simulations B 7
Ampoule filling height Solution volume is 3.6 (1) cm3; sensitivity
coefficients from Monte-Carlo simulations B 6
Solution density Between 1 g/cm3 and 1.01 g/cm
3 as requested
in the protocol; sensitivity coefficients from
Monte-Carlo simulations B 0.8
Droplets on the walls of
the ampoule Evaluated by Monte-Carlo simulation B < 1
Relative combined standard uncertainty 10
7. Comparison result and degrees of equivalence
The comparison result is taken as the weighted mean of all the measured AE values. The
standard uncertainty u(AE) is obtained by adding quadratically the SIRTI combined
uncertainty from Table 4 and the uncertainty stated by the participant for the 99m
Tc
measurement (see Table 2). The correlation between the CNEA or the LNMRI/IRD and the
BIPM due to the use of the same 99m
Tc half-life is negligible in view of the small contribution
of this half-life to the combined uncertainty of the measurements. The K4 comparison result is
given in Table 5 as well as the linked result Ae in the BIPM.RI(II)-K1.Tc-99m comparison
which was obtained by multiplying AE by the linking factor L = 12 173 (20). The linking
factor was obtained through the measurement of three 99m
Tc ampoules from the LNE-LNHB
and the NPL in both the SIRTI and the SIR [10].
Metrologia 2013, 50, Tech. Suppl. Series 06023
10/18
Table 4b: Uncertainty budget for the SIRTI measurement at the LNMRI/IRD
Uncertainty contributions
due to Comments
Evaluation
method
Relative
standard
uncertainties
104
99mTc/
94Nb measurement
ratio including live-time,
background , decay
corrections and
threshold setting
Standard uncertainty of the weighted mean of
34 measurements, taking into account the
correlation due to the 99m
Tc half-life A 2.7
Long-term stability of
the SIRTI
Weighted standard deviation of 56 series,
each series consisting of 10 measurements A 0.3
Nb reference source
No.3 instead of No.1 Weighted standard deviation of 15 series,
each series consisting of 10 measurements A 0.7
Effect of decay on the
live-time correction Maximum measurement duration evaluated
from [16] B < 1
SIRTI drift at high count
rate Mean possible drift over all
99mTc
measurements at the LNMRI/IRD. B 4
Possible shift of SIRTI
response Ratio of responses before and after the
comparison B 4
Ampoule dimensions From the IRMM report [17] and sensitivity
coefficients from Monte-Carlo simulations B 7
Ampoule filling height Solution volume is 3.77 cm3; sensitivity
coefficients from Monte-Carlo simulations B 7
Solution density Between 1 g/cm3 and 1.01 g/cm
3 as requested
in the protocol; sensitivity coefficients from
Monte-Carlo simulations B 0.8
Relative combined standard uncertainty 12
Table 5: BIPM.RI(II)-K4.Tc-99m comparison results and link to the BIPM.RI(II)-K1.Tc-99m
comparison
NMI, date
Measurement
method
ACRONYM*
Solution
volume
/cm3
AE
/kBq
u(AE)
/kBq
Linked Ae
/kBq
u(Ae)
/kBq
CNEA,
Nov. 2012
HPGe efficiency
curve #
UA-GH-GR-00-00-00 3.592 67 13.16 0.17 160 200 2 100
LNMRI/IRD,
July 2013
Ionization chamber 4P-IC-GR-00-00-00 calibrated by
4β(LS)-(NaI)
anticoincidence 4P-LS-CE-NA-GR-AC
3.769 23 12.71 0.14 154 700 1 700
* See appendix 1 #
obtained using Monte-Carlo simulations and, 152
Eu and 57
Co sources traceable to the CNEA
coincidence system (4P-PC-BP-NA-GR-DC) and the PTB respectively (see text).
Metrologia 2013, 50, Tech. Suppl. Series 06023
11/18
Every participant in the K4 comparison is entitled to have one result included in the key
comparison database (KCDB) as long as the laboratory is a signatory or designated institute
listed in the CIPM MRA. Normally, the most recent result is the one included. Any participant
may withdraw its result only if all the participants agree.
The key comparison reference value (KCRV) for 99m
Tc has been defined in the frame of the
BIPM.RI(II)-K1.Tc-99m comparison using direct contributions to the SIR. The most recent
updated value is 153 240 (220) kBq as detailed in reference [18]. The LNMRI/IRD K4 result
agrees with the KCRV within one standard uncertainty.
