BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:What can we learn from the electromagnetic dipole response respons e in atomic nuclei? DTSTART;VALUE=DATE-TIME:20231130T134000Z DTEND;VALUE=DATE-TIME:20231130T140500Z DTSTAMP;VALUE=DATE-TIME:20261016T120603Z UID:indico-contribution-473-3444@indico.tlabs.ac.za DESCRIPTION:Speakers: Mathis Wiedeking (University of the Witwatersrand an d iThemba LABS)\nThe gamma-ray decay of nuclear states in the quasi-contin uum offers valuable insights into nuclear structure effects and constraint s on nucleosynthesis processes. Measurement of Nuclear Level Densities (NL Ds) and Photon Strength Functions (PSFs) has played a pivotal role\, and w ill continue to do so\, as we enter a highly promising era for innovative measurements. This is primarily due to the establishment of advanced resea rch infrastructure by numerous institutes worldwide. These institutes have made significant enhancements to particle and gamma-ray detection efficie ncies\, as well as the development or upgrade of radioactive ion beam faci lities. Concurrently\, new experimental and analytical techniques have eme rged\, enabling more reliable studies of PSFs and NLDs\, even for unstable nuclei. This progress undoubtedly promises unparalleled insights into nuc lear structure and provides crucial reaction rates for nucleosynthesis pro cesses. \n\nIn this presentation\, I will provide an overview of the major experimental and analytical advancements made and how they have laid the groundwork for ambitious measurements of PSFs and NLDs at radioactive and stable ion beam facilities. Additionally\, I will discuss recent progress in investigating the nuclear structure underlying resonances\, with a part icular focus on the scissor's mode and the unexplained low-energy enhancem ent. The measurement of PSFs and NLDs also significantly enhance our under standing of nucleosynthesis processes\, as will be demonstrated.\n\nThis w ork is supported by the National Research Foundation of South Africa under grant number 118840.\n\nhttps://indico.tlabs.ac.za/event/119/contribution s/3444/ LOCATION: URL:https://indico.tlabs.ac.za/event/119/contributions/3444/ END:VEVENT BEGIN:VEVENT SUMMARY:Description Of Low-Lying Collective States in Osmium Isotopes in t he Boson Expansion Theory DTSTART;VALUE=DATE-TIME:20231130T153000Z DTEND;VALUE=DATE-TIME:20231130T154500Z DTSTAMP;VALUE=DATE-TIME:20261016T120603Z UID:indico-contribution-473-3385@indico.tlabs.ac.za DESCRIPTION:Speakers: Hideo Sakamoto (Gifu University)\nNeutron-rich nucle i with A ~ 190 provide a characteristic testing ground for microscopic the ories of nuclear structures. There are quite a few indications that a prol ate-oblate shape transition takes place at around N = 116 in this region [ 1\, 2]. \n \nThe microscopic description of anharmonicities in nuclear qua drupole collective motions\, in terms of the fermion degrees of freedom\, is a long-standing and fundamental subject in the study of nuclear ma ny-body systems. The boson expansion theory (BET) is a promising method for the subject if the coupling to non-collective states i s faithfully included in the calculation [3]. It allows us to ta ke into account higher-order terms neglected in the RPA\, and the adia batic condition for particle motions can be avoided. \n \nIn this work\, the low-lying collective states in osmium isotopes are investiga ted microscopically by means of the BET with the self-consistent eff ectiv e interactions [4]. The fermion Hamiltonian is comprised of the QQ interaction with its self-consistent higher-order (many-body) terms [5 ]\, monopole- and quadrupole-pairing interactions in addition to the sp herical limit of the Nilsson Hamiltonian. The Kishimoto-Tamura meth od of normal-ordered linked-cluster expansion of the modified Maru mori boson mapping [6] is applied to construct the microscopic boson imag e of the Hamiltonian and that of the E2 operator. The potential energy sur faces and the structures of boson wave functions for some relevant low-lyi ng collective states are illustrated [7]. Calculated level structures and electromagnetic properties are compared with the available experimental da ta. \n \n[1] P. Sarriguren\, R. R.