The evaluation of an on-site monitoring program for activity meter quality assurance with exemption-level sources.

This paper discusses the feasibility of a monitoring program for the quality assurance status of activity meters. We sent a questionnaire to clinical nuclear medicine departments of medical institutions, requesting information on their activity meters and quality assurance practices. On-site visits were conducted with exemption-level standard sources (Co-57, Cs-137 and Ba-133) for dose calibrators in nuclear medicine departments including physical inspection, accuracy and reproducibility. A method offering a quick check on the detection efficiency of the space dimension inside the activity meters was also introduced. For dose calibrator quality assurance, the daily checks had the highest implementation. However, annual checks and upon acceptance/after a repair check were reduced to 50% and 44%, respectively. The accuracy results of dose calibrators showed that all models exceeded the ±10% criteria with Co-57 and Cs-137 sources. The reproducibility results showed that some models exceeded the ±5% criteria with Co-57 and Cs-137 sources. The appropriate application of exemption-level standard sources considering the uncertainty that affects the measurement is discussed.

Antioxidative activity of water extract of sweet potato leaves in Taiwan.

This study reports the preparation of four varieties of water extract from sweet potato leaves from Taiwan, including TNG10, TNG57, TNG66 and YSP, and evaluates their antioxidative activity. The EC50 values (scavenging DPPH radicals) of TNG10, TNG57, TNG66 and YSP were 0.27±0.01, 0.19±0.01, 0.41±0.02, and 0.31±0.02mg/ml, respectively, on a freeze-dry weight basis. The total phenolic contents of these water extracts were in the order: TNG57>TNG10>TNG66>YSP. The TNG10 and TNG57 extracts exhibited better reducing power and scavenging effects of superoxide radicals than did TNG66 and YSP. At a concentration of 1mg/ml, TNG10 and TNG57 significantly protected HaCaT cells from H2O2-induced cytotoxicity. The water extracts of YSP had more flavonoids than had those of TNG66 which may have contributed to their higher activity in many antioxidative assays. These results suggest that the water extracts of all four varieties of sweet potato leaves, and especially TNG10 and TNG57, display potent antioxidative effects.

Intercomparison of conventional and QuickScan dicentric scoring for the validation of individual biodosimetry analysis in Taiwan.

PURPOSE: The dicentric chromosome assay (DCA), the gold standard for radiation biodosimetry, evaluates an individual absorbed radiation dose by the analysis of DNA damage in human lymphocytes. The conventional (C-DCA) and QuickScan (QS-DCA) scoring methods are sensitive for estimating radiation dose. The Biodosimetry Laboratory at Institute of Nuclear Energy Research (INER), Taiwan, participated in intercomparison exercises conducted by Health Canada (HC) in 2014, 2015 and 2018 to validate the laboratory's accuracy and performance. MATERIAL AND METHODS: Blood samples for the conventional dose response curve for Taiwan were irradiated with 0, 0.25, 0.5, 1, 2, 3, 4 and 5 Gy. Ten blind blood samples were provided by HC. Either or both of two methods of conventional (C) or QuickScan (QS) scoring could be chosen for the HC's intercomparison. For C-DCA triage scoring, only cells with 46 centromeres were counted and each scorer recorded the number of dicentrics in the first 50 metaphases or stopped scoring when 30 dicentrics were reached. Scorers also recorded how much time it took to analyze 10, 20, and 50 cells. Subsequently, the data were entered into the Dose Estimate software (DoseEstimate_v5.1) and dose estimates were calculated. With QS-DCA scoring, a minimum of 50 metaphase cells (or 30 dicentrics) were scored in apparently complete metaphases without verification of exactly 46 centromeres. RESULTS: For the blinded blood samples irradiated at HC and shipped to INER, the mean absolute deviation (MAD) derived after scoring 50 cells for C-DCA and QS-DCA was <0.5 Gy for all three intercomparisons, meeting the criteria for acceptance. CONCLUSION: The results indicated that the Biodosimetry Laboratory at INER can provide reliable dose estimates in the case of a large-scale radiation accident.

Primary standardization of (67)Ga radiopharmaceuticals.

The two-dimensional extrapolation technique and dead time extrapolation technique of 4pibeta-gamma-coincidence counting were used to standardize the activity of (67)Ga. The counting results of the two absolute counting techniques showed good agreement while the two-dimensional extrapolation technique could save about 50% of the total counting time in this study. The accuracy of the Capintec CRC-15R radionuclide calibrator used by the radiopharmacy of INER was studied in this research. A new calibration setting number, 99, was recommended to the radiopharmacy of INER in the Bayer 10mL sterile empty vial geometry.