The degree of equivalence of a particular NMI, i, with the KCRV is expressed as the
difference Di with respect to the KCRV
KCRVe ii AD (1)
and the expanded uncertainty (k = 2) of this difference, Ui , known as the equivalence
uncertainty, hence
)(2 ii DuU , (2)
taking correlations into account as appropriate [19].
The degree of equivalence between any pair of NMIs, i and j, is expressed as the difference
Dij in their results
jijiij AADDD ee (3)
and the expanded uncertainty of this difference Uij where
),(2-4)(4 ee
2222
jijiijij AAuuuDuU (4)
where any obvious correlations between the NMIs (such as a traceable calibration) are
subtracted using the covariance u(Aei, Aej), as is the correlation coming from the link of the
SIRTI to the SIR. The covariance between two participants in the K4 comparison is given by
u(Aei, Aej) = Aei Aej (uL /L)2
(5)
where uL is the standard uncertainty of the linking factor L given above. However, the CCRI
decided in 2011 that these pair-wise degrees of equivalence no longer need to be published as
long as the methodology is explained.
Table 6 shows the matrix of the degrees of equivalence with the KCRV as they will appear in
the KCDB. It should be noted that for consistency within the KCDB, a simplified level of
nomenclature is used with Aei replaced by xi. The introductory text is that agreed for the
comparison. The graph of the degrees of equivalence with respect to the KCRV (identified as
xR in the KCDB), is shown in Figure 5. The graphical representation indicates in part the
degree of equivalence between the NMIs but obviously does not take into account the
correlations between the different NMIs.
Metrologia 2013, 50, Tech. Suppl. Series 06023
12/18
Conclusion
The BIPM ongoing key comparison for 99m
Tc, BIPM.RI(II)-K4.Tc-99m, currently comprises
six results and is linked to the BIPM.RI(II)-K1.Tc-99m comparison. The last two K4 results
have been analysed with respect to the KCRV determined for this radionuclide in the frame of
the K1 comparison, and with respect to the other six results of the K1 comparison and the
other K4 comparison results. The degrees of equivalence have been approved by the CCRI(II)
and are published in the BIPM key comparison database.
Other results may be added when other NMIs contribute with 99m
Tc activity measurements to
the K4 or K1 comparisons or take part in other linked Regional Metrology Organization
comparisons. It should be noted that the final data in this paper, while correct at the time of
publication, will become out-of-date as NMIs make new comparisons. The formal results
under the CIPM MRA [7] are those available in the KCDB.
Metrologia 2013, 50, Tech. Suppl. Series 06023
13/18
Table 6. Table of degrees of equivalence and introductory text for 99m
Tc
Key comparison BIPM.RI(II)-K1.Tc-99m
MEASURAND :
Equivalent activity of 99m
Tc
Key comparison reference value: the SIR reference value for this radionuclide is xR = 153.24 MBq, with a standard uncertainty uR = 0.22 MBq.
xR is computed as the mean of the results obtained by primary methods.
The degree of equivalence of each laboratory with respect to the reference value is given by a pair of terms: Di = (xi - xR) and Ui, its expanded uncertainty (k = 2), both expressed inMBq, with n the number of laboratories, Ui = 2((1-2/n)ui
2 + (1/n
2)ui
2)1/2
when each laboratory has contributed to the reference value (see Final Report).
When required, the degree of equivalence between two laboratories is given by a pair of numbers: Dij = Di - Dj = (xi - xj) and Uij, its expanded uncertainty (k = 2), both expressed in MBq. The approximation Uij
2 ~ 2
2(ui
2 + uj
2) may be used.
Linking BIPM.RI(II)-K4.Tc-99m to BIPM.RI(II)-K1.Tc-99m
The value xi is the SIRTI equivalent activity for laboratory i participant in BIPM.RI(II)-K4.Tc-99m multiplied by the linking factor to BIPM.RI(II)-K1.Tc-99m (see Final report).
The degree of equivalence of laboratory i participant in BIPM.RI(II)-K4.Tc-99m with respect to the key comparison reference value is given by a pair of terms: Di = (xi - xR) and Ui, its expanded uncertainty (k = 2), both expressed in MBq.
The approximation Ui = 2(ui2 + uR
2)1/2
is used in the following table.
