Nuclear Spectroscopy Division

Division info:

Scientific activity of the group is focused on studies of properties of nuclei far from the valley of beta stability. Phenomena studied include exploration of limits of nuclear stability, new exotic decay modes and their mechanisms, evolution of nuclear structures and shapes with the change of N/Z ratio. Of special interest are nuclei close to the doubly magic systems (⁴⁸Ni, ⁷⁸Ni, ¹⁰⁰Sn, ¹³²Sn), isotopes with equal number on neutrons and protons. Results of these studies are important for development of nuclear models as well as e.g. for the description of astrophysical processes of nucleosynthesis.

Nuclei far from stability are produced with extremely low cross sections and are usually overwhelmed by less exotic reaction products which are produced with much higher probabilities. Therefore, to study properties of most exotic species we employ most effective production mechanisms, various separation methods and specialized detection techniques. Neutron-deficient nuclei are being produced in a fusion-evaporation or fragmentation reactions. To produce neutron-rich nuclei we apply neutron- or proton- induced fission of heavy targets or fission of U-238 projectiles accelerated to relativistic energies. We use various separation techniques to select wanted reaction products e.g. in-flight separation of energetic reaction products or on-line mass separation with thermal source or ion-guide.

Most of our experimental work we perform at the world leading laboratories (GSI-Darmstadt, MSU-East Lansing, JYFL-Jyväskylä, ILL-Grenoble) which can offer sufficient production rates of exotic nuclei and proper instrumentation. At Warsaw cyclotron our group in collaboration with the Division of Nuclear Physics is conducting experiments at the on-line mass separator with the ion-guide. Recently, fast alpha decays of isotopes in the actinide region have been investigated. At the University of Jyväskylä members of our group were involved in development of a new very promising technique of separation of monoisotopic beams by combination of ion-guide technique and Penning trap. Application of this technique lead to a significant progress in studies of the decay of neutron-rich isotopes of refractory elements (Mo, Tc, Ru, Rh, Pd).

Spectroscopic studies of nuclei far from stability require highly efficient, selective detection systems. Recently our group in collaboration with the Division of Particles and Fundamental Interactions developed a novel detector for studies of rear nuclear decays with emission of low energy charged particles. This detector works as a time projection chamber with optical readout (OTPC) and allows for a 3-dimentional reconstruction of trajectories of emitted particles. The most spectacular result obtained with the use of this detector was the first measurement of energy and angular correlation between protons emitted in the two-proton decay of Fe-45. Moreover, a new decay mode of Fe-45 - three proton emission after beta decay – has been observed for the first time. Recently, with the use of the OTPC detector the two-proton radioactivity of doubly magic Ni-48 has been observed for the first time.

Members of our group have an expertise in a total gamma-ray absorption spectroscopy measurements. Contrary to other methods, this technique provides reliable data on the strength distribution in beta decays with large decay energies. Our group has performed extensive studies of beta strength distribution in the decays of neutron-deficient nuclei in the region of Sn-100. We are involved in a construction of a new modular total gamma-ray absorption spectrometer which will be used to study the “decay heat” of the fuel of nuclear reactors.

Another experimental method being developed by our group is the advanced technique of lifetime measurements of nuclear levels in the subnanosecond range. Here we employ detection system based on state of the art detectors with LaBr3 scintillators offering excellent timing properties and very good energy resolution. Our future work will be concentrated on implementation of digital electronics and signal processing algorithms.