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.

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.

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.

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.

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.

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%.

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%.

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.