• Nuclear Engineering and Technology
• /
• v.49 no.4
• /
• pp.792-800
• /
• 2017

The essential requirement of a material to be used for engineering purposes at nuclear establishments is its ability to attenuate the most penetrating ionizing radiations, gamma $({\gamma})-rays$. Mostly, high-Z materials such as heavy concrete, lead, mercury, and their mixtures or alloys have been used in the construction of nuclear establishments and thus termed as nuclear engineering materials (NEM). The NEM are classified into two categories, namely opaque and transparent, depending on their behavior towards the visible spectrum of EM waves. The majority of NEM are opaque. By contrast, various types of glass, which are transparent to visible light, are necessary at certain places in the nuclear establishments. In the present study, ${\gamma}-ray$ shielding behaviors (GSB) of six glass samples (transparent NEM) were evaluated and compared with some opaque NEM in a wide range of energy (15 keV-15 MeV) and optical thickness (OT). The study was performed by computing various ${\gamma}-ray$ shielding parameters (GSP) such as the mass attenuation coefficient, equivalent atomic number, and buildup factor. A self-designed and validated computer-program, the buildup factor-tool, was used for various computations. It has been established that some glass samples show good GSB, thus can safely be used in the construction of nuclear establishments in conjunction with the opaque NEM as well.

• Progress in Superconductivity
• /
• v.9 no.2
• /
• pp.162-166
• /
• 2008

We are developing a sensitive gamma ray spectrometer based on superconducting transition edge sensors. The detector consists of a small piece of high purity Sn as an absorber and a Ti/Au bilayer as a temperature sensor. It is designed to measure the thermal signal caused by absorption of gamma rays. The mechanical support and the thermal contact between the absorber and the thermometer were made with Stycast epoxy. The bilayer was formed by e-beam evaporation and patterned by wet etching on top of a $SiN_X$ membrane. A sharp superconducting transition of the film was measured near 100 mK. When the film was biased to the edge of the transition, signals were observed due to single photon absorption emitted from an $^{241}Am$ source. The measured spectrum showed several characteristic peaks of the source including 59.5 keV gamma line. The full with at half maximum was about 900 eV for the 59.5 keV gamma line. The background was low enough to resolve low energy lines. Considerations to improve the energy resolution of the gamma ray spectrometer are also discussed.

• Journal of Radiation Protection and Research
• /
• v.42 no.3
• /
• pp.158-165
• /
• 2017

Background: Nuclear facilities in South Korea have generally adopted pressurized ion chambers to measure ambient gamma ray exposure rates for monitoring the impact of radiation on the surrounding environment. The rates assessed with pressurized ion chambers do not distinguish between natural and man-made radiation, so a further step is needed to identify the cause of abnormal variation. In contrast, using NaI(Tl) scintillation detectors to detect gamma energy rates can allow an immediate assessment of the cause of variation through an analysis of the energy spectra. Against this backdrop, this study was conducted to propose a more effective way to monitor ambient gamma exposure rates. Materials and Methods: The following methods were used to analyze gamma energy spectra measured from January to November 2016 with NaI detectors installed at the Korea Atomic Energy Research Institute (KAERI) dormitory and Hanbat University. 1) Correlations of the variation of rates measured at the two locations were determined. 2) The dates, intervals, duration, and weather conditions were identified when rates increased by $5nSv{\cdot}h^{-1}$ or more. 3) Differences in the NaI spectra on normal days and days where rates spiked by $5nSv{\cdot}h^{-1}$ or more were studied. 4) An algorithm was derived for automatically calculating the net variation of the rates. Results and Discussion: The rates measured at KAERI and Hanbat University, located 12 kilometers apart, did not show a strong correlation (coefficient of determination = 0.577). Time gaps between spikes in the rates and rainfall were factors that affected the correlation. The weather conditions on days where rates went up by $5nSv{\cdot}h^{-1}$ or more featured rainfall, snowfall, or overcast, as well as an increase in peaks of the gamma rays emitted from the radon decay products of $^{214}Pb$ and $^{214}Bi$ in the spectrum. This study assumed that $^{214}Pb$ and $^{214}Bi$ exist at a radioactive equilibrium, since both have relatively short half-lives of under 30 minutes. Provided that this assumption is true and that the gamma peaks of the 352 keV and 1,764 keV gamma rays emitted from the radionuclides have proportional count rates, no man-made radiation should be present between the two energy levels. This study proved that this assumption was true by demonstrating a linear correlation between the count rates of these two gamma peaks. In conclusion, if the count rates of these two peaks detected in the gamma energy spectrum at a certain time maintain the ratio measured at a normal time, such variation can be confirmed to be caused by natural radiation. Conclusion: This study confirmed that both $^{214}Pb$ and $^{214}Bi$ have relatively short half-lives of under 30 minutes, thereby existing in a radioactive equilibrium in the atmosphere. If the gamma peaks of the 352 keV and 1,764 keV gamma rays emitted from these radionuclides have proportional count rates, no man-made radiation should exist between the two energy levels.

