Scientific Colloquium Webinars 2020

We propose three Scientific Colloquium Webinars by the end of 2020. They will be held every weeks on Monday at 16h.

Monday 30/11 (16h):
150 years of the periodic table – from a nuclear physics perspective,
Araceli LOPEZ-MARTENS, IJCLab Orsay

At the dawn of the 20th century, most scientists believed that matter was made up of atoms and that what distinguished the atoms of different elements was their mass. It was this mass that was used to classify the elements. The chemists of the time quickly became aware of periodicities in the chemical behaviour of certain elements that they tried to translate into tables, the most famous of which was that of the Russian chemist Dmitri Mendeleev. In Mendeleev’s table, the elements were arranged by increasing atomic mass, some cells were left empty and the position of the elements was given by the letter Z, from the German word zahl (number). In this colloquium, I will show how discoveries in nuclear physics have transformed our understanding of the atom, how they have given its true meaning to the periodic table and how they have completed the 7 periods of the periodic table up to the last known element: oganesson.

The pdf of the talk is here.

Monday 07/12 (16h):
Sixty years of multineutron quest: game over or game on?
Miguel MARQUÉS, LPC Caen

Already in the early 1960s, when physicists started to move away from the valley of stability, some crazy ones tried to create « neutral nuclei » in their laboratories. They didn’t succeed, but the task was a very difficult (while fascinating) one, both from the construction and the detection points of view. Fascination overcame difficulty and other physicists kept trying to find these objects, that would defy nuclear theory as we know it, all through the XX century. Finally, in this XXI century two signals of a possible tetraneutron state close to threshold were obtained, first at GANIL and then at RIKEN, that were weak but have not been contested yet. They have triggered a lot of new theoretical calculations, as well as new generation experiments that try to reveal something that has eluded firm evidence for sixty years already. I will review some of the most exotic experiments, highlight their merits and drawbacks, and show why the present ones think they will succeed where so many others have failed. The game might be over soon, whatever the outcome!

The pdf of the talk is here.

Monday 14/12 (16h):
Nucleosynthesis: new perspectives from gamma-ray astronomy
Vincent TATISCHEFF, IJCLab Orsay

Measurements of gamma-ray photons from cosmic sources of nuclear radiation have advanced our knowledge of the origin of the chemical elements. Many isotopes are synthesized in exploding stars – novae, supernovae, kilonovae –, some of which are radioactive and emit specific gamma-ray lines that can be detected by space telescopes. Radioisotopes with a relatively short lifetime can be used to directly characterize the individual explosion events or the first stages of the stellar remnant, while long-lived radioactivites, with lifetimes much longer than the characteristic time between events that synthesize them, can produce a diffuse gamma-ray emission in the sky. Observations in the MeV gamma-ray band offer a privileged diagnostic tool with respect to other measurements based on atomic spectroscopy, thanks to the penetration power of high-energy photons and the association of gamma-lines to specific isotopes. In this colloquium, I will review the progress made in recent years in our understanding of nucleosynthesis thanks to some remarkable gamma-ray observations, and then discuss the prospects that a new, more sensitive gamma-ray space observatory could offer us.

The pdf of the talk is here.

Contacts: O. Dorvaux, J. Dudouet, A. Korichi, O. Lopez, J. Margueron, O. Sorlin, J.-C. Thomas, M. Vandebrouck, G. Verde.