Универзитет у Новом Саду, Природно-математички факултет
Abstract
Jedan od najvažnijih parametara nuklearne strukture su redukovane verovatnoće prelaza, koje se indirektno mogu odrediti iz vremena života pobuđenih stanja jezgra. U srednje teškim parnoparnim jezgrima, redukovane verovatnoće prelaza E2 multipolnosti, B(E2;↓), daju informaciju o kolektivnim efektima i deformaciji datog jezgra. Često se bliska neparno-parna jezgra analiziraju poredeći energije i B(E2;↓) vrednosti stanja sa onim u bliskim parno-parnim jezgrima. Jedan od često korišćenih metoda za određivanje vremena života reda ps je metod uzmicanja Doplerovog pomeranja, sa tzv. plunger uređajem i uz upotrebu metode diferencijalne krive raspada. Jezgra od interesa se mogu pobuditi u neka od nisko pobuđenih stanja od značaja putem različitih nuklearnih reakcija, poput Kulonove ekscitacije, fuzione evaporacije, dubokog-neelastičnog rasejanja itd. U ovom radu su merena vremena života nisko pobuđenih stanja u parnim jezgrima 70,72,74Zn i 76,78Ge, kao i u neparnim 73,75Ga i 75,77Ge i to koristeći metod uzmicanja Doplerovog pomeranja, a jezgra su nastala prilikom reakcije duboko-neelastičnog rasejanja projektila 208Pb na meti 76Ge. Proizvedena jezgra su identifikovana pomoću VAMOS++ masenog spektrometra po principu događaj-po-događaj, a γ zraci emitovani pri prelazu na niža i na osnovno stanje, detektovani su pomoću AGATA detektorskog niza. U cilju rešavanja sistematskih problema koji se mogu javiti pri analizi vremena života plunger metodom, postojeći metod za procenu vremena života od interesa je poboljšan pomoću dva različita pristupa. zmerena vremena života su poslužila za određivanje redukovanih verovatnoća prelaza, B(E2;↓) i B(M1;↓), koje su upoređivane sa prethodnim rezultatima dobijenim drugim metodama. Sem toga, deo ovog rada se sastoji od teorijskih proračuna modela ljusaka, pomoću kojih su određene redukovane verovatnoće prelaza i energije stanja, radi poređenja sa onim eksperimentalno dobijenim. U neparnim jezgrima, teorijski proračuni su korišćeni i za određivanje prirode pobuđenih stanja, kuplovanjem nesparenog nukleona na okolna parna jezgra.One of the most important benchmarks of nuclear structure are reduced transition probabilities, which can be indirectly determined from the lifetimes od excited states. In the medium heavy even-mass nuclei, reduced transition probabilities of E2 multipole transitions, B(E2;↓), can give information on collectivity and deformation of a given nucleus. Often times, odd-mass nuclei can be analyzed by comparing level energies and B(E2;↓) values with the corresponding ones in neighbouring even-mass nuclei. One of often used methods for determining level lifetimes of order of ps is recoil distance Doppler shift method (abbr. RDDS), with the use of so called plunger device and differential decay curve method (abbr. DDCM). Nuclei of interest can be produced and excited to low-lying states by various nuclear reactions, such as Coulomb excitation, fusionevaporation, deep-inelastic scattering etc. In this thesis, lifetimes of low-lying states in evenmass nuclei 70,72,74Zn and 76,78Ge, as well as oddmass nuclei 73,75Ga and 75,77Ge were measured, using the RDDS method. Nuclei of interest were produced by deep-inelastic reaction with 208Pb beam impinging on a 76Ge target. Recoils were identified on an event-by-event basis with VAMOS++ mass spectrometer, while emitted γ rays were detected using the AGATA detector array. In order to resolve systematic discrepancies which can arise in lifetime measurements using the plunger method, the existing method for lifetime determination was improved by two different approaches. Using the obtained level lifetimes, corresponding reduced transition probabilities B(E2;↓) and B(M1;↓) were deduced, and compared withprevious results obtained using different methods. Moreover, a part of this thesis is based on theoretical shell model calculations, used to calculate level energies and reduced transitions probabilities in order to compare them with the experimentally obtained ones. In odd-mass nuclei, shell model calculations were used for determining the nature of the states as well, by coupling the odd nucleon to neighbouring evenmass core
