Svenska fysikersamfundet

Kärnfysiksektionens hemsida

Kärnfysikermöte XXV

Abstracts

Light charged particle emission in the reaction 251Cf(nth, f).

Andreas Oberstedt

Örebro University

High resolution measurements of light charged particles (LCP) emitted in thermal neutron-induced fission of 252Cf* (E* = 6.2 MeV) have been performed with the recoil mass-separator LOHENGRIN at ILL in Grenoble. For this compound nuclear system emission yields of LCPs, their mean kinetic energies and widths have been obtained for 8 isotopes with nuclear charges Z>2. For 13 further isotopes the emission yields were estimated on the basis of systematics on their kinetic energy distributions. 34Al and 36Si emission has been observed for the first time in thermal neutron-induced fission.

Status of the investigation of fission-fragment characteristics in the reaction 238U(n, f) around the vibrational resonances at En = 1 MeV

Evert Birgersson

Örebro University

The parameterisation of fission-fragment distributions in terms of so-called fission modes in the nuclear energy landscape of the deforming nucleus between the ground state and the scission point led to a the first quantitative predictions of fission yields based on reaction cross-section data. Recent calculations predict visible changes in the shape of the fission-fragment mass and total kinetic energy distribution for the reaction 238U(n, f) in the vicinity of the vibrational resonances around En = 1 MeV. In order to test the predictive power of these model calculations measurements will be performed at the IRMM in Geel, Belgium, a Joint Research Centre of the EC using a 7 MV van de Graaff accelerator for production of quasi mono-energetic neutrons. The experimental challenges will be discussed as well as the analysing procedure presented based on feasibility tests performed earlier.

Origin of the nuclear symmetry energy in relativistic mean field theory

Shufang Ban

Physics Department, Stockholm

The physical origin of the nuclear symmetry energy (NSE) is studied within the relativistic mean field theory. Based on the nuclear binding energies calculated with and without mean isovector potential for several isobaric chains we confirm earlier Skyrme-Hartree-Fock results that the NSE depends on the mean level spacing and an effective isovector potential strength. The detailed analysis shows that the NSE reveals a quadratic dependence due to the mean isoscalar potential and, completely unexpectedly, the presence of a strong linear component in the isovector potential. The latter generates a nuclear symmetry energy in RMF theory that is proportional to T(T+1) isospin dependence, which is variance to the non-relativistic calculation, while in good agreement with empirical values.

Spectroscopy of extremely neutron deficient tellurium isotopes, at the end point of the rp-process path

Baharak Hadinia

Physics Department, Stockholm

It has recently been predicted that the 106Te and 107Te nucleus constitute the end point of the astrophysical rp-process due to a closed Sn-Sb-Te cycle preventing heavier elements from forming. Thus, low-lying excited states in 107Te and 106Te should provide valuable input for further studies of the rp-process path. Gamma-ray transitions in the extremely neutron-deficient nucleus 106Te and 107Te have been identified for the first time using the 54Fe(54Fe,2n)106Te* and 58Ni(52Cr,3n)107Te* reactions respectively. The experiments were performed at the K130 Cyclotron Accelerator Laboratory of the University of Jyväskylä, Finland. Prompt gamma rays produced at the target position were detected by the JUROGAM gamma-ray spectrometer and those belonging to 106Te and 107Te were selected based on the recoil identification provided by the RITU gas-filled recoil separator and the GREAT focal plane spectrometer using the recoil decay tagging technique.

Intensity Interferometry in Heavy-Ion Collisions

Johan Helgesson

Malmö University

An introduction to the use of intensity interferometry in heavy-ion collisions at intermediate energies will be given. Recent developments, such as imaging, renormalization and model independent determination of emission chronology of non-identical particles, will be discussed and selected experimental results will be shown.

Omega production in  p+d  ® ³He + w at threshold energies

Karin Schönning

Department of radiation sciences, Uppsala

The differential cross section at theta = 180 degrees of the p+d  ® ³He + w reaction was measured at SATURNE in the mid-nineties at 20 different beam energies, and it was found that it was very suppressed near the kinematical threshold. The reason for the suppression has been debated among theoreticians as well as experimentalists. To come to an end of the debate, more data on the total cross section is desirable. The CELSIUS/WASA collaboration has been taking data during 35 shifts at two different beam energies: Tp=1450 MeV and Tp=1360 MeV, corresponding to excess energies of 63 MeV and 19 MeV, respectively. The WASA detector system, until very recently an integrated part of the CELSIUS storage ring at the The Svedberg Laboratory in Uppsala, covered the major part of the final state particle phase space at both energies and for the two most important decay channels. In this talk, I will introduce You to the physics motivation of the measurements, followed by a brief overview of the WASA detector and explain how the measurements were performed. Finally I will summarise the latest results of the data analysis, started in August of 2005.

WASA at COSY - Symmetries and Symmetry Breaking

Magnus Wolke

Nuclear Physics Institute, FZ Juelich (IKP FZJ)

The physics programme for WASA at COSY focuses on the fate of fundamental symmetries and their violation. Precision studies of eta and etaprime decays, as well as production experiments in isospin filter reactions, provide well suited tools in this respect and will be key experiments of the new facility at COSY Juelich. Aspects of the physics programme are discussed and the road map towards first data taking beginning of 2007 is outlined.