[en] Self-Powered Neutron Detectors(SPND) are currently used to estimate the power generation distribution and fuel burn-up in several nuclear power reactors in Korea. While they have several advantages such as small size, low cost, and relatively simple electronics required in conjunction with those usage, they have some intrinsic problems of the low level of output current, a slow response time, the rapid change of sensitivity which makes it difficult to use for a long term. In this paper, Monte Carlo simulation is accomplished to calculate the escape probability as a function of the birth position of emitted beta particle for a geometry of rhodium-based SPNDs. A simple numerical method calculates the initial generation rate of beta particles and the change of generation rate due to rhodium burn-up. Using the simulation result, the burn-up profile of rhodium number density and the neutron sensitivity are calculated as a function of burn-up time in reactors. The sensitivity of the SPND decreases non-linearly due to the high absorption cross-section and the non-uniform burn-up of rhodium in the emitter rod. In addition, for improvement of some properties of rhodium-based SPNDs which are currently used, this paper presents a new material and modified geometry. From searching nuclear data, Ag¹⁰⁹ is chosen as a replacing material for rhodium. Silver has a low neutron absorption cross-section and a high beta energy and a low density when it is compared with rhodium. The sensitivity and the density change of silver as a function of burn-up are calculated using this method. Also, this paper compares the initial sensitivity of a solid type with its of a tube type. The initial sensitivity is increased with the new material and the tube type. Silver is also found to be used for longer time than rhodium. The method used here can be applied to the analysis of other types of SPNDs and will be useful in the optimum design of new SPNDs for long term usage

[en] The conventional nuclear imaging system, which has widely been used in non-destructive testing, examination of nuclear contamination, disposal of nuclear fuel, transportation, and storage of high-level radioactive waste, provides the directional information of radiation sources such as the location or the distribution as an image of the radioactivity superimposed on a vision image of the same field of view. It is also possible to provide the radiation energy information in real time and distinguish two sources having different energies. But there are some issues to be considered to improve the system performance; (1) A special pinhole collimator is necessary for its application in the high-energy gamma-ray field. The conventional knife-edge pinhole collimator is not suitable for high-energy radiation field because much radiation scatters in the vicinity of the pinhole aperture and blurs the image. (2) In order to estimate the interaction position of gamma rays within the radiation detector, Anger algorithm is usually used in the nuclear imaging system. This method can be easily implemented and works well a medical gamma camera based on multi-PMT (a 2-D array of photomultiplier tubes). But Anger algorithm is not suitable for a nuclear imaging system using a single PSPMT (position sensitive PMT) because its output signals are not linear and are not uniform. (3) In addition to nuclear image, if the value of real-time exposure dose rate is supplied in the nuclear imaging system, it will be much useful. But the conventional system cannot measure the real-time exposure dose rate when obtaining the gamma image. For the optimum aperture design, a new-channeled collimator was introduced to reduce the image degradation by the scattering radiation, and its characteristics were analyzed by Monte Carlo simulation. Resolutions defined as the full-width at half-maximum (FWHM) of point spread functions and efficiency are calculated for collimators with several pinhole diameters from 4 mm to 8mm and channel heights from 2 mm to 10 mm. The efficiencies and resolutions of the channeled collimator are compared with those of the conventional knife-edge collimator. From the results, it was verified that the nuclear image by the new collimator was better than that by the conventional collimator. The optimum channel height (2 mm) and diameter of the pinhole collimator (4 mm) are also proposed based on the simulation results. To correct image distortion, an alternative method, a maximum likelihood position estimation (MLPE) method instead of an Anger position algorithm was introduced. Generally there are two ways to implement the MLPE method: (1) an experimental method, and (2) a computer simulation method. In this paper, the MLPE method using simulation instead of experiments, which can consider all stochastic processes converting the location of gamma-ray interaction with scintillator into position signals, has been proposed, implemented, and compared to the conventional algorithm. From the analysis and comparison of images, the quality of image from the MLPE was better than that of the conventional algorithm. We also verified the simulation method by comparison of simple phantom images obtained by simulation method and by experimental method for a small gamma camera consisting of a NaI (Tl) and a PSPMT. From these results, it is proposed that the simulation method could be applied for nuclear imaging system because the results of simulation MLPE is similar with those of experimental MLPE. Dose conversion unit (DCU), which is composed of a single channel analyzer (SCA), a read only-memory (ROM), a digital-to-analog converter (DAC), and a microprocessor, was proposed in order to measure the real-time exposure dose rate. The performance of the DCU incorporated with the theoretically calculated dose conversion factors was evaluated by measurement of exposure dose rates as a function of distance between gamma ray source and detector for several standard sources. The exposure dose rates measured by the DCU are deviated with the calculated values based on gamma factor within an 11.5%. A new portable nuclear imaging system combined with the DCU was developed for obtaining both gamma image and real-time exposure dose rate simultaneously

