A Study on the Shielding Ability of Current Aerospace Materials

우종관,Sue Lynn Lee,Dong LIU 한국물리학회 2019 새물리 Vol.69 No.2

Space radiation is one of the biggest concerns for manned spaceflights, and along with the swift development of spaceflight enterprises, research on materials to be use as shields against space radiation has become increasingly important. In this study, we summarize the major composition of space radiation and define the human phantom scoring volume, the shielding materials and the geometry of shielding structure. Then, we comprehensively consider the radiation shielding properties of various materials, together with a consideration of the mass problems associated with those shielding materials. The radiation shielding ability of materials against certain space radiation particles was appraised from the perspectives of radiation dose. The results showed for shielding materials that of about the same mass, employing composites and non-metal materials as shielding materials rather than metals or alloys was more advantageous. In addition, in practical applications, the cabin walls of spaceships usually consist of multiple layers. In this situation, cabin wall that combines high-density layers and low-density layers alternately has the optimal shielding effect.

펠티에 소자를 이용한 안개상자 개발

우종관,권진영,박상태 대한방사선방어학회 2011 방사선방어학회지 Vol.36 No.3

A Simulation Study to veto the Cosmic Proton with a Polystyrene Scintillator

우종관,Dong Liu 한국물리학회 2020 새물리 Vol.70 No.1

Most cosmic particles around a detector in space near the Earth are protons. Sometimes, we need to reject the protons to enhance the efficiency of particle experiments. In this study, we try to find the proper thickness of a polystyrene scintillator to reject protons by using a Monte Carlo simulation tool, GEANT4, which is a common tool in high-energy experimental physics. We assume that a detector is shielded by a cylindrical shell polystyrene scintillator. Then, we inject protons, with energies from 150 MeV to 10 GeV into the polystyrene scintillator. The multiple scattering between a proton and the polystyrene molecules causes the protons to lose energy and finally stop. By calculating the energy of proton lost in the scintillator, we could obtain information on the shielding ability of polystyrene against cosmic protons.

Investigation of a Multi-radiotherapy Method: BNCT followed by Proton Therapy

우종관,Dong LIU 한국물리학회 2021 새물리 Vol.71 No.11

In this paper, a multi-radiotherapy method is proposed, which combine proton therapy with boron neutron capture therapy (BNCT). In this multi-radiotherapy method, BNCT is implemented, firstly, in which, the 4He ion and 7Li ion are emitted to destroy the local cell with the radiation of thermal neutron, and normally they stop at inside of the local cell due to their short decay ranges. As a result, a large number of 7L ions are accumulated in the target cell. Then, proton therapy is implemented. Based on the nuclear bombardment reaction 7Li (p, alpha) 4He, beside of the dose from the original proton beam, an additional dose contribution might be induced by two alpha particles (each has energy of about 8.7 MeV) emitted for a target cell. For evaluating the new multi-radiotherapy method, are used the Monte Carlo method. Through analyzing the dose distribution of this multi-radiotherapy method and comparising BNCT and proton therapy, we can conclud that under similar distributions of the physical dose, the multi-radiotherapy method may potentially enhance the radiation destruction efficiency for target cells.

The Comparison Study on Dose Distribution of 6He and 4He Ion Beams

우종관,Dong LIU 한국물리학회 2021 새물리 Vol.71 No.2

In this study, we evaluate the dose distributions of 4He and 6He ion beams under the same irradiation settings by using the Monte Carlo method. For the simulations, we defined a water phantom that which includes three normal regions and one target region for measuring the dose deposition in various regions. In addition, we define the 4He and the 6He ion beams with specified parameters. Then, we obtain the distributions of the doses and the tracks of 4He and 6He ion beams and calculate the dose deposited in each region. The calculated results show that in the proximal volume, lateral volume, distal volume, and target volume, the dose depositions of the 4He ion beam are 73.77%, 31.44%, 73.5%, and 98.50% of that of 6He ion beam. In conclusion, we can say from the aspect of physical dose distribution, that the 4He ion beam is more ideal than the 6He ion beam. To more objectively evaluate the therapatic effects of 4He and 6He ion beams, in our need experiment-based study, we will consider the biological effects of 4He and 6He ion beams.

An Investigation of Muon Therapy

우종관,Dong Liu 한국물리학회 2020 새물리 Vol.70 No.2

The muon is a subatomic particle that includes the positive and negative muon with a charge of 1 and 1, respectively. For the mass, the muon is heavier than the electron. As for a proton beam, the muon beam shows a Bragg peak when it interacts with materials. Therefore, the muon beam, as well as the proton beam, can also be considered as a candidate for radiotherapy. In this study, based on the Monte Carlo method, we defined a water phantom that which included a target volume and three interesting volumes. Then, the interaction processes of proton, positive and negative muon beams in materials were simulated. Moreover, the dose depositions of proton beam, positive and negative muon beams in each volume were calculated. An analysis of the calculated results, showed that compared to a proton beam, especially the negative muon beam, had an advantage in reducing the physical dose deposition in the upstream volume of the target.

