The two-body photodisintegration of He-3 has been investigated using tagged photons with energies from 14-31 MeV at MAX-lab in Lund, Sweden. The two-body breakup channel was unambiguously identified ...by the (nonsimultaneous) detection of both protons and deuterons. This approach was made feasible by the overdetermined kinematic situation afforded by the tagged-photon technique. Proton-and deuteron-energy spectra were measured using four silicon surface-barrier detector telescopes located at a laboratory angle of 90 degrees with respect to the incident photon-beam direction. Average statistical and systematic uncertainties of 5.7% and 6.6% in the differential cross section were obtained for 11 photon-energy bins with an average width of 1.2 MeV. The results are compared to previous experimental data measured at comparable photon energies as well as to the results of two recent Faddeev calculations which employ realistic potential models and take into account three-nucleon forces and final-state interactions. Both the accuracy and precision of the present data are improved over those obtained in the previous measurements. The data are in good agreement with most of the previous results, and favor the inclusion of three-nucleon forces in the calculations.
Elastic scattering of photons from 12C has been investigated using quasi-monoenergetic tagged photons with energies in the range 65 - 115 MeV at laboratory angles of 60 deg, 120 deg, and 150 deg at ...the Tagged-Photon Facility at the MAX IV Laboratory in Lund, Sweden. A phenomenological model was employed to provide an estimate of the sensitivity of the 12C(g,g)12C cross section to the bound-nucleon polarizabilities.
Models of auroral processes have been advanced in which the ionosphere plays an active role in stimulating auroral particle precipitation. The validity of these suggestions can be investigated by ...releasing an artificial plasma cloud into the ionosphere and studying the effects. To this end, the sounding rocket experiment Trigger, comprising a diagnostic and a chemical release payload, was conducted. As a consequence of the release, a drastic increase of the field‐aligned charged particle flux was observed over the approximate energy range 10 eV to more than 300 keV, starting about 150 ms after the release and lasting about 1 s. There is also evidence of a second particle burst, starting 1 s after the release and lasting for tens of seconds. In addition, there is evidence for a periodic train of particle bursts occurring with a 7.7‐s period from 40 to 130 s after the release. A transient electric field pulse of 200 mV/m appeared just before the particle flux increase started. Electrostatic wave emissions around 2 kHz, as well as a delayed perturbation of the E region below the plasma cloud were also observed. Some of the particle observations are interpreted in terms of field‐aligned electrostatic acceleration a few hundred kilometers above the injected plasma cloud. It is suggested that the accelerating electric field was created by an instability driven by field‐aligned currents caused by the plasma cloud release. This paper gives an overview of the experiment design and the general result. Particular observations and their interpretation are discussed in more detail in companion papers.
The two-body photodisintegration of 3He has been investigated using tagged photons with energies from 14 -- 31 MeV at MAX-lab in Lund, Sweden. The two-body breakup channel was unambiguously ...identified by the (nonsimultaneous) detection of both protons and deuterons. This approach was made feasible by the over-determined kinematic situation afforded by the tagged-photon technique. Proton- and deuteron-energy spectra were measured using four silicon surface-barrier detector telescopes located at a laboratory angle of 90deg with respect to the incident photon-beam direction. Average statistical and systematic uncertainties of 5.7% and 6.6% in the differential cross section were obtained for 11 photon-energy bins with an average width of 1.2 MeV. The results are compared to previous experimental data measured at comparable photon energies as well as to the results of two recent Faddeev calculations which employ realistic potential models and take into account three-nucleon forces and final-state interactions. Both the accuracy and precision of the present data are improved over the previous measurements. The data are in good agreement with most of the previous results, and favor the inclusion of three-nucleon forces in the calculations.
The first data from MAX-lab in Lund, Sweden on pion production in photonuclear reactions at threshold energies, is presented. The decrease of the total yield of pi+ in gamma + 12C, 27Al reactions ...below 200 MeV as well as differential, dsigma/dOmega, cross sections follow essentially predictions from an intranuclear cascade model with an attractive potential for pion-nucleus interaction in its simplest form. Double differential, d2sigma/dOmegadT, cross sections at 176 MeV show, however, deviations from the model, which call for refinements of nuclear and Coulomb potentials and possibly also for coherent pion production mechanisms.
IntroductionThe earth sciences differ from other scientific disciplines in their focus on processes one cannot easily repeat or control. Examples are the nucleation of earthquakes as brittle failure ...along faults, or the creeping flow processes in the Earth's interior driving plate tectonics and the geologic activity of our planet. The inherent experimental limitations and the indirect nature of our observations explain the need for sophisticated modeling approaches. And with continued growth of computer hardware performance, the crossing of some long-standing thresholds in capacity and capability computing is finally underway. For instance, it is now feasible to implement earth models having in excess of 1–10 billion grid points, a number that matters because it allows us to overcome in three-dimensional (3-D) models the disparate length scales characteristic of key geologic phenomena: an earthquake rupturing a fault segment over a distance of some 100 km while emanating seismic energy throughout the planet (10 000 km), or the peculiar nature of plate tectonics with deformation concentrated along narrow plate boundaries of 10–100 km width separated by plates of dimension 1 000–10 000 km. But capable hardware and raw compute power are not sufficient by themselves to advance demanding earth system simulations. Equally critical are sophisticated software, visualization tools, data portals, and shared middleware and software libraries, collectively known as cyberinfrastructure.Cyberinfrastructure forms a comprehensive modeling environment to integrate computing hardware, data, networks, digitally enabled sensors, observatories, and experimental facilities.
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