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A new version of the tracer technique for absolute measurements of EC emitters
NUCLEM INSTRUMENTS & METHKNDS IN P"VS RESEARCH a
Nuclear Instruments and Methods in Physics Research A312 (1992) 59-63 North-Holland
A new version of the tracer technique for absolute measurements of EC emitters A. Chylinski
The Radioisctope Research Centre, 05-400 Swierk, Poland A new version of the tracer technique for measurements of EC radionuclides is presented. In the experiment, both the coincidence and anticoincidence methods were used simultaneously . This paper presents the results of " I Cs and "Fe activity measurements when traced by r39 Ce and by 54 Mn . The results obtained by the tracer technique depend on the amount of pure beta emitter relative to the tracer amount in the source . 1n this new version of the tracer technique, this question is eliminated . A 4 ,rrp-y coincidence counting system with liquid scintillation detectors in both channels was used and the coincidence extrapolation method was applied with an efficiency function for X-ray and electron counting in the liquid scintillator detector . 131
1 . Introduction
2. The counting method of
The tracer technique applied to p-emitters and specially to electron-capture (EC) radionuclides has not been very popular and successful up to now . This paper presents a successful new app:oach developed for the tracer technique to measure two EC radionuclides, 131 Cs and 55Fe. The new approach includes a new mathematical formulation, the application of two radionuclides as tracers for " I Cs and additional use of the anticoincidence method for verification . In all cases, liquid scintillation techniques have been used as the most convenient for this purpose . The liquid scintillation counter as well as the electronic system used are described elsewhere in these Proceedings [7].
The only results of decay are X-ray fotons, or Auger electrons, emitted alternatively . All the values of X and e A and for PK and (OK are given in Fig . 1 . To get the radioactive concentration of the radionuclide in question ( );) Cs in this case) the following procedure has to be applied . First, the activity of the tracer sample in the counting vial is measured and then the sample of 13i CS is added to the counting vial with the tracer sample and the total activity is measured. The activity of the "' Cs sample is obtained by subtracting the tracer activity from the total activity in the counting vial. From now on, we will use the following notation: NOT - decay rate for the tracer sample,
54Xe 131
Fig. 1 . Decay scheme for 131Cs.
PK = 0.843, EK,x
Cs
QEC 0.35 talc (MTW)
= 30 keV . E,:,,, =
0168-9002/92/$05 .00 O 1992 - Elsevier Science Publishers B.V . All rights reserved
24
keV,
w=
0.829 .
111(a). COINCIDENCE METHODS
A. Chyliilski / Ahsohite measarements of EC emitters
60
- count rate of X and CA channel with liquid scintillation counter, N,, -- count rate in the -y-channel with NATO scintillation counter, coincidence count rate, N, counting efficiency of X and CA in the liquid EKI scintillation counter for the tracer sample, counting efficiency in NATO scintillation EN counter, probability of an electron capture from the PKI K-shell, cß - counting efficiency of -y-rays in the liquid scintillation counter . We can now formulate the following basic equations: NI
NI _
NOT[ PKIEK1 + (1
PKIEKI
NY = NOTE-y,
)01 ,
-
N,
_
NOT 1+
1 - EI EI
( 6)
N,, = Nuz:( 1
(7 )
_P)EIEy .
After transformation of eqs . (5), (6) and (7), one obtains NI I: Ny
= NR~1 oI:
N,
1
+
-EI EI
+P E2
After extrapolation of NI NyIN, as a function of (1 E 1)IE 1 to E 1 = 1, the decay rate of the tracer sample is obtained to be: NOT = NI Ny IN, 1
and for the anticoincidence case: NOT = NINYI(NY - NAJ .
All the corrections for dead time, resolving time and background are to be applied and, in order to present the basic equations for obtaining the total activity of the tracer sample plus the 13I Cs sample in the counting vial, the following notations have to be added : NILE - count rate of the tracer sample plus the 131 Cs sample, probability of an electron capture in the KP K2 shell for 131 Cs, (1 - p) - contribution of the decay rate of the tracer sample to the total sample, contribution of the decay rate of 131 Cs to the P total sample, R correction factor resulting from random coincidence of tracer and 131 Cs decays, counting efficiency of X and CA in the liquid E K2 scintillation counter for the 131 Cs sample . Calling
- P) +P 12 _ E I I
,
-E 1 I
(9)
= 0~,
eq. (8) can be rewritten as NI Ny
~ .
