Neutron-induced fission reactions play a key role in the nucleosynthesis of heavy elements. The description of fission recycling during r-process nucleosynthesis, relies on model predictions of fission reactions. To this end, various models are used in literature for calculating the fission rates and the mass distribution of fission fragments for a number of heavy and highly unstable actinides. In order to provide a reliable description of reaction rates for Th, U and heavier actinides, current efforts are underway for refining models with a comprehensive and self-consistent description of the fission process. In this respect, new fission data on a variety of actinides are needed, as the predictive power of current models can only by improved by comparison with a large set of experimental results. The 235U(n,f) cross section is one of the most important neutron cross-section standards, and therefore it is recognized as a convenient reference for other reaction cross-section measurements at thermal energy and between 0.15 MeV and 200 MeV. Outside these energy ranges the cross section is either not so well known or not measured yet, as for example above 200 MeV, where evaluations can only rely on theoretical calculations. With the continuous effort for the improvement of standard cross sections by the International Atomic Energy Agency (IAEA) together with nuclear data evaluators' teams, the longstanding quest for accurate and reliable 235U(n,f) cross section data turns out to be still pending, for neutron energies above 20 MeV (only 2 data sets are present in the 20-200 MeV energy region). In particular, fission measurements relative to the neutron-proton elastic scattering, which is considered the primary reference for neutron cross section measurements, are still highly requested. The neutron time-of-flight facility, n_TOF, at CERN, offers the possibility to study neutron-induced reactions thanks to the extremely wide neutron energy spectrum available in its experimental area, from thermal up to 1 GeV. In the recent years, dedicated measurement campaigns were carried out to provide accurate and precise cross section data of the 235U(n,f) reaction, in a low energy region, up to 10 MeV, as well as in the high energy region from 10 MeV to 500 MeV. The experimental apparatus used in the measurements at high neutron energies, which involved the efforts of several research institutions (INFN, PTB and IPN, in addition to CERN), consisted of three flux and two fission detectors, allowing to simultaneously record the number of neutrons impinging on the 235U samples (incident neutron flux), as well as fission events, as a function of the neutron energy. The neutron flux measurement is based on the neutron-proton elastic scattering reaction, and it exploits the detection of the recoil protons from the n-p reaction in a polyethylene target using three Proton Recoil Telescopes. The fission events have been recorded with a fission ionization chamber, as well as by a parallel plates avalanche counters (PPAC) detector, specifically designed for operation at n_TOF. The experimental apparatus and data analysis will be presented, with a focus on the results obtained in the high-energy region, above 200 MeV. A comparison with current model descriptions of the fission process at high neutron energies will be included in the comparison with the experimental results obtained at n_TOF.

The lowest metallicity stars in the Milky Way Halo are the fossil records of the earliest star-forming environments in the universe. Their chemical abundance patterns help us understand primordial nucleosynthesis, the mass function of the first stars, and the pathways that led to the chemical complexity we observe today. However, there is still debate about when (and for how long) the universe transitioned from metal-free to the first chemical enrichment episodes that triggered low-mass star formation. In that context, metal-poor stars with enhancements in elements formed by the r-process can hold valuable clues to this intricate cosmic puzzle. Such stars are rare and difficult to find, so I'll review some of the methods and tools astronomers use to increase their chances of identifying these chemically peculiar stars within the ever-increasing astronomical stellar databases. I will also talk about the serendipitous discovery and chemo-dynamical analysis of SPLUSJ1424, an old, low-mass, extremely metal-poor halo star enhanced in elements formed by the r-process. At [Fe/H]=-3.39, this is one of the lowest metallicity stars with measured Th and has the highest Th/Eu ratio observed to date, making it part of the "actinide-boost" category. Analysis suggests that the gas cloud from which SPLUSJ1424-2542 was formed must have been enriched by at least two progenitor populations, including a supernova explosion of metal-free stars and a neutron star merger event.

Emittance is one of the beam characteristics that dominantly determines the performance of particle accelerator applications. Since the development of RF-photocathode gun, tremendous efforts have been made to enhance emittance. There have been several fundamental understandings and technological improvements. For last 7 years, Argonne Wakefield Accelerator (AWA) facility has participated in this effort as part of its facility improvement project. We have developed several techniques and equipment that can improve emittance or may help to identify issues from the gun and laser. In this talk, I will begin with a brief introduction of ingredients for high-brightness beam generation and relevant AWA's recent research activities. Later, I will share our previous activities on laser uniformity, cathode characterization and nonlinear effect correction. Additionally, the talk will include introduction of several well-known emittance diagnostics, along with two newly developed methods.