Home Science Nuclear Chemistry

Radioactive Isotopes

Nuclear Chemistry

What are radioactive isotopes?

Radioactive isotopes or radioisotopes of a radioactive element are atoms of the same element with different mass numbers. Isotopes of a particular radioactive element have the same number of protons (atomic number) but varying numbers of neutrons inside the nuclei. Isotopes possess identical chemical properties due to their identical electronic configuration. It is formed due to the spontaneous radioactive decay of alpha, beta, gamma particles in form of energy. Radioactive isotopes of lead, uranium, thorium, iodine, sodium, and cobalt are used by researchers in radioactive medicine in radiotherapy, biology, agricultural chemistry, trace chemical analysis, and radioactive nuclear power generation process.

Radioactive isotopes examples

Chlorine-35 and chlorine-37, carbon-12 and carbon-14, oxygen-16 and oxygen-18, hydrogen-1 and hydrogen-2 are the most common examples of isotopes. The radioactive decay series show different isotopes of radioactive elements given below the picture,

Examples of radioactive isotopes or radioisotopes of Lead, Uranium, and Thorium in decay series and uses in medicine

Continuous emission of alpha, beta, and gamma rays from radioactive uranium and thorium formed the most stable non-radioactive isotopes of lead. This process formed the list of radioactive decay series or chain and radioactive isotopes in nuclear physics and chemistry.

Alpha and beta radiation

Alpha decay example

The decay of alpha rays within the radioactive atoms loses two units of atomic number and four units of mass number. For example, if a radioactive isotope having mass number = M and atomic number = Z. Therefore, after the emission of the alpha particle, the atomic and mass number of newborn radioactive isotope = (Z – 2) and (M – 4) respectively.

Emission of beta particle

The emission of a beta particle from the nuclei of the radioactive isotope increases the atomic number by one unit and mass numbers remain unchanged. For example, when an element ejected a beta particle the atomic number of newborn radioisotope = (Z + 1).

Group Displacement Law

In 1913 Soddy define the law of radioactivity to describe the position of the radioactive isotopes or radioisotopes in the periodic table known as group displacement law. This law states, when an alpha particle is emitted in a radioactive decay step, the product displaced two places to the left in the periodic table but the radiation of beta particles results in a displacement of the product to one place to the right.

In the year when Soddy proposes the group displacement law, the knowledge of the atomic structure or electronic orbital configuration was still incomplete. He proposes this law by extensive chemical studies on the disintegration products of different radioisotopes. Soddy coined the term isotopes for such elements as they occupying the same position in the periodic table.

Radioactive decay series

Uranium is the first discovered radioactive f-block elements with an atomic number 92. Since uranium-238 successive decay to form the most stable isotope of lead-208. It is an example of radioactive decay series. Hence the radioactive elements continue to successive disintegration till the daughter elements become a stable non-radioactive isotope of lead. The mother elements along with all the daughter elements are called the radioactive decay series.

Uranium-238 decay series

Unstable uranium-238 decays to form the most stable radioactive isotope of lead-206. The entire route involves eight alpha and six beta emissions. The mass number of all the decay products given by 4n +2 (n = 59 for uranium-238). Therefore, these series are known as 4n +2 series ( n = an integer).

Radioactive isotopes of Uranium 238 Decay Series (4n+2)

Uranium-235 decay series

Radioactive uranium-235 or (4n+3) series start with uranium-235 and ends with lead – 207. Therefore, seven alpha and four beta radiate in the entire route of radioactive emission.

Thorium-232 decay series

Unstable radioactive thorium-232 undergoes successive decay to form the most stable radioactive isotope of lead with mass number 208. Therefore, the entire decay chain of thorium-232 involves six alpha and four beta emissions. This is called the 4n radioactive decay series.

Uses of radioactive isotopes

A list of radioactive isotopes like hydrogen, carbon, oxygen, nitrogen, sodium, cobalt, iodine, sulfur, etc is very much used in different disciples like research, medicine, agriculture, biology, trace analysis, and analytical problems. The uses of radioactive isotopes may be classified into the following types,

  • Uses of radioactive isotopes in medicine
  • Uses of radioisotopes in chemistry
  • Radiocarbon dating
  • Uses of radioisotopes in agriculture

Uses of radioactive isotopes in medicine

Radiation therapy of radioactive isotopes uses mainly as a weapon to kill the affected tissue in the human body in our daily life. It is used mainly in radiotherapy for cancer treatment or used as electromagnetic spectrum radiation in medicine.

Iodine-131 treatment

A radioactive isotope of iodine-131 uses in external radiation therapy for the treatment and diagnosis of thyroid gland disorders in the human body. After drinking a solution of sodium iodide containing iodine-131, the radioactive iodine moves preferentially to the thyroid gland. The beta emission from iodine-131 destroys the malignant cells without affecting the rest of the body.

Uses of cobalt-60

The radioactive cobalt-60 isotope is an example of a gamma emitter with definite wavelengths. It is used in radiation therapy for inhibits the malignant tissue or treatment of cancer in radiation therapy.

Uses of sodium 24

Sodium-24 isotope is used in the abnormality of the blood circulation in the human body. Therefore, the doctor injected the vein of the patient with sodium salt containing sodium-24 isotope.

Phosphorus-32 Used in blood cancer

Phosphorus-32 isotope is used in leukemia therapy or the treatment of blood cancer. Leukemia is the overproduction of white blood cells in the human body.

Radioactive isotopes in chemistry

Radioactive isotopes have played a key role in the evaluation of reaction mechanisms and chemical kinetics in chemistry.

Isotopic labelling examples

  • The mechanism of esterification is easily evaluated by using an oxygen isotope. The process of esterification has two possible mechanisms. First carboxylic acid OH may react with the hydrogen atom of the alcohol to eliminate water. The second alcohol OH reacts carboxylic hydrogen of acid. If the alcohol oxygen is labeled with O-18, then two cases arise, the ester will carry O-18 or the ester does not carry O-18 but water carries O-18 isotope. In reality, both possible mechanisms have been observed.
  • Isotopic labelling of sulfur-35 has been using to establish the non-equivalency of the two sulfur atoms in thiosulfate ion.
  • All the iodine in HgI4 ion is equivalent proved by isotopic labelling of iodine.

Uses of radioisotopes in agriculture

Radioactive isotopes in agriculture are used to determine essential constituents intake from fertilizer and the same constituents from the soil. For example, we were given some superphosphate to the plants labeled with phosphorus-32 (a beta emitter). The plants do not distinguish between radioactive phosphorus from superphosphate and phosphorus from soil. After a certain period of growth, the plants are burnt. The quantity of phosphorus and phosphorus-32 in the ash can be determined by chemical analysis. The fact tells us that the amount of labeled radioactive isotope consumed by the plant.