- Email: [email protected]
The absolute counting of 125I
Applied Radiation and Isotopes 52 (2000) 523±526
The absolute counting of
www.elsevier.com/locate/apradiso
125
I
Ming-Chen Yuan*, Wen-Song Hwang Institute of Nuclear Energy Research, P.O. Box 3-10, Lungtan 325, Taiwan
Abstract The Institute of Nuclear Energy Research (INER) participated in a comparison of activity organized by the Electrotechnical Laboratory (ETL, Japan). At this occasion, 125I was measured. Seven laboratories of the Asia Paci®c region carried out measurements and ETL, at the same time, took part in BIPM SIR measurements. Two measurement methods developed by INER, the sum-peak coincidence counting with two 76 76 mm NaI(Tl) detectors and the 4pe-X coincidence counting technique with eciency extrapolation, were used to standardize the activity of 125I. The results from the two methods are 2.6% dierent. INER's results agree with the results of the regional comparison and the BIPM SIR. # 2000 Elsevier Science Ltd. All rights reserved. Keywords:
125
I; Comparison; The sum peak coincidence counting; The 4pe-X coincidence counting
1. Introduction INER participated in a comparison of activity organized by ETL, Japan in 1998 (Hino, 1999). Seven laboratories of the Asia Paci®c region measured the 125I activity and ETL submitted in parallel a sample to the BIPM SIR system. At this occasion, ETL prepared and delivered the radioactive solution to each laboratory. The solution contained 0.75 mg NaI lÿ1, 50 mg Ki lÿ1, 200 mg LiOH lÿ1 and 50 mg Na2S2O3 lÿ1 in 0.1 M NaOH. 125 I is an electron-capture decay nuclide and its decay scheme is given in Fig. 1 (Firestone and Shirley, 1996). 125 I emits 35 keV g-rays (about 6.6%) from the electron capture (EC) transition, and a number of KXrays, conversion electrons and Auger electrons are emitted from both the EC and the gamma transition.
* Corresponding author. Tel.: +886-3-471-1400 ext. 7672; fax: +886-3-471-4132. E-mail address: [email protected] (M.-C. Yuan).
The probability of K-capture, Pk, is 0.797 2 0.001, the total conversion coecient, a, is 13.65 2 0.55, the Kconversion coecient, aK, is 12.01 2 0.36 and the KX¯uorescence yield, oK, is 0.875 2 0.018 (Lederer and Shirley, 1978). To measure the activity concentration of the solution, sum-peak coincidence counting with two 76 76 mm NaI(Tl) and 4pe-X coincidence counting with eciency extrapolation were both used.
2. Sum-peak coincidence counting method The sum-peak coincidence counting method was studied in a series of papers by Brinkman et al. (1963a,b, 1965). In this method, for a nuclide producing two photons in coincidence and no bÿ or EC transition to the ground level, the disintegration rate, N0, is given by: N0 T
A1 A2 , A12
0969-8043/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 4 3 ( 9 9 ) 0 0 2 0 4 - 3
1
524
M.-C. Yuan, W.-S. Hwang / Applied Radiation and Isotopes 52 (2000) 523±526
Fig. 1. Decay scheme of
125
I (Firestone and Shirley, 1996).
where T is the total count rate extrapolated to zero energy, and A1, A2 and A12 are the count rates of the two singles peaks and the sum-peak, respectively. Eldridge and Crowther (1964) used the method to measure the activity of 125I with a single NaI(Tl) detector. They measured the count rate of unresolved KXand g-rays in the singles peaks and the (KX+g) rays sum peak, and assumed that there was negligible loss of energy by Compton scattering. Then Eq. (1) can be written in the form:
In this work, the source was sandwiched between two 76 76 mm NaI(Tl) detectors to provide nearly a 4p geometry O=4p10:9). Ten sources were prepared on conducting VYNS ®lms 115 mg cmÿ2 VYNS coated with 120 mg cmÿ2 Au and the diameter of the active area is below 5 mm. To minimize the eect of the background and dead time, the source activity was controlled to ensure count rate about 5000 sÿ1. A gamma spectrum is shown in Fig. 2. The full line refers to data detected by this system and the dashed line to the data detected by a beryllium-window HPGe detector. Two gamma windows were set for this system between 13 and 40 keV and between 40 and 73 keV to obtain the singles peak area and sum peak area count rates, respectively. All these data were corrected for dead time, background and accidental summing (Dias and Koskinas, 1995)
3. 4p pe-X coincidence counting method
where AI is the count rate of unresolved KX and grays singles peak area, AII the count rate of KX+grays sum peak area, P1 the probability per decay of the KX ray in the electron capture branch, i.e. P1 Pk oK 0:69720:015, P2 the sum of the probability per decay of the g-and KX rays arising from internal conversion, i.e. P2 1 aK oK = 1 a 0:78620:040: In 1992, Martin and Taylor used the same equation and a Ge detector to standardize 125I.
