The time delays in fission induced by bombardment of W with 180 MeV 32S, 240-255 MeV 48Ti, 330-375 MeV 58Ni, and 390 MeV 74Ge have been measured by observation of crystal blocking. Nearly all results are consistent with exponential decay with lifetimes of order 10-18 s which depend weakly on the atomic number of the composite nucleus. This is inconsistent with the Bohr-Wheeler model of fission from a compound nucleus in statistical equilibrium at each stage in a neutron evaporation cascade and supports a picture of strongly damped quasifission. A simple diffusion model with one-body dissipation reproduces roughly the observed time scale and the exponential decay. It suggests that the outer fission barrier could play a significant role in the observed, very slow decays.
J. U. Andersen, J. Chevallier, J. S. Forster, S. A. Karamian, C. R. Vane, J. R. Beene, et al. (2008). Attosecond time delays in heavy-ion induced fission measured by crystal blocking. PHYSICAL REVIEW. C, NUCLEAR PHYSICS, 78 (2008), 064609-1-064609-17 [10.1103/PhysRevC.78.064609].
Attosecond time delays in heavy-ion induced fission measured by crystal blocking
MALAGUTI, FRANCO;UGUZZONI, ARNALDO
2008
Abstract
The time delays in fission induced by bombardment of W with 180 MeV 32S, 240-255 MeV 48Ti, 330-375 MeV 58Ni, and 390 MeV 74Ge have been measured by observation of crystal blocking. Nearly all results are consistent with exponential decay with lifetimes of order 10-18 s which depend weakly on the atomic number of the composite nucleus. This is inconsistent with the Bohr-Wheeler model of fission from a compound nucleus in statistical equilibrium at each stage in a neutron evaporation cascade and supports a picture of strongly damped quasifission. A simple diffusion model with one-body dissipation reproduces roughly the observed time scale and the exponential decay. It suggests that the outer fission barrier could play a significant role in the observed, very slow decays.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.