i. What do you understand by the term rate of decay and give its mathe

1.	i. What do you understand by the term rate of decay and give its mathematical expression. ii. Why is minus sign required in the expression of decay rate?
Answer» i. Rate of decay of a radioelement denotes the number of nuclei of its atoms which decay in unit time. It is also called activity of radioelement. Rate of decay at any time t can be expressed as follows : Rate of decay (activity) = \(-\frac{dN}{dt}\) Where, dN is the number of nuclei that decay with in time interval dt. ii. Minus sign in the expression indicates that the number of nuclei decreases with time. Therefore, dN is a negative quantity. But, The rate of decay is a positive quantity. The negative sign is introduced in the rate expression to make the rate positive.

i. What do you understand by the term rate of decay and give its mathematical expression. ii. Why is minus sign required in the expression of decay rate?

Answer»

i. Rate of decay of a radioelement denotes the number of nuclei of its atoms which decay in unit time. It is also called activity of radioelement.

Rate of decay at any time t can be expressed as follows :

Rate of decay (activity) = \(-\frac{dN}{dt}\)

Where,

dN is the number of nuclei that decay with in time interval dt.

ii. Minus sign in the expression indicates that the number of nuclei decreases with time.

Therefore,

dN is a negative quantity.

But,

The rate of decay is a positive quantity.

The negative sign is introduced in the rate expression to make the rate positive.