Radioactive dating methods / Радиоактивные методы датирования

Radioactive dating methods involve radioactive isotopes of various elements and, of the 1400 to 1500 nuclides known presently, more than four-fifths are radioactive although most of them do not occur naturally because of their very rapid rates of radioactive decay. To obtain the ages of rocks and minerals, naturally occurring radioisotopes are used which continued to exist long after the Big Bang because of their extremely slow decay rates. This is the case with 238U, 235U, 232Th, 87Rb and 40K. However, some arise from the decay of long lived, naturally occurring radioactive parents, among them 234U, 230Th and 226Ra. And a few may be created by natural nuclear reactions, for instance 14C (radiocarbon), lOBe and 3H (tritium). While today, artificial radioisotopes have been introduced into the environment by thennonuclear testing and the operation of nuclear fission reactors and particle accelerators. Whatever its source, radioactivity is significant with regard to geochronology and radioactive dating researches really began in an attempt to detennine the age of the Earth. This was not long after Henri Becquerel' s discovery of it in 1896 and the work of Marie Curie who found that thorium and uranium minerals emit radiation and later identified two new elements, polonium and radium. In fact, it is from the latter that the word "radioactivity" derived. So by 1913, it became possible for serious investigations to be made regarding our planet's age, a matter referred to by Arthur Holmes as indelicate, adding that they were in progress anyhow because "Science knows no shame". Subsequently, dramatic developments have taken place and detennining the ages of minerals, rocks, archaeological and historical objects and so on is now routine. The major methods for achieving this are discussed in this chapter of which the main aim is to provide a brief perspective of the subject which is actually vast in scope.  <...>