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.
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We are grateful to the ALICE staff for providing excellent beams, and to the authors of Ref. 5 as well as Dr. C. Roulet for their help in some measurements. We are indebted to Prof. J.D. Garrett for making available the modified version of the GROGI-2 code used in Copenhagen. We also wish to thank Dr. J. Barrette and Prof. J.M. Alexander for stimulating discussions and critical reading of the manuscript.
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Cabot, C., Gauvin, H., Sergolle, H. et al. Competition between few nucleon emission andγ-ray deexcitation for the reaction systems65Cu+87Rb and40Ar+110Pd. Z Physik A 322, 393–414 (1985). https://doi.org/10.1007/BF01412074
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DOI: https://doi.org/10.1007/BF01412074