Alpha-gamma decay studies of 255Rf, 251No and 247Fm

The decay of the isotopes ²⁵⁵Rf, ²⁵¹No and ²⁴⁷Fm produced in the reactions , and was investigated by means of α-γ spectroscopy. Previously observed γ transitions in coincidence with α decays of ²⁵⁵Rf were confirmed, their energies and line intensities were measured more precisely, and their multipolarities were determined as E1. In ²⁵¹No a new isomeric state at E ^* > 1700keV with a half-life of ≈ 2μs was identified. The decay of ²⁴⁷Fm was measured more precisely. A partial level scheme of the daughter nucleus ²⁴³Cf could be established.     

Loss of collectivity in 79Rb

High-spin states in ⁷⁹Rb were populated in the reaction at E(beam) = 60 MeV. The lifetimes of the excited states of the positive-parity yrast band and of the negative-parity band in ⁷⁹Rb were measured by the Doppler Shift Attenuation Method. The deduced transition quadrupole moments Q_t are found to have a decreasing trend with rotational frequency for both the bands, consistent with those found experimentally in neighbouring nuclei. An erratum to this article is available at .     

Alpha-gamma decay studies of 255No

The decay of ²⁵⁵No was investigated by means of α-γ spectroscopy. The isotope was produced in the reactions ²⁰⁸Pb(⁴⁸Ca, n)²⁵⁵No, , and $²³⁸U(²²Ne, 5n)²⁵⁵No$. Levels of the daughter nucleus ²⁵¹Fm were assigned by α-γ coincidence measurements and on the basis of systematics. Level energies were determined precisely using measured γ-rays. The results are compared with the known level schemes of the lighter isotones ²⁴⁷Cm and ²⁴⁹Cf as well as with data for ²⁵³No.     

ω- πγtransition form factor in proton-proton collisions

Dalitz decays of ω and ρ mesons, and , produced in pp collisions are calculated within a covariant effective meson-nucleon theory. We argue that the ω transition form factor is experimentally accessible in a fairly model-independent way in the reaction pp → ppπ⁰ e ⁺ e ^- for invariant masses of the π⁰ e ⁺ e ^- subsystem near the ω pole. Numerical results are presented for the intermediate-energy kinematics of envisaged HADES experiments.     

Di-electrons from η -meson Dalitz decay in proton-proton collisions

The reaction is discussed within a covariant effective meson-nucleon theory. The model is adjusted to data of the subreaction . Our focus is on di-electrons from Dalitz decays of η -mesons, , and the role of the corresponding transition form factor . Numerical results are presented for the intermediate-energy kinematics of HADES experiments.     

Spin- {\frac{{3}}{{2}}} beyond the Rarita-Schwinger framework

We employ the two independent Casimir operators of the Poincaré group, the squared four-momentum, p², and the squared Pauli-Lubanski vector, W², in the construction of a covariant mass m, and spin- projector in the four-vector spinor, ψ_μ. This projector provides the basis for the construction of an interacting Lagrangian that describes a causally propagating spin- particle coupled to the electromagnetic field by a gyromagnetic ratio of .     

Isotopic dependence of fusion probabilities for neutron-deficient and -rich colliding nuclei

Isotopic dependence of the fusion dynamics is studied by analyzing the collision of a large number of isotopes of Ca and Ni with 0.6 N/Z 2. This study, which results from the Skyrme energy density formalism, reveals that the addition of neutrons favors fusion of reacting partners, whereas the reverse happens with the removal of neutrons. The fusion barrier heights and positions follow a non-linear second-order dependence on ( -1 ), whereas fusion cross-sections can be parameterized by a straight line.-1     

\alpha-decay spectroscopy of light odd-odd Bi isotopes - II: 186Bi and the new nuclide 184Bi

