Pulse Shape Analysis of Alpha Particles for the 100kg XMASS Proto-type Detector

XMASS는 드물게 일어나는 물리적 현상을 일본 Kamioka의 매우 낮은 백그라운드의 환경에서 측정하고자 하는 목적을 가지는 지하 실험이다. XMASS의 주된 물리적 목표는 차가운 암흑 물질, 중성미자가 없는 이중 베타 붕괴 (neutrinoless double beta decay) 그리고 낮은 에너지의 중성미자를 높은 수준으로 정제된 액체 제논을 검출기를 사용하여 탐색하는 것이다. 현재는 원형(原型,prototype) 검출기가 주조되었으며 이 원형 검출기를 사용하여 두 개의 테스트 실험이 행해졌다. 대부분의 알파가 ^(238)U과 ^(232)Th의 붕괴 체인에서 기인하는데 이 붕괴 체인에서 나오는 베타와 감마가 낮은 에너지의 백그라운드에 영향을 주기 때문에 알파 입자의 분석은 WIMP(Weakely Interacting Massive Particle) 탐색에 있어 매우 중요하다. 알파의 양을 측정하면 ^(238)U과 ^(232)Th의 양을 추정할 수 있고 이를 통해 낮은 에너지의 베타와 감마의 양을 확실히 알 수 있다. 또한 일단 ^(238)U과 ^(232)Th 체인에서 기인하는 알파의 양을 확실히 알기만 하면 베타 백그라운드의 경우 베타와 감마의 지연된 코인시던스(delayed coincidence)를 이용하여 줄일 수 있다. 따라서 만약 ^(238)U과 ^(232)Th의 양이 많을 경우에는 베타 백그라운드를 이 방법으로 줄이는 것이 가능하다. 마지막으로 알파 입자는 검출기 주변의 다른 물질들과 반응해서 중성자를 만들어낸다. (α,n) 반응에 의해 생성되는 이러한 중성자들은 WIMP의 시그널을 모방하므로 검출기의 민감도를 저해하는 주요 원인이 될 수 있다. 그러므로 검출기와 관련된 알파 입자에 대한 주의 깊은 연구는 전체 백그라운드의 모양과 백그라운드의 원인을 이해하는데 매우 중요하다. 이 논문에서는 두번째 테스트 실험에서 얻어진 섬광 아날로그-디지털-변환기(Flash Analog-Digital Converter)의 데이터를 이용한 알파 입자 분석에 대한 결과를 보여주고자 한다. 먼저 섬광 아날로그-디지털-변환기를 이용한 알파와 감마의 분리를 통해서 검출기의 알파 입자의 양을 추정하였다. 또한 알파 입자의 위치 정보로부터 알파의 원인을 설명할 수 있는 간단한 모형을 제안하며 이 모형이 데이터와 일치하는 결과를 예측함을 보일 것이다. 액체 제논을 보일 것이다. 액체 제논을 회수하는 과정에서 데이터에 나타났던 제논의 기체상에서 기인하는 알파로 생각되는 입자 역시 소개될 것이다.;XMASS is an underground experiment aimed at searching for rare phenomena under an ultra-low background environment located in Kamioka mine of Japan. The main physics goals of XMASS are to investigate cold dark matter, nuetrinoless double beta decays, and low-energy solar neutrinos by using high purity liquid xenon detector. A prototype detector was constructed and 2 series of test experiments were carried out with the detector. Alpha particle analysis is very important to WIMP (Weakly Interacting Massive Particle) search because alpha mostly comes from ^(238)U and ^(232)Th chain and the gamma and beta from these chains influence the low energy background. Through measuring the amount of alpha, we can estimate the amount of ^(238)U and ^(232)Th and can obtain the amounts of low energy gamma and beta exactly. In addition, once we know the amount of alpha from ^(238)U and ^(232)Th chain, there is a method which can reduce the beta background using delayed coincidence with beta and alpha from these chains. Even in case that the amount of ^(238)U and ^(232)Th are large, it is possible to reduce the beta background using this method. Finally, alpha particles produce neutrons from interactions with other materials surrounding the detector. These neutrons from the (α, n) reactions mimic the WIMP signal, which may be a crucial factor that limits the sensitivity of the detector. Therefore a careful study of alpha particles related to the detector is important to understand the overall background shape and the origin of the backgrounds. In this thesis, based on the second test experiment, alpha particle analysis using the data taken with flash ADCs (Flash Analog-to-Digital Converter) would be presented. Through alpha-gamma separation using flash ADCs, the amount of alpha in the detector is estimated. From the location information of alpha particles, a simple model which can explain the origin of alpha is suggested and this model shows consistent expectation with the data. The particles, most likely alpha particles, from the gas phase of Xe in our data during the extraction process of LXe from the detector also would be introduced.Contents Abstract = iii Ⅰ. Introduction = 1 1.1 Overview = 1 1.2 What is Dark Matter? = 1 1) Evidence of DM = 1 2) Importance of DM search in cosmology = 3 3) Candidates of DM = 3 4) Direct WIMP Detection = 5 5) Status of direct WIMP searches = 5 1.3 Scintillation Mechanism and Pulse Shape Discrimination = 7 1) Principle of Scintillation = 7 2) Decay Time Component = 7 3) Interaction Processes in Liquid Xenon = 8 4) Pulse Shape Discrimination = 9 1.4 Key Idea to Measure DM - Self Shielding = 10 1.5 Why Liquid Xenon? = 13 1.6 Purpose of This Thesis = 13 Ⅱ. Experimental Setup = 15 2.1 Kamioka Underground Observatory = 15 2.2 100kg Proto-type Detector = 16 1) Dimensions of Detector = 16 2) Photo-Multiplier Tubes (PMT) = 17 3) Background Shielding = 18 2.3 Purification of Liquid Xenon = 20 2.4 Electronics = 22 Ⅲ. Results and Discussions = 24 1) Alpha and Gamma Separation with PSD Parameter = 24 2) Confirmation of Alpha = 25 3) PSD Cut for Alpha Particles = 28 4) Two Decay Components fitting of Alpha and Gamma = 29 5) Locational Distribution of Alpha = 31 6) Feasible Simple Model for Alpha Estimates = 32 7) Unknown (X) Particle = 37 Ⅳ. Conclusion = 42 Reference = 44 논문개요 = 4

