Artificial radioactivity

Artificial radioactivity

Artificial radioactivity or induced radioactivity was discovered by Irene Curie and F. Joliot in 1934. This is also known as man-made radioactivity. The phenomenon by which even light elements are made radioactive by artificial or induced methods is called artificial radioactivity.

Curie and Joliot showed that when lighter elements such as boron and aluminium were bombarded with α-particles, there was a continuous emission of radioactive radiations, even after the α−source had been removed. They showed that the radiation was due to the emission of a particle carrying one unit positive charge with mass equal to that of an electron. This particle is known as positron and the reaction is

₅B¹⁰ + ₂He⁴ → ₇N^13* + ₀n¹

The nitrogen atom is radioactive and decays with a half life of about 10.1 minutes into a stable isotope of carbon with the emission of a positron

₇N^13* → ₆C¹³ + ₁e⁰

In the case of Aluminium,

₁₃Al²⁷ + ₂He⁴ → ₁₅P^30* + ₀n¹

Radio-phosphorous decays into a stable isotope of silicon with the emission of a positron. The half life of radioactive phosphorous is about 3 minutes.

₁₅P^30* → ₁₄Si³⁰ + ₁e⁰

Artificial radioactivity follows the same laws of natural radioactivity. Artificial radioactive elements emit electrons, positrons, neutrons and γ rays.

Production of artificial radio-isotopes

(i) Artificial radio-isotopes are produced by placing the target element in the nuclear reactor, where plenty of neutrons are available.

(1) ₁₅P³¹ + ₀n¹ → ₁₅P^32* + γ,     and       (2) ₁₁Na²³ + ₀n¹ → ₁₁Na^24* + γ

(ii) Another method of production of artificial radio-isotope is to bombard the target element with particles from particle accelerators like cyclotron.

₁₁Na²³ + ₁H² → ₁₁Na^24* + ₁H¹