Alpha-decay of the new nuclide ¹⁸⁴Bi has been studied in the complete-fusion reaction ⁹³Nb(⁹⁴Mo, 3n)¹⁸⁴Bi at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of recoil- , recoil- - analysis and excitation functions measurements. Two -decaying isomeric states in ¹⁸⁴Bi with half-life values of 13(2) ms and 6.6(1.5) ms were identified. The -branching ratio of ¹⁸⁰Tl was deduced for the first time as . Improved data on the fine-structure -decay of ¹⁸⁶Bi were obtained in the ⁹³Nb(⁹⁵Mo, 2n)¹⁸⁶Bi reaction. A similarity of the decay energies and half-life values of ^184,186Bi is pointed out and a possible explanation for this effect is suggested.Received: 14 March 2003, Revised: 29 April 2003, Published online: 2 September 2003PACS: 23.60.+e decay - 27.70.+q - 27.80.+w K. Heyde: Present address: EP-ISOLDE, CERN, CH-1211, Geneva 23, Switzerland.     

A new determination of the γπ → ππ anomalous amplitude via πe<Superscript>-</Superscript> → π<Superscript>-</Superscript>e<Superscript>-</Superscript>π<Superscript>0</Superscript> data

We discuss the reaction π^-e^- → π^-e^-π⁰ with the purpose of obtaining information on the γπ → ππ anomalous amplitude _3π. We compare a full calculation at (p⁶) in chiral perturbation theory and various phenomenological predictions with the existing data of Amendolia et al. By integrating our theory results using Monte Carlo techniques, we obtain σ = 2.05 nb at (p⁶) and σ = 2.17 nb after including the dominant electromagnetic correction. Both results are in good agreement with the experimental cross-section of σ = (2.11±0.47) nb. On the basis of the ChPT results one would extract from the experimental cross-section as amplitudes _3π^(0)extr = (9.9±1.1) GeV^-3 and _3π^(0)extr = (9.6±1.1) GeV^-3, respectively, which have to be compared with the low-energy theorem _3π = e/(4π²F_π³) = 9.72GeV^-3. We emphasize the need for new data to allow for a comparison of experimental and theoretical distributions and to obtain _3π with smaller uncertainty.     

Isomeric and ground-state decay of 215 Bi

A new high-spin isomer in ²¹⁵Bi, with a half-life of 36.9(6) s, has been identified at the PSB-ISOLDE on-line mass separator using the pulsed-release technique combined with the element selective RILIS source. A decay scheme of Bi was constructed and complemented with the low-spinstructure observed in Bi decay. The population of a cascade on top of the level in ²¹⁵Poprovides evidence for Gamow-Teller -decay of the high-spin ²¹⁵Bi isomer.Received: 3 March 2003, Revised: 10 June 2003, Published online: 9 October 2003PACS: 23.20.Lv transitions and level energies - 27.80.+w - 29.30.Kv X- and -ray spectroscopyV. Fedoseyev: Present address: ISOLDE, CERN-PPE, CH-1211, Geneva 23, Switzerland.M. Górska: Present address: GSI, Darmstadt, D-64220, Germany.M. Huhta: Present address: Nokia, Tampere, Finland.     

\alpha-decay spectroscopy of light odd-odd Bi isotopes - I: 188,190Bi nuclei

Detailed fine-structure -decay studies of ^188,190Bi were performed using the complete-fusion reactions of ^50,52Cr ions with a ¹⁴²Nd target at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of recoil- , recoil- - /X-ray and excitation function measurements. Improved data on the -decay of ^188,190Bi were obtained and a number of new low-lying excited states in the daughters ^184,186Tl were observed. An intruder, presumably 10^- state was identified in ¹⁸⁴Tl, extending the systematics of such states in the odd-odd Tl nuclei beyond the neutron mid-shell at N = 104. Some technical aspects of experiment at recoil separators are also discussed.Received: 14 March 2003, Revised: 1 May 2003, Published online: 2 September 2003PACS: 23.60.+e decay - 27.70.+q - 27.80.+w C.D. OLeary: Present address: Department of Physics, University of York, York, UK.M.J. Taylor: Present address: Department of Physics and Astronomy, Rutgers Univesity, NJ, USA.L. Weissman: Present address: NSCL, Michigan State University, East Lansing, MI 48824-1321 USA.K. Heyde: Present address: EP-ISOLDE, CERN, CH-1211, Geneva 23, Switzerland.     

