Gamma-ray spectroscopy studies at GANIL: Status and perspectives

The SPIRAL facility started to deliver radioactive beams in September 2001 and some experiments have been performed in particular using the EXOGAM array. These experiments will be briefly described and the first outputs will be shown. The in-beam performances of EXOGAM will also be discussed.Received: 29 January 2003, Published online: 9 March 2004PACS: 29.30.Kv X- and -ray spectroscopy - 23.20.Lv transitions and level energies - 25.60.Pj Fusion reactions - 25.70.De Coulomb excitation     

Double-spin asymmetries in electron-nucleon scattering in Halls B and C at JLab

Three experiments at JLab have measured the double polarization asymmetries ) in the nucleon resonance region, using polarized electron beams incident on polarized proton and deuteron targets. The analysis for the first experiment, eg1a in Hall B, is nearly finished and preliminary values of the spin structure function g₁(x, Q²) and the first moment (x) have been extracted. The other two experiments, one in Hall B and one in Hall C, are still analysing data. Some results are presented.Received: 1 November 2002, Published online: 15 July 2003PACS: 24.70.+s Polarization phenomena in reactions     

Coupling a CLOVER detector array with the PRISMA magnetic spectrometer

Following the commissioning of the PRISMA large-acceptance spectrometer, installed at the Laboratori Nazionali di Legnaro (LNL), an international nuclear-structure collaboration has started to develop a large -ray setup to be installed in the target position of the spectrometer. The array is based on the EUROBALL composite CLOVER detectors. In this contribution the CLOVER detector array is described and its expected performance figures discussed. This new setup, by using the high-intensity heavy-ion beams provided by the LNL ALPI linac, will push the study of nuclear structure towards moderately neutron-rich nuclei by means of quasi-elastic and deep inelastic reactions.Received: 15 December 2002, Revised: 28 April 2003, Published online: 23 March 2004PACS: 29.40.Wk Solid-state detectors - 29.30.Kv X- and -ray spectroscopy     

High-resolution in-beam particle-gamma coincidence spectroscopy

A short summary of the present status of prompt particle decays in the mass region is presented. It includes recent results from a GAMMASPHERE experiment, which aimed at the combined high-resolution spectroscopy of light charged particles and -rays to allow for more detailed studies of known decays and the identification of new cases of discrete prompt proton and -particle emission from highly and superdeformed states.Received: 10 October 2002, Published online: 17 February 2004PACS: 23.50. + z Decay by proton emission - 23.60. + e decay - 27.40. + z - 27.50. + e      

Gamma-ray spectroscopy of nuclei with large deformations

The large multidetector gamma-ray arrays (such as GAMMASPHERE, EUROBALL, and GASP) have played a central role in nuclear-structure studies during the past decade. In this paper I will discuss recent results from experiments on nuclei with very large deformations, including: the measurement of the spins, parities, and excitation energies of superdeformed bands in ¹⁵²Dy; the observation of extreme deformations in ¹⁰⁸Cd and the evidence for hyper-intruder states; the study of superdeformed nuclei around , which provide an opportunity to test our microscopic understanding of collective excitations; and lifetimes of strongly deformed triaxial bands in ¹⁶³Lu. I will conclude with a brief discussion on the next generation gamma-ray detector array, GRETA.Received: 9 December 2002, Published online: 17 February 2004PACS: 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 21.10.Tg Lifetimes - 29.30.Kv X- and -ray spectroscopy     

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     

Lasers in nuclear physics --A review

Lasers have played an important role for the development of new spectroscopy techniques yielding spins, electromagnetic moments and charge radii of many unstable nuclei. More recently, similar techniques have been introduced to manipulate atoms and thus to prepare beams or samples of radioactive atoms for various applications including nuclear spectroscopy and decay studies. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: rainer.neugart@uni-mainz.de     

Exploring superdense matter at RHIC

I report first results on Au + Au collisions at GeV per nucleon pair from all four experiments at the Relativistic Heavy Ion Collider.Received: 30 September 2002, Published online: 22 October 2003PACS: 25.75.Dw Particle and resonance production     

Experimental review of charmonium spectroscopy

Charmonium spectroscopy is one of the best means of making precision study of QCD, the strong-interaction component of the Standard Model of particle physics. Recent progress in the study of charmonium, the need for additional precision data, and the opportunities that the new facilities offer, are discussed.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.38.Qk Quantum chromodynamics: Experimental tests - 12.39.Pn Potential models - 13.25.Gv Decays of , , and other quarkonia - 14.40.Gx Mesons with S = C = B = 0, GeV (including quarkonia)     

Gamma-ray tracking with the MARS detector

The feasibility of the entire process of -ray tracking is demonstrated experimentally for the first time. The accuracy of the results is tested by the capability for Doppler correction of -rays emitted in flight. The resolution of the 847.8 keV ( ) transition detected with the MARS detector after Coulomb excitation of a ⁵⁶Fe beam could be improved from 15 keV to below 5 keV (FWHM).Received: 28 October 2002, Published online: 2 March 2004PACS: 29.30.Kv X- and gamma-ray spectroscopy - 29.40.Gx Tracking and position-sensitive detectors - 29.40.Wk Solid-state detectorsC.A. Ur: On leave from: NIPNE, Bucharest, Romania.     

