Neutrons from multifragmentation reactions

TL;DR

This study investigates neutron emission in multifragmentation reactions of Sn and La nuclei at high energies, using advanced detection and modeling to understand neutron multiplicities, source temperature, and nuclear symmetry energy modifications.

Contribution

It provides new insights into neutron production, source characteristics, and the need to modify liquid-drop parameters in hot nuclear environments, with implications for astrophysics.

Findings

Neutron multiplicities reach up to 12 and depend on isotopic composition.

Effective source temperature is approximately 3-4 MeV.

Significant reduction of the symmetry-term coefficient is necessary in models.

Abstract

The neutron emission in the fragmentation of stable and radioactive Sn and La projectiles of 600 MeV per nucleon has been studied with the Large Neutron Detector LAND coupled to the ALADIN forward spectrometer at SIS. A cluster-recognition algorithm is used to identify individual particles within the hit distributions registered with LAND. The obtained momentum distributions are extrapolated over the full phase space occupied by the neutrons from the projectile-spectator source. The mean multiplicities of spectator neutrons reach values of up to 12 and depend strongly on the isotopic composition of the projectile. An effective source temperature of T approx. 3 - 4 MeV is deduced from the transverse momentum distributions. For the interpretation of the data, calculations with the Statistical Multifragmentation Model for a properly chosen ensemble of excited sources were performed. The possible modification of the liquid-drop parameters of the fragment description in the hot environment is studied, and a significant reduction of the symmetry-term coefficient is found necessary to simultaneously reproduce the neutron multiplicities and the mean neutron-to-proton ratios <N>/Z of Z <= 10 fragments. Because of the similarity of the freeze-out conditions with those encountered in supernova scenarios, this is of astrophysical interest.