O( 1
(8)
0(1 -P)
and transforming eqs . (1), (2) and (3), the following relationship for the decay rate can be obtained : N, NY
NY = N(I j1 -p),- y ,
(2)
E1,
- EI)Û)+PE2 ], (5)
and with the definition
Calling NcINy =PKIEK1
+(1 - P)(l
Nil: = Nu ,,~ R[(I -P)EI
(1) 3
Nc - NOTPKIEKIEy .
sample :
N,
_-
IILR 1 +
1 EI
After extrapolation of N, NY N,,R
EI
E1
~~ .
(10)
- 1, one can obtain
= NO~,
(11)
The factor R can be determined as follows . The probability of a random coincidence between tracer and "pure" emitter is given by the following expression: V= [P( 1 - P)Z+ ( 1 - PK2)PIEII
(12)
Z =No ,:2-r,
(13)
-r being the pulse width, and consequently V -- [p(1 _P)N11j:2,r + ( 1 - PK2)P,EI'
(14)
where
Taking equations (12), (13) and (14), one obtains 1_ ( E I _V )
1_E I
For the anticoincidence method, the decay rate for the tracer plus the emitter is expressed as follows : NI1I:
_
(Ny-NAJR
(16)
,
and consequently, the activity of the Ao = ( Noy - Nu-r)Im2,
131
Cs emitter is (17)
E2 - EK2PK2,
where m, is the mass of 131 Cs in the total source . The parameter (1 -p), represents the percentage of tracer, and is given by successive approximations :
the basic equations can be formulated for the total
P = (NOI: - NOT) INII
A. Chyfihski / Absolute measurentents of EC entitters
3. Results of
131
N,INy . For p = 0, the probability (h,_ = 4~ . because
Cs measurements
The measurements of "3'Cs activity have been done using two tracers : 54 Mn and 139 Ce. Only K-shell effects are registered in the counting channel with liquid scintillator, while in the channel only the photopeak is counted . The extrapolation curve for the total source of 54Mn + 131 Cs is given in fig . 2, and the relationship for OE as a function of p (for three total sources), defined for p = 0 and p = 1, is given in fig . 3. According to eq. (9), the probability 01: for p = 1 is given by SDP =1)_
E2. -E I
1 - El and the efficiency
E,
61
may be obtained taking
E, =
p = 0 means "pure" tracer E' ? 'Cs). The extrapolation curve for the total source "'Cc + "'Cs is given in fig . 4, and the relationship for dh, as a function of p is given in fig. 5. The results of "rl C's activity measurements with 54 Mn and 139Ce as tracers are given in table 1 . 4. The counting method of 55 Fe
The counting method used for "Fe was the same as for 131 Cs with only one tracer applied : 54 Mn. Therefore the same equations and relationships as for ' -"Cs have been used. Also, only effects from the K-shell were counted . The decay scheme of -""Fe is given in fig . 6.
"'W Na l s,f'in+
X103 381 36 34 32 3028 26 24
f
2
Fig . 2. Extrapolation curve for
Q1
0.2
0.3
0.4
05
0.6
54 Mn + 131 Cs .
07
08
Fig. 3. Relationship for 0 as a function of p for
09 54
f
Mn + 131 Cs.
P
Iü(a) . COINCIDENCE METHODS
A. Chyliiiski / Absohite measurements of EC emitters
62
Nô
C3DCe+r3lCS1
Fig. 4. Extrapolation curve for 139Ce+ 131 Cs .
5. Results of 55 Fe measurements
6. Conclusions
The results of 55 17e activity measurements are given in table 1 . The whole counting procedure was the same as for 131 Cs with only one tracer, 54Mn.
The new version of the tracer technique with the correction factor (R) for random coincidence of Auger electrons or X-photons in a liquid scintillator, between
Fig. 5 . Relationship for ~h, as a function of p for 139 Ce + 131 Cs . Table 1 Results of measurements of "'Cs and Nuclide tracer S4M
Nuclide emitter
A uc.
