Wydział Fizyki UW > Badania > Seminaria i konwersatoria > Seminarium Fizyki Jądra Atomowego

Seminarium Fizyki Jądra Atomowego

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Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 10:15

Dr Gagandeep Singh (National Centre for Nuclear Research)

Low and medium mass neutron halos

The nuclear chart is full of phenomena hitherto unexplained. Of the roughly estimated 7000 nuclear species to exist in nature, only about 10% are known and studied. Owing to the Coulomb barrier, most of these lie on the neutron rich side of the valley of stability. Halos are a special class of these exotic nuclei where one or two nucleons decouple from a composite core and penetrate the classically forbidden region. They are weakly bound nuclei, with the continuum playing a major role in their description. I discuss the three-body Borromean system 31F, which is the last known isotope of the Fluorine chain and has been deemed as a p-wave halo, using a pseudostate approach with a transformed harmonic oscillator (THO) basis. Similarly, 34Na, analyzed using the post form finite range distorted wave Born approximation (FRDWBA) theory is a vital p-wave halo like 31F, but is a one-neutron halo candidate whose formation rate is crucial to 35Na, the most abundant neutron rich isotope of the Sodium chain. With the same basis discretizing the intermediate continuum as 31F, I then discuss two-neutron transfer reactions with 6He as an ideal candidate to understand the reaction mechanism due to the pairing interactions in the final nucleus. I weigh up scattering of the Cooper pair of the nucleons via the different states of the intermediate continuum through comparisons with a hypothetical bound case of 5He. Extending the possibilities for astrophysical applications, reaction rates for radiative neutron capture (n,γ) reactions involving some of these exotic nuclei would also be discussed.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 10:15

dr hab. Michał Kowal, prof. NCBJ (NCBJ)

A Question of Shape: New Mechanism Governing Superheavy Nuclei Survival

We demonstrate that hot superheavy nuclei do not retain spherical shapes, as traditionally assumed, but instead equilibrate in deformed —often oblate or triaxial— configurations at finite excitation energy. This behavior arises from a mechanism analogous to the Jahn--Teller effect: spherical systems exhibit high single-particle degeneracy near the Fermi surface, causing their shell corrections to damp out significantly faster with temperature than those of deformed shapes. Using a finite-temperature framework, we reveal a thermally induced inversion of the potential-energy landscape in the Z=118-120 region, where deformed minima become energetically favored at U ~= 30-50 MeV. This shape inversion fundamentally alters the competition between neutron evaporation and fission. We derive a deformation-dependent correction to the survival probability, revealing a systematic bias in estimates based on spherical ground-state properties. Our results identify a finite-temperature structure effect that calls for a revision of current models of superheavy nucleus synthesis and decay.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 10:15

dr Marco Rocchini (INFN - Istituto Nazionale di Fisica Nucleare, Division of Florence, Italy)

Spherical-oblate shape coexistence in 94Zr and the SPIDER Coulomb-excitation campaign at LNL

Low-energy Coulomb excitation is a powerful tool for studying collective properties and shape evolution in atomic nuclei. At the INFN Legnaro National Laboratories (LNL), we have been conducting a long-term experimental campaign using the SPIDER detector, an array of segmented silicon detectors specifically designed for Coulomb-excitation experiments. SPIDER has been used in combination with both the GALILEO gamma-ray spectrometer and, more recently, the AGATA gamma-tracking array.

In this talk, I will briefly introduce the SPIDER detector and provide an overview of the Coulomb-excitation measurements performed at LNL with the GALILEO and AGATA setups. I will then focus on the specific case of 94Zr, which represents our most recently completed analysis. This study marked the first application of the quadrupole sum rules method in the Zr isotopic chain and provided clear evidence of spherical-oblate shape coexistence in 94Zr. The experimental results will be discussed in the context of state-of-the-art nuclear models and quantum phase transitions.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 10:15

prof. Thomas Elias Cocolios (KU Leuven, Belgia)

Getting NSHAPE: combining laser spectroscopy with muonic atoms of exotic nuclei to reveal exciting features of the nuclear landscape

