Half-life in Nuclear Chemistry

Half-life in Nuclear Chemistry: A Lucid Explanation

The half-life of radioactive elements is an integral part of nuclear chemistry. This time occurs naturally in some of the radioactive elements, while it could be artificially stimulated in some other elements. This article gives a brief introduction to this concept 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 a result of the interaction between 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 element uranium emitted radiation. Marie Skłodowska-Curie turned her focus towards the study of radioactivity. She propounded the theory that radiation is proportional to the amount of radioactive element present at a given time. She also found out that radiation was a property of an atom. In her lifetime, she discovered the two radioactive elements, namely polonium and radium.

In 1902, another scientist, Fredrick Soddy, discovered that when radioactivity occurs, a nuclear reaction changes the nucleus of an atom, resulting in a change in the atom. He proposed that all naturally radioactive elements would decay into lighter elements.

Definition in Nuclear Chemistry

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

Formula

As mentioned above, half-life is a decay process of a radioactive element. Each and every radioactive element has its own value for half-life.

» For instance, 238U has a half-life of 4.5 billion years. That is, 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 grams. Here is a formula to calculate this factor for nuclear elements.

AE = Ao * 0.5t/t1/2

Where,
AE = Amount of substance left
Ao = Original amount of substance
t = Time elapsed
t1/2 = 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 this radioactive element would remain after 2000 years? The half-life of 14C is 5730 years.

AE = 157 × 0.52000/5730
AE = 157 × 0.50.35
AE = 157 × 0.7845
AE = 123.1665 ≈ 123

The amount of 14C left after 2,000 years would be 123 grams.

The three different types of natural radioactive decay include alpha radiation, beta radiation, and gamma radiation.

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

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