The 4pe-X coincidence counting was developed to standardize 109Cd (Martin and Taylor, 1987; Hino and Kawada, 1989) and 125I (Martin and Taylor, 1992). This method has the advantage of being independent from the decay scheme parameters. The activity, N0, was calculated from N4 pNX =NC N0 1 K NX =NC ÿ 1 4 N0 as NX/NC 4 1. N4p is the detection rate for Auger and conversion electrons in the 4p proportional counter, NX is the sum of the detection rates for KXand g-rays in the NaI detector, NC is the coincidence rate and K is a function of the decay scheme parameters. For the prompt g-transition, all the decay scheme parameters are eliminated by the extrapolation to NX =NC 1 (Martin and Taylor, 1992). In this work, the detector system consisted of a 4p pillbox shaped proportional counter and of a 1 mm thick NaI(Tl) crystal detector. The top and the bottom
Fig. 2. 125I gamma spectrum. A NaI spectrum (full line) and a HPGe spectrum (dashed line).
Fig. 3. Eciency function curve obtained by variation of the counter high voltage.
N0
P1 P2 AI AII 2 , 2 AII P1 P2
2
M.-C. Yuan, W.-S. Hwang / Applied Radiation and Isotopes 52 (2000) 523±526 Table 1 The measurement results of INER, this comparison and the BIPM SIR for
525
125
I
Method
INER (MBq gÿ1)
Measurement result/ETL
Sum peak (%) 4pe-X with high voltage variation 4pe-X with adding VYNS ®lms The average of this comparison The average of the BIPM SIR (without UVVVR)
15.2120.6 15.6121.3 15.5822.4
1.01120.007 1.03720.014 1.03520.025 1.02220.018 1.00520.030
Table 2 Summary of uncertainties One standard deviation (%)
Factor a b c d e f g h i j
Mean of results Count or ®t Accidental summing Decay-scheme parameters Weighing Background Dead time Decay correction Dilution Electrical equipment
Sum-peak
4pe-X (high voltage variation)
4pe-X (adding ®lms)
0.14 incl. In (a) < 0.24 0.3 < 0.3 < 0.01 < 0.02 0.02 0.01 < 0.2
1.2 incl. In (a) inapplicable inapplicable < 0.3 < 0.01 < 0.02 0.02 0.01 < 0.2
2.4 incl. In (a) inapplicable inapplicable < 0.3 < 0.01 < 0.02 0.02 0.01 < 0.2
0.6
1.3
2.4
Total (sum in quadrature)
wall of the 4p proportional counter is 4 mg cmÿ2 aluminum which minimizes the attenuation of the low energy KX- and g-rays. Two methods were used to vary the detection eciency of the 4p proportional counter. One used a high voltage variation and the other addition of absorbing foils. 13 sources were prepared on conducting VYNS ®lms and treated with Ludox. Ten of these sources were measured by varying the counter high voltage and the other sources were measured by adding thin conducting VYNS ®lms to reduce the eciency detection. Both methods show similar eciency function curves. One of the curves obtained by high voltage variation is show in Fig. 3.
high voltage and adding VYNS ®lms. The results from sum peak coincidence and 4pe-X methods are about 2.6% dierent. That might be caused by using dierent counting systems, methods or possibly defective dilution. Anyway, considering their uncertainty in 95% con®dence level, this dierence is still reasonable. ETL organized this comparison of activity and participated, in parallel, in the BIPM SIR measurements. Each result is normalized to ETL's result (15.05 2 0.4 % MBq gÿ1) and is shown in column 3 of Table 1. It shows the large uncertainties of the two comparisons' results and that causes INER's results agree with them and the two comparison agree with each other.
4. Results and conclusion
Acknowledgements
The sum peak coincidence method and the 4pe-X coincidence counting with varying high voltage and adding VYNS ®lms have been both used to measure the activity concentration of 125I. The results are listed in Table 1 and a summary of the uncertainty is listed in Table 2. All the uncertainties in this work are one standard deviation equivalents. Table 1 shows a good agreement of the results for the 4pe-X with varying
The authors are indebted to Dr. Hino (ETL) for the supply of the 125I solution, and the results of this program and that of the BIPM SIR.
