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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

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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.

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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

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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

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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

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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

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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].

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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

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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].

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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).

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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.

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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.

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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