The new double energy-velocity spectrometer VERDI
Résumé
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.
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