• Nuclear Engineering and Technology
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• v.41 no.6
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• pp.813-820
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• 2009

A rapid pneumatic transfer system (PTS) for an instrumental neutron activation analysis (INAA) is developed as an automatic irradiation facility involving the measurement of a short half-life nuclide and a delayed neutron counting system. Three new PTS designs with improved functions were constructed at the HANARO research reactor in 2006. The new system is composed of a manual system and an automatic system for both an INAA and a delayed neutron activation analysis (DNAA). The design and basic conception of a modified PTS are described, and the functions of system operation and control, radiation protection and emissions of radioactive gas are improved. In addition, a form of capsule transportation of these systems is tested. The experimental results pertaining to the irradiation characteristics with variation of the neutron flux and the temperature of the irradiation position with the irradiation time are presented, as is an analysis of the reference material for analytical quality control and uncertainty assessments.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.1
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• pp.42-46
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• 2016

The radioactive iodine ($^{131}I$) presents in the environment through the excrete process of nuclear medicine patients. In the detecting of low level of $^{131}I$ in the public water, the counting uncertainty has an effect on the accuracy and reliability of detecting $^{131}I$ radioactivity concentration. In this study, the contribution of sample amount, radioactivity concentration and counting time to the uncertainty was investigated in the case of public water sample. Sampling points are public water and the effluents of a sewage treatment plant at Sapkyocheon stream, Geumgang river. In each point, 1, 10 and 20 L of liquid samples were collected and prepared by evaporation method. The HPGe (High Purity Germanium) detector was used to detect and analyze emitted gamma-ray from samples. The radioactivity concentration of $^{131}I$ were in the range of 0.03 to 1.8 Bq/L. The comparison of the counting uncertainty of the sample amount, 1 L sample is unable to verify the existence of the $^{131}I$ under 0.5 Bq/L radioactivity concentration. Considering the short half-life of $^{131}I$ (8.03 days), a method for measuring 1 L sample was used. However comparing the detecting and preparing time of 1, 10 L respectively, detecting 10 L sample would be an appropriate method to distinguish $^{131}I$ concentration in the public water.

• Nuclear Engineering and Technology
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• v.40 no.4
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• pp.299-304
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• 2008

A detection system was set up to measure the neutron generation rate of a recently developed D-D neutron generator. The system is composed of a Si detector, He-3 detector, and electronics for pulse height analysis. The neutron generation rate was measured by counting protons using the Si detector, and the data was crosschecked by counting neutrons with the He-3 detector. The efficiencies of the Si and He-3 detectors were calibrated independently by using a standard alpha particle source $^{241}Am$ and a bare isotopic neutron source $^{252}Cf$, respectively. The effect of the cross-sectional difference between the D(d,p)T and $D(d,n)^3He$ reactions was evaluated for the case of a thick target. The neutron generation rate was theoretically corrected for the anisotropic emission of protons and neutrons in the D-D reactions. The attenuations of neutron on the path to the He-3 detector by the target assembly and vacuum flange of the neutron generator were considered by the Monte Carlo method using the MCNP 4C2 code. As a result, the neutron generation rate based on the Si detector measurement was determined with a relative uncertainty of ${\pm}5%$, and the two rates measured by both detectors corroborated within 20%.

• Journal of Radiation Protection and Research
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• v.45 no.2
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• pp.76-80
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• 2020

Background: To improve the measurement accuracy of liquid-scintillation counting for activity standardization, it is necessary to significantly reduce the background caused by thermal noise or after-pulses. We have therefore improved a movable 3 photomultiplier (3PM)-γ coincidence-counting method using the logical sum of three double coincidences for β events. Materials and Methods: We designed a new data-acquisition system in which β events are obtained by counting the logical sum of three double coincidences. The change in β-detection efficiency can be derived by moving three photomultiplier tubes sequentially from the liquid-scintillation vial. The validity of the method was investigated by activity measurement of ¹³⁴Cs calibrated at the Korea Research Institute of Standards and Science (KRISS) with 4π(PC)β-γ(NaI(Tl)) coincidence counting using a proportional counter (PC) for the β detector. Results and Discussion: Measurements were taken over 14 counting intervals for each liquidscintillation sample by displacing three photomultiplier tubes up to 45 mm from the sample. The dead time in each β- and γ-counting channel was adjusted to be a non-extending type of 20 ㎲. The background ranged about 1.2-3.3 s^-1, such that the contributions of thermal noise or after-pulses were negligible. As the β-detection unit was moved away from the sample, the β-detection efficiencies varied between 0.54 and 0.81. The result obtained by the method at the reference date was 396.3 ± 1.7 kBq/g. This is consistent with the KRISS-certified value of 396.0 ± 2.0 kBq/g within the uncertainty range. Conclusion: The movable 3PM-γ method developed in the present work not only succeeded in reducing background counts to negligible levels but enabled β-detection efficiency to be varied by a geometrical method to apply the efficiency extrapolation method. Compared with our earlier work shown in the study of Hwang et al. [2], the measurement accuracy has much improved. Consequently, the method developed in this study is an improved method suitable for activity standardization of β-γ emitters.

