Title Neutronski bogate teške jezgre Title (english) Heavy neutron rich nuclei Author Marko Crnac Mentor Suzana Szilner (mentor)Mentor Matko Milin (mentor)Committee member Matko Milin (predsjednik povjerenstva)Committee member Suzana Szilner (član povjerenstva)Committee member Krešimir Kumerički (član povjerenstva)Committee member Damir Bosnar (član povjerenstva)Committee member Ivica Smolić (član povjerenstva)Granter University of Zagreb Defense date and country 2018-12-11, Croatia Scientific / art field, NATURAL SCIENCES Abstract U ovom radu predstavljeni su rezultati proučavanja reakcija prijenosa nukleona u sustavu 94Rb + 208Pb na energiji oko Coulombove barijere. Osnovni cilj ovog rada bio je proučiti mogućnost upotrebe reakcija prijenosa nukleona za proizvodnju i pobuđenje neutronski bogatih teških jezgara oko jezgre 208Pb, posebno jezgara koje se na karti nuklida nalaze lijevo i ispod jezgre 208Pb. Produkti reakcije 94Rb + 208Pb detektirani su γ- spektrometrom Miniball u kombinaciji s čestičnim CD detektorom. Radioaktivni snop 94Rb ubrzan je akceleratorskim kompleksom ISOLDE na CERNu. U radu su identificirani elektromagnetski prijelazi vezani uz produkte nuklearne reakcije, gdje su različiti izotopi prepoznati pomoću poznatih elektromagnetskih prijelaza. Uz pomoć tabličnih vrijednosti energija γ zraka i njihovih intenziteta, izmjereni prijelazi pridruženi su izotopima nastalim reakcijom prijenosa nukleona, izotopima vezanim uz pozadinsko zračenje, ili izotopima koji pripadaju lancu raspada radioaktivnog snopa 94Rb. U mjerenjima pod snopom, većina opaženih elektromagnetskih prijelaza vezana je uz kratkoživuće izotope 94Sr i 93Sr. U mjerenjima u kojima je meta bila ozračena snopom, a nakon što je sam snop bio isključen, identificirani su elektromagnetski prijelazi vezani uz stabilni 94Zr, te dugoživuće izotope 93Y i 93Zr. Opaženi su i prijelazi vezani uz izotope koje pridružujemo prirodnoj radioaktivnosti, kao npr. 214Po, 214Bi i dr. Nakon prepoznavanja elektromagnetskih prijelaza vezanih uz prirodnu radioaktivnost, te vezanih uz raspad radioaktivnog snopa 94Rb, identificirali su se i oni elektromagnetski prijelazi koji su rezultat pobuđenja jezgara snopa i mete, te reakcija prijenosa nukleona. Identificirano je niz elektromagnetskih prijelaza koji odgovaraju lakšem fragmentu reakcije: 92Rb, 93Rb, 95Rb i 94Sr, te težem fragmentu reakcije: 207Pb i 209Pb. Usporedbom intenziteta tih raspada i relativnog udarnog presjeka u svakom kanalu prijenosa, zaključeno je da je prijenos neutrona od Rb prema Pb (94Rb + 208Pb → 93Rb + 209Pb) značajno snažniji kanal od prijenosa neutrona iz Pb prema Rb (94Rb + 208Pb → 95Rb + 207Pb). Ovaj zaključak nam govori da se reakcije prijenosa nukleona na energijama oko Coulombove barijere uz upotrebu radioaktivnih snopova mogu koristiti kao mehanizam dobivanja neutronski bogatih teških jezgri. Dodatna analiza trostrukih koincidencija, fragmenat-γ-γ, pomoći će u preciznijem uspoređivanju kaskada raspada i u razlučivanju mehanizma reakcije. Usporedba s nuklearnim modelima omogućit će preciznije određivanje ukupnog udarnog presjeka u različitim kanalima prijenosa nukleona.
Abstract (english) This work presents selected results of the analysis of nucleon transfer reactions in the 94Rb + 208Pb system at energy close to the Coulomb barrier. The main goal of this study was to investigate the ability of the nucleon transfer reactions in the production of heavy neutron-rich nuclei in the vicinity of 208Pb, in particular in the region of the nuclear chart east and south of 208Pb. The reaction products of 94Rb + 208Pb have been detected by the Miniball γ-spectrometer coupled to the particle CD detector. The radioactive beam 94Rb was accelerated by the ISOLDE accelerator complex at CERN. Using known energies and intensities of γ -rays, measured electromagnetic transitions have been associated with the isotopes produced in the nucleon transfer reaction, the isotopes produced by the decay of the radioactive 94Rb beam, and associated with the natural radiation. The strongest electromagnetic transitions observed while the beam was impinging on the target belong to the short-lived isotopes 94Sr and 93Sr. In the spectra detected when the beam was switched off, the dominant transitions are associated with the stable 94Zr, and long-lived 93Y and 93Zr isotopes. Strong transitions in isotopes related to the natural radioactivity, such as 214Po, 214Bi have also been observed. After the electromagnetic transitions related to natural radioactivity and the decay of the 94Rb isotopes have been identifed, the electromagnetic transitions resulting from the excitation of the beam-like and target-like nuclei were established. They correspond to the light reaction fragment: 92Rb, 93Rb, 95Rb and 94Sr, and to the heavy reaction fragment: 207Pb and 209Pb. By comparing the intensity of these decays and relative cross sections in each transfer channel, it was concluded that the neutron transfer from Rb to Pb (94Rb + 208Pb → 93Rb + 209Pb) was much stronger than the transfer of neutrons from Pb to Rb (94Rb + 208Pb → 95Rb + 207Pb). Such a conclusion strongly supports the use of the nucleon transfer reactions at energies close to the Coulomb barrier using radioactive beams for the production of the heavy neutron-rich nuclei. An additional analysis of triple coincidences, fragment-γ-γ, will help to define more accurately the deexcitation of nuclei and to gather further information about the reaction mechanism. Comparison with nuclear models will allow a more precise determination of the total cross section in different nucleon transfer channels.
Keywords
reakcije prijenosa nukleona
nuklearni raspadi
nuklearna struktura
208Pb
94Rb
γ spektrometar Miniball
ISOLDE
Keywords (english)
nucleon transfer reactions
radioactive decay
nuclear structure
208Pb
94Rb
Miniball γ spectrometer
ISOLDE
Language croatian URN:NBN urn:nbn:hr:217:437761 Study programme Title: Physics; specializations in: Research Type of resource Text File origin Born digital Access conditions Open access Terms of use Created on 2019-01-23 13:29:31
