Mole (unit) informal holiday in honor of the unit among chemists. The date is derived from the Avogadro number, which is approximately . It starts at 6:02 a.m. and ends at 6:02 p.m. Alternatively, some chemists celebrate June 2 or February 6, a reference to the 6.02 part of the constant. Mole (unit) The mole is the unit of measurement for amount of substance in the International System of Units (SI). Effective 20 May 2019, the mole is defined as the amount of a chemical substance that contains exactly (Avogadro's constant) constitutive particles, e.g., atoms, molecules, ions or electrons. This definition was
Cross section (physics) of the colliding system are , and , before and after the collision respectively, the differential cross section is given by where the on-shell matrix is defined by in terms of the S-matrix. Here is the Dirac delta function. The computation of the S-matrix is the main goal of the scattering theory. Although the SI unit of total cross sections is m, smaller units are usually used in practice. In nuclear and particle physics, the conventional unit is the barn b, where 1 b = 10 m = 100 fm. Smaller prefixed units such as mb and μb are also