The low-energy limit of validity of the intranuclear cascade model

The intranuclear cascade model is generally considered to be valid when the incident particle has a sufficiently small de Broglie wavelength to interact with individual nucleons. On this basis, a lower limit of 200 MeV is usually quoted for the incident energy in nucleon-induced reactions. Here this statement is questioned. A pragmatic approach is used, which compares the predictions of the Liège intranuclear cascade model with available data at incident energy between 40 and 250 MeV. It is found that this model gives surprisingly good results at energies well below the limit mentioned above. Results are also compared with the predictions of other models commonly used in this energy range. Received: 2 September 2002 / Accepted: 22 October 2002 / Published online: 6 March 2003 RID="a" ID="a"e-mail: cugnon@plasma.theo.phys.ulg.ac.be RID="b" ID="b"e-mail: P.Henrotte@ulg.ac.be Communicated by G. Orlandini     

Momentum distribution of relativistic nuclei with Hartree-Fock mesonic correlations

The impact of Hartree-Fock correlations on the nuclear momentum distribution is studied in a fully relativistic one-boson-exchange model. Hartree-Fock equations are exactly solved to first order in the coupling constants. The renormalization of the Dirac spinors in the medium is shown to affect the momentum distribution, as opposed to what happens in the non-relativistic case. The unitarity of the model is shown to be preserved by the present renormalization procedure. Received: 7 June 2002 / Accepted: 24 September 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: juan@nucle.us.es Communicated by G. Orlandini     

A consistent approximation scheme beyond RPA for bosons

In this paper, we develop a consistent extension of RPA for bosonic systems. In order to illustrate the method, we consider the case of the anharmonic oscillator. We compare our results with those obtained in mean-field and standard RPA approaches with the exact ones and show that they are very close to these ones. Received: 17 June 2002 / Accepted: 14 September 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: davesne@ipnl.in2p3.fr Communicated by A. Molinari     

Transfer reactions and sub-barrier fusion in 40Ca + 90, 96Zr

The two systems ⁴⁰Ca + ^90,96Zr have been studied by measuring nucleon transfer reactions at two energies near the Coulomb barrier, thus complementing the available sub-barrier fusion cross-sections. Angular distributions for various transfer channels have been determined. Significantly larger neutron transfer cross-sections are found for the target ⁹⁶Zr that exhibits the larger enhancement in the sub-barrier fusion cross-sections. All data have been analyzed with a new model for heavy-ion collisions that calculates simultaneously transfer cross-sections, fusion excitation functions and barrier distributions. The model gives a good account of both transfer and fusion data. Received: 2 May 2002 / Accepted: 4 June 2002 / Published online: 26 November 2002 RID="a" ID="a"e-mail: montagnoli@pd.infn.it, Fax +39049 8277102, Tel. +39049 8277117. RID="b" ID="b"On leave from the China Institute for Atomic Energy, 102413 Beijing, China. Communicated by C. Signorini     

Statistical properties of eigenvalues for an operating quantum computer with static imperfections

We investigate the transition to quantum chaos, induced by static imperfections, for an operating quantum computer that simulates efficiently a dynamical quantum system, the sawtooth map. For the different dynamical regimes of the map, we discuss the quantum chaos border induced by static imperfections by analyzing the statistical properties of the quantum computer eigenvalues. For small imperfection strengths the level spacing statistics is close to the case of quasi-integrable systems while above the border it is described by the random matrix theory. We have found that the border drops exponentially with the number of qubits, both in the ergodic and quasi-integrable dynamical regimes of the map characterized by a complex phase space structure. On the contrary, the regime with integrable map dynamics remains more stable against static imperfections since in this case the border drops only algebraically with the number of qubits. Received 19 June 2002 / Received in final form 30 September 2002 Published online 17 Decembre 2002 RID="a" ID="a"e-mail: dima@irsamc.ups-tlse.fr RID="b" ID="b"UMR 5626 du CNRS     

Shrinking  as a recipe for revealing classical-like properties of optical-potential cross-sections

A simple recipe for revealing classical-like properties of optical-potential cross-sections is proposed. The recipe is based on the fact that the classical properties are not expected to depend on the actual value of . This allows us to identify the classical-like characteristics of an optical-potential cross-section by simply repeating the calculation with different values of , and observing which properties of the cross-section are invariant. The method is applied to the cross-sections of a few optical potentials used to describe the recent data of light heavy-ion elastic scattering. An improved near-side/far-side decomposition is used to separate the near-side and far-side components of the optical-potential cross-sections. Received: 4 September 2001 / Accepted: 3 June 2002 / Published online: 26 November 2002 RID="a" ID="a"e-mail: anni@le.infn.it Communicated by V. Vento     

