Investigating the Phosphorus-30 Proton Capture Reaction in Classical Novae

AbstractAccurate modeling of classical nova nucleosynthesis is fundamentally dependent on thethermonuclear reaction rates of the nuclei involved. In particular, it has been shown thatthe30P(p,γ)31S reaction rate is the largest remaining source of uncertainty in the finalabundances of nuclei created in a classical nova involving an ONe white dwarf. Currently, adirect measurement of the30P(p,γ)31S reaction is not feasible due to the very low cross sectionfor proton capture at astrophysical energies. In addition, a radioactive ion beam of30P isnot available at a sufficient rate for a direct measurement. Previous attempts at constrainingthe30P(p,γ)31S reaction rate have been made using the Hauser-Feshbach statistical approachto calculate the cross section, however, the level density in31S is not sufficiently high forthis approach. A more accurate calculation can be made by assuming the reaction proceedsvia narrow and isolated resonances and employing resonant reaction theory. Considering thecontribution from individual resonance states, the calculation of the30P(p,γ)31S reaction rateat nova temperatures requires knowledge of the spin and parity assignments and resonancestrengths of the levels in31S just above the proton threshold. To obtain the relevant nucleardata, a measurement of the32S(p,d)31S∗reaction has been performed at the Texas A&MCyclotron Institute using a proton beam from the K150 cyclotron and a target consisting ofZnS deposited on a thin carbon backing. The newly commissioned, high-efficiency, particle-gamma array Hyperion was used in a configuration with 12 HPGe clover detectors and adE-E telescope of segmented annular silicon detectors downstream of the target position forthe detection of direct reaction products. In addition, a single silicon detector was placedupstream of the target for the detection of decay protons