Eta physics at threshold

The production of - and -mesons in elementary nucleon-nucleon collisions has been investigated at the synchrotrons CELSIUS, COSY and SATURNE. The high-quality proton beam with low emittance and small momentum spread permits to study the creation of these mesons very close to the kinematical threshold, where --due to the rapid growth of the phase space volume-- the total cross-section increases by orders of magnitude over a few MeV range of the excess energy. The magnitude and energy dependence of the total cross-section as well as the occupation distribution of the phase space serve as observables for investigating the mechanisms underlying the production processes and the interaction of mesons with nucleons. The precise data on the and creation via the reactions allowed to settle the general features of the - and -meson production and revealed the sensitivity of the mentioned observables to the nucleon-nucleon-meson final-state interaction. The particular production properties, like for example, the determination of the dominating exchange processes which lead to the excitation of the S ₁₁ nucleon isobar in the case of creation, must be established by confrontation with other observables. The present status of this investigation with an emphasis on the results of the COSY-11 Collaboration is briefly presented. The available data are interpreted in view of the production mechanism and the meson-nucleon interaction.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Le Meson production - 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV) - 13.85.Lg Total cross sections - 25.40.-h Nucleon-induced reactions     

Study of drip line nuclei through two-step fragmentation

We have studied the structure of light neutron-rich nuclei around N = 16 by employing the in-beam -ray spectroscopy technique using the fragmentation of secondary beams of ^25,26Ne, ^27,28Na and ^29,30Mg isotopes. This secondary-beam cocktail was obtained by the fragmentation of a ³⁶S beam at 77.5 MeV by the SISSI/GANIL facility. By a second-step fragmentation, we have measured -ray-residue coincidences in ^17-20C and ^23,24O and described the obtained levels in the framework of the shell model.Received: 31 October 2002, Published online: 24 February 2004PACS: 23.20.Lv transitions and level energies - 21.60.Cs Shell model - 27.20. + n - 27.30. + t      

Study of thermally excited nuclei through <Emphasis Type="Italic">E</Emphasis>1 and <Emphasis Type="Italic">E</Emphasis>2 decay from collective modes

The nuclear system at the limit of excitation energy and angular momentum is here studied in the case of the superdeformed nucleus ¹⁴³Eu using -spectroscopy techniques. The data are based on a EUROBALL experiment using the reaction ³⁷Cl + ¹¹⁰Pd Eu + 4n. The influence of thermal energy on superdeformed configurations is investigated through the analysis of the quasi-continuum spectra formed by E2 transitions among states of excited rotational bands with energy extending up to 4-5 MeV above the yrast line. In particular, the effective lifetimes of the discrete rotational bands forming ridge structures in - coincidence matrices is measured by a Doppler Shift Attenuation Method. The deduced quadrupole deformation of 10 eb indicates that the nucleus maintains its collectivity with increasing excitation energy, supporting the superdeformed character of the excited nuclear rotation. The obtained number of superdeformed discrete bands forming the ridge structures is found in good agreement with microscopic cranked shell model calculations including the decay-out process into the lower deformation minimum. In addition, the nuclear properties at higher excitation energies are investigated through the E1 -decay of the giant dipole resonance (GDR). It is found that the intensity of the superdeformed yrast and excited bands increases by a factor of approximately 1.6 when a coincidence with a high-energy -ray is required, showing the importance of the E1 cooling in the feeding mechanism of the superdeformed states.Received: 2 December 2002, Published online: 2 March 2004PACS: 21.10.Tg Lifetimes - 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 27.60. + j      

On the decay properties of 269Hs and indications for the new nuclide 270Hs

In bombardments of ²⁴⁸Cm with 143.7-146.8 MeV ²⁶Mg ions the nuclides ²⁶⁹Hs and presumably ²⁷⁰Hs were produced. After chemical isolation, Hs atoms were identified by observing genetically linked nuclear-decay chains. Three chains originating from ²⁶⁹Hs confirmed the decay properties observed previously in the decay of ²⁷⁷112. Two chains exhibited the characteristics expected for the new nuclide ²⁷⁰Hs, which was predicted to be a deformed doubly magic nucleus. From the measured MeV an -decay half-life of 3.6^+0.8_-1.4 s was estimated.Received: 18 July 2002, Revised: 3 April 2003, Published online: 22 July 2003PACS: 23.60.+e Alpha decay - 25.70.Gh Compound nucleus - 25.85.Ca Spontaneous fission - 27.90.+b      

Experiments on the search for the NN-decoupled NN\pi-resonance d’

The status on the search for NN-decoupled -resonances is reviewed with regard to recent experimental searches in the pionic double-charge exchange in nuclei, the two-pion production in nucleon-nucleon collisions, the photo pion-production on the deuteron and the electro pion-production in nuclei.Received: 30 September 2002, Published online: 22 October 2003PACS: 14.20.Gk Baryon resonances with S = 0 - 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV) - 25.40.Ve Other reactions above meson production thresholds (energies 400 MeV)     

