Synthesis and decay properties of superheavy atoms in nuclear reactions induced by stable and radioactive ion beams

This talk consists of two parts. The first one presents the results of investigations performed in 1998-2000 in Dubna on the synthesis of superheavy nuclei in reactions induced by ⁴⁸Ca ions. The radioactive decay properties of the nuclei, indicating a considerable increase in the α-decay and spontaneous fission half-lives of the isotopes of elements 110-116 when approaching the closed neutron shell at N = 184, are given. In the second part the possible ways of advancing into the region of more neutron-rich nuclei, using stable and radioactive ion beams, are discussed. Since so far no intense radioactive ion beams are available, some experiments with stable beams are considered as a test for the suggested ideas. Received: 1 May 2001 / Accepted: 4 December 2001     

Relativistic many-body theory with radioactive ion beams: Surface pion condensation

We critically review the present relativistic mean-field theory from the viewpoint of missing pions. We introduce the interesting experimental data on pionic states taken at RCNP. These data seem to suggest the occurrence of pion condensation in the nuclear surface. Qualitative discussion is made on the consequence of surface pion condensation on Gamow-Teller transitions and spin response functions and others. The radioactive ion beams are the tools of studying the unstable nuclei, which have extended nuclear surfaces. We shall start with radioactive ion beams the nuclear surface science, which includes the surface pion condensation as the important ingredient in addition to spin-orbit splitting and surface pairing. Received: 1 May 2001 / Accepted: 4 December 2001     

Potential and limitations of nucleon transfer experiments with radioactive beams at REX-ISOLDE

As a tool for studying the structure of nuclei far off stability the technique of γ-ray spectroscopy after low-energy single-nucleon transfer reactions with radioactive nuclear beams in inverse kinematics was investigated. Modules of the MINIBALL germanium array and a thin position-sensitive parallel plate avalanche counter (PPAC) to be employed in future experiments at REX-ISOLDE were used in a test experiment performed with a stable ³⁶S beam on deuteron and ⁹Be targets. It is demonstrated that the Doppler broadening of γ lines detected by the MINIBALL modules is considerably reduced by exploiting their segmentation, and that for beam intensities up to 10⁶ particles/s the PPAC positioned around zero degrees with respect to the beam axis allows not only to significantly reduce the γ background by requiring coincidences with the transfer products but also to control the beam and its intensity by single particle counting. The predicted large neutron pickup cross-sections of neutron-rich light nuclei on ²H and ⁹Be targets at REX-ISOLDE energies of 2.2 MeV ^. A are confirmed. Received: 9 October 2000 / Accepted: 28 January 2001     

Effects of quantum space time foam in the neutrino sector

We discuss violations of CPT and quantum mechanics due to interactions of neutrinos with space-time quantum foam. Neutrinoless double beta decay and oscillations of neutrinos from astrophysical sources (supernovae, active galactic nuclei) are analysed. It is found that the propagation distance is the crucial quantity entering any bounds on EHNS parameters. Thus, while the bounds from neutrinoless double beta decay are not significant, the data of the supernova 1987a imply a bound being several orders of magnitude more stringent than the ones known from the literature. Even more stringent limits may be obtained from the investigation of neutrino oscillations from active galactic nuclei sources, which have an impressive potential for the search of quantum foam interactions in the neutrino sector. Received: 5 June 2000 / Accepted: 12 July 2000     

Nuclear effects and higher twists in F3 structure function

We analyze the CCFR collaboration iron target data on the xF₃ structure function making particular emphasis on the extraction of the higher twist contributions from the data. Corrections for nuclear effects are applied in order to extract data on the structure function of the isoscalar nucleon. Our analysis confirms the observation made earlier, that the higher twist terms depend strongly on the level to which QCD perturbation theory analysis is applied. We discuss the impact of nuclear effects on the higher twist term as well as on the QCD scale parameter extracted from the fit to data. Received: 4 August 2000 / Accepted: 17 September 2000     

Experimental modeling of physical laws

A physical law is represented by the probability distribution of a measured variable. The probability density is described by measured data using an estimator whose kernel is the instrument scattering function. The experimental information and data redundancy are defined in terms of information entropy. The model cost function, comprised of data redundancy and estimation error, is minimized by the creation-annihilation process. Received 24 February 2000 and Received in final form 21 February 2001     

Rules extraction in short memory time series using genetic algorithms

Data mining is performed using genetic algorithm on artificially generated time series data with short memory. The extraction of rules from a training set and the subsequent testing of these rules provide a basis for the predictions on the test set. The artificial time series are generated using the inverse whitening transformation, and the correlation function has an exponential form with given time constant indicative of short memory. A vector quantization technique is employed to classify the daily rate of return of this artificial time series into four categories. A simple genetic algorithm based on a fixed format of rules is introduced to do the forecasting. Comparing to the benchmark tests with random walk and random guess, genetic algorithms yield substantially better prediction rates, between 50% to 60%. This is an improvement compared with the 47% for random walk prediction and 25% for random guessing method. Received 29 August 2000     

