The international reference system for beta-particle emitting radionuclides: Validation through the pilot study CCRI(II)-P1.Co-60.

The Bureau International des Poids et Mesures (BIPM) is developing a new transfer instrument to extend its centralized services for assessing the international equivalence of radioactive standards to new radionuclides. A liquid scintillation counter using the triple/double coincidence ratio method is being studied and tested in the CCRI(II)-P1.Co-60 pilot study. The pilot study, involving 13 participating laboratories with primary calibration capabilities, validated the approach against the original international reference system based on ionization chambers, which has been in operation since 1976. The results are in agreement and an accuracy suitable for purpose, below 5×10-4, is achieved. The pilot study also reveals an issue when impurities emitting low-energy electrons are present in the standard solution, which have a different impact on liquid scintillation counting compared to other primary measurement methods.

Activity measurement of mixed complex radionuclide like 152Eu with different methods.

152Eu has been standardized by three independent 4π ß-γ coincidence counting systems with beta detectors as proportional counter, plastic scintillator and liquid scintillator along with the CIEMAT/NIST method. The average activity concentration by primary methods was linked to key comparison reference value (KCRV) by comparing it with that of 4π γ ionization chamber (GIC) whose calibration factor was determined from the KCRV (BIPM.RI(II)-K1.Eu-152 and CCRI(II)-K2.Eu-152) and deviates from GIC by ± 0.16% indicating good agreement within standard uncertainties.

Standardisation of 133Ba by efficiency extrapolation method and calibration of ionisation chamber.

133Ba has been standardised by direct measurements for the first time in the laboratory using two counting systems: (i) the 4πß (plastic scintillator) -γ coincidence, (ii) the 4πß (proportional counter) -γ coincidence. Furthermore, this standardisation experiment demonstrates the performance and applicability of the recently developed 4πß (plastic scintillator)-γ coincidence system for radionuclides decaying with complex decay schemes as well as for e, X-γ emitters. Additionally, 133Ba solution standards were prepared to calibrate the pressurized 4π γ ionisation chamber and determination of the calibration coefficient. The En score is a statistical indicator of the agreement between two independent estimations. Thus, the performance of the PS system was compared to the result obtained with the PC system using the En score as specified in the ISO13528:2015. The results of measurements are acceptable if En â‰¦ 1.0. An En score of 0.2 was obtained which indicates that, the 133Ba activity concentration obtained by the 4πß (plastic scintillator) -γ coincidence and 4πß (proportional counter) -γ coincidence systems are in agreement. This paper presents the standardisation procedure, the results obtained by the measurements and their comparison.

Development of plastic scintillator based primary standard for activity measurements and its performance evaluation.

4πß-γ coincidence technique is a powerful tool and widely recognised method to determine the absolute activity concentration of radioactive solutions. A new plastic scintillator based coincidence system has been developed and established as a primary standard for radioactivity measurements. The performance of the system was evaluated by the standardisation of 60Co radioactive solution due to its simple decay scheme. The activity concentration results obtained by the new system were compared with the existing proportional counter and liquid scintillation based 4πß-γ coincidence systems. This paper discusses the design details of the new system and its performance evaluation.

Standardisation of Rhenium-188 and determination of calibration factors for secondary standard and radionuclide calibrator.

The use of Rhenium-188 for various therapeutic applications in the field of nuclear medicine has increased in recent years due to its favourable properties like decay scheme, cost effective availability and easy chemistry. Two independent measuring setups were used to standardise 188Re radioactive solution. The modus operandi of standardisation was 4πß-γ coincidence technique where the beta detection was done by proportional counting and liquid scintillation counting and the gamma detection was done by using NaI(Tl) detectors. The secondary standard, high pressure ionisation chamber type Centronic IG12, 20A was calibrated with the standardised 188Re solution and the sensitivity coefficient (pA MBq-1) was determined. To enhance the accuracy of the commercial radionuclide calibrator and to ensure that patients receive optimum dose of these radiopharmaceuticals, calibration number of the Capintec CRC-15ß radionuclide calibrator was also verified. This paper presents the standardisation of 188Re radioactive solution by primary methods and calibration of BARC secondary standard ionisation chamber system and a Capintec CRC-15ß radionuclide calibrator.

63Ni activity measurements a bilateral intercomparison.

