Nuclear Seminar

Study of the ⁴⁰Ca(a,g)⁴⁴Ti reaction for astrophysics with DRAGON

Dr. Christof Vockenhuber
TRIUMF, Vancouver, Canada

Monday, April 17, 2006   4:00 p.m.   NSH 124
(Refreshments served prior to seminar in NSH 124)

 

⁴⁴Ti with a half-life of 60 years is one of the few short-lived radionuclides which has been detected in space by g-ray astronomy and thus confirm ongoing nucleosynthesis. Since it is produced predominantly in supernovae during the alpha-rich freezeout, its measured abundance can be used to constrain supernova models. The ⁴⁰Ca(a,g)⁴⁴Ti reaction plays a key role in ⁴⁴Ti production. It has been studied partly in the past by prompt g-ray measurements. A recent integral measurement over a larger temperature regime by off-line counting of ⁴⁴Ti nuclei with AMS showed a significantly larger ⁴⁴Ti yield compared to previous results from prompt g-ray measurements.

In order to solve this discrepancy we have studied this reaction at the temperature regime of T₉ ~ 1.5 – 2.5 relevant for supernova nucleosynthesis. The measurement was performed in inverse kinematics at the recoil mass spectrometer DRAGON, located at the ISAC facility at TRIUMF (Vancouver, Canada). High-purity ⁴⁰Ca beam was accelerated to energies of 0.8 – 1.2 MeV/amu impinging on a windowless He gas target surrounded by a high-efficiency BGO g-ray detector array. ⁴⁴Ti recoils are separated from the ⁴⁰Ca beam by the recoil mass spectrometer and identified in an ionization chamber. The advantage of direct detection of ⁴⁴Ti recoils and prompt g rays allows a detailed study of this reaction over a large energy range with sufficient resolution to resolve individual resonances.