When required, the degree of equivalence between two laboratories i and j, one participant in BIPM.RI(II)-K1.Tc-99m and one in BIPM.RI(II)-K4.Tc-99m, or both participant in BIPM.RI(II)-K4.Tc-99m, is given by a pair of terms: Dij = Di - Dj and Uij, its expanded uncertainty
(k = 2), both expressed in MBq, where Uij = 2(ui2 + uj
2 - 2xixj(ul/l)
2)1/2
with ul being the uncertainty of the linking factor l when both laboratories are linked.
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These statements make it possible to extend the BIPM.RI(II)-K1.Tc-99m matrices of equivalence to the other participants in BIPM.RI(II)-K4.Tc-99m.
Lab i
Di Ui / MBq IRA 0.6 1.7
BEV 2.4 2.7 MKEH 1.2 3.3 PTB -0.5 1.1 LNE-LNHB -0.1 1.3 NPL 0.1 1.6
NIST -0.4 1.5 KRISS 0.9 2.8
NMIJ -0.8 2.2 NIM -0.1 2.4 CNEA 7.0 4.2 LNMRI/IRD 1.5 3.4
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Figure 5. Graph of degrees of equivalence with the KCRV for 99m
Tc
(as it appears in Appendix B of the MRA)
N.B. The right-hand axis gives approximate relative values only
-45
-30
-15
0
15
30
45
60
75
90
-6
-4
-2
0
2
4
6
8
10
12IR
A
BE
V
MK
EH
PT
B
LN
E-L
NH
B
NP
L
NIS
T
KR
ISS
NM
IJ
NIM
CN
EA
LN
MR
I/IR
D
[Di/x
R]
/ (k
Bq
/MB
q)
[Di=
(x
i-
xR)]
/ (
MB
q)
BIPM.RI(II)-K1.Tc-99m and BIPM.RI(II)-K4.Tc-99mDegrees of equivalence for equivalent activity of 99mTc
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References
[1] Ratel G., 2007, The Système International de Référence and its application in key
comparisons, Metrologia 44(4), S7-S16.
[2] Remit of the CCRI(II) Transfer Instrument Working Group, 2009, CCRI(II) working
document CCRI(II)/09-15.
[3] Bé M.-M., Chisté V., Dulieu C., Browne E., Chechev V., Kuzmenko N., Helmer R.,
Nichols A., Schönfeld E., Dersch R., 2004, Table of radionuclides,
Monographie BIPM-5, volume 1.
[4] NUDAT2.5, National Nuclear Data Center, Brookhaven National Laboratory, based on
ENSDF and the Nuclear Wallet Cards.
[5] Bouchard J., 2000, Appl. Radiat. Isot. 52, 441-446.
[6] Protocol for the ongoing comparison of 99m
Tc on site at the NMI, BIPM.RI(II)-K4.Tc-
99m, with the SIR Transfer Instrument. Published on the CIPM MRA KCDB website.
[7] CIPM MRA: Mutual recognition of national measurement standards and of calibration
and measurement certificates issued by national metrology institutes, International
Committee for Weights and Measures, 1999, 45 pp. http://www.bipm.org/pdf/mra.pdf.
[8] da Silva, C.J., Iwahara, A., Poledna, R., Bernardes, E.M.O., de Prinzio, M.A.R,
Delgado, J.U., Lopes, R.T., 2008, Standardization of Am-241, Sb-124 and I-131 by live-
timed anticoincidence counting with extending dead time, Appl. Radiat. Isot. 66, 886-
889
[9] Michotte C. et al., The SIRTI, a new tool developed at the BIPM for comparing activity
measurements of short-lived radionuclides world-wide, Rapport BIPM in preparation.
[10] Michotte C. et al., Calibration of the SIRTI against the SIR and trial comparison of 99m
Tc at the NPL. In preparation.
[11] Michotte C., Fitzgerald R., 2010, Activity measurements of the radionuclide 99m
Tc for
the NIST, USA in the ongoing comparison BIPM.RI(II)-K4.Tc-99m, Metrologia
47, Tech. Suppl., 06027
[12] Michotte C., Tae Soon Park, K.B. Lee, Jong-Man Lee and Sang Han Lee, 2012,
Comparison of 99m
Tc activity measurements at the KRISS using the new SIRTI of the
BIPM, Appl. Radiat. and Isot. 70, 1820-1824.