To assess the accuracy and capabilities of BARC, for standardization of 63Ni before participating in larger scale trial exercise to implement and test the methods for the extension of the SIR to ß emitters, a bilateral intercomparison was organised with National Metrology Institute of Japan (NMIJ), Japan. Standardization of 63Ni was carried out and the results were compared with those obtained from NMIJ to assess the accuracy and capabilities of the laboratories. The CIEMAT/NIST efficiency tracing technique based on 3H standard was used for measurement of 63Ni activity concentration at BARC, India whereas Triple to Double Coincidence Ratio (TDCR) method was used at NMIJ, Japan. The procedures adopted for the standardization of 63Ni by CIEMAT/NIST method at BARC and TDCR method at NMIJ are presented. The percentage deviation in activity concentration of 63Ni between BARC, India and NMIJ, Japan is 0.27%. To evaluate the performance of techniques used at both the laboratories, En score (k = 2) and degrees of equivalence was calculated. The En score of -0.12 and degrees of equivalence -0.06 kBq g-1 clearly indicates that the activity concentration of 63Ni measured at BARC, India and NMIJ, Japan are in excellent agreement and comparable within uncertainty limits and demonstrates the degrees of equivalence of the standards maintained at BARC, India and NMIJ Japan.

An automated LS(ß)- NaI(Tl)(γ) coincidence system as absolute standard for radioactivity measurements.

4πß-γ coincidence method is a powerful and widely used method to determine the absolute activity concentration of radioactive solutions. A new automated liquid scintillator based coincidence system has been designed, developed, tested and established as absolute standard for radioactivity measurements. The automation is achieved using PLC (programmable logic controller) and SCADA (supervisory control and data acquisition). Radioactive solution of 60Co was standardized to compare the performance of the automated system with proportional counter based absolute standard maintained in the laboratory. The activity concentrations determined using these two systems were in very good agreement; the new automated system can be used for absolute measurement of activity concentration of radioactive solutions.

Standardization of 68Ge-68Ga using 4πß(LS)-γ coincidence counting system for activity measurements.

68Ga has great scope for use in future for positron emission tomography (PET) imaging due to its very fast blood clearance and fast target localization, even though at present 18F is widely used. 68Ge in equilibrium with 68Ga (68Ge-68Ga) can also be used as a surrogate for 18F calibration, as 18F source standardization can be done at national metrology institute (NMI) but, these standards cannot be sent to nuclear medicine centers (NMCs) across India for calibration of isotope calibrators, due to the short half-life of 18F (110min). Providing 68Ge-68Ga standards to NMCs requires that first standardization must be carried out at NMI (BARC in India) to provide traceability to the measurements carried out at NMCs. In the present work, standardization of 68Ge-68Ga was carried out using 4πß(LS)-γ coincidence counting system and CIEMAT/NIST efficiency tracing technique. The decay scheme correction factors for two gamma windows were calculated by Monte Carlo technique using general purpose code FLUKA. The activity concentration values were normalized by the activity concentration obtained by 4πß(LS)-γ coincidence counting system using window-1. The final result reported to BIPM for 4πß(LS)-γ coincidence counting was calculated by taking arithmetic mean of activity concentrations obtained for two gamma windows. The normalized activity concentration obtained by 4πß(LS)-γ coincidence counting was 0.998±0.005 and that obtained using CIEMAT/NIST efficiency tracing was 1.002±0.007 which are in excellent agreement within uncertainty limits.

A primary standard for the measurement of alpha and beta particle surface emission rate from large area reference sources.

A large area windowless gas flow multi wire proportional counting system for the calibration of large area reference sources has been developed as a primary standard at Bhabha Atomic Research Centre (BARC). The counting system consists of a multi wire proportional counter (MWPC), vacuum system, gas flow system and pulse processing units. The MWPC detector assembly consists of a vacuum tight aluminum enclosure, multi wire grid and sliding source tray. Various detector characteristics like operating characteristics curve, Fe-55 spectrum for beta discriminator threshold setting and dead time of the measurement system were studied and determined in order to achieve an optimized detection capability. The surface emission rates of different source strengths were measured and their relative combined standard uncertainties were determined. Large Area Sources Comparison Exercise (LASCE) was organized by International Committee on Radionuclide Metrology (ICRM) working group and coordinated by National Institute for Ionising Radiation Metrology (ENEA), Italy, to demonstrate equivalence of surface emission rate measurements at the international platform. BARC participated in the programme and the results of LASCE are also discussed in this paper.

Performance demonstration of 4πß(LS)-γ coincidence counting system for standardization of radionuclides with complex decay scheme.

A standardization of (134)Cs and (131)I was carried out in order to demonstrate the performance and applicability of the 4πß(LS)-γ coincidence counting system for standardization of radionuclides with complex decay scheme. The coincidence analyzer, capable of analyzing coincidence between beta and two gamma windows simultaneously, was developed and used for the standardization. The use of this dual coincidence analyzer has reduced the total experimental time by half. The activity concentrations obtained using the 4πß(LS)-γ coincidence counting system, a 4πß(PC)-γ coincidence counting system, and the CIEMAT/NIST method are in excellent agreement with each other within uncertainty limits and hence demonstrates its performance for standardization of radionuclides decaying with complex decay scheme. Hence use of this 4πß(LS)-γ coincidence counting system can be an alternative method suitable to standardize radionuclides with complex decay scheme with acceptable precision.

