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  • 1
    Electronic Resource
    Electronic Resource
    A Penning trap mass spectrometer for the study of cluster ions (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 4902-4910 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A Penning trap system has been set up for storing and investigating cluster ions over time ranges from microseconds up to minutes. This enables studies of cluster reactions with extremely low cross sections and the observation of their time dependence in a new regime. The ions are created externally by laser vaporization, cooled by adiabatic expansion of a supersonic beam, and injected into the Penning trap. Detection of reaction products is achieved by combining the advantages of two complementary approaches, viz. the high resolution of Fourier transform mass spectrometry and the high sensitivity of single-ion counting with a time-of-flight mass spectrometer. The performance of the apparatus is illustrated by results of recent cluster experiments. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146172
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  • 2
    Electronic Resource
    Electronic Resource
    Search for strange matter by Rutherford backscattering (1989)
    [s.l.] : Nature Publishing Group
    Nature 337 (1989), S. 434-436 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] To set a useful sensitivity limit for experiments designed to search for strange matter, De Rujula and Glashow estimated the maximum concentration of strange nuggets in the Earth's crust3. They assume a value of ~10~24 g cm"3 for the local dark matter density of our Galaxy. Assuming that the whole ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/337434a0
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  • 3
    Electronic Resource
    Electronic Resource
    Auf der Suche nach „seltsamer” Materie (1991)
    Springer
    Naturwissenschaften 78 (1991), S. 489-496 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01131396
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  • 4
    Electronic Resource
    Electronic Resource
    Evidence for quasi-fission in40Ar+208Pb collisions near the coulomb-barrier (1987)
    Springer
    The European physical journal 326 (1987), S. 313-326 
    Details
    ISSN: 1434-601X
    Keywords: 25.70.Jj
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Fission-fragment angular distributions were measured in the reaction of40Ar with208Pb near the fusion barrier. For nearly symmetric mass-/charge splits we find angular distributions symmetric around θ=90 degrees, however, with unusually large anisotropies. These develop gradually into forward-backward asymmetric distributions as one moves away from mass-/charge symmetry. This indicates that non-compound fission (‘quasi-fission’) competes with true fusion-fission. The relative contribution of quasi-fission to the total fission cross section is somewhere between 51 and 85%. In the framework of the extra-push model this is equivalent to an extra-extra push energy for compound-nucleus formation inside the true fission saddle point of 4〈E xx 〈9 MeV in agreement with a recent empirical parametrization of fusion-barrier shifts based on fusion-fission cross sections. On the basis of cross sections for fusion-evaporation residues it had previously been concluded that fusion of40Ar with Pb isotopes occurs unhindered. Possible reasons for this apparent discrepancy are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01297586
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  • 5
    Electronic Resource
    Electronic Resource
    Competition between binary reactions and fusion in heavy-ion collisions at the Coulomb barrier (1992)
    Springer
    The European physical journal 342 (1992), S. 411-427 
    Details
    ISSN: 1434-601X
    Keywords: 25.70.Cd ; 25.70.Jj ; 25.70.Lm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mass and charge distributions for binary reaction channels have been measured for the reactions86Kr with76Ge,104Ru and130Te at the Coulomb barrier using chemical separations andγ-ray spectroscopy. These systems span the region where dynamical hindrance to complete fusion sets in. The binary reactions can be subdivided into two components associated withi) reflection from the outer potential barrier (quasielastic), andii) reseparation after passing the barrier (complex reactions). The sum of complex-reaction channels and evaporation residues from complete fusion can be reproduced by a barrier passing calculation. The fraction of the barrier passing flux leading to reseparation increases from 26±10% for the lightest system to more than 90% for the heaviest system. The data indicate that fusion hindrance is primarily caused by reseparation shortly after passage of the barrier before Swiatecki's conditional saddlepoint is overcome, resulting in partitions close to the entrance channel configuration. In addition, for the heaviest system, a quasifission component representing somewhat less than 20% of the barrier-passing flux was observed. From the missing masses of fragment pairs we can deduce that the reseparating complex-reaction products have kinetic energies well below the fusion barrier and share the excitation energy in a way similar to the sawtooth-like curve known from low-energy fission. The quasielastic, predominantly one- and two-nucleon transfer channels, have strongly varying cross sections for the three systems despite similar effectiveQ-values. A systematics of one-neutron transfer cross sections at the Coulomb barrier is established and shown to differ considerably from the smooth behaviour observed at energies 20–30% above the barrier. The connection to nuclear polarization phenomena and orbit matching is pointed out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01294952
