This book is an introductory textbook on the physical processes occurring in the Earth's radiation belts. The presentation is at the advanced undergraduate or first year graduate level, and it is appropriate for students who intend to work in some aspect of magnetospheric physics. The treatment is quantitative and provides the mathematical basis for original work in this subject. The equations describing the motion of energetic ions and electrons in the geomagnetic field are derived from basic principles, and concepts such as magnetic field representations, guiding centre motion, adiabatic invariance, and particle distribution functions are presented in a detailed and accessible manner. Relevant experimental techniques are reviewed and a summary is given of the intensity and energy spectra of the particle populations in the Earth's radiation belts. Problem sets are included as well as appendices of tables, graphs and frequently used formulas.

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1037the only negative ion which has been identified in HC1 by previous workers is Cl~. Charge transfer would not be expected to play a significant role if this were the ion in our experiment. The observed value of 0.71 ±0.02 cm 2 /v-sec is to be contrasted with that of 0.88 expected if Eq. (14) is applicable. This suggests that an orientation-dependent R~* interaction is important in this case, so that the mobility should vary as T 1/6 . If, however, these forces averaged out, so that only the INTRODUCTION R ADIATIVE capture of neutrons by Li 7 leads to an unstable isotope, Li 8 , which decays with about a 0.9 sec half-life by emitting electrons with a maximum energy of 13 Mev. 1 The residual nucleus, Be 8 , further decays into two alpha particles in about 10~1 5 second. Since the spin and parity of the ground state of Li 8 are 2, even, 2 and the spin and parity of the ground state of Li 7 are f, odd, the excited state of Li 8 formed by s-wave neutron capture in Li 7 will decay to the ground state by electric dipole emission. Calculations of the cross section for this process have been made by Thomas 3 and his results predict a cross section which decreases smoothly with increasing neutron energy. However, a maximum in the capture cross section might be expected near 250 kev because of a resonance in the total cross section of Li 7 at this energy. 4 The 2.28-Mev state in Li 8 , which is responsible for this resonance, has spin 3 and even parity and may decay to the ground state by 1 W. F. Hornyak and T.

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The adequacy of the known source and loss processes to populate the inner radiation belt with protons is examined by calculating the equilibrium trapped‐proton distribution, which would result from decay of albedo neutrons, energy‐loss collisions, and radial diffusion by changes in the third adiabatic invariant. The strength of the neutron source and the rates of atmospheric energy loss are obtained from available theoretical and experimental data, and the radial‐diffusion coefficient is adjusted to give agreement between theory and experiment for equatorially trapped protons with first invariants between 200 and 3000 Mev gauss−1. Since there is strong evidence for additional loss mechanisms above L=1.8, this comparison is limited to L<1.7, and in the calculation all processes above that boundary are simulated by setting the fluxes at 1.7 equal to the experimental values. The flux intensities, energy spectrums, and radial distributions obtained by this theory are in good agreement with observations, and the radial‐diffusion coefficient required is consistent with diffusion coefficients derived by a variety of other methods. It is concluded that these processes are adequate to explain the gross characteristics of protons of the inner radiation belt, although off‐equatorial protons have not been considered and the solar‐cycle variations have not been computed.