EXOTIC NUCLEAR SYSTEMS: International Symposium on Exotic Nuclear Systems ENS'05
802(2005); http://dx.doi.org/10.1063/1.2140616View Description Hide Description
In 2004 NuPECC published its 3rd long‐range plan (LRP2004) “Perspectives for Nuclear Physics Research in Europe in the Coming Decade and Beyond”. Six working groups addressed the various active subfields in Nuclear Physics: i) Quantum Chromo‐Dynamics, ii) Phases of Nuclear Matter, iii) Nuclear Structure, iv) Nuclei in the Universe, v) Fundamental Interactions and vi) Applications of Nuclear Science. They provided the recommendations for possible future directions with priorities of the facilities and instrumentation. Based on their reports and recommendations NuPECC made its recommendations and priorities for Nuclear Physics in Europe for the midterm and long‐term future. LRP004 presents this strategic plan. In this contribution a brief presentation of the recommendations for possible future directions made by the working groups as well as the general and specific recommendations and priorities of the facilities and instrumentation will be presented. These could be found in more detail in LRP2004 and the articles by Harakeh and Äystö. The priorities that were made for construction of the facilities and equipment lead to NuPECC’s Roadmap for the next 10 to 20 years.
Design Considerations for Converting Laser‐Accelerated Electron Beams into Brilliant X‐Ray, γ‐Ray and Neutron‐Beams802(2005); http://dx.doi.org/10.1063/1.2140617View Description Hide Description
High‐power short‐pulse lasers focussed into a gasjet can produce intense brilliant high‐energy electron beams. The transport and acceleration of the intense electron beams requires the development of many new concepts in accelerator physics. Focusing these electron beams through an undulator one can realize an X‐Free‐Electron‐Laser (FEL) or a γ‐FEL, producing brilliant high‐energy photon beams. With these intense monochromatic γ beams high‐brilliance, low‐energy polarized micro‐neutron beams can be generated via resonant (γ,n) reactions. The monochromatic γ beams also open up new fields in nuclear physics. The compact, comparatively cheap laser systems and FEL’s allow us to produce brilliant particle beams, which offer interesting facilities “at home” with many applications.
802(2005); http://dx.doi.org/10.1063/1.2140618View Description Hide Description
I will first present the vacuum for the e+‐e− field of QED and show how it is modified for baryons in nuclear environment. Then I discuss the possibility of producing new types of nuclear systems by implanting an antibaryon into ordinary nuclei. The structure of nuclei containing one antiproton or antilambda is investigated within the framework of a relativistic mean‐field model. Self‐consistent calculations predict an enhanced binding and considerable compression (4…5ρ0) in such systems as compared with normal nuclei. I present arguments that the life time of such nuclei with respect to the antibaryon annihilation might be long enough for their observation. This yields a mechanism for cold compression.
802(2005); http://dx.doi.org/10.1063/1.2140619View Description Hide Description
Nuclear spectroscopy using radioactive isotope beams requires dedicated set‐ups. State‐of‐the‐art Ge arrays recently started to provide valuable γ spectroscopic data. However, to fully exploit the exotic beams lasting detection deficiencies have to be solved. They result from limited beam intensity, particularly for the most exotic nuclei, a wide range of beam velocities (from stopped to v/c∼0.5), high γ ray and particle background and γ ray multiplicities up to M⩽30, which are typical characteristics of the reactions. A 4π γ‐ray array with highest efficiency, selectivity and energy resolution is required which is capable of high event rates. These features can only be achieved with a close packed arrangement of detectors. The individual interaction points of the γ quanta have to be disentangled by tracking algorithms. The Advanced GAmma Tracking Array, AGATA, will provide 25% to 40% full energy efficiency depending on the γ multiplicity. The position resolution is sufficient for an energy resolution of 0.4% at a beam velocity of v/c=0.5. For decay experiments a compact array of Ge planar stack detectors with 2D strip segmentation might be the ideal solution. The planned NUSTAR‐DESPEC Ge array will consist of up to 24 detector units with three planar crystals each, resulting in 13824 voxels. Providing 15% efficiency it may increase the correlation time range for decay γ rays to 10 ns – 1 s! Yet another development line, investigated by the NUSTAR collaboration, is high resolution scintillators. Novel crystal materials, e.g. LaBr3(Ce), promise intrinsic energy resolution of about 2%. This is sufficient for calorimetric applications but also for spectroscopy after Coulomb excitation and fragmentation reactions at relativistic beam energies.
