Zahlavi

About Department of Nuclear Reactions

Fundamental Research in a Direction of Nuclear Astrophysics and Exotic Nuclei

The nuclear astrophysics program has started at the late 90' and collaboration was first established with Texas A&M University and INFN LNS Catania. The program is based on indirect techniques and the aim is to study nuclear reactions with astrophysical importance from a stellar burning in CNO cycle to nuclear reactions in AGB stars and Big Bang nucleosynthesis questions. The experiments are partially conducted on U120M cyclotron located in NPI CAS Řež. There are two indirect methods that are utilized - Asymptotic Coefficients method (ANC) and Trojan Horse Method (THM). These methods allow to deduce an astrophysical S-factor or to probe energetic dependence of astrophysical S-factor and determine the properties of low lying resonances in the Gamow region even to the threshold and subthrershold region. Lately, a  collaboration with SPIRAL2/Ganil have been upgraded in the frame of astrophysical problems to a new level of European Associated Laboratory and we participate on construction of the new radioactive beam's facility SPIRAL2 that is opening new possibilities in the research. The activities concerning exotic nuclei aim to study the behavior of nuclear matter in extreme isospin conditions. The phenomenae as nuclear halo, breaking magic numbers, sudden onset of deformation and shape coexistence are under study in a collaboration with physics groups in Ganil, IFIN-HH Magurele, JINR Dubna and other.

Basic and Applied Research with Fast Neutrons and Charged Particles

Two types of fast neutron generators are being operated by The Departement of the Nuclear Reactions of the NPI. The neutrons are produced in the reactions of accelerated protons (cyclotron U-120M, energy range 17-35 MeV) with Li and Be target materials. Quasi-monoenergetic neutron spectrum with the neutron peak flux of 109 n/cm2/s is created by the reaction of accelerated protons with the thin Li target, the protons directed to the thick Be target produce continuous neutron spectrum with the integral flux of 1011 n/cm2/s in the closest irradiation position. A new neutron generator based on the intense proton beam accelerated by the cyclotron TR-24 and directed to the thick Be target is in construction. The first neutron beams with the maximum neutron flux of 1012 n/cm2/s and continuous neutron spectrum up to 23 MeV are expected in 2019.

The main activity of the neutron group are the studies of the nuclear reactions of intermediate energy neutrons (17-34 MeV). The measurements of the neutron cross-sections are performed by the irradiation of the studied material in neutron spectra and subsequent measurement of the produced residuals by gamma spectrometry methods (fast transport of the samples to the detectors is provided by the pneumatic post system). The neutron spectra produced by our generators are studied using the methods of neutron activation analysis, Time-Of-Flight and Proton Recoil Telescope. The collimator for the neutron beams was constructed in the frame of the research infrastructure CANAM. It enables new type of experiments and detector systems for (n,charged particle) and (n,g) reactions are developed on the collimated neutron beams. The neutron beams are used as well in the research of delayed neutrons and for electronics hardness tests.

The studies of reactions initiated with charged particles are of great importance in the design of new neutron facilities based on accelerators (eg. Accelerator Driven Systems). The studied materials are irradiated with well-defined proton (up to 35 MeV) and deuteron (up to 20 MeV) beams. The induced activity is then measured by the gamma-spectrometry. The theoretical description of the measured reaction cross-sections are developed in the collaboration with the group from IFIN-HH (Magurele, Romania).

The department actively contributes to the development of the SPIRAL2/NFS (Neutrons for Science) laboratory at GANIL (Caen, France). The irradiation/measurement station for the cross-section measurements on the charged particle beams was entirely developed by the NPI in the frame of the SPIRAL2-CZ project, and the measurements on this facility are part of the First-Day experiments of the SPIRAL2/NFS.