[en] High-LET particle radiation was registered in nuclear track recording plastic dosimeters worn on the wrists of Skylab astronauts and located in a heavily shielded film vault. The mission-average planar flux of high-LET particles with LET >= 100 keV/micron . tissue has been determined to be 2.7 +- 0.6 particles/cm² . day . 2π sr and 0.34 +- 0.4 particles/cm² . day . 2π sr, respectively, for the nine astronauts and for the film vault. Comparison of results representative of a wide range of shielding depths reveals that the magnitude and slope of the integral LET spectrum of high-LET particles inside spacecraft are proportional to the amount of shielding. (author)

[en] This paper introduces the innovative concept of SMA-based multi-ring (SBMR) self-centering damping devices and numerically evaluates their performance and effective design. The SBMR devices are passive metallic dampers consisting of two types of concentric circular rings with rectangular cross-section: (a) superelastic (SE) rings and (b) supplemental energy dissipating (ED) rings. The rings are tightly fitted into each other such that their diametric deformations are constrained. The SE rings are made of SE shape memory alloys (SMA) (e.g., Nitinol), thereby providing the SBMR devices with both self-centering and hysteretic damping. The ED rings are made of metals with higher hysteretic damping capacity to supplement the damping of the SE rings. The SBMR devices can resist both tension and compression (without buckling) in multiple directions, allowing their installation via cross-bracing systems. To evaluate the SBMR devices, they were simulated through 3D nonlinear finite element models. The general response/behavior of the proposed devices and the effects of brace design and orientation on their response were examined. The SBMR devices were found capable of producing more than 100% higher damping compared to single SE SMA rings, particularly under small deformations. Moreover, brace design and orientation were found to have little to no effect on the performance of the SBMR devices. (paper)

[en] Recent experiments at the LLNL Petawatt Laser have demonstrated the generation of intense, high-energy beams of electrons and ions from the interaction of ultra-intense laser light with solid targets. The focused laser intensities are as high as 6x10²⁰ W/cm², at which point the quiver energies of the target electrons extend to ∼10 MeV. In this new, fully relativistic regime of laser-plasma interactions, nuclear processes become important and nuclear techniques are required to diagnose the high-energy particle production. We describe recent experiments in which we have observed electrons accelerated to 100 MeV, photo-nuclear fission, positron-electron pair creation, monoenergetic electron jets and intense beams of protons emitted from the back surface of a laser-irradiated target

[en] SOFCAL is a hybrid instrument with both active and passive chambers to measure the proton and helium cosmic ray spectra from 0.2-10 TeV. An emulsion/x-ray film chamber is situated between a Cerenkov counter and an imaging calorimeter. Scintillating fibers (Sci-Fi) measure the electromagnetic (EM) cascades that develop in the calorimeter and identity the trajectory. The emulsion/x-ray film data provide an in-flight calibration of the Sci-Fi calorimeter. The data reduction techniques will be discussed and interim results of the analysis from a balloon flight will be presented

[en] The Petawatt laser at LLNL has opened a new regime of laser-matter interactions in which the quiver motion of plasma electrons is fully relativistic with energies extending well above the threshold for nuclear processes. In addition to -few MeV ponderomotive electrons produced in ultra-intense laser-solid interactions, we have found a high energy component of electrons extending to -100 MeV apparently from relativistic self-focusing and plasma acceleration in the underdense pre-formed plasma. The generation of hard bremsstrahlung, photo-nuclear reactions, and preliminary evidence for positron-electron pair production will be discussed

[en] The LLNL Peta-watt Laser has achieved focussed intensities up to 6 x 20 W/cm², which has opened a new, higher energy regime of relativistic laser-plasma interactions in which the quiver energies of the target electrons exceed the energy thresholds for many nuclear phenomena. We will describe recent experiments in which we have observed electrons accelerated to 100 MeV, photo-nuclear fission, and positron-electron pair creation. (authors)

[en] The Petawatt laser at LLNL has opened a new regime of laser-matter interactions in which the quiver motion of plasma electrons is fully relativistic with energies extending well above the threshold for nuclear processes. We have developed broad-band magnetic spectrometers to measure the spectrum of high-energy electrons produced in laser-solid target experiments at the Petawatt, and have found that in addition to the expected flux of ∼few MeV electrons characteristic of the ponderomotive potential, there is a high energy component extending to ∼100 MeV apparently from plasma acceleration in the underdense pre-formed plasma. The generation of hard bremsstrahlung, photo-nuclear reactions, and preliminary evidence for positron-electron pair production will be discussed