Emission of Scission Neutrons in the Sudden Approximation
نویسنده
چکیده
At a certain finite neck radius during the descent of a fissioning nucleus from the saddle to the scission point, the attractive nuclear forces can no more withstand the repulsive Coulomb forces producing the neck rupture and the sudden absorption of the neck stubs by the fragments. At that moment, the neutrons, although still characterized by their pre-scission wave functions, find themselves in the newly created potential of their interaction with the separated fragments. Their wave functions become wave packets with components in the continuum. The probability to populate such states gives evidently the emission probability of neutrons at scission. In this way, we have studied scission neutrons for the fissioning nucleus U, using two-dimensional realistic nuclear shapes. Both the emission probability and the distribution of the emission points relative to the fission fragments strongly depend on the quantum numbers of the pre-scission state from which the neutron is emitted. In particular it was found that states with Ωπ = 1/2+ dominate the emission. Depending on the assumed preand post-scission configurations and on the emission-barrier height, 30 to 50% of the total scission neutrons are emitted from 1/2+ states. Their emission points are concentrated in the region between the newly separated fragments. The upper limit for the total number of neutrons per scission event is predicted to lie between 0.16 and 1.73 (depending on the computational assumptions). PACS: 24.75.+i, 25.85.Ec keywords: Nuclear fission, scission neutrons, sudden approximation. 1 Corresponding author: [email protected] Preprint submitted to Elsevier 9 February 2008
منابع مشابه
Analysis of the Scission Neutrons by a Time-dependent Approach
In previous papers we studied the properties of the scission neutrons using two approaches: one stationary (the sudden approximation) and one time-dependent. The latter approach involves more complicated calculations but it is more realistic. In the frame of this approach we extend now our calculations to the time evolution of quantities such as: the spatial distribution of the emission points,...
متن کامل5 Analysis of fusion - fission dynamics by pre - scission neutron emission in 58 Ni + 208 Pb
متن کامل
Comparison between cross sections, saddle point and scission point barriers for the 32S+24Mg reaction
One of the principal characteristics of nuclear multifragmentation is the emission of complex fragments of intermediate mass. The statistical multifragmentation model has been used for many years to describe the distribution of these fragments. An extension of the statistical multifragmentation model to include partial widths and lifetimes for emission, interprets the fragmentation process as t...
متن کاملA Comparative Study of the Construction of Positron Emission Tomography/Computed Tomography Facilities in Three South African Hospitals
Introduction: Development of higher energy modalities such as positron emission tomography/computed tomography (PET/CT), has led to more complex shielding problems. This is due to several factors, such as the radiopharmaceutical relatively high-administered activity, high patient throughput, and high energies of 511 kilo-electron volt (keV) positron annihilation photon...
متن کاملII-10 Pastina formation in low density nucleonic matter – a mechanism for ternary fission
Approximately 0.3 % of binary fission decays observed in the spontaneous or thermal neutron induced fission of a heavy nucleus are accompanied by emission of an energetic light particle or fragment in a direction perpendicular to the axis defined by the separating massive fragments. Considerable theoretical and experimental effort has been directed towards understanding this type of ternary fis...
متن کامل