Properties of <Superscript>152</Superscript><Emphasis Type="Italic">Gd</Emphasis> collective states

The decays of ¹⁵²Tb (T _1/2 = 17.5 h) and ¹⁵²Gd excited states have been investigated by the analysis of -rays and -coincidences measured with the use of high-resolution HPGe detectors. The source of ¹⁵²Tb was prepared by chromatographic isolation followed by electromagnetic separation from a tantalum target irradiated by an internal proton beam of the LNP JINR phasotron. New and more precise data on the -transitions and excited states of ¹⁵²Gd are reported. Using previously published data on internal-conversion electrons many transition multipolarities are suggested, some of them with E0 admixture. The ratio was found for a number of low-lying levels, for most of the levels their spins, parities, and are given. The excited levels of ¹⁵²Gd were deduced from the analysis of -coincidences. The experimental level energies and reduced transition probabilities are compared with the calculations by phenomenological formulae as well as in the frameworks of theoretical models.Received: 21 May 2002, Revised: 26 May 2003, Published online: 18 November 2003PACS: 29.30.Kv X- and gamma-ray spectroscopy - 23.20.-g Electromagnetic transitions - 21.10.-k Properties of nuclei; nuclear energy levels - 21.60.-n Nuclear structure models and methodsJ. Adam: On leave from Nuclear Physics Institute of ASCR, e, Czech Republic.V.S. Pronskikh: On leave from Saint Petersburg State Institute of Technology, Russia     

Complete spectroscopy in high-spin cranking calculations

Exact and approximate quantum numbers of the cranked Nilsson-Strutinsky (CNS) formalism are exploited to calculate excited bands in fixed configurations with the energy of the individual bands minimized with respect to deformation for all spin values. The formalism is applied to ⁵⁹Cu, where all bands which appear important in the decay out of the superdeformed band are calculated.Received: 14 November 2002, Published online: 17 February 2004PACS: 21.10.Ma Level density - 21.60.Cs Shell model - 23.20.Lv transitions and level energies - 27.50. + e C. Andreoiu: Present address: Department of Physics, University of Guelph, Guelph, Ontario, Canada N1G 2W1.     

Associated strangeness production at threshold

The associated strangeness dissociation at threshold has been studied at the COSY-11 facility measuring the hyperon and the K ⁺ K ^- meson pair production. Measurements of the near-threshold and production via the reaction (S. Sewerinet al., Phys. Rev. Lett. 83, 682 (1999)) at COSY-11 have shown that the cross-section ratio exceeds the value at high excess energies ( MeV (A. Baldiniet al., Total Cross-Sections for Reactions of High-Energy Particles, Landolt-Börnstein, New Series, Vol. I/12 (Springer, Berlin, 1988))) by an order of magnitude. For a better understanding additional data have been taken between 13 MeV and 60 MeV excess energy. The near-threshold production of the charged kaon-antikaon pair is related to the discussion about the nature of the scalar states in the 1 GeV/c ² mass range, i.e. the f ₀(980) and a ₀(980) (O. Krehl, R. Rapp, J. Speth, Phys. Lett. B 390, 23 (1997)). The interpretation as a molecule is strongly dependent on the K- interaction which can be studied via the production channel. A first total cross-section value on the reaction at an excess energy of 17 MeV (C. Quentmeieret al., Phys. Lett. B 515, 276 (2001)), i.e. below the production threshold, was measured.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV) - 14.20.Jn Hyperons - 14.40.Aq , K, and mesons - 25.40.Ep Inelastic proton scattering     

Spectroscopic quadrupole moments of high-spin isomers in 193 Pb

The quadrupole interaction of high-spin isomers in ¹⁹³Pb implanted into solid Hg cooled at a temperature T = 170 K has been investigated by the time-differential perturbed -ray angular-distribution method. Spectroscopic quadrupole moment values of eb and 0.45(4) eb have been deduced for the 21/2^- and 33/2 ⁺ three-neutron states, respectively. A much higher value eb has been determined for the 29/2^- isomer, the band head of a magnetic rotational band.Received: 4 November 2002, Published online: 2 March 2004PACS: 21.10.Ky Electromagnetic moments - 27.80. + w      

Experimental signals of \sigma-mesons in nuclei and chiral symmetry

The interaction in the scalar isoscalar channel is studied as a function of the baryonic density in the framework of a chiral unitary approach which successfully reproduces vacuum - phase shifts. We present some results on the -meson pole, which is generated dynamically in our model, in nuclear matter. Finally, we analyze the ( ) reaction on nucleons and nuclei in the kinematical region where the scalar isoscalar scattering amplitude is influenced by the low mass of the in nuclei, and thus, presents a large enhancement close to the position of its pole. Indeed, we find, that the final-state interaction of the pions modified by the nuclear medium produces a large shift of strength of the two-pion invariant-mass distribution in the ( ) channel consistent with recent experimental data.Received: 30 September 2002, Published online: 22 October 2003PACS: 14.40.-n Properties of specific particles: Mesons - 25.20.-x Photonuclear reactions - 21.65. + f Nuclear matter