Since 2012 August Voyager 1 has been observing the local interstellar energy spectra of Galactic cosmic-ray nuclei down to 3 MeV nuc −1 and electrons down to 2.7 MeV. The H and He spectra have the same energy dependence between 3 and 346 MeV nuc −1 , with a broad maximum in the 10-50 MeV nuc −1 range and a H/He ratio of 12.2 ± 0.9. The peak H intensity is ∼15 times that observed at 1 AU, and the observed local interstellar gradient of 3-346 MeV H is −0.009 ± 0.055% AU −1, consistent with models having no local interstellar gradient. The energy spectrum of electrons (e − + e + ) with 2.7-74 MeV is consistent with E −1.30±0.05 and exceeds the H intensity at energies below ∼50 MeV. Propagation model fits to the observed spectra indicate that the energy density of cosmic-ray nuclei with >3 MeV nuc −1 and electrons with >3 MeV is 0.83-1.02 eV cm −3 and the ionization rate of atomic H is in the range of 1.51-1.64 × 10. This rate is a factor >10 lower than the ionization rate in diffuse interstellar clouds, suggesting significant spatial inhomogeneity in low-energy cosmic rays or the presence of a suprathermal tail on the energy spectrum at much lower energies. The propagation model fits also provide improved estimates of the elemental abundances in the source of Galactic cosmic rays.

On 25 August 2012, Voyager 1 was at 122 astronomical units when the steady intensity of low-energy ions it had observed for the previous 6 years suddenly dropped for a third time and soon completely disappeared as the ions streamed away into interstellar space. Although the magnetic field observations indicate that Voyager 1 remained inside the heliosphere, the intensity of cosmic ray nuclei from outside the heliosphere abruptly increased. We report the spectra of galactic cosmic rays down to ~3 × 10(6) electron volts per nucleon, revealing H and He energy spectra with broad peaks from 10 × 10(6) to 40 × 10(6) electron volts per nucleon and an increasing galactic cosmic-ray electron intensity down to ~10 × 10(6) electron volts.

Voyager 2 crossed the solar wind termination shock at 83.7 au in the southern hemisphere, approximately 10 au closer to the Sun than found by Voyager 1 in the north. This asymmetry could indicate an asymmetric pressure from an interstellar magnetic field, from transient-induced shock motion, or from the solar wind dynamic pressure. Here we report that the intensity of 4-5 MeV protons accelerated by the shock near Voyager 2 was three times that observed concurrently by Voyager 1, indicating differences in the shock at the two locations. (Companion papers report on the plasma, magnetic field, plasma-wave and lower energy particle observations at the shock.) Voyager 2 did not find the source of anomalous cosmic rays at the shock, suggesting that the source is elsewhere on the shock or in the heliosheath. The small intensity gradient of Galactic cosmic ray helium indicates that either the gradient is further out in the heliosheath or the local interstellar Galactic cosmic ray intensity is lower than expected.

In an attempt to understand the source and propagation of Galactic cosmic rays, we have employed the modiÐed weighted slab technique along with recent values of the relevant cross sections to compute primary to secondary ratios including B/C and sub-Fe/Fe for di †erent Galactic propagation models. The models that we have considered are the disk-halo di †usion model, the dynamical halo wind model, the turbulent di †usion model, and a model with minimal reacceleration. The modiÐed weighted slab technique will be brieÑy discussed and a more detailed description of the models will be given. We will also discuss the impact that the various models have on the problem of anisotropy at high energy and discuss what properties of a particular model bear on this issue. Subject headings : cosmic rays È di †usion È magnetic Ðelds È shock waves THE APPLICATION OF THE MODIFIED WEIGHTED SLAB TECHNIQUE TO SIMPLIFIED MODELSThe weighted slab technique has long been used in studying the propagation of cosmic rays in the Galaxy from their points of origin to their observation points near the Earth (Davis 1960 ;Ginzburg & Syrovatskii 1964 ;Ginzburg & Ptuskin 1976 ;Lezniak 1979 ; also see Webber 1997). Several approximations are used in deriving this technique, among them the assumption that energy loss and/or gain is not signiÐcant and that the propagation in, and loss from, the Galaxy may be described by a function of energy per nucleon alone. Both of these simpliÐcations are known to be untrue : for low energies, ionization energy loss can be signiÐcant and rigidity, or energy per charge, is believed to be the parameter that best describes propagation.Ptuskin, Jones, & Ormes (1996) showed how the weighted slab technique could be made exact for Galactic propagation models in which energy gains and losses were proportional to the same mass density that determined nuclear fragmentation and time-dependent processes, e.g., radioactive decay, do not play a role. This modiÐcation allows for the fact that particles had di †erent (usually higher) energies in the past, and hence di †erent propagation properties, and that propagation is considered to be a function of rigidity, although energy per nucleon is the proper parameter for nuclear fragmentation calculations. Strictly, this technique is rigorous only for models in which the particle propagation parameters are proportional to a single function of energy for each particle species, and hence does not apply to Galactic wind models or turbulent di †usion models. However, most of these models may be closely approximated by simpliÐed homogeneous models in which the mean path length has an exponential distribution with a mean path length that is a particular function of rigidity. It is models of this type and approximation that we discuss in this study. In this paper we present some results of the numerical simulations where the most recent set of spallation cross sections were used.It should be noted that these models bear a similarity to the well-known leaky-box model in that they a...

In a follow‐up study to the earlier work of Webber and Higbie (2003) on 10Be production in the Earth's atmosphere by cosmic rays, we have calculated the atmospheric production of the cosmogenic isotopes 3H, 7Be, 10Be, and 36Cl using the FLUKA Monte Carlo code. This new calculation of atmospheric yields of these isotopes is based on 107 vertically incident protons at each of 24 logarithmically spaced energies from 10 MeV to 10 GeV, 102 times the number used in the earlier calculation, along with the latest cross sections. This permits a study of the production due to solar cosmic rays as well as galactic cosmic rays at lower energies where isotope production is a very sensitive function of energy. Solar cosmic ray spectra are reevaluated for all of the major events occurring since 1956. In terms of yearly production of 10Be, only the February 1956 solar event makes a major contribution. For 36Cl these yearly SCR production contributions are 2–5 times larger depending on the solar cosmic ray energy spectra. We have determined the yearly production of 10Be, 36Cl, and other cosmogenic isotopes above 65° geomagnetic latitude for the time period 1940–2006 covering six solar 11‐year (a) cycles. The average peak‐to‐peak 11‐a amplitude of this yearly production is 1.77. The effects of latitudinal mixing alter these direct polar production values considerably, giving an average peak‐to‐peak 11‐a amplitude of 1.48 for the global average production.