Atomic nuclei that have same or nearly same amount of neutrons and protons have a key role in understanding underlying structure of nuclei and astrophysical processes like stellar evolution and creation of elements. The key quantity that is needed is their mass enabling, for example, modelling of astrophysical process that is responsible of creation of large fraction of different chemical elements. This project focuses on measuring masses of relevant nuclei of N∼Z up to tin-100, which has 50 neutrons and 50 protons. Existing data on this region is scarce. To access these nuclei and to perform the measurements, two world-leading facilities will be utilized: the Ion Guide Isotope Separator On-Line facility at accelerator laboratory of Ģֱ in Finland and Radioactive Isotope Beam Factory in Riken, Japan.
The project " Mass measurements of exotic N=Z nuclei (up to 100Sn) and the vicinity for nuclear physics and nuclear astrophysics studies (MASSPASS) " addresses many open questions in nuclear structure and nuclear astrophysics. The evolution of nuclear shell structure can be investigated by mass measurements of isotopic and isotonic chains. Masses also play an important role nuclear astrophysics. The region of the heavy N = Z nuclei and the vicinity near 100Sn on the chart of nuclides to be studied, has sparked interests for both nuclear astrophysics and nuclear structure for many years. Nuclear mass data along the heavy neutron-deficient N = Z line and its neighbors are crucial for the investigation of the rp- (rapid-proton capture) and the νp-(rapid-neutrino capture) processes. In addition, access to nuclei on (or more proton-rich than) the N = Z line is needed to solve key challenges related to many open questions in nuclear structure as well.
The masses of neutron-deficient exotic nuclei in the mass region near N=Z line will be measured with the Penning trap mass spectrometer JYFLTRAP of the Ion Guide Isotope Separator On-Line (IGISOL) facility of JYFL-ACCLAB in the Ģֱ/Finland and the Radioactive Isotope Beam Factory (RIBF) facility at RIKEN/Japan. IGISOL is by far the place to have achieved the highest resolution to do these measurements for the heavy N=Z area nuclei with the JYFL setup. The utilization of the TOF-ICR and the PI-ICR methods with a precision ~ 1 keV, while the nuclei with half-lives less than 100 ms down to few ms, the masses will be measured with the MR-TOF MS with a precision of few tens of keV. At RIBF, Bρ-TOF method simultaneously in conjunction with the Isochronous Mass Spectrometry (IMS) method with the Rare-RI Ring. The IMS method will be employed to address the masses of nuclei with half-lives ranging from 100 us to 1 ms with a precision of ~ 100 keV and the Bρ-TOF method will be used to measure the extremely short-lived nuclei with half-lives less than 1us. The masses of more than 20 nuclei will be measured at the IGISOL and RIBF Facilities.
The results will not only provide essential data for modeling rp-process and the νp-process in astrophysics, but also help reveal new insights into several open questions for nuclear structures such as: origin of the Wigner energy; super allowed GT decay of 100Sn; the location of the proton drip-line; deformation and the evolution of shell-closures (N=Z~40); test of mass models; isospin symmetry breaking; puzzle of two protons and one proton decay of 94Ag high level long isomer state; and the test of the CVC hypothesis.