Study of spectator tagging in the reaction np → ppπwith a deuteron beam

The reaction has been studied in a kinematically complete experiment at a single beam momentum GeV/c (T = 759MeV). All four ejectiles have been detected in the large-acceptance time-of-flight spectrometer COSY-TOF. We analyzed the data along the lines of the spectator model as a means to isolate the quasi-free reaction. The spectator proton was identified by its momentum and flight direction thus yielding access to the associated Fermi motion of the bound neutron. A comparison is carried out with Monte Carlo simulations based on two different parameterizations of the deuteron wave function. Up to a Fermi momentum of roughly 150MeV/c no significant deviations between experimental and simulated data of various observables were found from which we conclude that the deuteron can indeed be taken as a valid substitute for the neutron.     

Some physics highlights from the EUROBALL spectrometer

Exotic, neutron-rich proton-induced spallation products of ²³²Th and ²³⁸U obtained from the PS Booster ISOLDE facility have been investigated by - , - coincidence and spectrum-multiscaling measurements. A new method for the reduction of isobaric contamination enabled to study the unknown region beyond ²⁰⁸Pb for the decay chain A = 217. A new isotope ²¹⁷Bi with a half-life of s was discovered and its -decay studied. For the first time, a half-life value of s for the -decay of ²¹⁷Po was measured.Received: 3 March 2003, Revised: 13 May 2003, Published online: 30 September 2003PACS: 23.20.Lv transitions and level energies - 23.60.+e decay - 27.80.+w 190 A 219 - 29.30.Kv X- and -ray spectroscopyV. Fedoseyev: Present address: ISOLDE, CERN-PPE, CH-1211, Geneva 23, Switzerland.M. Górska: Present address: GSI, Darmstadt, D-64220, Germany.M. Huhta: Present address: Nokia, Tampere, Finland.     

Hadron production and phase changes in relativistic heavy-ion collisions

We study soft hadron production in relativistic heavy-ion collisions in a wide range of reaction energy, 4.8 GeV < < 200 GeV, and make predictions about yields of particles using the statistical hadronization model. In fits to experimental data, we obtain both the statistical parameters as well as physical properties of the hadron source. We identify the properties of the fireball at the critical energy threshold, 6.26 GeV < < 7.61 GeV, marking for higher energies the hadronization of an entropy-rich phase. In terms of the chemical composition, one sees a phase which at low energy is chemically under-saturated, and which turns into a chemically over-saturated state persisting up to the maximum accessible energy. Assuming that there is no change in physical mechanisms in the energy range 15 > ≥200 GeV, we use continuity of particle yields and statistical parameters to predict the hadron production at = 62.4 GeV, and obtain total yields of hadrons at = 130 GeV. We consider, in depth, the pattern we uncover within the hadronization condition, and discuss possible mechanisms associated with the identified rapid change in system properties at . We propose that the chemically over-saturated 2 + 1 flavor hadron matter system undergoes a 1st-order phase transition.     

Chiral perturbation theory for nucleon generalized parton distributions

We analyze the moments of the isosinglet generalized parton distributions H, E, , of the nucleon in one-loop order of heavy-baryon chiral perturbation theory. We discuss in detail the construction of the operators in the effective theory that are required to obtain all corrections to a given order in the chiral power counting. The results will serve to improve the extrapolation of lattice results to the chiral limit.     