Standardization of 109Cd by two methods.

109Cd is quite a useful nuclide for the calibration of X-ray spectroscopy, gamma-ray spectroscopy or as an excitation source in X-ray fluorescence. In this work, 4π(PC)e-X coincidence counting and 4π(LS)ce counting were used to determine the activity of the 109Cd solution. The two methods showed good agreement in their counting results. On the other hand, the mean value came from the results of the two methods was used to calibrate the well type ionization chambers to maintain the radioactivity measurement standard of 109Cd at INER.

Absolute counting of 188Re radiopharmaceuticals.

The Institute of Nuclear Energy Research (INER) has provided 188Re radiopharmaceuticals for hospitals in Taiwan. To enhance the accuracy of commercial radionuclide calibrators used by radiopharmacies and hospitals, and to ensure that patients receive proper doses of these radiopharmaceuticals, it is very important to standardize this nuclide. The 4pibeta-gamma coincidence counting method was used to standardize the mass activities of 188Re in this study. At the same time, three well type ionization chambers, Centronic IG11-N20, Centronic IG11-A20, and ISOCAL-IV, were calibrated by the standardized solutions of the nuclide. In this research, the calibration figures of ISOCAL-IV for the nuclide were consistent with the results of National Physical Laboratory (NPL, UK). The outcome implied that the results of coincidence counting did mutually agree. On the other hand, the radionuclide calibrator in the radiopharmacy was producing measurement errors of about 20% when using the manufacturers recommended calibration setting: an accurate correction factor has now been determined in this study.

Reference drums used in calibration of a plastic scintillation counter in a 4π counting geometry.

In this study, two kinds of reference drums were developed. One type was constructed with nine layers of large-area sources filled with different materials having five different densities. The other type of reference drums was constructed with nine rod sources filled with the same materials of different densities. The efficiency calibration of a plastic scintillation counter in 4π counting geometry using these two kinds of drums showed that rod-source drums resulted in higher counting efficiency than layered source drums. The counting rates obtained from rod-source drums were closer to those obtained from a standard drum with water solution than counting rates from drums with layered sources. The results of this study recommend to use reference drums with rod-sources to compensate the drawbacks of standard drums with water solution of not being able to adjust the density of material. The proposed reference drums improve the accuracy of radioactivity analysis for waste drums of different densities.

Comparison exercise on activity determination of radioactive waste drums in Taiwan.

The National Radiation Standard Laboratory of Taiwan organized in 2014 a comparison exercise by distributing 210 L drum-typed samples to seven radioactive waste analysis laboratories in Taiwan. Four drums were filled with uniformly distributed active carbon, water, resin and concrete, respectively and five drums were filled with cracked metals and heterogeneously distributed radioactive sources. Measurement uncertainties of participants results are in the range 3­40% (k=2) and about 96% of the reported results produced En values (ISO, 1997) smaller than one for drums with activity uniformly distributed. The minimum discrepancies, expressed as Bi values (ISO, 1997), of drums with heterogeneously distributed 137Cs and 60Co were 0.34 and 0.17, respectively.

The absolute counting of 166mHo, 58Co and 88Y.

In this study, absolute 4pi beta-gamma-coincidence counting was used to measure the mass activity of 166mHo, 58Co and 88Y. For 166mHo and 88Y, three gamma windows were set to study the systematic error caused by the different gamma window settings. To eliminate the effect arising from the large difference in counting efficiency of the 4pi beta counter between electron capture events and beta+ particles, the two-dimensional extrapolation method was used to measure 58Co. The measurement results for the three nuclides were linked with the BIPM SIR through two APMP regional comparisons, APMP.RI(II)-K2, Ho-166m and APMP.RI(II)K2.Co-58, Y-88. Results are presented.

The alpha and beta emitter measurement system in INER. Institute of Nuclear Energy Research.

An alpha/beta emitter measurement system used to calibrate surface sources following the guidelines of ISO 8769 has been established in Institute of Nuclear Energy Research (INER) around the year 2000. This system consists of a windowless proportional counter with a uniformity of 0.28% when measuring the emission rate of a source on a centered area of 100 mm x 150 mm, and a uniformity of 0.62% when the source area was 150 mm x 200 mm. Four 100 mm x 150 mm sources (90Sr + 90Y, 36Cl, 14C and 241Am) had been measured by this system. The measurement results of the above four sources when compared with those of National Physical Laboratory, UK (NPL) showed difference between the two laboratories of < 1%.

Measurement and calibration of metal and non-metal wastes produced from decommissioning.

