As opposed to what one could believe, the subject of the nucleosynthesis is still far from being closed. One still does not know with certainty from which gold comes for example, even if there is not a doubt that an important component of this core present in the galaxy comes directly from the supernovas. The nuclear astrophysicists always study the physics of the cores rich in neutrons but unstable which would be stage-keys for the nucleosynthesis of the elements heavy beyond iron by addition of neutrons according to two baptized processes “S (slow fox trot) process” and “R (fast) process”. For the first time, the spectroscopy gamma of a magnesium 36 core could be made.
Figure-1 :The “chart of the cores”. In black known stable cores and blue those unstable. The other colors correspond to hypothetical cores with the range of the accelerators (Credit: Michigan State University Board of Trustees).
This isotope of magnesium 24 is particularly interesting because it would be in a mysterious zone of the “chart of the cores” which one calls “Island of inversion”. One knows experiment which the nucleons in the cores have a very complex behavior but which can be described within certain limits by various models. One of them is the shell model which rests on the idea that, just like the electrons in an atom, the nucleons gather on energy levels forming of the layers similar to the electron shells explaining the chemical properties of the atoms.
It then appears “magic numbers” for the number of nucleons of the cores corresponding to particularly stable and similar cores, in the field of nuclear chemistry, with the rare gas atoms for atomic chemistry. These numbers for the protons and/or the neutrons appear indeed when the nuclear layers are filled. There are however limits with this model. One of them corresponds to card fields previously mentioned where the cores rich in neutrons are not spherical any more. Unsuspected characteristics of the nuclear forces between nucleons are more definitely visible there but they are also a challenge for the theorists. As these cores are unstable and disintegrate in lighter cores by beta decay, they are likely to intervene in the complex chain of the nuclear reactions at the origin of the heavy elements.
E case of magnesium 36 with 24 neutrons and 12 protons is interesting because it is sufficiently exotic to deliver important information and at the same time with the range of the terrestrial accelerators. The researchers of the National Superconducting Cyclotron Laboratory' S Coupled Facility Cyclotron of Michigan State University, with their Japanese and English colleagues, thus exposed beryllium targets to calcium 48 beams. Several nuclear reactions then occurred with in particular the appearance of silicon 38 cores. Which cores struck another target of beryllium producing in their turn some rare Mg 36 cores.
On 400.000 cores of If approximately 38 only one gives the magnesium isotope sought at the time of this collision. The analysis of the gamma rays produced by the disintegrating Mg 36 cores, confirmed that it formed well part of the named area “Island of inversion” by the nuclear Engineering in physics. A stone moreover at the building of science was thus brought and one should a little better include/understand the origin of the elements which surround us.