Nuclear charge radii are known to be impactful to further our understanding of the nuclear landscape, from kinks at magic numbers to onset of deformation or the dramatic odd-even staggering in the neutron-deficient mercury isotopes. Recent developments at CERN ISOLDE, like the Perpendicularly-Illuminated Laser Ion Source & Trap (PI-LIST) has enabled the study of neutron-rich polonium and actinium isotopes, helping delineate the region of octupole deformation north-east of 208Pb.
While laser spectroscopy gives access to changes in charge radii across long chains of isotopes, those measurements rely on atomic parameters which determination from large-scale atomic calculations result in large systematic uncertainties, often obscuring the nuclear information. It is possible to benchmark those laser spectroscopy data against absolute charge radii, when those are available. However, given that none of the odd-Z elements nor any element beyond Pb have more than 2 stable isotopes, none of those have so far such data available.
At the Paul Scherrer Institute in Villigen, Switzerland, the muX collaboration has developed an approach to study muonic x rays for samples as small as 10 µg. This has enabled a new program, named ReferenceRadii, exploring absolute charge radii from aluminium to curium.
Recent highlights from PI-LIST and ReferenceRadii, and their impact will be presented.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 10:15

Dr Aafke Kraan (University of Pisa, Włochy)

Nuclear Fragmentation Measurements for Particle Therapy and Beyond

FOOT (FragmentatiOn Of Target) is an experimental program in applied nuclear physics focused on the understanding of nuclear fragmentation processes. Understanding these fragmentation processes is important in two major contexts: improving cancer treatments that use hadron beams and assessing radiation risks for astronauts during space missions. The FOOT physics program foresees a set of measurements conducted in both direct and inverse kinematics, employing particle beams and targets relevant to particle therapy and radiation protection in space. The principal objective is to determine double-differential cross sections—measured as functions of the emission angle and the energy of the produced fragments—in the energy interval from about 100 to 800 MeV per nucleon. The experiment aims to reach a measurement accuracy better than approximately 5%. For this purpose, the FOOT collaboration has developed two experimental setups. One setup uses nuclear emulsion detectors and is optimized for identifying fragments with charge Z≤3. The second setup relies on electronic detector systems and is intended primarily for detecting lighter fragments with charge Z≥2.

In this seminar the physics motivations of the experiment will be discussed, followed by an overview of the apparatus. Several preliminary and recent results will be presented, focusing on topics such as fragment charge identification, new measurements obtained with helium beams, and recent determinations of fragmentation cross sections. Future plans will also be discussed.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 10:15

Dr. Behruz Kardan (IKF, Goethe-Universität Frankfurt, Germany)

Flow phenomena at high nuclear densities with HADES

Heavy-ion collisions in the few-GeV energy range create strongly interacting matter at extreme baryon densities, comparable to those in neutron star mergers. Precise measurements of the dense-matter Equation-of-State in this regime are therefore essential for the understanding of neutron stars.

We present new results from HADES (High-Acceptance Dielectron Spectrometer) located at the SIS18, GSI Darmstadt, the only current setup capable of measuring rare and penetrating probes at the high baryochemical potential frontier of the QCD phase diagram. High-statistics measurements of collective flow for protons and light nuclei are reported in Au+Au and Ag+Ag collisions at s^1/2_NN= 2.42 and 2.55GeV, along with recent Au+Au data at s^1/2_NN= 1.98, 2.07, 2.16, and 2.24GeV, extending the excitation function to lower beam energies (200 - 800)A MeV. Beyond directed and elliptic flow, flow coefficients v_n up to 6th order are measured for the first time in this energy range, enabling a 3D characterization of angular particle emission in momentum space. Furthermore, the event-by-event flow fluctuations can be explored via correlations between the different flow coefficients, providing even stronger constraints on the Equation-of-State, and will also be presented.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 10:15

mgr Jan Miśkiewicz (IFT UW)

Double beta decay within the Skyrme density-functional framework

Double beta decay is among the rarest radioactive processes, observed only in a few even–even nuclei near the valley of stability. Although the phenomenon itself is well established, it provides a stringent consistency test for nuclear states predicted within contemporary theoretical frameworks. Such validation is of paramount importance for reliable modeling of the yet unobserved neutrinoless double beta (0νββ) decay process.
The presentation focuses on the foundations of 2νββ decay and on the the- oretical treatment of spherical (48Ca) and highly triaxial (76Ge) 2νββ-active nuclei within a Skyrme SV density-functional No-Core CI (DFT-NCCI) frame- work developed by our group. The approach restores rotational symmetry and mixes states projected from self-consistent mean-field configurations obtained by solving the Hartree–Fock equations with a density-independent local Skyrme interaction.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 10:15

dr Olga Polak (Narodowe Centrum Badań Jądrowych)

