We measured the total capture cross section of the O16(n,γ)O17 reaction, as well as partial cross sections leading to the ground (Jπ=5/2+) and first-excited (Jπ=1/2+) states in O17. The measurement was carried out at average neutron energies of 157, 349, 398, 427, 468, 498, and 556 keV by using pulsed neutrons produced via the Li7(p,n)Be7 reaction and a γ-ray detection system based on an anti-Compton NaI(Tl) spectrometer. We observed the interference effect between the 3/2- resonance state at 4554 keV of O17, corresponding to a neutron energy of 411 keV in the center-of-mass system, and a nonresonant contribution in the capture process. The measured partial cross sections are in good agreement with theoretical calculations obtained taking into account the interference between the 3/2- resonance and a nonresonant p-wave direct radiative capture contribution. Using the present results, together with our previous measurement, we derived the Maxwellian-averaged capture cross sections (MACS) for thermal energies between kT=5 and 100 keV, key quantities for s process nucleosynthesis studies in massive stars.
Nonresonant p -wave direct capture and interference effect observed in the O 16 (n,γ) O 17 reaction
Mengoni A.
2020-01-01
Abstract
We measured the total capture cross section of the O16(n,γ)O17 reaction, as well as partial cross sections leading to the ground (Jπ=5/2+) and first-excited (Jπ=1/2+) states in O17. The measurement was carried out at average neutron energies of 157, 349, 398, 427, 468, 498, and 556 keV by using pulsed neutrons produced via the Li7(p,n)Be7 reaction and a γ-ray detection system based on an anti-Compton NaI(Tl) spectrometer. We observed the interference effect between the 3/2- resonance state at 4554 keV of O17, corresponding to a neutron energy of 411 keV in the center-of-mass system, and a nonresonant contribution in the capture process. The measured partial cross sections are in good agreement with theoretical calculations obtained taking into account the interference between the 3/2- resonance and a nonresonant p-wave direct radiative capture contribution. Using the present results, together with our previous measurement, we derived the Maxwellian-averaged capture cross sections (MACS) for thermal energies between kT=5 and 100 keV, key quantities for s process nucleosynthesis studies in massive stars.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