Chiral magnetism of the nucleona

We study the quark mass expansion of the magnetic moments of the nucleon in a chiral effective field theory including nucleons, pions and delta-resonances as explicit degrees of freedom. We point out that the usual power counting applied so far to this problem misses important quark mass structures generated via an intermediate isovector M1 nucleon-delta transition. We propose a modified power counting and compare the resulting chiral extrapolation function to available (quenched) lattice data. The extrapolation is found to work surprisingly well, given that the lattice data result from rather large quark masses. Our calculation raises the hope that extrapolations of lattice data utilizing chiral effective field theory might be applicable over a wider range in quark masses than previously thought, and we discuss some open questions in this context. Furthermore, we observe that within the current lattice data uncertainties the extrapolations presented here are consistent with the Padé fit ansatz introduced by the Adelaide group a few years ago. Received: 23 April 2002 / Accepted: 18 July 2002 / Published online: 17 December 2002 RID="c" ID="c"e-mail: themmert@physik.tu-muenchen.de RID="d" ID="d"e-mail: weise@ect.it Communicated by A. Sch?fer     

2H( 3He, t)2p reaction at 2 GeV

The exclusive ²H( ³He, t)2p reaction has been studied at 2 GeV for energy transfers up to 500 MeV and triton angles up to 3.4^°. The protons were measured in the large acceptance magnetic detector DIOGENE, in coincidence with the forward tritons detected in a dedicated magnetic arm. The energy transfer spectra extend well above the pion threshold. However, in the region of Δ excitation, the yield is less than 10% of the inclusive ²H( ³He, t) cross-section, which indicates the small contribution of the ΔN ↦ NN process. The angular distributions of the two protons in their center of mass have been analysed as a function of energy transfer and triton angle and a Legendre polynomial decomposition has been achieved. These data have been compared to a model based on a coupled-channel approach for describing the NN and NΔ systems. Received: 21 October 2002 / Accepted: 15 November 2002 / Published online: 11 March 2003 RID="a" ID="a"e-mail: ramstein@ipno.in2p3.fr RID="†" ID="†"Deceased. RID="†" ID="†"Deceased. RID="d" ID="d"Present adress: School of Engineering, J?nk?ping University, P.O. Box 1026, S-551 11 J?nk?ping, Sweden. Communicated by M. Gar?on     

Optimized Monte Carlo analysis for generalized ensembles

We present a new, maximum-likelihood based method to combine data from a multiple number of Monte Carlo simulations performed within any type of ensemble. The method offers an efficient iterative scheme to obtain the density of states of a wide range of energies as well as of other macroscopic variables. It should in particular be useful for the study of systems with a rough energy landscape. Received 4 June 2002 Published online 14 October 2002 RID="a" ID="a"e-mail: borg@alf.nbi.dk     

New solutions of the shape equation

The general shape equation describing the forms of vesicles is a highly nonlinear partial differential equation for which only a few explicit solutions are known. These solvable cases are briefly reviewed and a new analytical solution which represents the class of the constant mean curvature surfaces is described. Pearling states of the tubular fluid membranes can be explained as a continuous deformation preserving membrane mean curvature. Received 2 February 2002 / Received in final form 4 February 2002 Published online 2 October 2002 RID="a" ID="a"e-mail: mladenov@obzor.bio21.bas.bg     

Enhanced neutron pair transfer and collective excitations in the system 206Pb + 118Sn at barrier energies

