Question

What is the half-life period?

Answer 1

- Hint: Half-life period is defined as the time period in which a quantity decreases to half of its initial value. This is mainly used in nuclear physics to study more about radioactive decay.

Complete step-by-step solution -

Half-life period is defined as the time period in which a quantity decreases to half of its initial value. It is denoted by $t_{\dfrac { 1 }{ 2 }}$. It is mainly used in studying the age of rocks in the archeology department and also useful in studying radioactive elements decay. Radioactive elements are unstable elements that disintegrate to form other stable elements with emission of radioactive energy in the form of waves.
For example, initially if there are N number of molecules of a radioactive element that decays constantly, the time in which the molecules of the element reduce to $\dfrac { N }{ 2 }$ is known as the half life period of that particular radioactive element. Any radioactive element has its own unique value of half life period.

Additional Information:
The half life period of few unstable isotopes are as follows:
$uranium\quad 238\quad -\quad 4.4\quad \times \quad { 10 }^{ 9\quad }$years
$uranium\quad 235\quad -\quad 7.1\quad \times \quad { 10 }^{ 8\quad }$years
$thorium\quad 229\quad -\quad 7.5\quad \times \quad { 10 }^{ 4\quad }$years
$radium\quad 226\quad -\quad 1624\quad$ years
$francium\quad 223\quad -\quad 22\quad$ minutes

Note: There is a chance of misunderstanding here. You might think that half life period is equal to half of the time required by the element to disintegrate completely. This assumption is wrong because it only happens when the element decays at a constant rate. But, in general the rate of disintegration of an element is directly proportional to quantity of element present at that instant.