Study of exotic nuclei at ISOLDE

Dette prosjektet dekker medlemskapet i ISOLDE kollaborasjonen på CERN. ISOLDE har en rik historie med å produsere radioistoper, og er i dag det laboratoriet med størst utvalg av eksotiske partikkelstråler i verden. Et fokus i dette prosjektet er å undersøke skallstrukturen til eksotiske atomkjerner med uvanlig forhold mellom antall protoner og nøytroner og, nært knyttet til dette, utviklingen av deformasjon og formeksistens i atomkjerner. Universitetet i Oslo leder et eksperiment for å måle kjernens fasong og kollektivitet i 140Sm med HIE-ISOLDE. Dette eksperimentet, som ble gjennomført i august 2017, gir innsikt i hvordan deformasjon oppstår når nøytroner fjernes fra stabile samarium kjerner. Et annet mål med dette prosjektet er å utvide den så kalte "Oslo-metoden" for å studere resonanser i gamma styrkefunksjoner til eksotiske kjerner. Dette har blitt mulig etter oppgraderingen til HIE-ISOLDE. Universitetet i Oslo ledet det første eksperimentet av denne typen i November 2016. Det er viktig å undersøke om resonansene sett i flere stabile kjerner, også er til stede i nøytron-rike kjerner. Hvis de finnes i nøytronrike kjerner vil det påvirke sannsynligheten for nøytroninnfangst, og dermed utfallet av store nettverk beregninger som undersøker hvordan grunnstoff tyngre enn jern er dannet i universet.

ISOLDE membership has provided access for Norwegian researchers to the world's premier radioactive beam facility, and unique opportunities for them to lead international research projects at the forefront of science. The ISOLDE program increases the international profile and visibility of nuclear physics at UiO. UiO is recognized as one of the leading institutions within the collaboration, and one of the key drivers of its science program. ISOLDE membership has provided unique opportunities for Master and PhD students to participate in large international research projects, has resulted in both PhD and Master theses at UiO, and provided training to students that boosted their career opportunities. It also made it possible for Master students from UiO to spend extended periods at CERN to conduct research supervised by CERN scientists. Norway has high demand for graduates with experience in nuclear science and multidisciplinary subjects, linking nuclear with material and medical science.

Nuclear structure studies have been limited to stable or near stable isotopes in the past. The availability of radioactive ion beams (RIB) enlarges the scope of such studies considerably as exotic nuclei far from stabilty become accessible for the first time. The ISOLDE facility at CERN has a long history of producing radioactive ions. The acceleration of these ions with the REX accelerator offers unique possibilities and makes ISOLDE the facility with the widest variety of RIB world wide. The world-leading role of ISOLDE is about to be strengthened with an energy and intensity upgrade (HIE-ISOLDE). The scientific subject of the proposed project is the shell structure of nuclei far from stability and, closely related to that, the development of nuclear shapes and shape coexistence. A recent Oslo-led experiment to study shapes in neutron-deficient rare earth isotopes, tok data on 140Sm in 2012. The follow-up experiment to measure shapes and collectivity in 140Sm with HIE-ISOLDE is expected to be scheduled in 2016. Another goal of this project is to extend the Oslo method to study level densities and radiative strength functions of exotic nuclei. This has become possible after the upgrade to HIE-ISOLDE. It is very important to investigate if the low energy enhancement seen in several stable nuclei, also is present in neutron rich nuclei. If present in neutron rich nuclei it will greatly influence the neutron capture cross sections and so the outcome of large network calculations of nucleosynthesis of elements heavier that Fe.