-Guzmán and L. M. Robledo\, Phys. Rev. C 77 (2008) 064322. \n[2] N. Al-Dahan et al.\, Phys. Rev. C 85 (2012) 3430 1. \n[3] A. Klein and E. R. Marshalek\, Rev. Mod. Phys. 63 (1991) 375. \n[ 4] H. Sakamoto and T. Kishimoto\, Nucl. Phys. A501 (1989) 205\; ibid. 242. \n[5] H. Sakamoto\, J. Phys.: Conf. Ser. 1023 (2018) 012003. \n[6] T. Kis himoto and T. Tamura\, Phys. Rev. C 27 (1983) 341. \n[7] H. Sakamoto\, Phy s. Rev. C 104 (2021) 034304\; J. Phys.: Conf. Ser. 1555 (2020) 012023.\n\n https://indico.tlabs.ac.za/event/119/contributions/3385/ LOCATION: URL:https://indico.tlabs.ac.za/event/119/contributions/3385/ END:VEVENT BEGIN:VEVENT SUMMARY:Low-energy dipole response in the Sn isotope chain: Pygmy or not p ygmy? DTSTART;VALUE=DATE-TIME:20231130T151500Z DTEND;VALUE=DATE-TIME:20231130T153000Z DTSTAMP;VALUE=DATE-TIME:20261016T120603Z UID:indico-contribution-473-3384@indico.tlabs.ac.za DESCRIPTION:Speakers: Peter von Neumann-Cosel ( Institut für Kernphysik\, Technische Universität Darmstadt\, D-64289 Darmstadt\, Germany)\, Maria Markova (University of Oslo)\, Ann-Cecilie Larsen (University of Oslo)\, E lena Litvinova (Western Michigan University)\nThe observation of resonance -like structure in the electric dipole response of heavy nuclei at energie s around or below the neutron\, commonly termed pygmy dipole resonance (PD R)\, has been a topic leading to considerable experimental and theoretical activities in recent years [1-4]. The interest has been triggered by atte mpts to understand the underlying structure but also because of its impact on the cross sections of (n\,γ) reactions relevant for the nucleosynthes is of heavy elements. Qualitatively all mean-field based models predict th e appearance of such a mode\, however\, with a broad range of predicted st rengths and energy centroids depending on the chosen interaction and model space. Many theoretical studies interpret the PDR to arise from neutron s kin oscillations\, which implies a dependence of the PDR strength on neutr on excess. The chain of Sn isotopes represents a particularly interesting case to test the impact of neutron excess on the low-energy E1 response in a systematic manner because their g.s. structure changes little. Here\, w e report results from a systematic investigation of the gamma strength fun ctions (GSFs) in Sn isotopes with mass numbers between 111 and 124. It is based on a combined data set from Oslo-type experiments (as described in R ef. [5]) and a study of the (p\,p’) reaction [6] at very forward angles\ , together covering an energy range 2 - 20 MeV. This allows a decompositio n of the low-energy dipole response with minimal assumptions into contribu tions from the tail of the giant dipole resonance and possible resonance-l ike structures on top. The excess strength is dominated by a peak at about 8 MeV seen in the isovector response only. For masses ≥118\, the data d emand the inclusion of a second peak centered at about 6.5 MeV and identif ied as the PDR by comparison with isoscalar probes [7\,8] and (γ\,γ’) experiments [9\,10]. Its strength corresponds to 0.1 - 0.5% of the TRK sum rule (much smaller than predicted in most theoretical investigations) but exhibits an approximately linear increase with mass number. The results a re also compared to ab initio-based microscopic models [11].\n\nSupported by the Research Council of Norway (project number 316116)\, the DFG under contract SFB 1245 (project 279384907)\, the GANIL visitor program\, US-NSF grant PHY-2209376\, and US-NSF career grant PHY-1654379.\n\n[1] N. Paar\, D. Vretenar\, E. Khan\, and G. Colò\, Rep. Prog. Phys. 70\, 691 (2007).\ n[2] D. Savran\, T. Aumann\, and A. Zilges\, Prog. Part. Nucl. Phys. 70\, 210 (2013).\n[3] A. Bracco\, E. Lanza\, and A. Tamii\, Prog. Part. Nucl. P hys. 106\, 360 (2019).