Investigating ~(13)C+~(12)C Reaction by the Activation Method. Sensitivity Tests

摘要

We have performed experiments to check the limits of sensitivity of the activation method using the new 3 MV Tandetron accelerator and the low and ultra-low background laboratories of the "Horia Hulubei" National Institute of Physics and Nuclear Engineering (IFIN-HH). We have used the ~(12)C+~(13)C reaction at beam energies E_(lab)= 6, 7 and 8 MeV. The knowledge of this fusion cross section at deep sub-barrier energies is of interest for astrophysical applications, as it provides an upper limit for the fusion cross section of ~(12)C+~(12)C over a wide energy range. A ~(13)C beam with intensities 0.5- 2 particleμA was provided by the accelerator and used to bombard graphite targets, resulting in activation with ~(24)Na from the ~(12)C(~(13)C,p) reaction. The 1369 and 2754 keV gamma-rays from ~(24)Na de-activation were clearly observed in the spectra obtained in two different laboratories used for measurements at low and ultralow background: one at the surface and one located underground in the Unirea salt mine from Slanic Prahova, Romania. In the underground laboratory, for E_(lab)= 6 MeV we have measured an activity of 0.085 ± 0.011 Bq, corresponding to cross sections of 1-3 nb. This demonstrates that it is possible to measure ~(12)C targets irradiated at lower energies for at least 10 times lower cross sections than before. β-γ coincidences will lead us another factor of 10 lower, proving that this installations can be successfully used for nuclear astrophysics measurements.