2017 Impact factor 2.799
Hadrons and Nuclei
Eur. Phys. J. A 2, 55-60

Alpha particle emission from the 198Pb compound nucleus:
comparison between the fusion-evaporation and the pre-scission channels

E. Vardaci1 - G. La Rana1 - A. Brondi1 - R. Moro1 - A. Principe1 - D. Fabris2 - G. Nebbia2 - G. Viesti2 - M. Cinausero3 - E. Fioretto3 - G. Prete3 - F. Lucarelli4 - E.M. Fiore5 - L. Fiore5 - V. Paticchio5 - P.F. Bortignon6

1 INFN and Dipartimento di Scienze Fisiche dell'Universita' di Napoli, I-80125 Napoli, Italy
2 INFN and Dipartimento di Fisica dell'Universita' di Padova, I-35131 Padova, Italy
3 INFN Laboratori Nazionali di Legnaro, I-35020 Legnaro (Padova), Italy
4 INFN and Dipartimento di Fisica dell'Universita' di Firenze, I-50125 Firenze, Italy
5 INFN and Dipartimento di Fisica dell'Universita' di Bari, I-70126, Italy
6 INFN and Dipartimento di Fisica dell'Universita' di Milano, I-20133, Italy

Received 29 April 1997 / Revised version 10 September 1997 Communicated by D. Schwalm

Abstract
The $\alpha$-particle emission from the 28Si+170Er fusion-evaporation reaction at 165 and 185 MeV has been measured and compared with published data relative to the pre-scission emission in the same reaction. The spectra in the two channels exhibit nearly the same shape in the low energy region, whereas in the high energy region the spectrum for the fusion-evaporation case features a larger apparent temperature. The interpretation of the difference in shape between the two decay channels is based on statistical model calculations which account for the effects due to the different length of the decay chain. Statistical model calculations with standard parameters describe well the gross features of the alpha particle spectra in the fusion-evaporation channel and the proton spectra in the pre-scission channel. On the contrary, the model predictions seem to overestimate by $\simeq$2 MeV the emission barrier for the alpha particles in the pre-fission channel. This effect is ascribed to the larger elongation of the nucleus during the fission process. An average axis ratio b/a$\sim$2 for the emitter is suggested.

PACS
25.70.Gh Compound nucleus - 25.70.Jj Fusion and fusion-fission reactions


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