• Journal of Astronomy and Space Sciences
• /
• v.33 no.2
• /
• pp.75-92
• /
• 2016

It is generally believed that the high energy emissions from isolated pulsars are emitted from relativistic electrons/positrons accelerated in outer magnetospheric accelerators (outergaps) via a curvature radiation mechanism, which has a simple exponential cut-off spectrum. However, many gamma-ray pulsars detected by the Fermi LAT (Large Area Telescope) cannot be fitted by simple exponential cut-off spectrum, and instead a sub-exponential is more appropriate. It is proposed that the realistic outergaps are non-stationary, and that the observed spectrum is a superposition of different stationary states that are controlled by the currents injected from the inner and outer boundaries. The Vela and Geminga pulsars have the largest fluxes among all targets observed, which allows us to carry out very detailed phase-resolved spectral analysis. We have divided the Vela and Geminga pulsars into 19 (the off pulse of Vela was not included) and 33 phase bins, respectively. We find that most phase resolved spectra still cannot be fitted by a simple exponential spectrum: in fact, a sub-exponential spectrum is necessary. We conclude that non-stationary states exist even down to the very fine phase bins.

• Nuclear Engineering and Technology
• /
• v.51 no.3
• /
• pp.719-722
• /
• 2019

Gamma-ray images generally suffer from a lot of noise because of low photon detection in the gamma camera system. The purpose of this study is to improve the image quality in gamma-ray images using a gamma camera system with a fast nonlocal means (FNLM) noise reduction algorithm with an acceleration function. The designed FNLM algorithm is based on local region considerations, including the Euclidean distance in the gamma-ray image and use of the encoded information. To evaluate the noise characteristics, the normalized noise power spectrum (NNPS), contrast-to-noise ratio (CNR), and coefficient of variation (COV) were used. According to the NNPS result, the lowest values can be obtained using the FNLM noise reduction algorithm. In addition, when the conventional methods and the FNLM noise reduction algorithm were compared, the average CNR and COV using the proposed algorithm were approximately 2.23 and 7.95 times better than those of the noisy image, respectively. In particular, the image-processing time of the FNLM noise reduction algorithm can achieve the fastest time compared with conventional noise reduction methods. The results of the image qualities related to noise characteristics demonstrated the superiority of the proposed FNLM noise reduction algorithm in a gamma camera system.

• Journal of Radiation Protection and Research
• /
• v.43 no.3
• /
• pp.85-96
• /
• 2018

Background: A variety of inorganic scintillators have been developed and improved for use in radiation detection and measurement, and in situ gamma-ray spectrometry in the environment remains an important area in nuclear safety. In order to verify the feasibility of promising scintillators in an actual environment, a performance test is necessary to identify gamma-ray peaks and calculate the radioactivity from their net count rates in peaks. Materials and Methods: Among commercially available scintillators, $LaBr_3(Ce)$ scintillators have so far shown the highest energy resolution when detecting and identifying gamma-rays. However, the intrinsic background of this scintillator type affects efficient application to the environment with a relatively low count rate. An algorithm to subtract the intrinsic background was consequently developed, and the in situ calibration factor at 1 m above ground level was calculated from Monte Carlo simulation in order to determine the radioactivity from the measured net count rate. Results and Discussion: The radioactivity of six natural radionuclides in the environment was evaluated from in situ gamma-ray spectrometry using an $LaBr_3(Ce)$ detector. The results were then compared with those of a portable high purity Ge (HPGe) detector with in situ object counting system (ISOCS) software at the same sites. In addition, the radioactive cesium in the ground of Jeju Island, South Korea, was determined with the same assumption of the source distribution between measurements using two detectors. Conclusion: Good agreement between both detectors was achieved in the in situ gamma-ray spectrometry of natural as well as artificial radionuclides in the ground. This means that an $LaBr_3(Ce)$ detector can produce reliable and stable results of radioactivity in the ground from the measured energy spectrum of incident gamma-rays at 1 m above the ground.