[en] Self-Powered Neutron Detectors (SPNDs) are currently used to estimate the power generation distribution and fuel burn-up in several nuclear power reactors in Korea. In this paper, Monte Carlo simulation is accomplished to calculate the escape probability of beta particle as a function of their birth position for the typical geometry of rhodium-based SPNDs. Also, a simple numerical method calculates the initial generation rate of beta particles and the change of generation rate due to rhodium burn-up. Using the simulation and the numerical method, the burn-up profile of rhodium density and the neutron sensitivity are calculated as a function of burn-up time in the reactor. The sensitivity of the SPNDs decreases non-linearly due to the high absorption cross-section and the non-uniform burn-up of rhodium in the emitter rod. In addition, for improvement of some properties of rhodium-based SPNDs which are currently used, this paper presents a new material. The method used here can be applied to the analysis of other types of SPNDs and will be useful in the optimum design of new SPNDs for long term usage

[en] In order to measure noble gas in the air, sampling technology is very important and n process manual of sampling is needed. This report has following contents: - development of first reduction step of water in air - development of second reduction step of water and CO2 - development of xenon and krypton sampling in air - development of first enrichment method in air sample This method will be applied in analysis of noble gas and education of novel analysts. Also, it is directly applied in reduction technology of noble gas in nuclear power facilities

[en] Environmental Radiation Monitoring was carried out with measurement of environment. Radiation and environmental radioactivity analysis on the sites of KAERI nuclear facilities and Seoul Research Reactors and their environments. The average level of environmental radiation dose measured by an ERM and the accumulated radiation dose by a TLD were almost same level compared with the previous years. The activity of gross alpha and gross beta, Tritium, Uranium and Strontium in environmental samples showed a environmental level. The radioactivities of most γ -radionuclides in air particulate, fallout, rain water and ground water were less than MDA except ⁴⁰K or ⁷Be which are natural radionuclides. However, not only ⁴⁰K or ⁷Be but also ¹³⁷Cs or ¹³¹I were detected in the soil, sediment and surface water

[en] An ultra-low background gamma spectrometer at underground laboratory using hybrid Compton suppression and anti-coincidence method is developed. The designed ultra-low background gamma spectrometer is composed of HPGe detector, NaI scintillation detectors for Compton suppression, and plastic scintillation sensors as a guard detector for the background reduction, and electronic circuits for signal processing. Influence of radon radionuclide is studied in order to test performance of the designed system. The background increase problem of radon will be solved by ventilation and injection of pure nitrogen gas. Using this setup system, measurement of small sample is performed without the chemical preprocessing The results of measurement were compared with those results with conventional alpha spectrometer and two results were similar from within uncertainty range

[en] Personal dosimeters based on PIN detectors have been widely used because of their simplicity and real time operation. In this paper, the optimal filter thickness and material designed by the Monte Carlo method is 1.0 mm Al plus 0.2 mm Cu. From the results of radiation characteristic analyses, the developed dosimeter has good performance when it is compared with the other conventional those as described below; The linearity due to the change of radiation intensity is kept within 8 % in 10 Sv ∼ 4 Sv, and the relative energy response to 137Cs is almost constant within ±10 % for above 65 keV. Generally the relative energy response of conventional dosimeter using a PIN diode is within ±20 %. For minimizing the non-linear sensitivity on energy, dose conversion algorithm was presented, which was able to consider pulse number as well as pulse amplitude related to absorbed energies. When dose conversion algorithm was used, the linearity of sensitivity was better about 38 % than that of dosimeters without usage of the electronic dose conversion algorithm

[en] 1. Completion of fabrication of gamma radiation detector for gamma-ray and for ERMS - Completion of fabrication of a large volume ionization chamber for monitoring gamma-ray - Completion of performance evaluation of radiation detector - Completion of development of an ionization chamber for high dose rate monitoring and for low dose rate - Completion of development of a remote communication module 2. Completion of development of integrated solutions for the analysis of dose rate, stabilization of an intelligent radiation monitoring system, performance test for field use, and construction of mass production - Completion of development of stabilization technology for an intelligent radiation monitoring system - Completion of performance test for field use - Completion of structural construction for user

[en] Surveys of radioactive contamination were performed for imported foodstuffs in 2003. The following samples among imported foodstuffs were selected from markets and Korea Food and Drug Administration(KFDA); the imported samples from country associated with the Chernobyl nuclear accident, the samples produced around the nuclear power plants or nuclear tests, the foodstuffs reported as radioacitive contamination materials in foreign country. After pretreatments such as drying and homogenization, samples were analyzed. The ¹³⁷Cs radionuclide was only measured among the regulation radionuclides(¹³⁷Cs, ¹³⁴Cs, ¹³¹I) of food code. All foodstuffs except Inonotus Obliquus(Chaga mushooms) are less than 17.0 Bq/kg or below the Minimum Detectable Activity (MDA). The activity concentrations of Chaga mushrooms from Russia ranged up to 131.25 Bq/kg which is almost 35% of the maximum permitted level of food code. The fraction of imported foodstuffs having meaningful radioactivity is small, however, the radioactive contamination survey of imported foodstuffs is still needed

[en] The MDA value has been estimated in radioactivity analysis of noble gas in atmosphere. It is proposed how to reduce MDA in ultra low background sample and introduced several type of MDA used in the field. The minimum MDA value for total xenon is 0.4 mBq/m³ and the range of MDA value is almost below 1 mBq/m³. This factor is lower than that value proposed from the company of Germany. Here the MDA of ⁸⁵Kr is proposed and the minimum time is determined