Group Displacement Law

Soddy and Fajan summarised the a and b - particle emission in the form of the law known as Group Displacement Law.

"The emission of a - particle by an element results in the formation of a new element which lies two places to the left of the parent element and the emission of b - particle results in the formation of a new element which lies one place to the right of the parent element in the periodic table."

During radioactive emission, the new element formed as a result of b - emission is an isobar of the parent element.

During radioactive emissions, the product formed as a result of the emission of an a - particle followed by the emission of two b - particles is an isotope of the parent element.

In addition to the a, b, g emissions, two other types of decay processes are also observed i.e., b⁺ emission and k - capture.

b⁺ emission

A positively charged beta particle (b⁺) is known as a positron. The emission of a positron (b⁺) results in the decrease of atomic number by one unit. It is now believed that b - emission involves the transformation within the nucleus of a neutron to proton or proton to neutron.

An example of b⁺ emission is

k - capture

In some nuclides, the nucleus may capture an electron from the K - shell. The vacancy created is filled by electrons from higher levels giving rise to characteristic X - rays. This process is known as K - electron capture or simply K - capture. An example of k - capture is

The change in the nucleus is represented as

The neutron produced remains in the nucleus. The atomic number decreases by one unit as a result of K - capture.