Cosmic Ray Flux Variations in Lunar and near-Earth Environments

다국어 초록 (Multilingual Abstract)

On the surface of the Earth, the variation of Galactic Cosmic Ray (GCR) intensity depends on the GCR energies, solar winds, and the local Earth’s magnetic fields. Solar activities such as solar flares and coronal mass ejections (CMEs) or interactions with the Earth's magnetosphere also have a strong influence on the variation of GCR intensity. On the other hand, because the Moon has both weak magnetic fields and thin atmospheres, the radiation environments at the Moon might be very different from those on the Earth. Major factors affecting the lunar radiation environments are not local magnetic fields or the magnetosphere but solar winds, GCRs, and solar energetic particles. We may figure out the cosmic ray flux variations in the lunar radiation environments by understanding the physical characteristics of ionizing radiations. The major events in the variations of GCR intensity in the Earth are Forbush Decrease (FD) and Ground Level Enhancement (GLE). In order to find out if these events take place in the lunar radiation environments, we analyzed various observational data related with cosmic ray flux variations. Those data are mostly obtained from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument and include the data of interplanetary magnetic field (IMF), interplanetary shock (IP), and interplanetary coronal mass ejection (ICME) related to FD and the data of Solar Flare and Coronal Mass Ejection related to GLE. We have found 19 FD-like CR events similar to the FDs recorded in the Earth using the CR data observed by CRaTER instrument in the lunar environment during the period of June 2009 through October 2013. We have verified that all FD-like CR events are associated with the ICMEs, which are composed of IP shocks and magnetic clouds (MC). Also, we have found 66 GLE-like CR events similar to the GLEs recorded in the Earth during the period of June 2009 through April 2014. We have also verified that most of GLE-like events are associated with the solar flares involving solar energetic particles. In this dissertation, we state our conclusion; there are GCR intensity variation events looking like FD and GLE even in the lunar radiation environments.

국문 초록 (Abstract)

지구에서의 우주선 플럭스의 변화는 우주선의 에너지, 태양풍, 지구 자기장의 영향을 많이 받는다. 태양 플레어와 코로나 질량 방출과 같은 태양활동과 지구자기권과의 상호작용 또한 우주선 플럭스 변화에 지대한 영향을 주고 있다. 반면에, 달에서의 약한 자기장과 얇은 대기로 인해, 달 방사선 환경에서는 지구에서 발생하는 상호작용과 상대적으로 많이 다르다. 달 방사선 환경에서의 중요한 요소는 자기장이나 자기권이 아니라 태양풍 입자, 우주선, 태양 고에너지 입자들이다. 이러한 이온화된 방사선의 물리적인 특성을 이해함으로써, 우리는 조금이나마 달 방사선 환경에서의 우주선 플럭스의 변화를 이해 할 수 있다. 지구에서의 우주선 플럭스의 주된 변화들은 Forbush Decrease (FD)와 Ground Level Enhancement (GLE)이다. 달 방사선 환경에서도 이러한 변화들이 있는지를 이해하기 위해서 우리는 Cosmic Ray Telescope for the Effects of Radiation (CRaTER) data를 중심으로 해서 FD와 관련된 IMF, IP, ICME 자료와 GLE와 관련된 태양 플레어와 코로나 질량 방출과 같이 우주선 플럭스 변화와 관련된 관측 자료를 분석하였다. 이러한 분석을 통해, 지구에서 발생하는 FD, GLE와 유사한 현상들을 달 방사선 환경에서 발견하였다. 달에서 발견된 FD와 유사한 CR event는 모두 ICME와 관련이 있었으며, GLE와 유사한 CR event는 태양 고에너지 입자와 관련 있는 태양 플레어와 연관이 있었다. 이를 통해 우리는 이 논문에서 행성간 공간인 달 방사선 환경에서도 FD와 GLE와 같은 우주선 플럭스 변화 이벤트가 존재한다고 결론내리고자 한다.

목차 (Table of Contents)

• 1. Introduction 1
• 1.1 Cosmic Ray 1
• 1.2 Forbush Decrease 3
• 1.3 Ground Level Enhancement 4
• 1.4 Lunar Radiation Environment 5
• 1.5 CRaTER (Cosmic Ray Telescope for the Effects of Radiation) 7
• 1.6 Aim and Scope of This Research 12
• 2. Forbush Decrease in the Lunar Radiation Environment observed by the CRaTER on the LRO 14
• Abstract 14
• 2.1 Introduction 15
• 2.2 Data and Methods 17
• 2.3 Results 20
• 2.4 Discussion and Conclusion 26
• 3. Ground Level Enhancement in the Lunar Radiation Environment observed by the CRaTER on the LRO 27
• Abstract 27
• 3.1 Introduction 28
• 3.2 Data and Methods 30
• 3.3 Results 32
• 3.4 Discussion and Conclusion 40
• 4. Lunar Cosmic Ray Radiation Environments during Luna and Lunar Reconnaissance Orbiter missions 41
• Abstract 41
• 4.1 Introduction 42
• 4.2 Data and Methods 44
• 4.3 Results 46
• 4.4 Conclusion 53
• 5. A Design of Solar Proton Telescope for Next Generation Small Satellite 55
• Abstract 55
• 5.1 Introduction 56
• 5.2 Simulation using the GEANT4 61
• 5.3 Methods and Results 63
• 5.4 Conclusion and Summary 71
• 6. Conclusion 73
• Appendix 75
• References 84
• Abstract in Korean 96