Stable Radioactive Isotopes
Radioactive Uranium, Thorium, and Lead form the most stable isotopes having the same atomic numbers but the different atomic numbers or total number protons and neutrons in the nucleus. Most of these radioisotopes emission forming radioactive decay series and uses in nuclear power generation, but some other isotope use in medicine, and agriculture.
Thus isotope of a particular element has the same number of protons but different numbers of neutrons inside the nucleus of an atom.
Radioactive Decay Emission
Emission of alpha rays within the radioactive nucleus loses two units of atomic number and four units of mass number.
Let a radioactive element,
mass number= M
Atomic number = Z
Then the new element,
mass number = (M – 4)
atomic number = (Z – 2)
But the emission of beta rays from the radioactive nucleus increases an atomic number one unit and mass numbers remain unchanged.
Thus when an element ejected beta rays the mass number of the element has the same but atomic number = (Z + 1).
88Ra226 → 88-2Rn226-4 + 2He4(α)
90Th234 → 91Pa234 + 1e0(β)
Examples of Radioactive Decay Series
Uranium is the first discovered radioactive elements. Uranium in the 6th group in the periodic table with atomic number 92 and mass number 238. Since uranium-238 successive decay to form the most stable isotopes of lead-208 is an example of radioactive decay series.
Therefore the mother along with all the daughter elements down to the most stable isotope of lead is the examples of radioactive decay series.
Uranium-238 to Lead-206 Decay Chain
Uranium-238 decay to form the most stable isotope of lead-206. The entire route involves eight alpha and six beta radiation.
All the above decay products of uranium-238 given by (4n +2) where n = mass number of the isotopes.
Uranium 235 to Lead 207 Decay Chain
Uranium-235 isotopes or (4n+3) series starts with uranium – 235 and ends with lead – 207. Thus seven alpha and four beta radiate in the entire route of emission.
Decay of Thorium 232 to Lead 208
Thorium-232 undergoes successive decay to form the most stable radioactive isotopes of lead with mass number 208.
Therefore the entire decay chain of thorium-232 involves six alpha and four beta emission. This is the 4n radioactive decay series.
Group Displacement Law for Radioisotopes
In 1913 Soddy proposed to use the law to describe the position of the radioactive isotopes in the periodic table known as group displacement law. This law state as
- When an alpha particle 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.
He further uses the term isotopes when the product belonging to the same group had identical chemical properties but their radioactivity was different.
Uses of radioactive isotopes
Radioactive isotopes used in many fields like medicine, biology, agriculture, trace analysis. Thus the radioactive isotopes are classified according to their uses.
Uses of Radioisotope Iodine-131
We use radioisotopes iodine-131 for thyroid gland disorder. When we drink a solution of sodium iodide containing sodium-131.
Since the radioisotopes of iodine moves to the thyroid gland. Therefore the radiation or beta emission destroys the malignant cells without affecting the rest of the body.
Uses of Radioisotopes of Cobalt-60
Radioisotopes of cobalt-60 is a good gamma rays emitter. Therefore cobalt-60 is used to inhibit the growth of malignant tissue for the treatment of cancer.
Uses of Radioisotopes of Sodium-24
For the abnormality of the circulation of blood, we use a small amount of a sodium chloride solution contain sodium-24 radioisotopes. Thus sodium chloride solution injected into a vein of the patient.