Cs C's 'S Fe
411 .6 407.8 853.7
`~
n
"'Mn
55 Fe
[kßq/g]
6
11,71"1
0.51 0.86 0.51
A ,A.
h
412.4 408.2 u53.1
0.55 0.98 0.80
[kßq/gi
11/1,1
A [kBq/g]
S
4120 408.0 853 .4
0.23 0.51 0.39
[C71J
A. Chylinski / Absolute measurenrents of EC emitters
63 2.6 y
20
11
1007
26Fe s5
6.0
05
OEC 0.232 talc 0.231 talc
Fig. 6. Decay scheme for "Fe.
PK = 0.881, EKX = 6
keV, E KA = 5 keV, w = 0.321 .
-001f6
0.1
02
0.3
0.4
0.5
0.6
0.7
08
0.9
f
Fig. 7. Relationship for (b,- as a function of p for 54 Mn+ 5`Fe.
the radionuclide used as a tracer and the radionuclide to be measured, seems to solve the problem of the discrepancy between the tracer technique and other methods, which had previously affected these type of measurements . References [1] A . Chylinski and et al ., Nucl . Instr. and Meth . 98 (1972) 109. [2] A. Chylinski and T. Radoszewski, Isotopenpraxis 17 (3) (198()) 118.
[3] A. Chylinski and T. Radoszewski, Int. Symp . of Comecon Countries, Czopak, Hungary. Budapest, vol . 1 (1984) pp . 225-237. [4] J . Legrand et al ., Table de Radionucléides, LMRI, CEA, Saclay (1983) . [5] P. Zelazny and T. Radoszewski, private communication OPiDI (1983) . [6] R. Broda, K. Pochwalski and T. Radoszewski, Appl . Radiat . Isot . 39(2) (1988) . [7] A. Chylinski and T. Radoszewski, these Proceedings (Int . Symp . on Radionuclide Metrology and its Applications. Madrid, Spain, 1991) Nucl . Instr. and Meth . A312 (1992) 76.
Ilka) . COINCIDENCE METHODS
Nuclear Instruments and Methods in Physics Research A312 (1992) 59-63 North-Holland
A new version of the tracer technique for absolute measurements of EC emitters A. Chylinski
The Radioisctope Research Centre, 05-400 Swierk, Poland A new version of the tracer technique for measurements of EC radionuclides is presented. In the experiment, both the coincidence and anticoincidence methods were used simultaneously . This paper presents the results of " I Cs and "Fe activity measurements when traced by r39 Ce and by 54 Mn . The results obtained by the tracer technique depend on the amount of pure beta emitter relative to the tracer amount in the source . 1n this new version of the tracer technique, this question is eliminated . A 4 ,rrp-y coincidence counting system with liquid scintillation detectors in both channels was used and the coincidence extrapolation method was applied with an efficiency function for X-ray and electron counting in the liquid scintillator detector . 131
1 . Introduction
2. The counting method of
The tracer technique applied to p-emitters and specially to electron-capture (EC) radionuclides has not been very popular and successful up to now . This paper presents a successful new app:oach developed for the tracer technique to measure two EC radionuclides, 131 Cs and 55Fe. The new approach includes a new mathematical formulation, the application of two radionuclides as tracers for " I Cs and additional use of the anticoincidence method for verification . In all cases, liquid scintillation techniques have been used as the most convenient for this purpose . The liquid scintillation counter as well as the electronic system used are described elsewhere in these Proceedings [7].
The only results of decay are X-ray fotons, or Auger electrons, emitted alternatively . All the values of X and e A and for PK and (OK are given in Fig . 1 . To get the radioactive concentration of the radionuclide in question ( );) Cs in this case) the following procedure has to be applied . First, the activity of the tracer sample in the counting vial is measured and then the sample of 13i CS is added to the counting vial with the tracer sample and the total activity is measured. The activity of the "' Cs sample is obtained by subtracting the tracer activity from the total activity in the counting vial. From now on, we will use the following notation: NOT - decay rate for the tracer sample,
54Xe 131
Fig. 1 . Decay scheme for 131Cs.