• Journal of Advanced Marine Engineering and Technology
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• v.15 no.5
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• pp.23-29
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• 1991

Uncertainty is studied in the measurements of average packing density, thickness of packed spheres and transmittance in the experiments to study the effect of the bed height and the existence of the bed side walls on the transmittance of radiative energy through packed spheres. The packing density of the bed is obtained by counting the number of the spheres packed in three pipes with different heights. The bed height of the packed spheres is estimated from the number of spheres contained in the bed by using the relation between the bed height and the sphere number. The transmittance is obtained by dividing the intensity of the transmitted laser beam by the incoming-beam intensity. From the analysis, the uncertainity in the measurements of transmittance is shown to be less than 10.2%(95% coverage).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.685-688
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• 2004

This paper addresses the study on developing the angular vibration calibration system which requires the highly accurate measurement technique of the amplitude and period of an oscillating angular motion. Two developed models for the low and high frequency ranges are introduced and their main features are also compared. In addition to the angular vibration exciters, a new measurement method, referred to the 'equi-angle sampling method', is proposed and its theoretical backgrounds are introduced. The proposed method is shown to provide much less measurement uncertainty, compared the fringe counting method. Experimental results demonstrate what amount of angular vibration amplitude measurement uncertainty is improved by suing the proposed equi-angle sampling method.

• Journal of Radiation Protection and Research
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• v.23 no.4
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• pp.237-242
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• 1998

The goal of this work was to optimize the liquid scintillation counting techniques for the determination of C-14 in environmental samples such as biological and air samples. Carbon-14 activities in most environmental samples were measured with direct $CO_2$ absorption method. The highest figure of merit was found through the variation of Carbosorb $E^{TM}$ and Permatluor $V^{TM}$ ratio, in the measurement windows. The best condition was 1:1 volume ratio. Average 2.35 g of $CO_2$ was reproducibly absorbed in the 20 ml mixture within 40 min. The counting efficiency determined by repeated analysis of NIST oxalic acid standard and the background count rate were measured to be $58.8{\pm}1.4%$ and $1.88{\pm}0.06\;cpm$, respectively in case of saturated solution. The correction curves of counting efficiency for partially saturated solutions and for saturated solutions with quenching were prepared, respectively. The overall uncertainty of the sample specific activity for near background levels was estimated to be about 7 % for 4 hours counting at 95 % confidence level. The long-term stability of samples has been checked for all the counting techniques over a two week periods, and no apparent change in counting efficiency and background level was found at that time.

• Nuclear Engineering and Technology
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• v.36 no.2
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• pp.121-126
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• 2004

3-PM liquid scintillation counting using the geometry-efficiency variation technique has been applied to the activity measurement of $^{204}T1$, which decays to $^{204}Hg\;and\;^{204}Pb\;by\;{\beta}^-$ and E.C., respectively. The TDCR values K have been derived over a wide range, 0.78 < K < 0.97, by displacing the detectors up to 50 mm away from an unquenched liquid scintillation sample $^{204}Tl$. The derived plots of the logic sums of double coincidences $N_D(K)$ very K vary linearly in the observed regions. The fractions of losses due to electron capture decay have been taken into account by employing a PENELOPE Monte Carlo simulation. The calibrated activity is 102.3 kBq at a reference date of July 1st, 2002 (UT) with a combined uncertainty of $0.63\%$. This is consistent with the value determined by means of the CIEMAT/NIST method at KRISS.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.11
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• pp.1123-1131
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• 2008

In this study, measurement uncertainty of instrumental neutron activation analysis was evaluated for ambient As concentration in PM2.5. Expanded uncertainties of the measurements were calculated by applying both ISO-GUM approximation and Monte Carlo Simulation(MCS). The estimate of As concentration on a specific day by the Monte Carlo Simulation differed from that of ISO-GUM approximation by less than 4%. Relative expanded uncertainties of As concentrations from a total number of 60 PM2.5 samples were also estimated to be more or less than 10% with 95% confidence level using the Monte Carlo Simulation. Sensitivity test of the measurement uncertainties showed that $\gamma$-ray counting error(62.3%), efficiency(18.5%), air volume(12.3%), neutron flux(2.3%), and absolute gamma-intensity(1.8%) are major factors of uncertainty variations.

• Nuclear Engineering and Technology
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• v.13 no.4
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• pp.229-236
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• 1981

The boron content in reactor grade aluminum has been determined by means of a capture gamma-ray counting method. The experimental detection limit is found to be 5.7% ppm with 10% uncertainty. In order to improve the sensitivity, the boron is preconcentrated from aluminum by cation exchange resin system. The accuracies of both methods, i.e., one by the direct measurement and the other by the measurement after preconcentration, are checked by an additive method. The results show good agreements with less than 5% deviation.