Citation
Owens, Aaron James (1973) CosmicRay Scintillations. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3NFQSF03. https://resolver.caltech.edu/CaltechTHESIS:08222018111448400
Abstract
This Thesis reports the observation and theoretical interpretation of a new physical phenomenon. Cosmicray "scintillations" are temporal fluctuations in the counting rate of a detector pointing in a fixed direction in space. Powerspectral analyses of energeticparticle counting rate data are used to demonstrate that scintillations are a statistically significant, persistent, and interesting feature of the cosmicray flux observed near earth for a wide range of frequencies (10^{7} Hz to 10^{4} Hz) and energies (~1 MeV to 10 GeV protons, 3 to 12 MeV electrons). The observed power spectra of cosmicray scintillations are approximately power laws in frequency with exponents of 1.5 to 2.0, and for protons the relative scintillations are a rapidlydecreasing function of energy.
Quantitative theoretical models, based on generalized quasilinear solutions of the collisionless Liouville equation with a stochastic magnetic field, are presented for the production of cosmicray scintillations by random magnetic fields in the magnetosheath and in interplanetary space. It is shown that the ~110 MeV proton scintillations observed during quiet times inside the magnetosphere are probably caused by fluctuations in the magnetic field of the magnetosheath. Scintillations of highenergy particles (≳1 GeV/nucleon) are probably generated by the stochastic interplanetary magnetic field. The detailed theoretical prediction for the power spectrum of the flux from neutron monitors, including the effect of the earth's rotation on the interplanetary scintillations model, is calculated and shown to be in excellent agreement with observations from the Alert and Deep River Neutron Monitors. The shape and amplitude of the observed spectra, and in particular a broad enhancement in the Deep River spectrum near one cycle per day, are explained by the theory.
This investigation gives relations for the power spectrum P^{j}(f) of the cosmicray flux of the form
P^{j}(f)/j_{0}^{2} = A(f) (P^{B}(f)/B_{0}^{2}) δ^{2}
where j_{0} is the average flux, P^{B}(f) is the power spectrum of a component of the magnetic field, B_{0} is the average magnetic field strength, and δ is the cosmicray anisotropy. The factor A(f) is a frequencydependent function which exhibits enhancements near frequencies corresponding to cyclotron resonances (and near 1 cycle per day for neutron monitors) but which is essentially constant for 1 MeV  10 GeV proton scintillations at frequencies ≾10^{4} Hz. The cosmicray scintillations thus can provide information about magnetic fluctuations, and neutronmonitor power spectra can give information about the interplanetary magnetic field from groundbased measurements. The shape of the theoretical spectrum near cyclotron resonances depends strongly on nonlinear terms in the generalized quasilinear equations, so scintillations may provide a useful test of nonlinear plasma theories. The agreement of the theory of scintillations with observation supports the standard theory of cosmicray diffusion near earth and the relation between the diffusion coefficient and magneticfield fluctuations. Thus the previously ignored "noise" in the cosmicray intensity may contain much useful information.
Item Type:  Thesis (Dissertation (Ph.D.))  

Subject Keywords:  (Physics and Economics)  
Degree Grantor:  California Institute of Technology  
Division:  Physics, Mathematics and Astronomy  
Major Option:  Physics  
Minor Option:  Economics  
Thesis Availability:  Public (worldwide access)  
Research Advisor(s): 
 
Thesis Committee: 
 
Defense Date:  21 May 1973  
Funders: 
 
Record Number:  CaltechTHESIS:08222018111448400  
Persistent URL:  https://resolver.caltech.edu/CaltechTHESIS:08222018111448400  
DOI:  10.7907/3NFQSF03  
Related URLs: 
 
Default Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided.  
ID Code:  11155  
Collection:  CaltechTHESIS  
Deposited By:  INVALID USER  
Deposited On:  27 Aug 2018 17:08  
Last Modified:  15 Jul 2024 22:54 
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