문화예술교육정책의 평가기준에 대한 연구

학위논문(석사) --서울대학교 대학원 :협동과정(미술교육전공),2010.2.Maste

인플루엔자 바이러스의 PA와 PB2 중합효소 및 판코니 빈혈 증후군 단백질의 구조와 기능에 대한 NMR 연구

학위논문(박사) - 한국과학기술원 : 화학과, 2014.2, [ viii, 67 p. ]Influenza RNA polymerase is composed of three subunits, PA, PB1, and PB2, which interact with each other for transcription and replication of the viral RNA genome in the nucleus of infected cells. PB2’s RNA-binding 627-domain (residues 535-693), located in the C-terminus, presents a highly basic surface around residue K627 and has been proposed to interact with viral or cellular factors, resulting in host adaptation. However, the function of this domain is not yet characterized in detail. In this study, I identified RNA-binding activity and RNA-binding surfaces in both the N-terminal and basic C-terminal regions of PB2 using NMR experiments. Through mutagenesis studies, I confirmed which residues directly interact with RNA and mapped their locations on the RNA-binding surface. In addition, by luciferase activity assays, I showed that influenza virus polymerase activity may correlate with the interaction between PB2 and RNA. Representative host adaptive mutations Q591K/R and E627K were found to be located on the RNA-binding surface and were confirmed to directly interact with RNA and to affect polymerase activity. From these results, I suggest that influenza virus polymerase activity may be regulated through the interaction between PB2’s 627-domain and RNA and that consequently host adaptation of the virus may be influenced. Influenza A viruses are viral pathogens that cause both seasonal influenza epidemics and global pandemics. Although there are effective drugs such as the neuraminidase inhibitors oseltamivir (Tamiflu) and zanamivir (Relenza), influenza virus can have resistance to these drugs by the long-term use. Therefore, new anti-viral drug have to be developed to prevent the epidemic and pandemic by influenza virus. In particular, influenza virus polymerase PA subunit contains the endonuclease activity, which creates a capped RNA primer during viral transcription, and high conserved sequence among influenza strains. On account of this significance, PA ...한국과학기술원 : 화학과

SeqA와 hemimethylated, fully methylated DNA의 상호작용에 관한 NMR 연구.

학위논문(석사) - 한국과학기술원 : 화학과, 2008.2, [ v, 59 p. ]I. NMR study on the interactions of the SeqA protein with hemimethylated and fully methylated DNA Replication of Escherichia coli chromosomal DNA initiates at a unique site, oriC, and occurs precisely once per cell cycle. Methylation of oriC by Dam methylase, which methylates N6 of adenine in the GATC sequences, enables SeqA to negatively regulate both primary and secondary replication initiation. SeqA delays the primary replication initiation at fully methylated oriC until a cell reaches its critical mass, counteracting the DnaA protein that activates replication initiation. After replication is initiated, SeqA specifically binds the hemimethylated GATC sites, as the daughter strands are transiently unmethylated, and sequesters oriC from Dam methylase and DnaA, thus preventing secondary replication initiation within a single cell cycle. In the absence of SeqA, E. coli cells are viable, but initiation of DNA replication is asynchronous and occurs several times during each cell cycle. In the present study, our object is to examine the dynamics of SeqA with binding of DNAs. The DNAs used in this study contain the hemimethylated and fully methylated GATC sequence. The flexibility of a protein has been suggested as an important factor in a protein-ligand or a protein-nucleic acid interaction. In the crystal structure of the SeqA (51-181 amino acids) with the hemimethylated DNA, it was known that the hemimethylated $^mA:T$ pair of the DNA associates with the L3 loop of SeqA. Although the crystal structure of the SeqA C-terminal segment (51-181 amino acids) has been determined in a complex with hemimethylated DNA, it is meaningful to examine the dynamics of SeqA with DNA in order to understand the precise protein-DNA interaction. To identify the possibility of the progress of this object, we confirmed the $^1H-^{15}N$ HSQC spectrum of SeqA alone with well dispersed pattern and carried out the chemical shift perturbation experiment. II. NMR study of the inter...한국과학기술원 : 화학과