At energies below the Coulomb barrier, neutron transfer and Coulomb excitation have been measured in a very heavy asymmetric nuclear system, in ²⁰⁶Pb + ¹¹⁸Sn. These are semi-magic nuclei showing super-fluid properties. Particle-γ coincidence techniques using 5 Euroball Cluster detectors (EB), combined in a set-up with the Heidelberg-Darmstadt NaI Crystal Ball (CB), have been used. Position-sensitive detectors allowed the observation of scattering processes covering angles from 110 up to 150 degrees. The fragments are identified via the known γ-decays of the lowest excited states using the high resolution of EB. Using the unique feature of the set-up with the CB, transfer to well-defined final channels with known quantum numbers is selected using the high-efficiency multiplicity filter of the CB with no second γ-ray, i.e. without feeding. The data are analysed using the semi-classical approach and transfer probabilities are obtained. Coulomb excitation has been analysed using known transition probabilities. The enhancement is deduced for the two-neutron transfer populating the low-lying super-fluid 2⁺ states in ¹²⁰Sn and ¹¹⁶Sn, while the 2n transition remains in the ground state for the ^20NPb nuclei. Large enhancements up to EF ≃ 10³ are observed. This is the first observation of neutron pair transfer enhancement for a heavy nuclear binary system with super-fluid properties with experimentally separated levels. The calculations with microscopic 2-neutron wave functions, with configuration mixing over six shell model configurations and using the coupled reaction channels approach, reproduce well the observed probabilities and the enhancement. Received: 27 August 2002 / Accepted: 9 December 2002 / Published online: 25 March 2003 RID="a" ID="a"e-mail: oertzen@hmi.de Communicated by D. Schwalm     

Structure and reactions of halo nuclei: An entangled approach

Halo nuclei are characterised by their weak binding, large spatial extent and hence a quite pronounced, yet highly correlated, few-body structure. This is typically in terms of a well-defined core plus one or more valence nucleons. Over the past decade the properties of halo nuclei have been studied theoretically using a range of reaction models, many of which having served us well for half a century or more in the study of less exotic, “mean-field”, nuclei. However, it is now clear that for many reactions with halo nuclei, it is not appropriate to disentangle (factorise out) the structure information from the reaction information. That is, the few-body nature of these systems requires few-body reaction models in which the nuclear structure and reaction mechanisms are necessarily entangled. This talk will briefly review the physical assumptions made by various reaction models, and point to areas where progress is being made to extend their range of applicability in order to provide further insights into halo structure. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: j.al-khalili@surrey.ac.uk     

Genetic Algorithms as a tool in the study of aperiodic order,with application to the case of X-Ray diffraction spectra of GaAs-AlAs multilayer heterostructures

We present the first application of Genetic Algorithms to the analysis of data from an aperiodically ordered system, high resolution X-Ray diffraction spectra from multilayer heterostructures arranged according to a deterministic or random scheme. This method paves the way to the solution of the “inverse problem”, that is the retrieval of the generating disorder from the investigation of the spectra of an unknown sample having non crystallographic, non quasi-crystallographic order. Received 18 March 2002 / Received in final form 3 July 2002 Published online 31 October 2002 RID="a" ID="a"e-mail: Evelyne.Lutton@inria.fr RID="b" ID="b"CNRS UMR 8502     

Candidates for chiral doublet bands in 136Nd

The even-even nucleus ¹³⁶Nd was studied via in-beam γ-ray spectroscopy using the ¹⁶O + ¹²⁵Te reaction at 100 MeV and the EUROBALL array. One new dipole band was observed. Together with a previously identified dipole band, whose position in the level scheme is revised, the new band forms a doublet structure similar to the recently observed chiral bands in the odd-odd neighboring nuclei. This would be the first case of a chiral doublet in an even-even nucleus. Received: 23 May 2002 / Accepted: 30 September 2002 / Published online: 27 November 2002 RID="a" ID="a"e-mail: costel.petrache@unicam.it RID="b" ID="b"Present address: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. RID="c" ID="c"Present address: Gesellschaft für Schwerionenforschung D-64291 Darmstadt, Germany. Communicated by C. Signorini     

High-spin study of odd- A 49In isotopes beyond the neutron mid-shell

The ^{115, 117, 119, 121}In nuclei have been produced as fission fragments in three reactions induced by heavy ions: ¹²C + ²³⁸U at 90MeV bombarding energy, ¹⁸O + ²⁰⁸Pb reaction at 85MeV, and ³¹P + ¹⁷⁶Yb at 152MeV. Their level schemes have been built from gamma-rays detected using the EUROBALL III and IV arrays. High-spin states of ^{117, 119, 121}In nuclei have been identified for the first time. Moreover, isomeric states lying around 2.5MeV have been established in ^{119, 121}In from the delayed coincidences between the fission fragment detector SAPhIR and the gamma array. Most of the observed states can be described by coupling a proton g _9/2 hole to a Sn core, while the intruder band based on an orbital from the π[g _7/2/d _5/2] sub-shells behaves as the ground-state band of neighbouring Cd isotopes. Received: 24 May 2002 / Accepted: 11 June 2002 / Published online: 19 November 2002 RID="a" ID="a"e-mail: porquet@csnsm.in2p3.fr RID="b" ID="b"Present address: CEA-DIF, DAM/DCRE/SDE/LDN, 91680 Bruyères-le-Chatel, France. RID="c" ID="c"Present address: CSNSM IN2P3-CNRS and Université Paris-Sud 91405 Orsay, France. RID="d" ID="d"Present address: CEA/Saclay, DSM/DAPNIA/SPhN, 91191 Gif-sur-Yvette Cedex, France. Communicated by D. Schwalm     

