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  • 23.20C  (1)
  • 25.70. Jj  (1)
  • 1
    ISSN: 1434-601X
    Keywords: 25.70 ; 21.10M ; 23.20C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theγ ray continuum structures of the transitional Er isotopes withA∼154 are studied using the reaction74Ge(84Kr,xn)158−xEr atE lab=340 MeV. The measurements include energy spectra, total energies, multiplicities, angular distributions and lifetimes using the DSAM method. The analysis of data confirms the previously observed two-bump structure of the continuum radiation. A meticulous subtraction of discrete contributions proves the persistence of the low-energy bump even at high spins, i.e.I〉40ħ. The angular-distribution measurements assign predominant dipole structure to the bump atE γ=0.65 MeV, whereas the bump atE γ=1.3 MeV is of almost pure quadrupole character at high spins. The lifetime measurements give evidence for a strong enhancement of theB(E2) values of the upper bump,B(E2)/B sp〉130. Spin-selection studies reveal, in the spin rangeI=30−50ħ an almost constant energy for the 1.3 MeV bump,ΔE〈60 keV.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-601X
    Keywords: 24.60. Dr ; 25.70. Gh ; 25.70. Jj
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Bothγ-ray and neutron emission have been studied for the reaction systems65Cu(237MeV) +87Rb→152Dy* and40Ar(158MeV)+110Pd→150Gd*. By using a sum spectrometer in coincidence with neutron counters, Ge(Li) or Nal detectors, we have measured the totalγ-ray energy and the average totalγ-multiplicity distributions as well as the neutron spectra for various exit channels. These measurements provide strong evidence for thermal equilibrium in reactions involving a small number of emitted neutrons (i.e.87Rb(65Cu,n or 2n)) at rather high excitation energy (∼54MeV). This statistical emission of only a few neutrons is controlled by very strong y-ray competition: theγ-entry line is found not to be parallel to the yrast line. Instead the energy gap is about 8MeV for J∼27ħ and rises to at least 13MeV for J∼36ħ. There are some indications that the main part of the energy from this gap is removed by statisticalγ-ray cascades. The main features of the experimental data for both entrance channels are well reproduced by statistical model calculations with proper attention to the yrast line position and an adjustement of the dipoleγ-ray normalization coefficient. It is conceivable that the y-ray enhancement that we introduce may be related to a lack of knowledge of the absolute level densities at high energy and spin, or possibly to the presence of new or additional degrees of freedom that may enter into the competition between neutron andγ-ray emission.
    Type of Medium: Electronic Resource
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