Half Life in Nuclear Chemistry

Nuclear chemistry is a sub-branch of chemistry. This branch deals with the nuclear processes, radioactivity and nuclear properties. Chemical reactions are the result of the interaction of electrons on the nucleus of an atom while nuclear reactions are different from the traditional chemical reactions and involve the changes in the composition of the nuclei. A nuclear reaction releases enormous amount of energy.

The field of nuclear chemistry was expanded in 1896, when Henri Becquerel discovered that the uranium emitted radiation. Marie Sklodowska Curie turned her focus on studying radioactivity. She propounded the theory that radiation is proportional to the amount of radioactive element present at a give time. She also found out that radiation was a property of an atom. In her lifetime she discovered the two radioactive elements polonium and radium.

In1902, another scientist, Fredrick Soddy, discovered that when a radioactivity occurs; a nuclear reaction changes the nucleus of an atom resulting in the change in the atom. He proposed that all naturally radioactive elements would decay into lighter elements.

Half-Life – Definition

The half-life of a radioactive element is the time required for the element to decay to half of the original amount. For instance, half-life is the time period during which half of the atom of a radioactive element undergoes a nuclear process to be reduced into a lighter element.

Half-Life in Nuclear Chemistry - Half-life Formula

As mentioned above, half-life in Nuclear Chemistry is a decay process of a radioactive element. Each and every radioactive element has its own half-life. For instance, ²³⁸U has a half-life of 4.5billion years. That is, sup>238U would take 4.5 billion years to decay into other lighter elements. Another interesting fact is half-life of ¹⁴C is 5730 years and this is very helpful in geological dating of any archaeological material. You must know, the nuclear half-lives of various radioactive elements would range from tiny fractions of a second to many billion years.

You wouldn't be able to predict when a nucleus of a radioactive element would decay but you can calculate how much of the element would decay over a given period of time.

For instance, if you have 5 grams of a radioactive element, after decaying there would be just half the amount of the original i.e. 2.5 grams. After another half-life, the amount of radioactive element left would be 1.25 gram. Here is a formula to calculate half-life of a nuclear element.

A_E = A_o * 0.5^t/t_1/2

Where
A_E = amount of substance left
A_o = original amount of substance
t = elapsed time
t_1/2 = half-life of the substance

Try this problem out as an example. For instance, if you are given 157 grams of ¹⁴C, how much of ¹⁴C would be left after 2000 years. The half-life of ¹⁴C is 5730 years.

A_E = 157 * .5^2000/5730
Amount of ¹⁴C left after 2000 years would be 123 grams.

Three types of natural radioactive decay include alpha radiation, beta radiation and gamma radiation. An alpha radiation is the emission of two protons and two neutrons. An alpha emission is a positive charge and has a helium nucleus. A beta radiation emits more neutrons than protons and has negative charge. In a gamma radiation, the nucleus emits rays in the gamma part of the spectrum. Another interesting fact is a gamma ray has neither mass nor a charge.

While many radioactive elements decay naturally, you can also stimulate a nuclear reaction artificially. The artificially stimulated nuclear reactions are nuclear fusion and nuclear fission.