\n[4] E. Lanza\, L. Pellegri\, A. Vitturi\, and M. A ndrés\, Prog. Part. Nucl. Phys. 129\, 104006 (2023).\n[5] M. Markova et a l.\, Phys. Rev. Lett. 127\, 182501 (2021)\; Phys. Rev. C 106\, 034322 (202 2)\; Phys. Rev. C 108\, 014315 (2023).\n[6] S. Bassauer et al.\, Phys. Rev . C 102\, 034327 (2020).\n[7] J. Endres et al.\, Phys. Rev. Lett. 105\, 21 2503 (2010).\n[8] L. Pellegri et al.\, Phys. Lett. B 738\, 519 (2014).\n[9 ] K. Govaert et al.\, Phys. Rev. C 57\, 2229 (1998).\n[10] B. Özel-Tashen ov et al.\, Phys. Rev. C 90\, 024304 (2014).\n[11] E. Litvinova\, arXiv:23 08.07574 (2023).\n\nhttps://indico.tlabs.ac.za/event/119/contributions/338 4/ LOCATION: URL:https://indico.tlabs.ac.za/event/119/contributions/3384/ END:VEVENT BEGIN:VEVENT SUMMARY:Testing the generalized Brink-Axel hypothesis in heavy nuclei DTSTART;VALUE=DATE-TIME:20231130T150000Z DTEND;VALUE=DATE-TIME:20231130T151500Z DTSTAMP;VALUE=DATE-TIME:20261016T120603Z UID:indico-contribution-473-3364@indico.tlabs.ac.za DESCRIPTION:Speakers: Peter von Neumann-Cosel (Institut fuer Kernphysik\, TU Darmstadt)\nQuasicontinuum gamma decay following compound reactions - c ommonly called Oslo method - is probably the most important source of info rmation on the gamma strength functions and level densities of nuclei belo w particle threshold. A fundamental assumption in the analysis of Oslo-typ e data (and in fact all astrophysical reaction network calculations) is th e generalized Brink-Axel (BA) hypothesis\, whose applicability to the low- energy regime is under debate (see [1] and references therein). Since all other methods are based on the measurement of photoabsorption from the gro und state\, a test of the equivalence of results from absorption and emiss ion experiments in the same nuclei postulated by the BA hypothesis is most important. I will discuss inelastic proton scattering experiments perform ed at RCNP in extreme forward kinematics\, where relativistic Coulomb exci tation dominates the cross sections [2]. Such data provide information on the E1 [3] and M1 [4] parts of the GSF and their sum can be directly compa red to the compound-nucleus decay experiments. Furthermore\, their very go od energy resolution permits the extraction of level densities [5-7] and t hereby an independent test of the normalization methods applied in the ana lysis of Oslo-type data.\n[1] M. Markova et al.\, Phys. Rev. Lett. 127\, 1 82501 (2021)\n[2] P. von Neumann-Cosel and A. Tamii\, Eur. Phys. J. A 55\, 110 (2019)\n[3] S. Bassauer et al.\, Phys. Rev. C 102\, 034327 (2020)\n[4 ] S. Bassauer\, P. von Neumann-Cosel and A. Tamii\, Phys. Rev. C 94\, 0543 13 (2016)\n[5] I. Poltoratska et al.\, Phys. Rev. C 89\, 054322 (2014)\n[6 ] D. Martin et al.\, Phys. Rev. Lett. 119\, 182503 (2107)\n[7] M. Markova et al.\, Phys. Rev. C 106\, 034322 (2022)\n\nhttps://indico.tlabs.ac.za/ev ent/119/contributions/3364/ LOCATION: URL:https://indico.tlabs.ac.za/event/119/contributions/3364/ END:VEVENT BEGIN:VEVENT SUMMARY:Investigating the character of the PDR in 96Mo via one-nucleon tra nsfer reactions DTSTART;VALUE=DATE-TIME:20231130T144500Z DTEND;VALUE=DATE-TIME:20231130T150000Z DTSTAMP;VALUE=DATE-TIME:20261016T120603Z UID:indico-contribution-473-3374@indico.tlabs.ac.za DESCRIPTION:Speakers: Thuthukile Khumalo (iThemba LABS)\nThe low-lying E1 strength which has been termed the pygmy dipole resonance (PDR)\, manifest s as a concentration of 1$^{-}$ states below and around the neutron thresh old. It has thus far been observed in neutron-rich nuclei and its study ma y have implications on the nuclear equation of state and nucleosynthesis. Since its discovery\, there has been a great deal of work in an attempt to understand its nature\, both theoretically and experimentally. The degree to which the dipole states are collective is amongst the characteristics of the PDR under scrutiny. This study is an attempt to probe the nature of the PDR\, specifically the single-particle or collective character of the se states. One-nucleon transfer reactions are the probes of choice for thi s goal due to their selectivity in probing single-particle configurations. The neutron stripping reaction\, $^{97}$Mo(p\,d)$^{96}$Mo and the neutron pickup reaction $^{95}$Mo(d\,p)$^{96}$Mo\, were used to populate the nucl eus of interest\,$^{96}$Mo. The experiment was conducted at the MAGNEX fac ility of INFN-LNS in Catania\, Italy. The ejectiles were momentum-analyzed by the MAGNEX spectrometer and detected by its focal-plane detection syst em. In this talk\, the results of this experiment will be presented.