PK = 0.843, EK,x
Cs
QEC 0.35 talc (MTW)
= 30 keV . E,:,,, =
0168-9002/92/$05 .00 O 1992 - Elsevier Science Publishers B.V . All rights reserved
24
keV,
w=
0.829 .
111(a). COINCIDENCE METHODS
A. Chyliilski / Ahsohite measarements of EC emitters
60
- count rate of X and CA channel with liquid scintillation counter, N,, -- count rate in the -y-channel with NATO scintillation counter, coincidence count rate, N, counting efficiency of X and CA in the liquid EKI scintillation counter for the tracer sample, counting efficiency in NATO scintillation EN counter, probability of an electron capture from the PKI K-shell, cß - counting efficiency of -y-rays in the liquid scintillation counter . We can now formulate the following basic equations: NI
NI _
NOT[ PKIEK1 + (1
PKIEKI
NY = NOTE-y,
)01 ,
-
N,
_
NOT 1+
1 - EI EI
( 6)
N,, = Nuz:( 1
(7 )
_P)EIEy .
After transformation of eqs . (5), (6) and (7), one obtains NI I: Ny
= NR~1 oI:
N,
1
+
-EI EI
+P E2
After extrapolation of NI NyIN, as a function of (1 E 1)IE 1 to E 1 = 1, the decay rate of the tracer sample is obtained to be: NOT = NI Ny IN, 1
and for the anticoincidence case: NOT = NINYI(NY - NAJ .
All the corrections for dead time, resolving time and background are to be applied and, in order to present the basic equations for obtaining the total activity of the tracer sample plus the 13I Cs sample in the counting vial, the following notations have to be added : NILE - count rate of the tracer sample plus the 131 Cs sample, probability of an electron capture in the KP K2 shell for 131 Cs, (1 - p) - contribution of the decay rate of the tracer sample to the total sample, contribution of the decay rate of 131 Cs to the P total sample, R correction factor resulting from random coincidence of tracer and 131 Cs decays, counting efficiency of X and CA in the liquid E K2 scintillation counter for the 131 Cs sample . Calling
- P) +P 12 _ E I I
,
-E 1 I
(9)
= 0~,
eq. (8) can be rewritten as NI Ny
~ .
O( 1
(8)
0(1 -P)
and transforming eqs . (1), (2) and (3), the following relationship for the decay rate can be obtained : N, NY
NY = N(I j1 -p),- y ,
(2)
E1,
- EI)Û)+PE2 ], (5)
and with the definition
Calling NcINy =PKIEK1
+(1 - P)(l
Nil: = Nu ,,~ R[(I -P)EI
(1) 3
Nc - NOTPKIEKIEy .
sample :
N,
_-
IILR 1 +
1 EI
After extrapolation of N, NY N,,R
EI
E1
~~ .
(10)
- 1, one can obtain
= NO~,
(11)
The factor R can be determined as follows . The probability of a random coincidence between tracer and "pure" emitter is given by the following expression: V= [P( 1 - P)Z+ ( 1 - PK2)PIEII
(12)
Z =No ,:2-r,
(13)
-r being the pulse width, and consequently V -- [p(1 _P)N11j:2,r + ( 1 - PK2)P,EI'
(14)
where
Taking equations (12), (13) and (14), one obtains 1_ ( E I _V )
1_E I
For the anticoincidence method, the decay rate for the tracer plus the emitter is expressed as follows : NI1I:
_
(Ny-NAJR
(16)
,
and consequently, the activity of the Ao = ( Noy - Nu-r)Im2,
131
Cs emitter is (17)
E2 - EK2PK2,
where m, is the mass of 131 Cs in the total source . The parameter (1 -p), represents the percentage of tracer, and is given by successive approximations :
the basic equations can be formulated for the total
P = (NOI: - NOT) INII
A. Chyfihski / Absolute measurentents of EC entitters
3. Results of
131
N,INy . For p = 0, the probability (h,_ = 4~ . because
Cs measurements
The measurements of "3'Cs activity have been done using two tracers : 54 Mn and 139 Ce. Only K-shell effects are registered in the counting channel with liquid scintillator, while in the channel only the photopeak is counted . The extrapolation curve for the total source of 54Mn + 131 Cs is given in fig . 2, and the relationship for OE as a function of p (for three total sources), defined for p = 0 and p = 1, is given in fig . 3. According to eq. (9), the probability 01: for p = 1 is given by SDP =1)_
E2. -E I
1 - El and the efficiency
E,
61
may be obtained taking
E, =
p = 0 means "pure" tracer E' ? 'Cs). The extrapolation curve for the total source "'Cc + "'Cs is given in fig . 4, and the relationship for dh, as a function of p is given in fig. 5. The results of "rl C's activity measurements with 54 Mn and 139Ce as tracers are given in table 1 . 4. The counting method of 55 Fe
The counting method used for "Fe was the same as for 131 Cs with only one tracer applied : 54 Mn. Therefore the same equations and relationships as for ' -"Cs have been used. Also, only effects from the K-shell were counted . The decay scheme of -""Fe is given in fig . 6.