[13] Michotte C., Sato Y., Unno Y., Yunoki A., 2012, Activity measurements of the
radionuclide 99m
Tc for the NMIJ, Japan, in the ongoing comparison BIPM.RI(II)-K4.Tc-
99m, Metrologia 49, Tech. Suppl., 06013
[14] Michotte C., Nonis M., Liang J.C., Chen J., Liu H.R., Zhang M., Zhao Q., Yang Y.D.,
2013, Activity measurements of the radionuclide 99m
Tc for the NIM, China in the
ongoing comparison BIPM.RI(II)-K4.Tc-99m, Metrologia 50, Tech. Suppl., 06010
[15] Baerg A.P. et al., 1976, Live-timed anti-coincidence counting with extending dead-time
circuitry, Metrologia 12, 77-80.
[16] Fitzgerald R., 2009, The combined dead-time and decay effect on live-timed counting
systems with fixed, extending dead times. Transfer Instrument Working Group of the
CCRI(II), Document TIWG(II)/09-10.
[17] Sibbens G., 1991, A comparison of NIST/SIR-, NPL-, and CBNM 5 ml ampoules,
GE/R/RN/14/91, CEC-JRC Central Bureau for Nuclear Measurements, Belgium.
[18] Michotte C., Courte S., Ratel G., Moune M., Johansson L., Keightley J., 2010, Update
of the BIPM.RI(II)-K1.Tc-99m comparison of activity measurements for the
radionuclide 99m
Tc to include new results for the LNE-LNHB and the NPL, Metrologia
47, Tech. Suppl., 06026 .
[19] Ratel G., 2005, Evaluation of the uncertainty of the degree of equivalence, Metrologia
42, 140-144.
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Appendix 1. Acronyms used to identify different measurement methods
Each acronym has six components, geometry-detector (1)-radiation (1)-detector (2)-radiation
(2)-mode. When a component is unknown, ?? is used and when it is not applicable 00 is used.
Geometry acronym Detector acronym
4 4P proportional counter PC
defined solid angle SA press. prop. counter PP
2 2P liquid scintillation counting LS
undefined solid angle UA NaI(Tl) NA
Ge(HP) GH
Ge(Li) GL
Si(Li) SL
CsI(Tl) CS
ionization chamber IC
grid ionization chamber GC
bolometer BO
calorimeter CA
PIPS detector PS
Radiation acronym Mode acronym
positron PO efficiency tracing ET
beta particle BP internal gas counting IG
Auger electron AE CIEMAT/NIST CN
conversion electron CE sum counting SC
mixed electrons ME coincidence CO
bremsstrahlung BS anti-coincidence AC
gamma rays GR coincidence counting with efficiency tracing
CT
X - rays XR anti-coincidence counting with efficiency tracing
AT
photons (x + ) PH triple-to-double coincidence ratio counting
TD
photons + electrons PE selective sampling SS
alpha - particle AP high efficiency HE
mixture of various radiations
MX digital coincidence counting DC
Examples
method acronym
4(PC)-coincidence counting 4P-PC-BP-NA-GR-CO
4(PPC)-coincidence counting eff. trac. 4P-PP-MX-NA-GR-CT
defined solid angle -particle counting with a PIPS detector SA-PS-AP-00-00-00
4(PPC)AX-(Ge(HP))-anticoincidence counting 4P-PP-MX-GH-GR-AC
4 CsI-,AX, counting 4P-CS-MX-00-00-HE
calibrated IC 4P-IC-GR-00-00-00
internal gas counting 4P-PC-BP-00-00-IG
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Appendix 2. Uncertainty budget for the LNMRI/IRD primary measurement
4P-LS-CE-NA-GR-AC
Uncertainty contributions due to
Comments Evaluation
method
Relative
standard
uncertainties
104
Efficiency extrapolation
(fitting procedure) *
Uncertainty determined for an
extrapolation to β = 1using least-squares
method, Lavenberg-Marquardt algorithm
A 73
Background B 65
Decay correction of Tc-99m B 9
Mo-99 impurity (minimum
detectable activity) Determined by HPGe gamma-ray
spectrometry B < 0.1
Weighing Variation of values of balance B 5
Live-time B 1
Relative combined standard uncertainty 98
* Including the contribution of counting statistics of 20 10–4