Elastic Scattering and Total Reaction Cross Section for the 6He + 27Al System

The elastic scattering of the radioactive halo nucleus 6He on 27Al target was measured at four energies close to the Coulomb barrier using the RIBRAS (Radioactive Ion Beams in Brazil) facility. The Sao Paulo Potential(SPP) was used and its diffuseness and imaginary strength were adjusted to fit the elastic scattering angular distributions. Reaction cross-sections were extracted from the optical model fits. The reduced reaction cross-sections of 6He on 27Al are similar to those for stable, weakly bound projectiles as {6,7}Li, 9Be and larger than stable, tightly bound projectile as 16O on 27Al.Comment: 7 pages, 1 table, 3 figure

Baltica cradle of early land plants? Oldest record of trilete spores and diversecryptospore assemblages; evidence from Ordovician successions of Sweden

The origin of land plants is one of the most important evolutionary events in Earth’s history. The mode and timing of the terrestrialization of plants remains debated and previous data indicate Gondwana to be the center of land-plant radiation at ~ 470–460 Ma. Here we present the oldest occurrences of trilete spores, probably the earliest traces of vascular land plants yet recorded. The spores occur in Ordovician, Sandbian (455 million years old) successions in central Sweden, once part of the paleocontinent Baltica. These strata are independently dated by marine microfossils (conodonts) and 206Pb/238U dating of volcanic ash deposits. Our discovery extends the record of trilete spores globally by ~8 million years, and for Baltica by ~25 million years. Additionally, cryptospore assemblages are identified revealing a diverse and stable mid-Ordovician (Darriwilian: ~ 460 Ma) vegetation of free-sporing plants. The formation of regolith substrates on land as a consequence of permanent plant cover must in turn have affected the marine biota. We link these early land plant spore occurrences to the extensive, nutrient-rich volcanic ash deposits and propose Baltica as the possible original region of the radiation of early land plants.Financial support was also provided by Fondo para la Investigación Científica y Tecnológica (FONCYT), PICT 2017-0532 to C. Rubinstein, and by the Swedish Research Council (VR) through Lund University Carbon Cycle Centre (LUCCI) to V. Vajda.</p