Progress on the 40Ca(α,)44Ti reaction using DRAGON

Chris OuelletSupervisor: Alan Chen

Experiment leader: Christof Vockenhuber

● Background on the 40Ca(α, )44Ti reaction● 40Ca(α, )44Ti using DRAGON ● Current work ● Future goals

Background on the 40Ca(α, )44Ti reaction

● 44Ti is considered signature of the α -rich freezeout during the expansion phase of a core collapse supernova (D. Arnett, Princeton University Press, 1996)

● The reaction has been agreed as key to production of 44Ti (The et al. ApJ 1998)

● Its half life is very well determined (59.2 ± 0.6 yr) (I. Ahmed, et al. Phys Rev Lett. 1998)

● Detection of its decay in supernova remnants (A.F. Ayudin

et al. Astronomy and Astrophysics 1994) allows for the rare calculation of the absolute total yield of a specific nuclide in a stellar nucleosynthesis event

COMPTEL observed 1.16 MeV -rays from the decay of 44Ti in the young supernova remnant Cas A (1994)

Background (Con't)

● Excess in presolar grains of 44Ca relative to other isotopes indicate significant 44Ti production in supernova (L.R. Nittler, et al. ApJ 1996)

● -ray spectroscopy in the 70's of this reaction determined many of the levels and some resonance strengths (e.g. J.J. Simpson, et al. Phys Rev C 1980)

● These prompt -ray studies only partly cover the energy region of interest

● Direct measurement is favorable

44Ti Energy Levels

● A recent (2000-2005) experiment involved activation of a 4He gas target by 40Ca beam and implantation of the recoils into a solid target

● The yield was then measured using the 44Ti/Ti ratio obtained through AMS (Nic VIII conference proceedings)

40Ca(α, )44Ti using DRAGON

● DRAGON allows detection of both the recoils and the -rays

● First data run end of May 2005 to test beam feasibility

● 44Ti recoils were detected and we measured the charge state distribution of the 40Ca beam

● A modified microwave source with a solid Ca sputter target produces >20 enA with very low 40Ar contamination (<0.5%)

● The accelerator gives DRAGON 40Ca7+ however ED1 is insufficiently powerful to bend the resulting recoils through the separator

● An additional silicone nitride foil was installed post gas target to boost the charge states of the beam

● Windowless gas target (H,He) surrounded by BGO -ray detector array

● Focal plane silicon strip detector or ion chamber for recoil identification

● High beam suppression: typical ratios are 1-100 recoils / 1013 beam ions

Charge State Distributions After Gas

Ion Chamber Schematic

Ion Chamber Singles Spectrum (1127 keV/u)

IC -Coincidence Spectrum

IC -Time of Flight-Coincidence Spectrum

Box projection method

Current Analysis

● Goal is to produce an excitation function

● Check the system by measuring the strong and well-established resonances around 1127 keV/u at various target pressures (1 – 8 Torr)

● The data we've taken covers a range of energies from 850 keV/u to 1150 keV/u

● Tabulate recoils and calculate yields

Preliminary Excitation Function

Preliminary Excitation Function

Summary and Future Goals

● Produced clean 40Ca beam (<0.5% Ar contamination) with sufficient intensity (>20 enA)● Installed CSB to boost the charges states of the recoils, making it acceptable to the spectrometer● Clearly identified 44Ti using the ion chamber, both in coincidence with the BGO array and in TOF through the separator● Covered a large range of energy and have seen resonances● Detailed analysis including -ray spectra is ongoing● Additional beam time is slotted to cover the low energy region● Ti charge state distribution will be measured using stable Ti beam