In-beam spectroscopy of 253, 254No

In-beam conversion electron spectroscopy experiments have been performed on the transfermium nuclei ^{253, 254}No using the conversion electron spectrometer SACRED in nearly collinear geometry in conjunction with the gas-filled separator RITU at the University of Jyv?skyl?. The experimental setup is discussed and the spectra are compared to Monte Carlo simulations. The implications for the ground-state configuration of ²⁵³No are discussed. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: rdh@ns.ph.liv.ac.uk RID="b" ID="b"Present address: GANIL, F-14021 Caen, France. RID="c" ID="c"Permanent address: IReS Strasbourg, IN2P3-CNRS, F-67037-Strasbourg, France. RID="d" ID="d"Present address: CEA/DIF DCRE/SDE/LDN F-91680 Bruyeres-le-Chatel. RID="e" ID="e"Present address: Daresbury Laboratory, Daresbury WA4 4AD, UK. RID="f" ID="f"Permanent address: IPN Lyon, IN2P3-CNRS, F-69037 Lyon, France.     

High-spin states in the <Superscript>97</Superscript>Tc nucleus

High-spin states in the ⁹⁷Tc nucleus have been studied by in-beam γ-ray spectroscopy with the reaction ⁸²Se(¹⁹F,4nγ) at 68 MeV incident energy. Excited states have been observed up to about 8 MeV excitation and spin 43/2. The observed level scheme is compared with results of shell model calculations. Received: 22 November 2002 / Accepted: 23 December 2002 / Published online: 18 March 2003 RID="a" ID="a"e-mail: bucurescu@tandem.nipne.ro RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="c" ID="c"Present address: Università di Padova, Padova, Italy. Communicated by C. Signorini     

Gamma-ray tracking: Utilizing new concepts in the detection of gamma-radiation

Gamma-ray tracking in a closed array of highly segmented HPGe detectors is a new concept for the detection of γ-radiation. Each of the interacting γ-rays is identified and separated by measuring the energies and positions of individual interactions and by applying tracking algorithms to reconstruct the scattering sequences, even if many γ-rays hit the array at the same time. The three-dimensional position and the energy of interactions are determined by using two-dimensionally segmented Ge detectors along with pulse-shape analysis of the signals. Such a detector will have new and much improved capabilities compared to current γ-ray spectrometer. One implementation of this concept, called GRETA (Gamma-Ray Energy Tracking Array), is currently being under development at LBNL. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: kvetter@lbl.gov     

The $-game

We propose a payoff function extending Minority Games (MG) that captures the competition between agents to make money. In contrast with previous MG, the best strategies are not always targeting the minority but are shifting opportunistically between the minority and the majority. The emergent properties of the price dynamics and of the wealth of agents are strikingly different from those found in MG. As the memory of agents is increased, we find a phase transition between a self-sustained speculative phase in which a “stubborn majority” of agents effectively collaborate to arbitrage a market-maker for their mutual benefit and a phase where the market-maker always arbitrages the agents. A subset of agents exhibit a sustained non-equilibrium risk-return profile. Received 5 June 2002 / Received in final form 21 November 2002 Published online 27 January 2003 RID="a" ID="a"e-mail: sornette@unice.fr RID="b" ID="b"CNRS UMR7536 RID="c" ID="c"CNRS UMR6622     

In-beam studies of very neutron-deficient heavy nuclei

The JYFL gas-filled recoil separator RITU, combined with Ge detector arrays and a SACRED magnetic solenoid spectrometer, has been successfully employed in recoil-decay-tagging (RDT) experiments in order to probe structures of very neutron-deficient heavy nuclei. The present contribution focuses on the light Pb region where the new data extend the systematics of shape-coexisting yrast states towards the proton dripline. Similarities between band structures and their relation to possible multi-particle multi-hole intruder excitations will be discussed. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: rauno.julin@phys.jyu.fi