Discrimination of Charged Particles in a Neutral Beam Line by Using a Solid Scintillation Detector

우종관,고재우,Dong Liu 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.2

In the past several decades, many studies have been conducted to search for non-baryonic dark matter, such as weakly interactive massive particles (WIMPs). In the search for WIMPs, charged particles incident on the detector are background particles because WIMPs are neutral. Charged particles originate from various sources, such as cosmic rays and laboratory materials surrounding the main detector. Therefore, a veto that discriminates charged particles can improve the particledetection efficiency of the entire experiment for detecting WIMPs. Here, we investigate in the thickness range of 1 mm to 5 mm, the optimal thickness of a polystyrene scintillator as a chargedparticle veto detector. We found that 3-mm-thick polystyrene provides the best performance to veto charged particles and the charged-particle background in the search for the WIMP signal. Furthermore, we fabricated 3-mm-thick and 5-mm-thick polystyrene charged particle veto detectors that will be used in an underground laboratory in the search for WIMP dark matter. After exposing those detectors are the actual beam line, we compared the rate of charged particles measured using those detectors and the rate simulated through a Monte Carlo simulation.

중성 케이온의 붕괴 $K_{L}^{0} \to \pi^{0}\pi^{0}$가 $K_{L}^{0}\rightarrow\pi^{0}\pi^{0}\gamma$ 사건으로 오인되는 확률에 대한 연구

우종관,고재우,Dong LIU 한국물리학회 2016 새물리 Vol.66 No.11

Neutral kaon decay, $K_{L}^{0}\rightarrow\pi^{0}\pi^{0}\gamma$, produces five gamma rays, decay rates of which can be calculated by using a chiral perturbation theory while neutral kaon decay, $K_{L}^{0}\rightarrow\pi^{0}\pi^{0}$, produces four gamma rays in the final state. However, the $K_{L}^{0} \to \pi^{0}\pi^{0}$ decay mode can be misunderstood as those of five gamma rays decay when $\pi^{0}$ produces a $e^{+}e^{-}$ pair and one gamma ray. In addition, distinguishing between the $K_{L}^{0}\rightarrow\pi^{0}\pi^{0}$ decay mode and the $K_{L}^{0}\rightarrow\pi^{0}\pi^{0}\gamma$ decay mode is difficult when the reconstruction masses of $K_{L}^{0}$ are about $500~\rm MeV$. In this paper, we proposed a way to distinguish between the two decay modes measured in a 2-dimensional-array CsI calorimeter, and we used GEANT4 to calculate the percent misunderstanding of the $K_{L}^{0}\rightarrow\pi^{0}\pi^{0}\gamma$ decay mode by the detector to be about 0.028\%. 중성케이온의 한 붕괴과정, $K_{L}^{0}\rightarrow\pi^{0}\pi^{0}\gamma$는 최종적으로 5개의 감마선이 방출된다. $K_{L}^{0}\rightarrow\pi^{0}\pi^{0}\gamma$ 붕괴의 붕괴율은 카이랄 섭동 이론 등으로 계산할 수 있다. $K_{L}^{0}\rightarrow\pi^{0}\pi^{0}$ 붕괴과정은 최종적으로 4개의 감마선을 방출하지만 $K_{L}^{0}\rightarrow\pi^{0}\pi^{0}$ 붕괴과정 가운데 하나의 파이온 ($\pi^{0}$)이 $e^{+}e^{-}\gamma$로 붕괴해서 검출기에 5개의 신호를 남길 수 있다. 재구성된 입사 입자 중성케이온 ($K_{L}^{0}$)의 질량 값이 $500~\rm MeV$일 경우에는 $K_{L}^{0}\rightarrow\pi^{0}\pi^{0}\gamma$ 붕괴와 구분이 어렵다. 이번 연구에서는 GENAT4 전산모사를 이용해서 $K_{L}^{0} \rightarrow \pi^{0}\pi^{0}$ 붕괴과정이 $K_{L}^{0} \rightarrow \pi^{0}\pi^{0}\gamma$ 붕괴로 오인될 경우에 대해서 연구 하였고 그 확률값이 $0.028 \%$임을 계산하였다.

A Pulse Shape Discrimination Method with CsI Using the Ratio of Areas for Identifying Neutrons and Gamma Rays

우종관,고재원,Silin Na,김용주,이효상 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.5

Identification of gamma rays and neutrons is a fundamental technique used in elementary particle physics experiments, such as the search for dark matter, double beta decay, etc. The pulse shape discrimination (PSD) methods with liquid and crystal scintillators, a well-known technology, have been under development for several decades. The PSD methods with crystal scintillators are known to be less stable and less effective than PSD methods with liquid crystals. Here, an improved PSD technique with a CsI crystal scintillator based on the well-known PSD methods with liquid scintillators is introduced. In this study, we found the possibility that the proposed PSD with a CsI crystal scintillator provides a performance to discriminate gamma rays and neutrons equivalent to that of a PSD with a liquid scintillator.

유한요소법을 이용한 조건에 따른 마모 영역별 2차원 프레팅 마모 해석

우종관(Jong Kwan Woo),배준우(Joon Woo Bae),이춘열(Choon Yeol Lee),채영석(Young Suck Chai) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3

In nuclear power plant, fretting wear, caused by flow induced vibration (FIV), can make a serious problem in a U-tube bundle in steam generator. In this study, finite element analysis of the fretting wear on the secondary side of the steam generator was investigated which arises between U-tubes and their supports or foreign objects. Using finite element method, two-dimensional models with cylindrical or plate supports were adopted to investigate the fretting wear problems. As boundary conditions, various combinations of loads are applied to verify different fretting mechanisms, such as stick only, stick-slip and gross slip wear. For this purpose, four different load conditions are considered and in the finite element analysis, ABAQUS are used with the program which is developed to calculate wear depth and modify input files at each cycle. As a result, regions for each wear mechanism are found and fretting wear map is constructed, which can be used as a reference or criterion for fretting wear experiments.