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Collisionless turbulence is common in astrophysical magnetic fields and plasmas. The determination of the transport of high-energy charged particles both parallel and perpendicular to the average magnetic field in such a system is of considerable interest. It is recognized that the turbulent magnetic field has important effects on the transport of charged particles and that the properties of different turbulence models may significantly affect the resulting transport properties. A number of different magnetic turbulence models have been proposed in the last several decades. We present here the results of a study of charged particle transport in two new turbulent magnetic field models that have not been previously considered and include newly described characteristics. We investigate the effect of energetic charged particle motion in these new models. We use a method (D A Roberts, 2012) that optimizes phase angles of a set of circularly polarized, transverse modes with Kolmogorov power-law enveloped amplitudes to construct magnetic field fluctuations with nearly constant |B| but with large variances in the components Bx, By, Bz, as is observed in the Solar Wind. Charged particle scattering coefficients are determined through computer simulations. The results are compared with those from previous isotropic and composite turbulence models. We studied charged particle transport in the turbulent magnetic field with global anisotropy and compared with the isotropic turbulence. We found that the magnetic turbulence with global anisotropy and isotropy have similar effects on charged particle transport from 1𝑀𝑒𝑉 up to 10𝐺𝑒𝑉. We proposed a general framework for a multi-scale synthesis with the scale- dependent, localized anisotropic feature incorporated. We run test particle simula- tions in the field by the two-scale algorithm to calculate the transport coefficients for charged particles with different energies. We found that the local anisotropy has the significant difference from the previous model in the effect on charged particle transport. The parallel transport (𝑘∥) decreases while the perpendicular transport (𝑘⊥) increases compared with the isotropic and globally anisotropic field models, the difference is enhanced as the local anisotropy is enhanced, and there is an order of magnitude increase in the ratio of perpendicular to parallel transport coefficients. We proposed a simple power spectrum synthesis method based on the Fourier analysis to extract the large and small scale power spectrum from any single space- craft observation with a long enough period and a high sampling frequency. We applied the method to the solar wind measurement by the magnetometer onboard the ACE spacecraft and reconstructed the large scale isotropic 2D spectrum and the small scale anisotropic 2D spectrum.

We formulate a variational method to obtain the binding energies of a charged particle in presence of an electric dipole and a magnetic field aligned along the dipole. First, we test the method by obtaining the critical dipole moment for a point dipole, as well as a finite dipole in the absence of a magnetic field. A few larger dipole moments supporting a zero energy bound state are also obtained. Adding a magnetic field of ~ 20 - 100 T, we show that for a rigid and stationary dipole of moment 2.54 D, the electron binding energy increases by 15% - 66%. Our approach also shows the absence of a critical dipole moment in presence of an aligned magnetic field. / Thesis / Master of Science (MSc)

Incident 0.5 to 2.5 MeV charged particle beams were used to ionize the inner-shells of selected targets and study their subsequent emission of characteristic x-rays. ⁹Be⁺ ions were used to examine K-shell x-ray production from thin F, Na, Al, Si, P, Cl, and K targets, L-shell x-ray production from thin Cu, An, Ge, Br, Zr and Ag targets, and M-shell x-ray production from thin Pr, Nd, Eu, Dy, Ho, Hf, W, Au, Pb and Bi targets. L-shell x-ray production cross sections were also measured for ²⁷Al⁺ ions incident upon Ni, Cu, Zn, As, Zr, and Pd targets. M-shell x-ray production cross sections were measure for ²⁷Al⁺ and ⁴⁰Ar⁺ ions incident upon Pr, Nd, Gd, Dy, Lu, Hf, Au, Pb, Bi, and U targets. These measurements were performed using the 2.5 MV Van de Graaff accelerator at North Texas State University. The x-rays were detected with a Si(Li) detector whose efficiency was determined by fitting a theoretical photon absorption curve to experimentally measure values. The x-ray yields were normalized to the simultaneously measured Rutherford backscattered (RBS) yields which resulted in an x-ray production cross section per incident ion. The RBS spectrum was obtained using a standard surface barrier detector calibrated for to account for the "pulse height defect." The experimental results are compared to the predictions of both the first Born and ECPSSR theories; each of which is composed of two parts, the direct ionization (DI) of the target electron to the continuum and the capture (EC) of the target electron to the projectile. The first Born describes DI by the Plane-Wave-Born-Approximation (PWBA) and EC by the Oppenheimer-Brinkman-Kramers treatment of Nikolaev (OBKN). ECPSSR expands upon the first Born by using perturbed (PSS) and relativistic (R) target electron wave functions in addition to considering the energy loss (E) of the projectile in the target and its deviation from straight line trajectory (Coulomb deflection (C)). The measurements presented show that the first Born theories overestimate the measured results rather significantly for all experiments using the ⁹Be beams to examine the inner shell x-rays, while the ECPSSR predictions fir the measured data much better. For incident ²⁷Al and ⁴⁰Ar ions, the measured results are not predicted by the theories. The first Born generally over-predicts the data for low target atomic numbers while under-predicting at high atomic numbers. The ECPSSR theory greatly under-predicts the results (factors of 10³ to 10²⁰). Reasons for this behavior are discussed as well as suggestions for future experiments.

