Papal tiara papal tiara. For instance, the Rider-Waite tarot deck, currently the widest-circulated deck in existence, depicts "The Hierophant" or pope as wearing a papal tiara and carrying a papal cross. Papal tiara The papal tiara is a crown that was worn by popes of the Catholic Church from as early as the 8th century to the mid-20th. It was last used by Pope Paul VI in 1963 and only at the beginning of his reign. The name "tiara" refers to the entire headpiece, no matter how many crowns, circlets or diadems have adorned it through the ages, while the three-tiered form
Neutron cross section of the order of "π r" or roughly 10 cm (thus justifying the definition of the barn). However, if measured experimentally ( "σ" = "R" / ("Φ N") ), the experimental cross sections vary enormously. As an example, for slow neutrons absorbed by the (n, γ) reaction the cross section in some cases (xenon-135) is as much as 2,650,000 barns, while the cross sections for transmutations by gamma-ray absorption are in the neighborhood of 0.001 barn (See here for more example of cross sections). The "nuclear cross section" is consequently a purely conceptual quantity representing how big the nucleus should