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Experimental study of deep-inelastic reactions at forward angles. Possible applications for S3

Iulian Stefan (Institut de Physique Nucléaire d'Orsay, France)

11h00 GANIL seminar room (105)

a coffee will be served 15mn before

 

 

Deep-inelastic collisions (DIC) between complex nuclei were rst observed in the '60s, but only in the '70s the importance of the new reaction mechanism was recognized. These processes acquired the name deep-inelastic, or dumped collisions or multinucleon transfer reactions.
Characteristic features of DIC include: formation of a system which rotates , exchange of nucleons governed by the N/Z equilibration, damping of the relative kinetic energy between the reaction partners, transfer of relatively high angular momentum into intrinsic spin of the reaction products, and, eventually, separation into two fragments which retain the identities of the projectile (quasi-projectile) and target nuclei (quasi-target). During all those processes
evaporation for nucleons can happen to reduce the excitation energy. The maximum of the reaction cross section for products of multi-nucleon transfer moves toward forward angles with the number of nucleons exchanged, not least due to the geometrical focusing. However, it is not clear if the most exotic quasi-projectiles can survive the strong dissipative interaction towards forward angles. No information is available on the survivability of the most exotic species at 0 degrees in part due to the dicult experimental conditions for such measurements, such as beam separation at relatively low beam energy, large charge state distribution and broad transverse momentum distribution of DIC products.

In the present contribution, the production of exotic neutron-rich species in DIC for the reactions induced by 18O beam on a 238U target will be shown and commented. The measurement was performed at GANIL facility using the LISE achromatic spectrometer. The experiment used high intensity (up to 1 eA) 8.5 AMeV beam of 18O8+ impinging on 1 mg/cm2 thick 238U placed in the first object focal point of the Lise spectrometer (D3). Momentum distributions and reaction cross-sections for exotic quasi-projectiles emitted at angles <= 1 degree are compared with prediction by deep inelastic transport (DIT) calculations coupled with evaporation code ( Gemini++). The experimental results over the survivability of the exotic species will be presented.

The issue of predicting the cross section at 0 degrees for exotic nuclei produced in DIC is important in view of the foreseen availability of large acceptance 0 degrees magnetic spectrometers, which are being constructed to use high intensity and intermediary energy beams (5-15 AMeV) such as the S3 facility at GANIL. The selection of DIC exotic products at 0 degrees, could become the only method for in-flight production of secondary beams of neutron-rich
nuclei at low energy.

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