Microscopic description of nuclear deformations

doctoral thesis

• Title (croatian): Mikroskopski opis deformacija atomske jezgre
• Author: Luka Lotina
• Mentor: Kosuke Nomura (mentor)
• Committee member: Tamara Nikšić (predsjednik povjerenstva)
• Committee member: Nils Paar (član povjerenstva)
• Committee member: Tea Mijatović (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2024-07-02, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

In this thesis, a microscopic model, based on the nuclear energy density functional, which can be used to analyse hexadecapole correlations in nuclei, is constructed and presented. Using the model, axial hexadecapole deformations were explored in the rare-earth region, as well as the effects those deformations have on the low-lying energy spectra and transition strengths of even-even rare-earth nuclei. A self-consistent mean-field calculation with a relativistic energy density functional DD-PC1 was performed on even-even isotopes of Nd, Sm, Gd, Dy and Er (Z = 60 − 68) in the N ≈ 90 region, with constraints on axial quadrupole and hexadecapole deformation parameters β20 and β40. The low-lying excitation energies and transition strengths were calculated by constructing the mapped sdg interacting boson model, whose parameters were derived by fitting them to the potential energy surface from the mean-field calculation. The results show that the mapped sdg interacting boson model can be successfully constructed and applied to even-even rare-earth nuclei, and that including the hexadecapole deformations in the model is necessary in order to successfully reproduce the energies of the (Jπ ≥ 6+) yrast states for nuclei with the neutron number near the magic number N = 82. The description of B(E2) transitions between the higher-lying yrast states, is improved by this model, compared to the simpler model which does not include g bosons. It is also shown that the inclusion of the g boson in the interacting boson model is necessary if one wants to reproduce large B(E4) tran- sition strengths from higher-lying 4+ states to the 0+ ground state, however, the experimental data on such transitions in rare-earth nuclei is limited.

Abstract (croatian)

U ovom radu predstavljen je mikroskopski model, temeljen na nuklearnom energijskom funkcionalu gustoće, koji se može koristiti za analizu heksadekapolnih korelacija u atomskim jezgrama. Koristeći ovaj model, analizirane su aksijalne heksadekapolne deformacije u području rijetkih zemnih metala, kao i učinci navedenih deformacija na niskoležeći spektar pobuđenih stanja i na snage prijelaza među pobuđenim stanjima u parno-parnim jezgrama iz skupine rijetkih zemnih metala. Izračuni u okviru samokonzistentnog modela srednjeg polja, s relativističkim energijskim funkcionalom gustoće DD-PC1, provedeni su na parno-parnim izotopima Nd, Sm, Gd, Dy i Er (Z = 60 − 68) u području oko N = 90, s ograničenjima postavljenima na aksijalne kvadrupolne i heksadekapolne deformacijske parametere β20 i β40. Energije niskoležećih pobuđenih stanja i snage prijelaza izračunate su pomoću sdg modela interagirajućih bozona, pri čemu su vrijednosti parametara Hamiltonijana danog modela određene mapiranjem površine potencijalne energije, izračunate pomoću modela srednjeg polja, na Hamiltonijan modela interagirajućih bozona. Dobiveni rezultati pokazuju da se mapirani sdg model interagirajućih bozona može uspješno konstruirati i primijeniti na parno-parne jezgre rijetkih zemnih metala, te da je uključivanje heksadekapolnih korelacija u model interagirajućih bozona nužno da bi se uspješno reproducirale izmjerene vrijednosti energija viših stanja Jπ ≥ 6+ iz vrpce osnovnog stanja, u jezgrama s neutronskim brojem blizu N = 82 magičnog broja. Također, sdg model može uspješnije predvidjeti B(E2) snage prijelaza između viših stanja u vrpci osnovnog stanja, u usporedbi s jednostavnijim sd modelom. Pokazano je i da je uključivanje g bozona u model interagirajućih bozona nužno za izračun velikih vrijednosti B(E4) snaga prijelaza između viših 4+ stanja i osnovnog stanja, međutim, veoma je malo eksperimentalnih podataka vezanih uz te prijelaze u jezgrama rijetkih zemnih metala.

• Keywords: xial hexadecapole deformations; rare-earth nuclei; relativistic energy density functional; sdg interacting boson model; low-lying spectra; yrast states; transition strengths
• Keywords (croatian): ksijalne heksadekapolne deformacije; jezgre rijetkih zemnih metala; relativistički energijski funkcional gustoće; sdg model interagirajućih bozona; niskoležeći spektar pobuđenih stanja; vrpca osnovnog stanja; snage prijelaza
• Language: english
• URN:NBN: urn:nbn:hr:217:069400
• Promotion: 2024
• Project: Number: TTP-2018-07-3554; Title: Exotic Nuclear Structure and Dynamics; Title: Exotic Nuclear Structure and Dynamics; Acronym: ExoNSD; Leader: Kosuke Nomura; Jurisdiction: Croatia; Funder: Hrvatska zaklada za znanost; Funding stream: Tenure Track Pilot Programme
• Study programme: Title: Doctoral study; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti u području prirodnih znanosti (doktor/doktorica znanosti u području prirodnih znanosti)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2024-07-22 08:46:53