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3He/4He ratio has been known as a promising channel for research of cosmic ray propagation in the Galaxy. Most of 3He’s in cosmic rays are known as secondary particles which are produced by spallation of 4He with interstellar materials (ISM). Due to the stable nature of 3He, measurement of 3He/4He ratio is known as a good opportunity to study cosmic ray propagation using nuclear isotopes unlikely to the other unstable nuclear isotope measurements. In addition, thanks to the long-term plan of AMS-02 experiment, precision results about solar activity can be expected from such experiment.
The Alpha Magnetic Spectrometer (AMS-02) is a general purpose high energy particle physics experiment designed to pursue deeper understanding of fundamental nature of anti-matter and dark matter from cosmic rays. Also, precise measurement of properties of various particles in cosmic rays is one of the most important missions of AMS-02. The detector consists of several subdetectors which have their own distinctive functionality and capability. The AMS Transition Radiation Detector (TRD) provides information of trajectories of incident particles and can be used to distinguish light particles such as leptons, for example, electron and positron from massive nuclei. The AMS Silicon Tracker measures momentum of particle by measuring the gyromagnetic curvature and electric charge of incident particle. The AMS Time of Flight (TOF) provides electric charge and timing information of trespassing particle with timing resolution of 150 ps. The Ring Imaging Čerenkov Detector reconstructs electric charge and particle speed with beta resolution better than 0.1 % for NaF radiator and 0.01 % for aerogel radiator.
In this thesis, combining information from various subdetectors, we have selected helium candidates from the AMS-02 data which we collected six years from 2011 to 2017. Total 167,315,045 helium events are selected and we measured the flux ratio of 3He and 4He as a function of kinetic energy per nucleon from 0.25 GeV/n to 12.8 GeV/n.
As a result of this study, we found that 3He/4He ratio slowly increases in 0.25-2 GeV/n region and slowly decreases in 2-12.8 GeV/n. The remarkable point of this measurement is the precision and the energy range. The uncertainties of each measurement point are better than 1.5 % in the energy range of interest. Also, this is one of the most highest energy measurement accessible by now with such a precision. The measured difference of spectral indices of 3He and 4He fluxes, diffusion coefficient Δ=γ3-γ4, in 5-12 GeV/n energy range is 0.2514±0.0598. The diffusion coefficient based on 3He/4He flux ratio measurement has never been observed in this energy range and therefore we compared this result with those of several other previous experiments of B/C flux ratio measurements and it shows a good agreement to each other.
Thesis Advisor: Prof. Guinyun Kim