References Brinkman, G.A., Aten Jr., A.H.W., Veenboer, J.Th., 1963a.
526
M.-C. Yuan, W.-S. Hwang / Applied Radiation and Isotopes 52 (2000) 523±526
Absolute standardization with a NaI(Tl) crystal. I. Int. J. Appl. Radiat. Isot. 14, 153±157. Brinkman, G.A., Aten Jr., A.H.W., Veenboer, J.Th., 1963b. Absolute standardization with a NaI(Tl) Crystal. II. Int. J. Appl. Radiat. Isot. 14, 433±437. Brinkman, G.A., Aten Jr., A.H.W., Veenboer, J.Th., 1965. Absolute standardization with a NaI(Tl) crystal. IV. Int. J. Appl. Radiat. Isot. 16, 15±18. Dias, M.S., Koskinas, M.F., 1995. Accidental summing correction in 125I activity determination by the sum-peak method. Appl. Radiat. Isot. 46, 945±948. Eldridge, J.S., Crowther, P., 1964. Absolute determination of 125 I in clinical applications. Nucleonics. 22, 56. Firestone, R.B., Shirley, V.S. (Eds.), 1996. Table of Isotopes, 8th ed. Wiley-Interscience, New York.
Hino, Y., Kawada, Y., 1989. Standardization of 109Cd by 4pe-X coincidence counting with a conventional gas ¯ow counter and measurement of the 88-keV gamma-ray intensity. Appl. Radiat. Isot. 40, 78±83. Hino, Y., 1999. Review of recent works and projects of ETL, Contribution to the 15th meeting of CCRI(II), 31 May to 2 June 1999. Lederer, C.M., Shirley, V.S. (Eds.), 1978. Table of Isotopes, 7th ed. Wiley-Interscience, New York. Martin, R.H., Taylor, J.G.V., 1987. Standardization of 109Cd by a 4pe-X coincidence method. Appl. Radiat. Isot. 38, 781±786. Martin, R.H., Taylor, J.G.V., 1992. The standardization of 125 I: a comparison of three methods. Nucl. Instr. Meth. Phys. Res. A 312, 64±66.
The absolute counting of
www.elsevier.com/locate/apradiso
125
I
Ming-Chen Yuan*, Wen-Song Hwang Institute of Nuclear Energy Research, P.O. Box 3-10, Lungtan 325, Taiwan
Abstract The Institute of Nuclear Energy Research (INER) participated in a comparison of activity organized by the Electrotechnical Laboratory (ETL, Japan). At this occasion, 125I was measured. Seven laboratories of the Asia Paci®c region carried out measurements and ETL, at the same time, took part in BIPM SIR measurements. Two measurement methods developed by INER, the sum-peak coincidence counting with two 76 76 mm NaI(Tl) detectors and the 4pe-X coincidence counting technique with eciency extrapolation, were used to standardize the activity of 125I. The results from the two methods are 2.6% dierent. INER's results agree with the results of the regional comparison and the BIPM SIR. # 2000 Elsevier Science Ltd. All rights reserved. Keywords:
125
I; Comparison; The sum peak coincidence counting; The 4pe-X coincidence counting
1. Introduction INER participated in a comparison of activity organized by ETL, Japan in 1998 (Hino, 1999). Seven laboratories of the Asia Paci®c region measured the 125I activity and ETL submitted in parallel a sample to the BIPM SIR system. At this occasion, ETL prepared and delivered the radioactive solution to each laboratory. The solution contained 0.75 mg NaI lÿ1, 50 mg Ki lÿ1, 200 mg LiOH lÿ1 and 50 mg Na2S2O3 lÿ1 in 0.1 M NaOH. 125 I is an electron-capture decay nuclide and its decay scheme is given in Fig. 1 (Firestone and Shirley, 1996). 125 I emits 35 keV g-rays (about 6.6%) from the electron capture (EC) transition, and a number of KXrays, conversion electrons and Auger electrons are emitted from both the EC and the gamma transition.
* Corresponding author. Tel.: +886-3-471-1400 ext. 7672; fax: +886-3-471-4132. E-mail address: [email protected] (M.-C. Yuan).