Hyperon-nucleon single-particle potentials with low-momentum interactions

Single-particle potentials in Hartree-Fock approximation for different hyperon-nucleon (YN channels are calculated in the framework of the effective low-momentum YN interaction . In contrast to the nucleon-nucleon interaction, the available experimental data for the YN interaction are scarce. As a consequence, no unique YN low-momentum potential can be predicted from the various bare potentials. The resulting momentum- and density-dependent single-particle potentials for several different bare OBE models and for chiral effective field theory are compared to each other.     

\pi\pi correlations in \gamma + A reactions

Preliminary differential cross-sections of the reactions and with A = ¹ H, ¹² C, and ^nat Pb are presented. A significant nuclear-mass dependence of the invariant-mass distribution is found in the channel. The dependence is not observed in the channel. The in-medium observation in the channel is consistent with an in-medium modification of the interaction in the I = J = 0 channel, changing width and pole position of a resonant state.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Le Meson production - 21.65. + f Nuclear matterJ.G. Messchendorp: For the TAPS and A2 Collaborations     

The one-body and two-body density matrices of finite nuclei with an appropriate treatment of the center-of-mass motion⋆

The one-body and two-body density matrices in coordinate space and their Fourier transforms in momentum space are studied for a nucleus (a nonrelativistic, self-bound finite system). Unlike the usual procedure, suitable for infinite or externally bound systems, they are determined as expectation values of appropriate intrinsic operators, dependent on the relative coordinates and momenta (Jacobi variables) and acting on intrinsic wave functions of nuclear states. Thus, translational invariance (TI) is respected. When handling such intrinsic quantities, we use an algebraic technique based upon the Cartesian representation, in which the coordinate and momentum operators are linear combinations of the creation and annihilation operators and for oscillator quanta. Each of the relevant multiplicative operators can then be reduced to the form: one exponential of the set { } times another exponential of the set { }. In the course of such a normal-ordering procedure we offer a fresh look at the appearance of “Tassie-Barker” factors, and point out other model-independent results. The intrinsic wave function of the nucleus in its ground state is constructed from a nontranslationally-invariant (nTI) one via existing projection techniques. As an illustration, the one-body and two-body momentum distributions (MDs) for the ⁴He nucleus are calculated with the Slater determinant of the harmonic-oscillator model as the trial, nTI wave function. We find that the TI introduces quite important effects in the MDs.     

Octupole-deformed molecular bands in 21Ne

Cluster states up to 12 MeV in the stable light nucleus ²¹Ne, based on the ¹⁶O + n + α molecular configurations, have been populated in the incomplete-fusion reaction ¹⁶ ₈O(⁷₃Li, np)²¹₁₀Ne at 29.4 MeV. The observation of both intra- and inter-band transitions leads to a re-interpretation of some levels in the K^π = ^- and K^π = ^- bands. The implications of this re-ordering on the octupole doublet bands are examined. The data allow a more accurate determination of some previously uncertain level energies. The “missing” I^π = ^- level is also discussed.     

Molecular dynamics in nanophase-separated comb-like poly( $ \upalpha$- n-alkyl $ \upbeta$-L-aspartate)s

A series of poly( -n-alkyl -L-aspartates) which are nanophase self-assembled comb-like polymers has been studied by dielectric spectroscopy in a broad frequency range ( 10^-23×10⁶ Hz), with n-alkyls side chains of various lengths, 10n18. In every member of the series the same relaxations were identified after the decomposition of the experimental isothermal trace in up to three peaks with relaxation times distributions. The strength, width and average relaxation time for all the relaxation modes were determined for each material. Besides the local low temperature, Arrhenius modes, two relaxation modes, and , present a cooperative character whose dynamics are not affected by the side chains melting. The relaxation is a polyethylene-like glass transition of the amorphous side chains and its dynamics is strongly dependent on the n value due to the increasing restrictions imposed by the self-assembled confinement. The strength of the relaxation mode increases as the lateral chains loose their 2D order. The restricted chopstick motion of the rigid rods is thought to be the origin of the mode; this motion is hindered at temperatures where the cage size decreases as a result of the increasing disorder with temperature.