Development of liquid scintillation based 4πß(LS)-γ coincidence counting system and demonstration of its performance by standardization of 6°Co.

A single-vial, single-PMT 4πß(LS)-γ coincidence counting system has been developed at the Radiation Safety Systems Division, BARC. It has advantages of simple sample preparation, higher counting efficiency and the absence of self absorption over the conventional proportional counter based 4πß(PC)-γ coincidence counting system. The performance of the system is demonstrated by standardizing a (60)Co solution using the 4πß(LS)-γ coincidence counting system, 4πß(PC)-γ coincidence counting system and CIEMAT/NIST method and comparing the results obtained by each method. The detection efficiency of liquid scintillation counter of the 4πß(LS)-γ coincidence counting system was varied by color quenching, by chemical quenching and by varying the bias voltage applied to the LSC PMT. For the proportional counter based 4πß(PC)-γ coincidence counting system the detection efficiency was varied by source self absorption. The activity concentrations obtained using the 4πß(LS)-γ coincidence counting system, the 4πß(PC)-γ coincidence counting system and the CIEMAT/NIST method are comparable within the uncertainty limits.

Standardization of ¹³¹I: implementation of CIEMAT/NIST method at BARC, India.

The CIEMAT/NIST efficiency tracing method using ³H standard was implemented at Radiation Safety Systems Division, Bhabha Atomic Research Centre (BARC) for the standardization of ¹³¹I radioactive solution. Measurements were also carried out using the 4π ß-γ coincidence counting system maintained as a primary standard at the laboratory. The implementation of the CIEMAT/NIST method was verified by comparing the activity concentration obtained in the laboratory with that of the average value of the APMP intercomparison (Yunoki et al., in progress, (APMP.RI(II)-K2.I-131)). The results obtained by the laboratory is linked to the CIPM Key Comparison Reference Value (KCRV) through the equivalent activity value of National Metrology Institute of Japan (NMIJ) (Yunoki et al., in progress, (APMP.RI(II)-K2.I-131)), which was the pilot laboratory for the intercomparison. The procedure employed to standardize ¹³¹I by the CIEMAT/NIST efficiency tracing technique is presented. The activity concentrations obtained have been normalized with the activity concentration measured by NMIJ to maintain confidentiality of results until the Draft-A report is accepted by all participants. The normalized activity concentrations obtained with the CIEMAT/NIST method was 0.9985 ± 0.0035 kBq/g and using 4π ß-γ coincidence counting method was 0.9909 ± 0.0046 kBq/g as on 20 March 2009, 0 h UTC. The normalized activity concentration measured by the NMIJ was 1 ± 0.0024 kBq/g. The normalized average of the activity concentrations of all the participating laboratories was 1.004 ± 0.028 kBq/g. The results obtained in the laboratory are comparable with the other international standards within the uncertainty limits.

Quality audit programme for (99m)Tc and (131)I radioactivity measurements with radionuclide calibrators.

The use of radiopharmaceuticals in nuclear medicine for diagnosis and therapy has increased over the years with (99m)Tc and (131)I being most widely used. Quality audit programmes for radioactivity measurements of (131)I have been ongoing and the 12th audit was recently conducted among seventy nuclear medicine centres (NMC) in India. An audit for the activity measurements of (99m)Tc was conducted for the first time among ten NMCs in Mumbai, India. These programmes for radioactivity measurements have become very important to establish traceability of measurements to national and international standards and ensure accurate calibration of radionuclide calibrators. The results of both the audits are very encouraging. Ninety-four percent of the NMCs for (131)I activity measurements were within a window of +/-10% and for (99m)Tc one NMC was deviating more than +/-10%. The methodology adopted for the audit and results are discussed in detail in this paper.

Standardization of 192Ir solution at BARC.

A radioactive solution of 192Ir was standardized at Bhabha Atomic Research Centre (BARC) under the international intercomparison programme of the Bureau International des Poids et Measures (BIPM) by 4pibeta-gamma coincidence and 4pigamma counting techniques, which are primary and secondary methods of standardization, respectively. The activity concentration of the 192Ir solution obtained by the efficiency extrapolation technique and as reported to BIPM was 203.15 kBq g(-1) with a combined uncertainty of +/-0.3%. The activity concentration determined by 4pigamma counting was 202.88 kBq g(-1) with a combined uncertainty of +/-1.3%. These measurement results are comparable within the uncertainty limits. Detailed uncertainty budget for both the primary and secondary methods are included.