Dipole-strength distribution below the particle emission threshold in tin-124 and tin-112.

摘要

Dipole-strength distributions around the neutron emission threshold have been measured in 124Sn and 112Sn at the free electron laser facility at Duke University. In total, 103 ground state transitions were observed in 124Sn, and 13 ground state transitions were observed in 112Sn. The use of the 100% linearly polarized gamma-ray beam at the free electron laser allows for very accurate parity measurements. The spin and parity of 22 levels were confirmed, and 57 new parities were assigned in 124Sn. In 124Sn, 22 new levels were observed in 124Sn, and 13 new levels were observed in 112Sn. A method was developed in this thesis to determine the flux of the incident Compton-scattered gamma-ray beam. The procedure was tested using both a well known transition in 11B, and previous 124Sn measurements. The integrated cross section, decay widths, and reduced transitions strengths were calculated for each of the 103 ground state transitions. The summed transitions strength exhausted 0.54% of the energy weighted sum rule in 124Sn, 0.12% of the energy-weighted-sum rule in 112Sn. Energy-averaged absorption cross sections were compared with previous measurements above the neutron separation energy in 124Sn. An examination of the entire energy spectra in 124Sn shows that the strength below 10 MeV has an average energy of 8.25 +/- 0.32 MeV which corresponds to 5.27% of the total strength below 25 MeV. The average properties of this energy region were extracted and compared with predictions from various theoretical models.