Research activities in the field of nuclear astrophysics

    The mission of the ATOMKI Nuclear Astrophysics Group (NAG) is to gain and distribute new scientific results concerning nuclear astrophysics. Our primary goal is to performe basic experimental research aiming at reactions relevant to various scenarios of nucleosynthesis. Besides we intend to reveal the structure of nuclei important in the genesis of elements. We carry out our research in close collaboration with institutes in Germany, Italy, Japan and USA. Our scientific projects are funded by the Hungarian Scientific Research Fund (OTKA), the European Commission and various bilateral agreements.

Study of the astrophysical p-process

    One of the most important research fields of the astrophysical group is the experimental study of the astrophysical p-process. This research activity is also supported by the European Research Council.

    The stable neutron-deficient isotopes of the elements with charge number Z>34 are classically referred to as p-nuclei and the main stellar process synthesizing them is called p-process. The process mostly develops in the O-Ne-rich layers of Type II supernovae as a result of the transformation of preexisting s- or r-nuclides by photodisintegrations of the (γ,n), (γ,α) and (γ,p) type. The modeling of the process requires a computation of an extended reaction network involving thousands of reactions. For this purpose, all the reaction rates in the heavy element region are calculated with the help of the Hauser-Feshbach type statistical model. Experimental data on sub-Coulomb cross sections for charged particle captured by heavy nuclei are very scarce. As a stringent test of the statistical model calculations, we measure (α,γ) and (p,γ) cross sections on various nuclei using mainly the activation technique. The experiments are usually carried out at the Van de Graaff and cyclotron accelerators of ATOMKI.

The following isotopes have been studied so far:

  • Proton-induced reactions: 70,76Ge, 74,76,82Se, 84,85,87Sr, 85Rb, 106,110Cd
  • Alpha-induced reactions: 70Ge, 106Cd, 113In, 144Sn, 151Eu

Alpha-nucleus potentials at astrophysically relevant energies

    Alpha-nucleus potentials are important ingredients for the calculation of (γ,α) photodisintegration rates in the astrophysical p-process. It has been shown that there are large uncertainties for the prediction of (γ,α) reaction rates because of the limited knowledge of a-nucleus potentials at the astrophysically relevant energies. For obtaining reliable a-nucleus optical potential parameters, we are conducting a systematic study of (α,α) elastic scattering on various heavy nuclei, and measure the scattered angular distributions with high accuracy at low energy bombardment. For the experiments, the precision scattering chamber installed at the ATOMKI Cyclotron is used.

The following isotopes have been studied so far: 144Sm, 82Mo, 112,124Sn, 89Y, 106,110,116Cd.

Underground experiments at the LUNA facilities

    The LUNA (Laboratory for Underground Nuclear Astrophysics) facility installed at the Laboratori Nazionali del GranSasso (LNGS) provides a unique possibility for measuring very low cross sections because of a very low background radiation condition owing to 1400 m of rock overburden. In this low background environment, the two LUNA accelerators are able to measure nuclear reactions at very low energies.

    Some researchers of the ATOMKI nuclear astrophysics group are members of the LUNA collaboration. In recent years the following reactions have been studied: d(p,γ)3He, 14N(p,γ)15O, 3He(4He,γ)7Be, 15N(p,γ)16O, 25Mg(p,γ)26Al, and some more are in progress. More detail about the collaboration can be found at the LUNA website.

Study of exotic nuclei

    Radioactive/Rare Ion Beams (RIB) became the major tool to study the structure of exotic nuclei often important in explosive scenarios. In addition, the Coulomb dissociation method proved to be useful in the determination of cross sections where short lived isotopes are involved. We have collaboration with the RIKEN RIPS group for high energy reaction studies, as well as with the CNS CRIB group for low energy reaction studies.

Half-life determination

    The precise knowledge of decay half-lives of radioactive isotopes plays an important role in various sub-fields of nuclear astrophysics. In cross section measurements carried out by the activation method the half-life of the reaction product influences directly the cross section determination. Where not sufficient literature data has been found, we have carried out direct half-life measurements. The half-lives of the following isotopes have been measured: 148Gd, 110Sn, 109In, 154Tbm, 133Cem.

    A recently proposed theory suggested that the half-lives of radioactive nuclei can depend on the temperature and host material. This prediction was tested measuring the decay of 7Be and 74As in various environments. The 74As has also been studied at extremely low temperature. No effect on the half-life was observed.

Application of 7Be isotope

    At the ATOMKI cyclotron radioactive 7Be is routinely produced for various purposes. The astrophysically important 7Be(p,γ)8B reaction has been studied in the framework of international collaborations. The decay of 7Be has been studied in various metallic environments. 7Be has also been used in wear measurements.