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  • 6
    Electronic Resource
    Electronic Resource
    Fusion-fission in the reaction76Ge+170Er (1984)
    Springer
    The European physical journal 317 (1984), S. 55-64 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Radiochemical yield measurements were performed to study mass- and charge distributions in the reaction of76Ge ions with170Er in the c.m. energy range from 222 MeV through 272 MeV. The magnitude of the resulting cross-section for fusion-fission is significantly lower than expected and is explained within the framework of Swiatecki's Extra-Push model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01420448
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  • 7
    Electronic Resource
    Electronic Resource
    Search for supermassive nuclei in nature (1991)
    Springer
    The European physical journal 338 (1991), S. 357-361 
    Details
    ISSN: 1434-601X
    Keywords: 14.80.Pb ; 25.70-z ; 29.40Jz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on a search for supermassive nuclei in nature with masses up to 107 amu. Such exotic nuclei might consist, for example, of stable strange matter, which comprises a mixture of up, down, and strange quarks, or of relic particles from the early Universe. The experiments are based on Rutherford backscattering of heavy ions, preferably238U, from various target samples. The measured parameters of a detected particle are its time-of-flight, scattering angle, and specific ionization. From this information the mass of the target nucleus can be inferred. Upper limits for the abundance of strange supermassive nuclei with massesA−4·102 to 107 amu relative to the number of nucleons were found to be in the range 10−11 to 10−15. For the narrower mass rangeA −103 to 104 amu the limit is 2· 10−17.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01288200
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  • 8
    Electronic Resource
    Electronic Resource
    Unusual excitation-energy division in quasi-fission reactions between50Ti,54Cr and58Fe with207,208Pb at the barrier (1987)
    Springer
    The European physical journal 328 (1987), S. 255-256 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01290670
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  • 9
    Electronic Resource
    Electronic Resource
    Angular distributions in quasi-fission reactions: Evidence for incomplete relaxation of the tilting mode (1985)
    Springer
    The European physical journal 320 (1985), S. 529-530 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Angular distributions of fission-like fragments have been measured for50Ti+208Pb and56Fe+208Pb collisions. Z-dependent asymmetries around Θincm= 90° preclude their interpretation in terms of compound nucleus fission with the transition state theory. Fits of the data with a simple ansatz for statistical angular momentum fluctuations (tilting) give evidence for an incomplete relaxation of the tilting mode in quasi fission reactions. Recently, there has been much focus on “fusion-fission” angular distributions in heavy systems with unusually large “anisotropies” /1–5/ if compared to expectations based on the transition state theory (TST) and on rotating liquid drop model (RLDM) saddle point shapes. The validity of these expectations for very heavy systems is being questioned /6/ and modifications of the TST /7,8/ are being vividly discussed /9,10/. Deviations from the RLDM expectations are being associated with the onset of quasi-fission reactions /1,3,5,11,12/ occuring whenever complete fusion is suppressed by dynamical entrance channel limitations /13/. We have measured differential cross sections d2 σ/dωdZ as a function of scattering angle Θcm for quasi-fission fragments from50Ti +208Pb collisions at 5.0 and 5.5 MeV/A and56Fe +208Pb collisions at 5.7, 6.1, 6.8, 8.3 MeV/A. The measurements involved an off-line X-ray activation technique /14/ where up to 15 catcher foils representing slices of lab. angles of 5° were measured simultaneously by 15 absolutely calibrated Ge low-energy photon spectrometers. Transformation of the cross sections into the centre of mass system was performed by assuming full momentum transfer and by using the experimental total kinetic energies of Ref./11/. Examples for distributions of d2σ/dΩdZ are given in Fig 1. Qualitatively similar results are obtained at the other bombarding energies and with the56Fe projectile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01415731
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  • 10
    Electronic Resource
    Electronic Resource
    Fragmentation of gold clusters stored in a penning trap (1994)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 8 (1994), S. 401-402 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The collision-induced dissociation of positively charged gold clusters (2-23 atoms) stored in a Penning trap has been studied. After collisions with rare gases, excited clusters predominantly decay by emission of one or two atoms. The loss of two atoms occurs most probably through the emission of a dimer rather than by a sequential evaporation. The minimum kinetic energies of clusters required to induce dissociation exhibit a pronounced odd-even effect. Clusters with an even number of delocalized electrons are more stable than those with an odd number.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290080512
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