These are quantities (i.e., things that are measured), not dimensions. There are only seven dimensions: length, mass, time, electric current, thermodynamic temperature, amount of substance and luminous intensity. See page 105 of the International Bureau of Weights and Measures definition of the SI system: http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf (page 13 of the PDF file).
Also, half-life isn't a unit: it's a quantity of dimension time (i.e., it's a thing that's measured in seconds, in the same sense that length is a thing measured in metres). |