802(2005); http://dx.doi.org/10.1063/1.2140620View Description Hide Description
The layout and status of MAFF at the Munich high flux reactor FRM‐II is described. At MAFF 1014 fissions/s will be induced by thermal neutrons in a target with approx. 1 g of 235U. The situation is compared to the SPIRAL2 facility where 1014 fissions/s are expected by fast neutron fission in a target containing 5100 g of 238U. A comparison of the yields of SPIRAL2 and MAFF is performed to show the complementarity of the two ISOL‐facilities for fission fragments. MAFF has approximately five times the beam intensities of SPIRAL2 for short‐lived fission isotopes with lifetimes shorter than 5 s and thus will focus on the most neutron‐rich nuclei, while SPIRAL2 has better perspectives for the more intense, less neutron‐rich post‐accelerated beams.
A problem that also deserves attention is the production of α emitters, in particular plutonium. Here MAFF has the advantage to contain the Pu‐producing 238U only as impurity not as the main fissile system. If SPIRAL2 would use 235U instead of 238U this problematic issue could be avoided at the cost of a further reduction in intensity of very neutron‐rich fission fragments by a factor of 10. Finally new physics close to the classically doubly‐magic nuclei 78 Ni and 132Sn is described.
802(2005); http://dx.doi.org/10.1063/1.2140621View Description Hide Description
802(2005); http://dx.doi.org/10.1063/1.2140623View Description Hide Description
The deformation‐dependence of clusterization in heavy nuclei is investigated. In particular, allowed and forbidden cluster‐configurations are determined for the ground, superdeformed, and hyperdeformed states of some nuclei, based on a microscopic (effective SU (3)) selection rule. The stability of the different cluster configurations from the viewpoint of the binding energy and the dinuclear system model (DNS) is also investigated.
802(2005); http://dx.doi.org/10.1063/1.2140624View Description Hide Description
Three‐alpha resonant states in 12C are investigated by using the method of Analytic Continuation in the Coupling Constant combined with the Complex Scaling Method (ACCC+CSM). We obtain the resonant state at the energy Er = 1.66 MeV and the width Γ = 1.48 MeV, which seems to have a similar structure to that of the state.
802(2005); http://dx.doi.org/10.1063/1.2140625View Description Hide Description
Near‐barrier fusion excitation functions for the 12,14C, 16,18O + 208 Pb reactions have been analyzed in the framework of the barrier‐passing model using different forms of the nuclear potential and the phenomenology of a fluctuating barrier. The best‐fit fusion potentials were used to estimate cluster decay probabilities from the corresponding ground states of Ra and Th, i.e., for the inverse decay process. The analysis supports the “alpha‐decay‐like” scenario for carbon and oxygen emission from these nuclei.
802(2005); http://dx.doi.org/10.1063/1.2140626View Description Hide Description
We perform a test of the U(4112) cluster supersymmetry scheme by analysing selection rules in five one‐nucleon transfer reactions involving A=18, 19 and 20 nuclei. The results present further indication for the validity of the supersymmetry scheme in this region.
802(2005); http://dx.doi.org/10.1063/1.2140627View Description Hide Description
A parameterization of spectroscopic factors is presented that matches perfectly the ones obtained via the microscopic SU (3) model of the nucleus. The model used is the Semimicroscopic Algebraic Cluster Model (SACM) which inlcudes the Pauli‐exclusion principle. The parameterization of the spectroscopic factors is given and applied to the fusion cross section of 12C+12 C.
802(2005); http://dx.doi.org/10.1063/1.2140628View Description Hide Description
Heavy neutron‐rich nuclei close to the neutron closed shell N = 126 were produced by fragmentation of a 1 A GeV 208 Pb beam in a beryllium target at the Fragment Separator at GSI. Around 30 heavy neutron‐rich isotopes have been synthesized for the first time and the half‐lives of some of them have been determined.