Production of neutron-rich isotopes in fission of uranium induced by neutrons of 20 MeV average energy

In the context of a parameter study conducted by several laboratories for future European radioactive beam facilities based on fast-neutron induced fission, in particular for the SPIRAL-II project at GANIL, we have measured the yields of neutron-rich isotopes in the mass range of 88 to 144. These nuclei were obtained as fission products of natural uranium bombarded by neutrons of 20 MeV average energy emitted by a thick carbon target irradiated by 50 MeV deuterons. Yields have been measured using on-line mass separation with the ion-guide method. Compared with proton-induced fission at 25 MeV the magnitude of cross-sections, except for the symmetric region, is similar. Z-distributions of isobars have the same width, 0.7 charge units, but their maxima are shifted by about 0.8 charge units, favouring production of the neutron-richer isobars. Our data allow calculations of absolute cross-sections for fission of natural uranium induced by neutrons of about 20 MeV. Received: 10 July 2000 / Accepted: 27 October 2000     

Low–energy photodisintegration of 9Be and α+α+n→9Be +γ reactions at astrophysical conditions

A semi–microscopic model for the low–energy photodisintegration of the ⁹Be nucleus is constructed, and the experimental data are analyzed with its help. The older radioactive isotope data are supported by this analysis. The theoretical photodisintegration cross section is derived. The astrophysical rates for the reaction α+α+n→⁹Be+γ and the reverse photodisintegration of ⁹Be are calculated. The new reaction rate for α+α+n→⁹Be+γ is compared with previous estimations. Received: 19 January 1998     

Challenge towards muonic atom formation with unstable nuclei

X-ray spectroscopy of muonic atoms is an important tool to obtain information on the nuclear charge distribution of nuclei. It has been successfully used for many years to study stable isotopes in condensed or gaseous states. A new method has been proposed to extend muonic atom X-ray spectroscopy to the use of radioactive isotope beams to form muonic atoms with unstable nuclei. This new method allows studies of the nuclear properties and nuclear sizes of unstable atoms by means of the muonic X-ray method at facilities where both negative muon and radioactive nuclear beams would be available. Progress of a feasibility study at RIKEN-RAL muon facility is also reported. Received: 1 May 2001 / Accepted: 4 December 2001     

Value-at-risk prediction using context modeling

In financial market risk measurement, Value-at-Risk (VaR) techniques have proven to be a very useful and popular tool. Unfortunately, most VaR estimation models suffer from major drawbacks: the lognormal (Gaussian) modeling of the returns does not take into account the observed fat tail distribution and the non-stationarity of the financial instruments severely limits the efficiency of the VaR predictions. In this paper, we present a new approach to VaR estimation which is based on ideas from the field of information theory and lossless data compression. More specifically, the technique of context modeling is applied to estimate the VaR by conditioning the probability density function on the present context. Tree-structured vector quantization is applied to partition the multi-dimensional state space of both macroeconomic and microeconomic priors into an increasing but limited number of context classes. Each class can be interpreted as a state of aggregation with its own statistical and dynamic behavior, or as a random walk with its own drift and step size. Results on the US S&P500 index, obtained using several evaluation methods, show the strong potential of this approach and prove that it can be applied successfully for, amongst other useful applications, VaR and volatility prediction. The October 1997 crash is indicated in time. Received 2 September 2000 and Received in final form 12 October 2000     

Spectral analysis of 208Pb muonic atom

We have applied to the ²⁰⁸Pb muonic atom a series of recurrence relations relating the moments of the ground-state density and the energy differences between the 1s level and the states of the line. The large amount of precise experimental data and the electromagnetic character of the interaction allow a detailed test of the method for determining the ground-state density and reconstructing the local equivalent potential. Though the present work is limited to the study of the efficiency for a given trial density, it results in a semi-quantitative analysis with an accuracy better than 1%. Received: 18 December 2000 / Accepted: 18 April 2001     

A polarization relation and the measurement of the longitudinal response in pseudoscalar meson electroproduction off the nucleon

For pseudoscalar meson electroproduction off the nucleon in parallel kinematics a relation between three polarization observables is derived. It is shown that, without Rosenbluth separation, a measurement of the longitudinal strength can be achieved through three different ways. They are discussed with preliminary MAMI data for the reaction in the energy range of the resonance. Received: 30 March 2000 / Accepted: 8 May 2000     

