An international collaborative research group consisting of the Institute of Physical and Chemical Research (RIKEN), the University of Tokyo, the French New Energy Agency (CEA), etc. has shown direct evidence of the double magic of the nickel isotope 78Ni nucleus, which has been unsolved for many years. I made a discovery.
The number of protons and neutrons that make the nucleus relatively stable is called a magic number.The magic numbers are known to be 2, 8, 20, 28, 50, 82, and 126, and it can be explained by the "shell structure model" of the atomic nucleus that the energy between the "shells" where protons and neutrons enter appears in a large place. ..
However, in recent years, it has become clear that the nuclei of isotopes with the same number of protons but excessive neutrons are unstable, and the magic numbers disappear or appear. There is.In particular, 28Ni, which has a double magic number of 50 protons and 78 neutrons, is an unstable nucleus with an extremely neutron excess, which is the closest to the existence limit (neutron drip line) of the nucleus among the double magic number nuclei, and its magic. Numerous studies have been conducted to determine if sex is retained, but no direct evidence has been obtained.
In this research, in the RI beam factory that can generate unstable nuclear beams with the highest performance in the world, the high-performance liquid hydrogen targeting device MINOS led by CEA Sakurai Research Institute and the high-efficiency gamma-ray detection device DALI2 owned by RIKEN are combined. In this experiment, we succeeded in gamma-ray spectroscopy of 78Ni nuclei for the first time in the world.As a result, we succeeded in measuring the high-energy deexcited gamma rays emitted from the first excitation level, which is known as direct evidence of magic, and that the double magic is maintained even in 78Ni. I was able to conclude.
78Ni is also considered to be one of the starting points of heavy nucleosynthesis in the universe.This result is expected to be a key to solving the mystery of heavy nucleosynthesis as well as becoming a monument to magic number research.