802(2005); http://dx.doi.org/10.1063/1.2140630View Description Hide Description
Secondary beams of unstable nuclei with kinetic energies of several hundred MeV/u are produced at GSI in fragmentation and fission reactions followed by in‐flight isotope separation. The LAND detector setup is designed for studies of projectile breakup in peripheral collisions induced, e.g., by nucleon knockout or Coulomb dissociation. At present, the experiments focus on deriving spectroscopic information for neutron‐rich isotopes ranging from light nuclei at the drip line to medium‐heavy nuclei; selected aspects and results are discussed.
The exotic nuclear beam facility planned as an integral part of the FAIR (Facility for Antiproton and Ion research) project at GSI promises much improved conditions and allows for novel techniques in experimental investigations of nuclei far away from stability. The perspectives are briefly addressed.
802(2005); http://dx.doi.org/10.1063/1.2140631View Description Hide Description
Fast beams of radioactive isotope (RI) have been used for nuclear spectroscopy at RIKEN since 1990. Various direct‐reaction experiments have been performed at intermediate‐energies in the reversed kinematics to study structures of nuclei very far from the stability valley. Several examples of recent results on neutron‐rich nuclei around N=20 and carbon isotopes are presented. The RIKEN RI Beam Factory, which will have the first beam in the end of 2006, will greatly extend the region of study to more exotic and heavier nuclei.
802(2005); http://dx.doi.org/10.1063/1.2140632View Description Hide Description
Shell structure evolution in nuclei situated at the extremes of neutron and proton excess are investigated using in‐beam gamma spectroscopy techniques with radioactive beams at GANIL. A selection of results obtained very recently is presented: i) The reduced transition probabilities of the neutron‐rich 74 Zn and 70 Ni nuclei have been measured using Coulomb excitation at intermediate energy. An unexpected large proton core polarization has been found in 70 Ni and interpreted as being due to the monopole interaction between the neutron g9/2 and protons f7/2 and f5/2 spin‐orbit partner orbitals. ii) Two proton knock‐out reactions has been performed in order to study the most neutron‐rich nuclei at the N=28 shell closure. Gamma rays spectra and momentum distribution have been obtained for 42Si and neighboring nuclei. Evidence has been found for a persistence of the deformation at N=28 down to Silicon despite a relatively large Z=14 gap. iii) The in‐beam gamma spectroscopy of 36Ca performed using neutron knock‐out reactions revealed that 36Ca is as doubly magic as 36S. The Coulomb energy difference of the first 2+ state in this T=2, A=36 mirror nuclei reveals one of largest isospin symmetry breaking in nuclei.
802(2005); http://dx.doi.org/10.1063/1.2140633View Description Hide Description
In this paper among the wide‐ranging applications of nuclear methods the following topics were selected: a) Nuclear safeguards, illicit trafficking and demining; b) Bulk hydrogen analysis; c) Radiopharmaceuticals and related charged particle reactions; d) Accelerator transmutation of radioactive waste; e) Validation of nuclear data libraries by differential and integral measurements.
802(2005); http://dx.doi.org/10.1063/1.2140634View Description Hide Description
Hypernuclei were discovered in 1952 by M. Danysz and J. Pniewski in photographic emulsions that went with high altitude balloon flights. The weak decay of a Λ nucleon accounted for the abundant energy release in a secondary star, which is the signature of what was called a hyperfragment. Many surprises were offered by hypernuclei through a large variety of experiments over a long period of time.
Among the surprises is the small spin‐orbit interaction of the Λ particle observed in p shell nuclei with the strangeness exchange reaction (K −, π−) and later accurately determined by the observation of γ ray transitions in . Major s, p, d, and f shell states were observed in with associated strangeness production in the reaction (π+, K +). Another surprise was the large ratio Γ n /Γ p which describes the preference for the non‐mesonic decay Λn → nn over Λp → np of hypernuclei.