Resumen de Espectroscopía de rayos gamma en haz en la región alrededor del núcleo doblemente mágico 132Sn
This thesis is focussed on the region around the doubly magic nucleus 132Sn (Z=50 and N=82).
The nuclei situated in this region of the nuclear chart are of great interest both for nuclear structure investigations and nuclear astrophysics. By studying these systems, information about the evolution of nucleon-nucleon correlations, quadrupole collectivity and single-particle energies can be obtained. New experimental information allows the test of different nuclear models and examine their validity in this region of the nuclear chart.
In order to study the neutron-rich nuclei located in the vicinity of 132Sn, in April 2015 an experiment was carried out at the Radioactive Isotope Beam Factory at the RIKEN Nishina Center, Japan. The radioactive beam was produced by the in-flight abrasion fission of a primary beam of 238U at 345 MeV/u bombarding a 4-mm-thick beryllium target. The exotic nuclei to be investigated were selected and identified using the BigRIPS in-flight separator. After the selection and identification, the neutron-rich radioactive isotopes were transported to the focal point, F8, where they impinged on two different reaction targets of carbon and gold. Surrounding these targets was the DALI2 spectrometer, which was used to detect the rays emitted by the decay of excited states in several N=82-84, Z 50 isotopes. Finally, the reaction products exited the target and were identified by the ZeroDegree spectrometer.
The reduced transition probability B(E2; 0+1 ! 2+1 ) for the first excited 2+ state of the neutronrich 136Te nucleus, with two protons and two neutrons outside the 132Sn core, was determined via Coulomb excitation in inverse kinematics at intermediate energies. A value of B(E2) = 0.191(26) e2b2 was extracted from measured differential cross sections on gold and carbon targets in order to take into account both the Coulomb and the nuclear excitation contributions.
Our experimental B(E2) value is compared to the previous values from literature and to different theoretical calculations. In addition, 133Sn was studied via the one-neutron knockout from a 134Sn projectile. Besides the known rays emitted from the decay of the single-particle states, additional -ray strength was observed above the neutron separation energy, extending up to about 5.5 MeV. These excited states are interpreted as neutron-hole states that are populated through the removal of a neutron from the closed N=50-82 shell of the 134Sn projectile. The ability of -ray emission to compete with neutron decay is explained taking into account the structure of the initial and final states, and the resultant wave-function overlap. Lastly, experimental inclusive cross sections for the multiple knockout of neutrons and protons were derived from different projectiles at energies around 165 MeV/u. The experimental values have been compared to predictions from state-of-the-art calculations based on a Monte Carlo description of the cascade and evaporation processes obtained with the INCL-ABLA reaction code
