Researchers from Osaka University’s Research Center used measurements from a calcium foil irradiated with protons for Nuclear Physics, in partnership with the Australian National University, Japan Atomic Energy Agency, the University of Tokyo, and GIT AM University, to indicate the transition power between different nuclear setups in calcium-40.
Transition strengths between spin-0 states for nuclei with atomic masses below 50. The green point shows the strength of the transition between the superdeformed state and the ground state of 40Ca, which has the smallest value. The red points are experimental values, and the dashed line is a curve inversely proportional to the 2/3 power of the mass number A, showing the trend between the spin-0 states concerning the mass. Image Credit: E. Ideguchi.
The transition from the extended “superdeformed” state to a regular, spherical state was found to be much less likely than anticipated due to quantum interference. This research could contribute to a greater understanding of how elements form in supernovae.
Some isotopes are referred to as “magic” in nuclear physics as they consist of precisely the correct number of protons or neutrons to make a complete shell. The initial magic numbers are 2, 8, 20, 28, and 50. Calcium-40, the amplest form of calcium, is known as “doubly magic” since its nucleus contains 20 protons and 20 neutrons.
This isotope has a high degree of stability. With magical nuclei, different shapes of the nucleus seem to have very similar energies, allowing for coexistence. This symbolizes the simultaneous quantum superposition of multiple protons and neutron conformations.
The method by which a nucleus in the “superdeformed” conformation shaped like an extended rugby ball decays into the lowest-energy spherical shape remains an important mystery.
To define the method, the scientists used measurement results of electron and positron emission from decay transitions between multiple states of calcium-40 nuclei.
We observed evidence that the decay from the superdeformed excited state to the spherical ground state is unexpectedly suppressed in a calcium-40 nucleus.
Eiji Ideguchi, Study First Author, Osaka University
The researchers discovered that the transition strength between these states is so low due to destructive quantum interference between coexisting shape setups of related energies.
Protons were shot at a calcium target to gather experimental results, and the electrons and positrons generated from excited states were evaluated.
This work deepens our understanding of coexisting deformation states that are unique to nuclei.
Tibor Kibédi, Senior Author, Osaka University
This study may aid researchers in better understanding the processes that emerge from the various elements in the Universe, as well as the impressive stability of magical nuclei.
Journal Reference:
Ideguchi, E., et al. (2022) Electric Monopole Transition from the Superdeformed Band in 40Ca. Physical Review Letters. doi.org/10.1103/PhysRevLett.128.252501.