\n\nTh is work is based on the research supported in part by the National Researc h foundation (NRF)\nof South Africa grant number 118846\n\nhttps://indico. tlabs.ac.za/event/119/contributions/3374/ LOCATION: URL:https://indico.tlabs.ac.za/event/119/contributions/3374/ END:VEVENT BEGIN:VEVENT SUMMARY:Study of the K quantum number of pygmy states in 154Sm DTSTART;VALUE=DATE-TIME:20231130T143000Z DTEND;VALUE=DATE-TIME:20231130T144500Z DTSTAMP;VALUE=DATE-TIME:20261016T120603Z UID:indico-contribution-473-3378@indico.tlabs.ac.za DESCRIPTION:Speakers: Refilwe Molaeng (iThemba LABS and University of the Witwatersrand)\nThis study aims to understand the Pygmy Dipole Resonance ( PDR) in the deformed 154Sm nucleus. Despite previous efforts\, the interpr etation of the behavior and nature of this low-energy resonance remains un clear with respect to the effects of neutron excess and deformation in nuc lei. This further limits the predictive power of exotic nuclei properties. The current study uses the (γ\, γ′) technique to explore dipole state s from 3.5 MeV to the neutron separation threshold (8 MeV). The experiment was performed with the improved γ 3 setup available at the HIγS facilit y of the Triangle Universities Nuclear Laboratory. The setup allows for me asurements by the asymmetry method of the character of the populated trans itions in order to distinguish between the contribution of 1− and 1+ sta tes which in particular is important in the study of a deformed nucleus. T he high beam resolution mode (< 2%) available at HIγS allows for the meas urement of the decay branching ratio to the first 2 + state. This will hel p to identify the K quantum number of different excited states and the PDR as a function of excitation energy. The motivation for the study along wi th experimental details will be provided. The initial data analysis will b e discussed and an overview of future comparisons will be given.\n\nhttps: //indico.tlabs.ac.za/event/119/contributions/3378/ LOCATION: URL:https://indico.tlabs.ac.za/event/119/contributions/3378/ END:VEVENT BEGIN:VEVENT SUMMARY:Theoretical approaches describing low-lying dipole states DTSTART;VALUE=DATE-TIME:20231130T140500Z DTEND;VALUE=DATE-TIME:20231130T143000Z DTSTAMP;VALUE=DATE-TIME:20261016T120603Z UID:indico-contribution-473-3336@indico.tlabs.ac.za DESCRIPTION:Speakers: Edoardo G. Lanza ()\nThe presence of the low-lying d ipole states on stable and unstable nuclei with neutron excess - known as Pygmy Dipole Resonances (PDR) - is well established in theoretical and ex perimental studies. The isospin mixed nature of the PDR allows to study th e excitation with isovector and isoscalar probes.\nThe theoretical approac hes devoted to investigate this new mode extend from the macroscopic colle ctive models to the microscopic mean-field theories\; all of them reproduc ing the isospin mixing feature. \nDetailed investigation on the reaction m echanisms are in order when isoscalar probes are used. Cross section calcu lations - based on detailed structure descriptions - are calculated within semiclassical Coupled Channel equations with particular attention to the construction of the nuclear potential and radial form factors with the mic roscopic transition densities. \nA short review will be presented on both structure and dynamic approaches paying attention to some of the few quest ions that remain to be clarified.\n\nhttps://indico.tlabs.ac.za/event/119/ contributions/3336/ LOCATION: URL:https://indico.tlabs.ac.za/event/119/contributions/3336/ END:VEVENT END:VCALENDAR