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Exotic nuclei and two-proton radioactivity Marek Pfützner (University of Warsaw)

Discovery of radioactivity at the end of XIX century opened a window on a completely new world of physical phenomena and gave birth to many new branches of science.

An important role at the beginning of this scientific revolution was played by Maria Skłodowska Curie who, while investigating radioactivity, discovered two new chemical elements: polonium and radium. Maria and her husband Pierre Curie, were studying natural radioactivity, emanated by uranium and thorium which exist in nature. In thirties of XX century the daughter of Maria, Irene, and her husband Frederic Joliot, were the first to synthesize in laboratory new, artificial radioactivity. At this time also the first particle accelerators came into operation, suddenly giving a new momentum to discoveries of subatomic world and to creation of new radioactive species. Expanding of the nuclear world is continuing until today and still it will continue for a long time.

Presently, we know about 3300 nuclei, including 252 stable ones.

The latter form the so called stability line on the nuclear chart. Producing new nuclei, far from this stability line, with a strongly violated balance between the number of neutrons and the number of protons, and thus called exotic, is becoming very difficult. However, due to constant developments of acceleration and detection techniques, the progress in this field is going on. An important breakthrough, about 30 years ago, was the introduction of radioactive beam methods which allowed production, full in-flight identification, and detection of single, extremely exotic ions.

While expanding the nuclear chart, we discover also new radioactive processes.

In the doctoral thesis of Maria Curie (1903) we find description of three types of radioactivity: α, β, and γ. Irene and Frederic Joliot-Curie observed a new type of β decay (β+ ) in which a positron is emitted. Later, spontaneous fission was discovered (1940), emission of a proton (1982), emission of a heavy cluster, like an isotope of carbon (1984), and finally a simultaneous emission of two protons (2002).

The latter discovery, in which Polish physicists played an important role, was possible due to application of radioactive beam technique.

Nuclei and their decays represent a fascinating field of research by itself. The learning and understanding of the physical laws ruling in the nuclear domain has, however, much broader significance. Nuclear processes have important applications in many branches of engineering, in energy production, in medicine. Astrophysics, when explaining the structure and evolution of stars is using the nuclear knowledge. Properties of nuclei, including those most exotic, synthesized in minute quantities with large efforts in our laboratories, are key to understand cosmic processes in which chemical elements, forming the world around us, were produced.

Prof. dr hab. Marek Pfützner is engaged in experimental nuclear research, focused mainly on exotic nuclei, far from the beta stability.

He is employed in the Institute of Experimental Physics, at the Faculty of Physics, University of Warsaw.

He led projects in largest nuclear laboratories in the world, like GSI (Darmstadt, Germany), GANIL (Caen, France), CERN (Geneva, Switzerland), NSCL (East Lansing, USA), and RIKEN (Tokyo, Japan). He coauthored discovery of 230 new isotopes.

Among many of his research topics, one of the most important is the study of nuclear decays with emission of charged particles.

In 2002 he observed for the first time two-proton radioactivity.

In his team, a novel type of gaseous detector with optical readout was developed to study very rare nuclear decays. It helped to investigate in detail the mechanism of two-proton radioactivity and was instrumental in discovery of a new type of beta decay, followed by delayed emission of three protons.

Marek Pfützner is a coauthor of 230 research papers published in international journals. They were cited about 8000 times. He was awarded the Foundation for Polish Science Prize and the Zdzisław Szymański Prize.

October 17, 2020 at 11:00am

Auditorium of the Faculty of Physics, University of Warsaw

Credits:

Used photos by Marek Pfützner, Christopher Campbell (Unsplash)