Abstract
VERDI (VElocity foR Direct particle Identification) is a fission-fragment spectrometer recently put into operation at JRC-Geel. It allows measuring the kinetic energy and velocity of both fission fragments simultaneously. The velocity provides information about the pre-neutron mass of each fission fragment when isotropic prompt-neutron emission from the fragments is assumed. The kinetic energy, in combination with the velocity, provides the post-neutron mass. From the difference between pre- and post-neutron masses, the number of neutrons emitted by each fragment can be determined. Multiplicity as a function of fragment mass and total kinetic energy is one important ingredient, essential for understanding the sharing of excitation energy between fission fragments at scission, and may be used to benchmark nuclear de-excitation models. The VERDI spectrometer design is a compromise between geometrical efficiency and mass resolution. The spectrometer consists of an electron detector located close to the target and two arrays of silicon detectors, each located 50 cm away from the target. In the present configuration pre-neutron and post-neutron mass distributions are in good agreement with reference data were obtained. Our latest measurements performed with spontaneously fissioning 252Cf is presented along with the developed calibration procedure to obtain pulse height defect and plasma delay time corrections.
Highlights
In the fission process fragments with a very large distribution in mass, kinetic energy and excitation energy are created
Our latest measurements performed with spontaneously fissioning 252Cf is presented along with the developed calibration procedure to obtain pulse height defect and plasma delay time corrections
How the mass is shared between the nascent fragments is subject to many theoretical models, but none has yet managed to produce a predictive description of good accuracy [2,3,4,5] and very few have even started to consider the influence of excitation energy [6]
Summary
In the fission process fragments with a very large distribution in mass, kinetic energy and excitation energy are created. With the advent of accelerator driven system, fission yield dependence to excitation energy of the fissioning nuclei will become especially important [1]. How the mass is shared between the nascent fragments is subject to many theoretical models, but none has yet managed to produce a predictive description of good accuracy [2,3,4,5] and very few have even started to consider the influence of excitation energy [6]. Neutron multiplicities are directly related to how the excitation energy is shared at scission. Where MCf would be substituted by the mass of the appropriate compound nucleus if not spontaneous fission of 252Cf, as in this case, is studied
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