The probability of K-capture, Pk, is 0.797 2 0.001, the total conversion coecient, a, is 13.65 2 0.55, the Kconversion coecient, aK, is 12.01 2 0.36 and the KX¯uorescence yield, oK, is 0.875 2 0.018 (Lederer and Shirley, 1978). To measure the activity concentration of the solution, sum-peak coincidence counting with two 76 76 mm NaI(Tl) and 4pe-X coincidence counting with eciency extrapolation were both used.
2. Sum-peak coincidence counting method The sum-peak coincidence counting method was studied in a series of papers by Brinkman et al. (1963a,b, 1965). In this method, for a nuclide producing two photons in coincidence and no bÿ or EC transition to the ground level, the disintegration rate, N0, is given by: N0 T
A1 A2 , A12
0969-8043/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 4 3 ( 9 9 ) 0 0 2 0 4 - 3
1
524
M.-C. Yuan, W.-S. Hwang / Applied Radiation and Isotopes 52 (2000) 523±526
Fig. 1. Decay scheme of
125
I (Firestone and Shirley, 1996).
where T is the total count rate extrapolated to zero energy, and A1, A2 and A12 are the count rates of the two singles peaks and the sum-peak, respectively. Eldridge and Crowther (1964) used the method to measure the activity of 125I with a single NaI(Tl) detector. They measured the count rate of unresolved KXand g-rays in the singles peaks and the (KX+g) rays sum peak, and assumed that there was negligible loss of energy by Compton scattering. Then Eq. (1) can be written in the form:
In this work, the source was sandwiched between two 76 76 mm NaI(Tl) detectors to provide nearly a 4p geometry O=4p10:9). Ten sources were prepared on conducting VYNS ®lms 115 mg cmÿ2 VYNS coated with 120 mg cmÿ2 Au and the diameter of the active area is below 5 mm. To minimize the eect of the background and dead time, the source activity was controlled to ensure count rate about 5000 sÿ1. A gamma spectrum is shown in Fig. 2. The full line refers to data detected by this system and the dashed line to the data detected by a beryllium-window HPGe detector. Two gamma windows were set for this system between 13 and 40 keV and between 40 and 73 keV to obtain the singles peak area and sum peak area count rates, respectively. All these data were corrected for dead time, background and accidental summing (Dias and Koskinas, 1995)
3. 4p pe-X coincidence counting method
where AI is the count rate of unresolved KX and grays singles peak area, AII the count rate of KX+grays sum peak area, P1 the probability per decay of the KX ray in the electron capture branch, i.e. P1 Pk oK 0:69720:015, P2 the sum of the probability per decay of the g-and KX rays arising from internal conversion, i.e. P2 1 aK oK = 1 a 0:78620:040: In 1992, Martin and Taylor used the same equation and a Ge detector to standardize 125I.
The 4pe-X coincidence counting was developed to standardize 109Cd (Martin and Taylor, 1987; Hino and Kawada, 1989) and 125I (Martin and Taylor, 1992). This method has the advantage of being independent from the decay scheme parameters. The activity, N0, was calculated from N4 pNX =NC N0 1 K NX =NC ÿ 1 4 N0 as NX/NC 4 1. N4p is the detection rate for Auger and conversion electrons in the 4p proportional counter, NX is the sum of the detection rates for KXand g-rays in the NaI detector, NC is the coincidence rate and K is a function of the decay scheme parameters. For the prompt g-transition, all the decay scheme parameters are eliminated by the extrapolation to NX =NC 1 (Martin and Taylor, 1992). In this work, the detector system consisted of a 4p pillbox shaped proportional counter and of a 1 mm thick NaI(Tl) crystal detector. The top and the bottom
Fig. 2. 125I gamma spectrum. A NaI spectrum (full line) and a HPGe spectrum (dashed line).
Fig. 3. Eciency function curve obtained by variation of the counter high voltage.