"'W Na l s,f'in+
X103 381 36 34 32 3028 26 24
f
2
Fig . 2. Extrapolation curve for
Q1
0.2
0.3
0.4
05
0.6
54 Mn + 131 Cs .
07
08
Fig. 3. Relationship for 0 as a function of p for
09 54
f
Mn + 131 Cs.
P
Iü(a) . COINCIDENCE METHODS
A. Chyliiiski / Absohite measurements of EC emitters
62
Nô
C3DCe+r3lCS1
Fig. 4. Extrapolation curve for 139Ce+ 131 Cs .
5. Results of 55 Fe measurements
6. Conclusions
The results of 55 17e activity measurements are given in table 1 . The whole counting procedure was the same as for 131 Cs with only one tracer, 54Mn.
The new version of the tracer technique with the correction factor (R) for random coincidence of Auger electrons or X-photons in a liquid scintillator, between
Fig. 5 . Relationship for ~h, as a function of p for 139 Ce + 131 Cs . Table 1 Results of measurements of "'Cs and Nuclide tracer S4M
Nuclide emitter
A uc.
Cs C's 'S Fe
411 .6 407.8 853.7
`~
n
"'Mn
55 Fe
[kßq/g]
6
11,71"1
0.51 0.86 0.51
A ,A.
h
412.4 408.2 u53.1
0.55 0.98 0.80
[kßq/gi
11/1,1
A [kBq/g]
S
4120 408.0 853 .4
0.23 0.51 0.39
[C71J
A. Chylinski / Absolute measurenrents of EC emitters
63 2.6 y
20
11
1007
26Fe s5
6.0
05
OEC 0.232 talc 0.231 talc
Fig. 6. Decay scheme for "Fe.
PK = 0.881, EKX = 6
keV, E KA = 5 keV, w = 0.321 .
-001f6
0.1
02
0.3
0.4
0.5
0.6
0.7
08
0.9
f
Fig. 7. Relationship for (b,- as a function of p for 54 Mn+ 5`Fe.
the radionuclide used as a tracer and the radionuclide to be measured, seems to solve the problem of the discrepancy between the tracer technique and other methods, which had previously affected these type of measurements . References [1] A . Chylinski and et al ., Nucl . Instr. and Meth . 98 (1972) 109. [2] A. Chylinski and T. Radoszewski, Isotopenpraxis 17 (3) (198()) 118.
[3] A. Chylinski and T. Radoszewski, Int. Symp . of Comecon Countries, Czopak, Hungary. Budapest, vol . 1 (1984) pp . 225-237. [4] J . Legrand et al ., Table de Radionucléides, LMRI, CEA, Saclay (1983) . [5] P. Zelazny and T. Radoszewski, private communication OPiDI (1983) . [6] R. Broda, K. Pochwalski and T. Radoszewski, Appl . Radiat . Isot . 39(2) (1988) . [7] A. Chylinski and T. Radoszewski, these Proceedings (Int . Symp . on Radionuclide Metrology and its Applications. Madrid, Spain, 1991) Nucl . Instr. and Meth . A312 (1992) 76.
Ilka) . COINCIDENCE METHODS