The Notre Dame Nuclear Structure Laboratory (NSL) installed its Browne-Buechner spectrograph in the early 1970's for highly accurate energy measurements of nuclear reactions. Current renovation and upgrading of this spectrograph will enable operation of the magnet in a gas-filled mode, in particular for the study of nuclear reactions with low cross-sections of interest in nuclear astrophysics, especially stellar nucleosynthesis. One of the principle issues in measurements of extremely low abundances both by Accelerator Mass Spectrometry (AMS) and nuclear astrophysics, is the discrimination between the nuclei of interest and often very intense isobaric background. Recently the AMS technique of the gas-filled magnet has very successfully been used to overcome this in the study of both environmental noble gas traces (39Ar) and the measurement of cross sections of interest in stellar nucleosynthesis i.e. the 62Ni(n,γ)63Ni reaction.
Initial renovation of the Spectrograph has been completed with the installation of a modern vacuum system. Further to this a LabView based control system is being installed as well as a new detection system (consisting of a Parallel Plate Avalanche Counter (PPAC) and ionisation chamber) under development at Notre Dame in collaboration with Argonne National Laboratory (ANL).
Initial experiments for this system will include the 40Ca(α,γ)44Ti reaction and its role in 44Ti production in astrophysical phenomena, shown to be important through the measurement of 1.157 MeV light from supernovae remnants. Using the gas-filled magnet technique to separate 44Ca and 44Ti isobars, we hope to improve initial measurements of this reaction made at ANL and the Weizmann Institute. This technique will then be used to study the stellar abundance of certain p-process nuclei, which depend on the strength of the (γ,α) photodisintegration process. Experimental data for nuclear reactions involved in p-process networks is extremely scarce forcing a reliance on rate predictions. Data on (α,γ) reactions which are needed to derive the rates of the inverse photodisintegrations are especially lacking. In particular the gas-filled technique is well suited to study the 78Kr(α,γ)82Sr reaction comparing the energy dependence of the cross-section below 10MeV α bombarding energy to Hauser Feshbach predictions.
This presentation will also show the current stage of the renovation, future work required and details of proposed experiments, along with first results of this technique, which compliment the current astrophysical measurements in process at Notre Dame in conjunction with the Joint Institute for Nuclear Astrophysics (JINA), and their development of a new Recoil Mass Separator.
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See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)