The term
p-process (
p is for
proton) is used in two ways in the scientific literature concerning the
astrophysical origin of the elements (
nucleosynthesis). Originally it referred to a proton capture process which is the source of certain, naturally occurring, proton-rich
isotopes of the
elements from
selenium to
mercury. These
nuclides are called
p-nuclei and their origin is still not completely understood. Although it was shown that the originally suggested process cannot produce the p-nuclei, later on the term p-process was sometimes used to generally refer to any
nucleosynthesis process supposed to be responsible for the p-nuclei.