Decay of 83Sr and level structure of 83Rb

The excited states of the ⁸³Rb nucleus were investigated in radioactive decay of ⁸³Sr. The level scheme was established and for a number of levels spin-parity assignments are suggested on the basis of log ft values and γ-branching ratios. Combining with the high-spin states observed by the in-beam γ-ray spectroscopy of a previous decay work, the structure of the excited states of ⁸³Rb is discussed in the framework of the projected shell model. Received: 17 November 1999 / Accepted: 11 December 2000     

Status and prospects of synthesizing superheavy elements

The nuclear shell model predicts that the next doubly magic shell-closure beyond ²⁰⁸Pb is at a proton number between Z = 114 and 126 and at a neutron number N = 184. The outstanding aim of experimental investigations is the exploration of this region of spherical “Superheavy Elements”. This article describes the experiments that were performed at the GSI SHIP. They resulted in an unambiguous identification of elements 107 to 112. They were negative so far in searching for elements 113, 116 and 118 at SHIP; however, positive results were reported from experiments in Dubna on elements 114 and 116 and from experiments in Berkeley on element 118. The measured decay data are compared with theoretical predictions. Some aspects concerning the reaction mechanism and the use of radioactive beams are also presented. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: S.Hofmann@gsi.de     

The association of octadecyl-end-capped poly-(sodium 2-acrylamido-2-methylpropanesulfonates) in water and salt solutions: A study by fluorescence spectroscopy and isothermal titration calorimetry

Steady-state fluorescence spectroscopy and isothermal titration calorimetry (ITC) have been used to study the aggregation in aqueous solutions of poly-(2-acrylamido)-2-methylpropanesulfonic acids, sodium salt mono-endcapped with either N,N-di-n-octadecyl or N-4-[(1-pyrenyl)butyl]-N-n-octadecyl which were prepared by free radical polymerization of 2-(acrylamido)-2-methylpropane sulfonic acid (AMPS) initiated with the azo compounds, 4,4'-azobis{cyano-N,N-di-n-octadecyl}pentanamide and 4,4'-azobis{cyano-N,N-[4-(1-pyrenyl)butyl]-n-octadecyl}pentanamide, respectively. Both techniques indicate the occurrence of multimolecular aggregates in solutions of the polymers in water and in 0.2 M NaCl. The concentration range for aggregation is about 1-14 mmol AMPS l^-1 (0.5-2.7 g l^-1) in 0.2 M NaCl and the enthalpy of micellization, estimated from ITC data, is ∼100 J [mol AMPS]^-1. The accessibility of the chromophores to neutral molecules and to cationic species was assessed by quenching of fluorescence with nitromethane and thallium nitrate, respectively. The association of the mono-endcapped polymers is compared to that of PAMPS derivatives carrying hydrophobic groups randomly attached along the chain. Received 7 August 2000 and Received in final form 26 October 2000     

The role of secondary reggeons in central meson production

We estimate the contribution of f₂ trajectory exchange to the central and production. It is shown that secondary reggeons may give a large contribution to processes of double diffractive meson production at high energies. Received: 10 May 2000 / Accepted: 4 June 2000     

Prompt light particle emission in the 36Ar + 58Ni reaction at 95 MeV/nucleon

The prompt component at intermediate velocity of light charged particles is investigated. An improved coalescence model coupled to the intra-nuclear cascade code ISABEL is used to obtain light complex particle energy spectra and multiplicities as a function of impact parameter. The results are compared with experimental data from the ³⁶Ar + ⁵⁸Ni experiment at 95 MeV/nucleon, performed with the INDRA 4π detection system. The calculated prompt component is found to rather well reproduce proton spectra. For complex light charged particles the calculated components well populate the high energy part of spectra. Prompt emission can therefore explain the large transverse energies experimentally observed at mid-rapidity. Received: 27 July 2000 / Accepted: 20 November 2000     

Phenomenology of the deuteron electromagnetic form factors

A rigorous extraction of the deuteron charge form factors from tensor polarization data in elastic electron-deuteron scattering, at given values of the 4-momentum transfer, is presented. Then the world data for elastic electron-deuteron scattering is used to parameterize, in three different ways, the three electromagnetic form factors of the deuteron in the 4-momentum transfer range 0-7 fm⁻¹. This procedure is made possible with the advent of recent polarization measurements. The parameterizations allow a phenomenological characterization of the deuteron electromagnetic structure. They can be used to remove ambiguities in the form factors extraction from future polarization data. Received: 28 January 2000 / Revised version: 25 February 2000     

Crowd-anticrowd theory of multi-agent market games

We present a dynamical theory of a multi-agent market game, the so-called Minority Game (MG), based on crowds and anticrowds. The time-averaged version of the dynamical equations provides a quantitatively accurate, yet intuitively simple, explanation for the variation of the standard deviation (`volatility') in MG-like games. We demonstrate this for the basic MG, and the MG with stochastic strategies. The time-dependent equations themselves reproduce the essential dynamics of the MG. Received 28 August 2000 and Received in final form 23 September 2000