• Journal of the Korean institute of surface engineering
• /
• v.56 no.1
• /
• pp.84-93
• /
• 2023

The spent nuclear fuel is burned during the planned cycle in the plant and then generates elements such as actinide series, fission products, and plutonium with a long half-life. An 'interim storage' step is needed to manage the high radioactivity and heat emitted by nuclides until permanent-disposal. In the case of Korea, there is no space to dispose of high-level radioactive waste after use, so there is a need for a period of time using interim storage. Therefore, the intensity of neutrons and gamma-ray must be determined to ensure the integrity of spent nuclear fuel during interim storage. In particular, the most important thing in spent nuclear fuel is burnup evaluation, estimation of the source term of neutrons and gamma-ray is regarded as a reference measurement of the burnup evaluation. In this study, an analysis of spent nuclear fuel was conducted by setting up a virtual fuel burnup case based on CE16×16 fuel to check the total amount and spectrum of neutron, gamma radiation produced. The correlation between BU (burnup), IE (enrichment), and CT (cooling time) will be identified through spent nuclear fuel burnup calculation. In addition, the composition of nuclide inventory, actinide and fission products can be identified.

• Journal of Sensor Science and Technology
• /
• v.4 no.4
• /
• pp.1-9
• /
• 1995

The ${\gamma}$-ray deposition spectra were calculated by Monte Calro method to obtain the scintillation characteristics of the ${\gamma}$-ray for BGO scintillation detector with the spherical shape of 1.25 cm radius. The code used in calculating the ${\gamma}$-ray deposition spectra was made for personal computer with qbasic language. Also the ${\gamma}$-ray energy spectra of $^{22}Na$, $^{137}Cs$ and $^{207}Bi$ were measured with the detector. The energy dependent resolution below 2000 keV for the detector was determined by estimating the standard deviation of the photopeak fitted with gaussian function, and $X^{2}$ fitting using Nardi's empirical formula. The measured spectra of $^{22}Na$ and $^{137}Cs$ were compared with the broadened spectra which were obtained by broadening the calculated ${\gamma}$-ray deposition spectra with the energy dependent resolution. The absolute efficiency and the intrinsic peak efficiency of the detector were obtained by calculating the ${\gamma}$-ray deposition spectrum with the code.

• Journal of IKEEE
• /
• v.20 no.4
• /
• pp.337-343
• /
• 2016

This study conducted the gamma ray spectroscopic analysis of the microcolumnar CsI:Tl deposited onto the SiPMs using thermal evaporation deposition. The SEM measured thickness of microcolumnar CsI:Tl and of its individual columns. From the SEM observation, the measured thickness of CsI:Tl were $450{\mu}m$ and $600{\mu}m$. The gamma ray spectroscopic properties of microcolumnar CsI:Tl, $450{\mu}m$ and $600{\mu}m$ thick deposited onto the SiPMs were analyzed using standard gamma ray sources $^{133}Ba$ and $^{137}Cs$. The spectroscopic analysis of microcolumnar CsI:Tl deposited onto the SiPMs included the measurements of response linearity over the $^{137}Cs$ gamma ray intensity; and gamma ray energy spectrum. Furthermore from the gamma ray spectrum measurement of $^{133}Ba$ and $^{137}Cs$, $450{\mu}m$ thick CsI:Tl showed good efficiency when measured with $^{133}Ba$ and $600{\mu}m$ thick CsI:Tl was highly efficient when measured with $^{137}Cs$.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.2
• /
• pp.70.1-70.1
• /
• 2010

최근에 새롭게 발견된 초신성잔해 G353.6-0.7은 $\gamma$-ray source로부터 발견된 최초의 초신성 잔해이다. 이 초신성잔해의 중앙에서는 밝은 X-ray compact source, XMMU J173203.3-344518이 발견되었다. 우리는 위 X-ray compact source 근처에 IR source, IRAS 17287-3443이 매우 가까이 있음을 발견하고, Spitzer data를 이용하여 이 IR source에 대하여 자세히 분석한다. 24 um image에서 IR source는 bipolar feature를 보이며, 매우 강한 중앙지역은 8 um 에서도 extended feature를 보여준다. Spitzer IRS spectrum에서는 [Ne II] 12.88 um 방출선이 강하게 나오는 것이 특징이며, 우리는 또한 이 IR source에 embedded 된 것으로 의심되는 point source를 분석한다.