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Quasifree one-proton knockout reactions have been employed in inverse kinematics for a systematic study of the structure of stable and exotic oxygen isotopes at the R3B/LAND setup with incident beam energies in the range of 300–450 MeV/u. The oxygen isotopic chain offers a large variation of separation energies that allows for a quantitative understanding of single-particle strength with changing isospin asymmetry. Quasifree knockout reactions provide a complementary approach to intermediate-energy one-nucleon removal reactions. Inclusive cross sections for quasifree knockout reactions of the type AO(p,2p)A−1N have been determined and compared to calculations based on the eikonal reaction theory. The reduction factors for the single-particle strength with respect to the independent-particle model were obtained and compared to state-of-the-art ab initio predictions. The results do not show any significant dependence on proton-neutron asymmetry.
The quasi-free scattering reactions 11C(p, 2p) and 10,11,12C(p, pn) have been studied in inverse kinematics at beam energies of 300–400 MeV/u at the R3B-LAND setup. The outgoing proton-proton and protonneutron pairs were detected in coincidence with the reaction fragments in kinematically complete measurements. The efficiency to detect these pairs has been obtained from GEANT4 simulations which were tested using the 12C(p, 2p) and 12C(p, pn) reactions. Experimental cross sections and momentum distributions have been obtained and compared to DWIA calculations based on eikonal theory. The new results reported here are combined with previously published cross sections for quasi-free scattering from oxygen and nitrogen isotopes and together they enable a systematic study of the reduction of singleparticle strength compared to predictions of the shell model over a wide neutron-to-proton asymmetry range. The combined reduction factors show a weak or no dependence on isospin asymmetry, in contrast to the strong dependency reported in nucleon-removal reactions induced by nuclear targets at lower energies. However, the reduction factors for (p, 2p) are found to be ’significantly smaller than for (p, pn) reactions for all investigated nuclei.
A checklist with preliminary conservation assessments of native South American species of Acalypha is presented. This work is supported by the study of ca 6500 herbarium specimens and an in-depth literature review. As a result, 87 species (83 native and four introduced) and eight subspecies are accepted, and a further 395 names are considered synonyms. Geographical distribution, habitat, and altitudinal range for all species are also indicated. Brazil is the richest country in number of species of Acalypha (40), followed by Peru (32), Bolivia (29), Colombia and Ecuador—including Galapagos Islands—(24), Venezuela (18), Argentina (17), Paraguay (13), Guyana (8), Uruguay (5), French Guiana (4), and Suriname (3). The presence of the genus Acalypha in Chile is reported for the first time, alongside new country records of A. poiretii in Peru and A. venezuelica in Guatemala. The specimens previously identified as A. plicata from Colombia and Venezuela, are here considered belonging to A. cuspidata. The red list provided follows IUCN criteria and includes 39 species and three subspecies, 47% of total native species of Acalypha in South America: 16 species and one subspecies Critically Endangered (nine of them probably extinct), 15 species and two subspecies Endangered, and eight species Vulnerable.