Fission isomer studies in the actinide region at the IGISOL facility

Multi-humped fission barriers, as they occur in the actinide region, give rise to fission isomerism. Such barrier shapes can be described within various theoretical models. Experimentally measured observables of nuclear fission isomers—such as the half-life, excitation energy of the fission isomer, kinetic energy of the fission fragments, and the isomer-to-ground-state population ratio—allow for testing theoretical predictions and verifying the role of shell effects in nuclear structure.
Studies of the fission isomer properties of 240,242Am were performed at the IGISOL facility at the JYFL Accelerator Laboratory, University of Jyväskylä, Finland. Fission isomeric states were populated via deuteron-induced fusion–evaporation reactions on a 242Pu target. The decays of the fission isomers were detected using silicon detectors calibrated with a 252Cf fission source.
The measurements provided detailed information on kinetic energy spectra, total kinetic energies, and mass distributions for 240,242Am. A new method was proposed to derive post-neutron-emission mass distributions, as well as proton- and neutron-number multiplicity distributions of the fission fragments, from their kinetic energy distributions. In addition, the emission probabilities of prompt neutrons in the fission process were extracted. Using data for the 252Cf fission isomer as a reference, the validity of the method was verified.
The obtained results for 240,242Am and 252Cf are consistent with GEF model predictions and previous measurements. These findings contribute to a better understanding of shell effects and fission barrier structures in the actinide region.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 10:15

dr Aleksandra Fijałkowska (IFD, UW)

Wielki spektrometr wielkich możliwości

Seminarium poświęcone będzie technice pełnej absorpcji, będącej ważnym narzędziem w badaniach rozpadu beta egzotycznych jąder atomowych i towarzyszącego mu promieniowania gamma. W pierwszej części omówione zostaną podstawowe założenia techniki oraz powody, dla których stanowi ona skuteczną alternatywę dla klasycznych pomiarów spektroskopowych, m.in. w kontekście problemu Pandemonium.
W drugiej części seminarium zaprezentowane zostaną możliwości, jakie daje technika pełnej absorpcji w badaniach struktury jąder atomowych. Omówione zostaną przykłady eksperymentów, w których technika ta została wykorzystana w praktyce, w tym pomiary wykonane z użyciem detektora LUCRECIA w ISOLDE, CERN oraz układu MTAS w ośrodku FRIB. Pokazane wyniki zilustrują potencjał techniki pełnej absorpcji oraz jej znaczenie dla współczesnej fizyki jądrowej.

Zapraszamy na spotkanie o godzinie 10:15

Dr Cézar Domingo Pardo (Instituto de Física Corpuscular, Valencia, Hiszpania)

Neutron-capture reactions for stellar nucleosynthesis

Neutron-capture reactions drive the nucleosynthesis of all elements heavier than iron, both via the slow (s-) neutron-capture process during the evolution of low-mass AGB- and massive stars, as well as in the rapid (r-) neutron-capture process during explosive stellar environments.
Unstable s-process branching isotopes offer a unique insight about this mechanism of nucleosynthesis. Neutron-capture measurements on radioactive isotopes, in combination with spectroscopic observations of stellar photospheres and isotopic analysis of primitive meteorites, help to gather unique information about the physical conditions of the stellar environment and the chemical evolution of our galaxy. Experimentally, however, measuring neutron-capture cross sections on radioactive isotopes represents yet one of the most remarkable challenges, mainly due to the difficulties ascribed to the production of a high-quality sample for such experiments, as well as to the sensitivity and selectivity required for the capture reaction channel of interest.
This contribution will present a brief summary about the main s-process branching isotopes measured at CERN n_TOF over the last two decades, thereby showing the corresponding astrophysical implications of the different studies. It will be shown how upgrades in the neutron-beam facility, as well as novel detector developments, have led to a stunning progress in the measurement of radioactive samples. However, in most cases, important limitations still exist related to the lowest accessible isotopic half-life (> few y), the covered neutron-energy ranges (< few keV) and the statistical accuracy (>10%). Some of the future plans at CERN n_TOF to advance further in this field will be presented along with novel initiatives and efforts for overcoming current limitations for the measurement of short-lived nuclei.

Dołącz do spotkania Zoom od godz. 10:00 AM Warszawa
https://uw-edu-pl.zoom.us/j/98722620830?pwd=2wB3UY5ZQbISaeE1D2EVcxH6elnbCr.1

Identyfikator spotkania: 987 2262 0830
Kod dostępu: 917334

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