N0
P1 P2 AI AII 2 , 2 AII P1 P2
2
M.-C. Yuan, W.-S. Hwang / Applied Radiation and Isotopes 52 (2000) 523±526 Table 1 The measurement results of INER, this comparison and the BIPM SIR for
525
125
I
Method
INER (MBq gÿ1)
Measurement result/ETL
Sum peak (%) 4pe-X with high voltage variation 4pe-X with adding VYNS ®lms The average of this comparison The average of the BIPM SIR (without UVVVR)
15.2120.6 15.6121.3 15.5822.4
1.01120.007 1.03720.014 1.03520.025 1.02220.018 1.00520.030
Table 2 Summary of uncertainties One standard deviation (%)
Factor a b c d e f g h i j
Mean of results Count or ®t Accidental summing Decay-scheme parameters Weighing Background Dead time Decay correction Dilution Electrical equipment
Sum-peak
4pe-X (high voltage variation)
4pe-X (adding ®lms)
0.14 incl. In (a) < 0.24 0.3 < 0.3 < 0.01 < 0.02 0.02 0.01 < 0.2
1.2 incl. In (a) inapplicable inapplicable < 0.3 < 0.01 < 0.02 0.02 0.01 < 0.2
2.4 incl. In (a) inapplicable inapplicable < 0.3 < 0.01 < 0.02 0.02 0.01 < 0.2
0.6
1.3
2.4
Total (sum in quadrature)
wall of the 4p proportional counter is 4 mg cmÿ2 aluminum which minimizes the attenuation of the low energy KX- and g-rays. Two methods were used to vary the detection eciency of the 4p proportional counter. One used a high voltage variation and the other addition of absorbing foils. 13 sources were prepared on conducting VYNS ®lms and treated with Ludox. Ten of these sources were measured by varying the counter high voltage and the other sources were measured by adding thin conducting VYNS ®lms to reduce the eciency detection. Both methods show similar eciency function curves. One of the curves obtained by high voltage variation is show in Fig. 3.
high voltage and adding VYNS ®lms. The results from sum peak coincidence and 4pe-X methods are about 2.6% dierent. That might be caused by using dierent counting systems, methods or possibly defective dilution. Anyway, considering their uncertainty in 95% con®dence level, this dierence is still reasonable. ETL organized this comparison of activity and participated, in parallel, in the BIPM SIR measurements. Each result is normalized to ETL's result (15.05 2 0.4 % MBq gÿ1) and is shown in column 3 of Table 1. It shows the large uncertainties of the two comparisons' results and that causes INER's results agree with them and the two comparison agree with each other.
4. Results and conclusion
Acknowledgements
The sum peak coincidence method and the 4pe-X coincidence counting with varying high voltage and adding VYNS ®lms have been both used to measure the activity concentration of 125I. The results are listed in Table 1 and a summary of the uncertainty is listed in Table 2. All the uncertainties in this work are one standard deviation equivalents. Table 1 shows a good agreement of the results for the 4pe-X with varying
The authors are indebted to Dr. Hino (ETL) for the supply of the 125I solution, and the results of this program and that of the BIPM SIR.
References Brinkman, G.A., Aten Jr., A.H.W., Veenboer, J.Th., 1963a.
526
M.-C. Yuan, W.-S. Hwang / Applied Radiation and Isotopes 52 (2000) 523±526
Absolute standardization with a NaI(Tl) crystal. I. Int. J. Appl. Radiat. Isot. 14, 153±157. Brinkman, G.A., Aten Jr., A.H.W., Veenboer, J.Th., 1963b. Absolute standardization with a NaI(Tl) Crystal. II. Int. J. Appl. Radiat. Isot. 14, 433±437. Brinkman, G.A., Aten Jr., A.H.W., Veenboer, J.Th., 1965. Absolute standardization with a NaI(Tl) crystal. IV. Int. J. Appl. Radiat. Isot. 16, 15±18. Dias, M.S., Koskinas, M.F., 1995. Accidental summing correction in 125I activity determination by the sum-peak method. Appl. Radiat. Isot. 46, 945±948. Eldridge, J.S., Crowther, P., 1964. Absolute determination of 125 I in clinical applications. Nucleonics. 22, 56. Firestone, R.B., Shirley, V.S. (Eds.), 1996. Table of Isotopes, 8th ed. Wiley-Interscience, New York.
Hino, Y., Kawada, Y., 1989. Standardization of 109Cd by 4pe-X coincidence counting with a conventional gas ¯ow counter and measurement of the 88-keV gamma-ray intensity. Appl. Radiat. Isot. 40, 78±83. Hino, Y., 1999. Review of recent works and projects of ETL, Contribution to the 15th meeting of CCRI(II), 31 May to 2 June 1999. Lederer, C.M., Shirley, V.S. (Eds.), 1978. Table of Isotopes, 7th ed. Wiley-Interscience, New York. Martin, R.H., Taylor, J.G.V., 1987. Standardization of 109Cd by a 4pe-X coincidence method. Appl. Radiat. Isot. 38, 781±786. Martin, R.H., Taylor, J.G.V., 1992. The standardization of 125 I: a comparison of three methods. Nucl. Instr. Meth. Phys. Res. A 312, 64±66.