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Calculations have been carried out to determine the neutron flux induced in the earth's atmosphere by galactic protons and alpha particles at solar minimum for a geomagnetic latitude of 42°N. Neutron flux spectra in the energy range ∼10−8 to ∼105 Mev at various depths in the atmosphere were calculated by using Monte Carlo and discrete ordinates methods, and various comparisons with experimental data are presented. The magnitude and shape of the calculated neutron leakage spectrum at the particular latitude considered support the theory that the cosmic ray albedo neutron decay (Crand) mechanism is the source of the protons trapped in the inner radiation belt.

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A small-angle neutron study of vortex lattices in YBa2Cu307 showed a diffraction pattern with square symmetry when the applied field was along the c axis with the four main spots aligned with the crystallographic {l 10} directions. With the field 30° from the c axis, a hexagonal lattice exists. At intermediate angles, a fraction of the flux lines follow the c axis and the two lattices coexist. The temperature dependence of the intensity deviates markedly from conventional predictions. PACS numbers: 74.72.Bk, 61.12.Ex, In conventional type-II superconductors, when an applied field is above H c \ but below H C 2, flux lines penetrate the superconductor forming a 2D lattice. Small-angle neutron scattering (SANS) techniques have been used successfully [1,2] in the past to study these flux line lattices in traditional superconducting materials. Recently, similar experiments [3,4] have been carried out in high-TV superconductors.The properties of the flux lattice as a function of field and temperature are important both for a better understanding of the nature of the interaction causing pair formation in high-TV superconductors and also for applications of the material in devices. YBa2Cu3C>7 has one of the strongest pinning characteristics of all the high-TV superconductors and is of particular interest in applications since larger pinning leads to higher critical currents. The temperature (T) dependence of the London depth is vital information that can be measured using SANS. In the London model, the intensity of the Bragg peaks is proportional to the inverse fourth power of the London penetration depth (XL\ and hence, this length can be accurately determined. The angular dependence of the scattering yields information about the long-range order and symmetry of the flux lattice, as well as the average straightness of the individual lines.In this Letter we report on detailed measurements of the flux lattice in a large single-crystal sample of YBa2Cu3C>7 (YBCO). We made measurements with the field parallel to the c axis and with the field at an angle of up to 30° from the c axis. The T dependence of the intensity of the flux line scattering has been obtained much more accurately than in previous work. We also present the behavior of trapped flux as the temperature was varied.The measurements were made on a large twinned single-crystal sample of YBCO that weighed 7.8 g. The mosaic width of the nuclear 006 Bragg peak was approximately 0.7°. The specimen had a superconducting transition temperature of 92.4 K with a width of 1 K. The sample contained an impurity phase that was about 15% of the total crystal volume. This phase is found in well separated regions of the crystal and is expected not to alter the behavior of the fluxoid lattice to any large extent. The experiment was carried out on the W. C. Koehler 30-m SANS instrument at the Oak Ridge National Laboratory. The neutron wavelength was 4.75 A (8X/X~5%).The transmission of the single crystal was 70%. The instrumental resolution was roughly equal in horizontal and v...