Example for Coulomb excitation

The performance of EXOGAM has been calculated for a Coulomb excitation experiment using a beam of neutron-rich Ar. This experiment would aim to study the sudden onset of collectivity for neutron-rich nuclei near the neutron magic number (at least, on or near the stability line) of N = 28. The neutron-rich Ar isotopes such as ⁴⁶Ar are expected to be available at an intensity level of 10⁷ particles per second in the early stages of SPIRAL since the noble gases have favourable diffusion and effusion properties leading to fast and efficient extraction from the ion source. Rate calculations show that with the Cube-B arrangement of 4 segmented detectors it would be possible to perform a spectroscopic study of the first few excited states of these exotic nuclei with the first low intensity beams from SPIRAL. The detector performance was calculated for 662 keV and 1333 keV, with 0.075c, assuming that the scattering angle of the Coulomb excited beam was measured using an ancillary detector to within 3 degrees. Such a measurement is well within the capability of the TIARA array. For the Cube-B and the complete 90 degree 8-detector ring, the respective resolutions are 11.4 keV (7.6 keV) at 662 keV and 22.8 keV (14.9 keV) at 1333 keV respectively. Table 1 indicates that the extra 4 detectors in the 8-detector ring compensate for the extra distance from the target, and hence the same overall efficiency is essentially maintained. However, the 8-detector ring naturally exhibits less Doppler broadening. Hence, the complete ring is likely to be the better choice for Coulomb excitation studies that aim to measure accurately the excitation energies of nuclear levels.