This report described a radioactive waste reference drum which was established with large-area sources and metal slices. This reference drum could be applied in calibration or testing of drum counting systems having 4π counting geometry and being made with plastic scintillators. This metal reference drum has the advantages of easy operation, low natural background and it also has agreeable measurement efficiency calibration curves for the drum counting system as the non-metal reference drum studied previously. On the other hand, this study explored the counting efficiency variations of the drum counting system by simulations of the metal reference drum being filled with wastes up to different heights within the drum. With the exploration, it is feasible to correct the measurement errors caused by different quantities of waste filling.

Comparing standard Bonner spheres and high-sensitivity Bonner cylinders.

Standard Bonner spheres and proposed high-sensitivity Bonner cylinders were calibrated in a neutron calibration room, using a (252)Cf source. The Bonner sphere system consists of 11 polyethylene (PE) spheres of various diameters and 4 extended spheres that comprise embedded metal shells. Similar to the design of Bonner spheres, a set of Bonner cylinders was assembled using a large cylindrical (3)He tube as the central probe, which was wrapped using various thicknesses of PE. A layer of lead was employed inside one of the PE cylinders to increase the detection efficiency of high-energy neutrons. The central neutron probe used in the Bonner cylinders exhibited an efficiency of ∼17.9 times higher than that of the Bonner spheres. However, compared with the Bonner spheres, the Bonner cylinders are not fully symmetric in their geometry, exhibiting angular dependence in their responses to incoming neutrons. Using a series of calculations and measurements, this study presents a systematic comparison between Bonner spheres and cylinders in terms of their response functions, detection efficiencies, angular dependences and spectrum unfolding.

Proficiency test for clearance mixed-nuclide samples.

In 2010, the National Radiation Standard Laboratory held a proficiency test for measurement and analysis of clearance mixed-nuclide samples. Two types of samples, box-shape and drum-shape, containing (60)Co and (137)Cs mixed solutions were measured by the participating laboratories and their results were then compared with the reference values. Seven participants used plastic scintillator counting systems and two participants used HPGe spectrometer systems to join in this study, obtaining 40 measurement results. The evaluation results showed that all the participants passed the requirements of this proficiency test, E(n)≦1, and the discrepancy was between -25% and 50%.

The performance evaluation of a movable gamma-ray counting system for radwaste measurement.

Performance tests of a movable gamma-ray waste drum scanning system were carried out in this study. The scanner consists of a single HPGe detector on a movable cart with a 90° collimation angle to the observed item. The detection efficiency for (137)Cs was determined using the ISOTOPIC software. The activities of 35 low-level radioactive waste drums were measured using this system and compared with the results of two other measurement systems. This movable scanning system gave the same result as the other two systems with a relative spread (one standard deviation) of about 7.2%.

Evaluating practicability of an LSC method for routine monitoring gross alpha and beta activities in water samples in Taiwan.

A procedure using liquid scintillation counting for the monitoring of gross alpha and beta activities in environmental water was implemented to improve the conventional procedure using GFPC adopted in Taiwan. The new procedure was acquired through calibration and validation, and then was applied to the monitoring of surface water in Taiwan. This procedure can improve 2-4 times of detection efficiencies and takes only 70-80% of analysis time with reliable accuracy. With these features, the newly developed procedure is favorable during emergency situations.

Proficiency testing feasibility study for the measurement of gamma-emitting clearance samples.

A proficiency testing feasibility study program was proposed by the National Radiation Standard Laboratory (NRSL) of Taiwan to understand the capabilities of laboratories dealing with clearance measurements, and to issue related technical criteria for radioactive waste assay. In this program, twelve blind test samples with different levels of radioactivity, radionuclides and different packing densities were prepared. Seven laboratories participated in this program and fourteen instruments were tested. Participants were required to report their raw data to NRSL, which would evaluate the effects of the background, geometry and the packing density to obtain the final results of the participants. In this study, the typical uncertainties of the participants were around 24%, and about 70% of the measured results produced E(n) values, which were smaller than one.

The calibration and evaluation of a radioactive waste drum counting system.

The drum counting system was calibrated in this study. For (137)Cs, the counting efficiencies were around 14-1% when the density of the waste of the drum was changed from 0.15 to 2.3 g cm(-3). The effects of the background, hot spot, system linearity, sample density and weighing were also evaluated in this work. The combined standard uncertainty of the drum counting system for the (137)Cs in the density of 1g cm(-3) was around 12%. To verify the counting system, the drums containing radioactive solution were prepared by the NMI as the blind samples. A discrepancy below 15% was shown between the counting results and the reference values of the NMI.