Anthropomorphic phantoms are commonly used for testing radiation fields without the need to expose human subjects. One of the most widely known is RANDO phantom. This phantom is used primarily for medical X-ray applications, but a similar design known as "MATROSHKA" is now being used for space research and exposed to heavy ion irradiations from the Galactic environment. Since the radiation field in the phantom should respond in a similar manner to how it would act in human tissues and organs under an irradiation, the tissue substitute chosen for soft tissue and the level of complexity of the entire phantom are crucial issues. The phantoms, and the materials used to create them, were developed mainly for photon irradiations and have not been heavily tested under the conditions of heavy ion exposures found in the space environment or external radiotherapy. The Particle and Heavy-Ion Transport code System (PHITS) was used to test the phantoms and their materials for their potential as human surrogates for heavy ion irradiation. Stopping powers and depth-dose distributions of heavy charged particles (HCPs) important to space research and medical applications were first used in the simulations to test the suitability of current soft tissue substitutes. A detailed computational anthropomorphic phantom was then developed where tissue substitutes and ICRU-44 tissue could be interchanged to verify the validation of the soft tissue substitutes and and determine the required level of complexity of the entire phantom needed to achieve a specified precision as a replacement of the human body. The materials tested were common soft tissue substitutes in use and the materials which had a potential for the soft tissue substitute. Ceric sulfate dosimeter solution was closest to ICRU-44 tissue; however, it was not appropriate as the phantom material because it was a solution. A150 plastic, ED4C (fhw), Nylon (Du Pont Elvamide 8062), RM/SR4, Temex, and RW-2 were within 1% of the mean normalized difference of mass stopping powers (or stopping powers for RW-2) when compared to the ICRU-44 tissue, and their depth-dose distributions were close; therefore, they were the most suitable among the remaining solid materials. Overall, the soft tissue substitutes which were within 1% of ICRU-44 tissue in terms of stopping power produced reasonable results with respect to organ dose in the developed phantom. RM/SR4 is the best anthropomorphic phantom soft tissue substitute because it has similar interaction properties and identical density with ICRU-44 tissue and it is a rigid solid polymer giving practical advantages in manufacture of real phantoms.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19882号 / 理博第4209号 / 新制||理||1605(附属図書館) / 32959 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 中家 剛, 教授 谷森 達, 教授 永江 知文 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

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Conventional charged-particle imaging techniques--such as autoradiography--provide only two-dimensional (2D) images of thin tissue slices. To get volumetric information, images of multiple thin slices are stacked. This process is time consuming and prone to distortions, as registration of 2D images is required. We propose a direct three-dimensional (3D) autoradiography technique, which we call charged-particle emission tomography (CPET). This 3D imaging technique enables imaging of thick sections, thus increasing laboratory throughput and eliminating distortions due to registration. In CPET, molecules or cells of interest are labeled so that they emit charged particles without significant alteration of their biological function. Therefore, by imaging the source of the charged particles, one can gain information about the distribution of the molecules or cells of interest. Two special case of CPET include beta emission tomography (BET) and alpha emission tomography (𝛼ET), where the charged particles employed are fast electrons and alpha particles, respectively. A crucial component of CPET is the charged-particle detector. Conventional charged-particle detectors are sensitive only to the 2-D positions of the detected particles. We propose a new detector concept, which we call particle-processing detector (PPD). A PPD measures attributes of each detected particle, including location, direction of propagation, and/or the energy deposited in the detector. Reconstruction algorithms for CPET are developed, and reconstruction results from simulated data are presented for both BET and 𝛼ET. The results show that, in addition to position, direction and energy provide valuable information for 3D reconstruction of CPET. Several designs of particle-processing detectors are described. Experimental results for one detector are discussed. With appropriate detector design and careful data analysis, it is possible to measure direction and energy, as well as position of each detected particle. The null functions of CPET with PPDs that measure different combinations of attributes are calculated through singular-value decomposition. In general, the more particle attributes are measured from each detection event, the smaller the null space of CPET is. In other words, the higher dimension the data space is, the more information about an object can be recovered from CPET.

The CEBAF Large Acceptance Spectrometer for the 12 GeV era, known as CLAS12, uses the time of flight (TOF) system to identify charged particles from scattering events between the beam and target. The TOF system is divided into two parts: The Forward time of flight system, and the Central time of flight system. These two sub-systems subtend different polar angles of the detector geometry for wide acceptance of scattered particles. Reconstruction is the service used to identify particles from the interactions between the beam and target, called as a vertex or the point where the interaction occurs. The vertex position is traced back using the tracking system and the TOF system. The resolution of the detector affects the accuracy of the reconstructed vertex location. This paper’s goal will be to develop software for validation suite for CLAS12, which will include central and forward tracking plots. Plots will be developed to check the precision of the reconstructed vertices in both the central and forward detectors. This will be done assuming a target with zero dimension at 𝑣𝑧 = 0, and an extended target of 5 cm at 𝑣𝑧 = 0. This paper will also look at the TOF resolution, and identify particles using the TOF detectors and the effect of the vertex correction on the velocity vs. momentum plots.