One of the outstanding unsolved riddles of nuclear astrophysics is the origin of the so called “ p-process ” nuclei from A = 92 to 126 .
Both the lighter and heavier p -process nuclei are adequately produced in the neon and oxygen shells of ordinary Type II supernovae , but the origin of these intermediate isotopes , especially ^ { 92 , 94 } Mo and ^ { 96 , 98 } Ru , has long been mysterious .
Here we explore the production of these nuclei in the neutrino-driven wind from a young neutron star .
We consider such early times that the wind still contains a proton excess because the rates for \nu _ { e } and positron captures on neutrons are faster than those for the inverse captures on protons .
Following a suggestion by Fröhlich et al .
( 8 ) , we also include the possibility that , in addition to the protons , \alpha -particles , and heavy seed , a small flux of neutrons is maintained by the reaction p ( \bar { \nu } _ { e } ,e ^ { + } ) n. This flux of neutrons is critical in bridging the long waiting points along the path of the rp -process by ( n , p ) and ( n , \gamma ) reactions .
Using the unmodified ejecta histories from a recent two-dimensional supernova model by Janka , Buras , & Rampp ( 12 ) , we find synthesis of p -rich nuclei up to ^ { 102 } Pd .
However , if the entropy of these ejecta is increased by a factor of two , the synthesis extends to ^ { 120 } Te .
Still larger increases in entropy , that might reflect the role of magnetic fields or vibrational energy input neglected in the hydrodynamical model , result in the production of numerous r - , s - , and p -process nuclei up to A \approx 170 , even in winds that are proton-rich .