Abstract
In heavy ion reactions, in the case of N/Z asymmetry between projectile and target, the process leading to complete fusion is expected to produce pre-equilibrium dipole γ -ray emission. It is generated during the charge equilibration process and it is known as Dynamical Dipole. A new measurement of the dynamical dipole emission was performed by studying 16 O + 116 Sn at 12 MeV/u. These data, together with those measured at 8.1 MeV/u and 15.6 MeV/u for the same reaction, provide the dependence on the Dynamical Dipole total emission yield with beam energy and they can be compared with theoretical expectations. The experimental results show a weak increase of the Dynamical Dipole total yield with beam energies and are in agreement with the prediction of a theoretical model based on the Boltzmann–Nordheim–Vlasov (BNV) approach. The measured trend with beam energy does not confirm the rise and fall behavior previously reported for the same fused compound but with a much higher dipole moment.
Highlights
A new measurement of the dynamical dipole emission was performed by studying 16O + 116Sn at 12 MeV/u. These data, together with those measured at 8.1 MeV/u and 15.6 MeV/u for the same reaction, provide the dependence on the Dynamical Dipole total emission yield with beam energy and they can be compared with theoretical expectations
The experimental signature of the Dynamical Dipole (DD) emission is an excess of counts in the energy region of 10-20 MeV with respect to the statistical gamma decay of the giant dipole resonance (GDR), as for example shown in left panel of Figure 1
The analysis of the ‘symmetric’ reaction provides the statistical model and the GDR parameters used to extract the DD total yield from the high-energy gamma-rays spectrum measured in the ‘asymmetric’ reaction, namely 16O + 116Sn = 132Ce* at 12.1 MeV/u
Summary
The experiment was performed in Laboratori Nazionali di Legnaro by using the GARFIELD HECTOR apparatus. The HECTOR array [5] consists of eight large volume (about 14x18 cm) BaF2 crystals for the detection of high-energy rays. The GARFIELD (General ARray for Fragment Identification and for Emitted Light particles in Dissipative collision) array [6] measures light charged particles. It consists of E-E gaseous micro strip and CsI(Tl) scintillation detectors lodged in the same gas volume. The evaporated residues are detected in a wall of 32 PHOSWICH detectors, from FIASCO array [7], placed at forward angles
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