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Contact and projection electron radiography of static targets was demonstrated using a laser-plasma accelerator driven by a kilojoule, picosecond-class laser as a source of relativistic electrons with an average energy of 20 MeV. Objects with areal densities as high as 7.7 g/cm 2 were probed in materials ranging from plastic to tungsten, and radiographs with resolution as good as 90 μm were produced. The effects of electric fields produced by the laser ablation of the radiography objects were observed and are well described by an analytic expression relating imaging magnification change to electric-field strength., (© 2023. The Author(s).)

Purpose: Proton radiography may guide proton therapy cancer treatments with beam's-eye-view anatomical images and a proton-based estimation of proton stopping power. However, without contrast enhancement, proton radiography will not be able to distinguish tumor from tissue. To provide this contrast, functionalized, high- Z nanoparticles that specifically target a tumor could be injected into a patient before imaging. We conducted this study to understand the ability of gold, as a high- Z , biologically compatible tracer, to differentiate tumors from surrounding tissue. Approach: Acrylic and gold phantoms simulate a tumor tagged with gold nanoparticles (AuNPs). Calculations correlate a given thickness of gold to levels of tumor AuNP uptake reported in the literature. An identity, × 3 , and × 7 proton magnifying lens acquired lens-refocused proton radiographs at the 800-MeV LANSCE proton beam. The effects of gold in the phantoms, in terms of percent density change, were observed as changes in measured transmission. Variable areal densities of acrylic modeled the thickness of the human body. Results: A 1 - μ m -thick gold strip was discernible within 1 cm of acrylic, an areal density change of 0.2%. Behind 20 cm of acrylic, a 40 - μ m gold strip was visible. A 1-cm-diameter tumor tagged with 1 × 10 5 50-nm AuNPs per cell has an amount of contrast agent embedded within it that is equivalent to a 65 - μ m thickness of gold, an areal density change of 0.63% in a tissue thickness of 20 cm, which is expected to be visible in a typical proton radiograph. Conclusions: We indicate that AuNP-enhanced proton radiography might be a feasible technology to provide image-guidance to proton therapy, potentially reducing off-target effects and sparing nearby tissue. These data can be used to develop treatment plans and clinical applications can be derived from the simulations., (© 2021 Society of Photo-Optical Instrumentation Engineers (SPIE).)

Stellar wind standoff by a planetary magnetic field prevents atmospheric erosion and water loss. Although the early Earth retained its water and atmosphere, and thus evolved as a habitable planet, little is known about Earth's magnetic field strength during that time. We report paleointensity results from single silicate crystals bearing magnetic inclusions that record a geodynamo 3.4 to 3.45 billion years ago. The measured field strength is approximately 50 to 70% that of the present-day field. When combined with a greater Paleoarchean solar wind pressure, the paleofield strength data suggest steady-state magnetopause standoff distances of < or = 5 Earth radii, similar to values observed during recent coronal mass ejection events. The data also suggest lower-latitude aurora and increases in polar cap area, as well as heating, expansion, and volatile loss from the exosphere that would have affected long-term atmospheric composition.