For example, all carbon atoms have six protons; isotopes of carbon can have 6, 7, or 8 neutrons (Table 1).

Radioactive isotopes (also called , which is an electron, or negatively charged nuclear particle.

radiometric dating isotopes chart-22

Three isotopes of uranium occur in nature: U-238 (99.3% of all U in natural systems), U-235 (0.7%), and U-234 (0.005%).

All of them are naturally-occuring radiogenic isotopes, and (as we have seen above) begin decay chains with geologically long half-lives.

The sample must have originally contained 4 units of parent material, and 25% of the parent material (U-235) remains.

Examination of the curve above shows that time equivalent to two half-lives have passed, or approximately 1.4 billion years.

The Table of Radionuclides documents the naturally-occurring radioisotopes.

Some isotopes decay and immediately produce a stable daughter product.

Results of such studies are most effeective if enough time has passed to let a substantial amount of the daughter product grow (perhaps 10%), and are of limited use if morethan six half-lives have passed (because not enough of the parent material remains to study).

Dating of archaeological samples is commonly conducted using C-14, which has a half-life of 5730 y.

Knowing the value of a specific isotope's half-life, it is possible to determine the age of a geologic or archaeologic sample by evaluating the amount of parent and daughter isotopes in it.