Question

Barn is the unit of nuclear cross section. It is equal to:
A. $${10}^{-20}{\text{m}}^2$$
B. $${10}^{-28}{\text{m}}^2$$
C. $${10}^{-30}{\text{m}}^2$$
D. $${10}^{-14}{\text{m}}^2$$

Answer 1

Hint: Recall the basics of nuclear cross section. We can guess that the unit of nuclear cross section is meter square in the SI system of units as the nuclear cross section refers to the area of the nucleus. Check the actual value of the area of nucleus or value of one barn in the SI system of units.

Complete step by step answer:
We have given that the unit of nuclear cross section is a barn.

The value of 1 barn is equal to $${10}^{-28}{\text{m}}^2$$ which is equal to the approximate area of the nucleus in an atom.
$$1\text{barn}={10}^{-28}{\text{m}}^2$$

So, the correct answer is “Option B”.

Additional Information:
The nuclear cross section of a nucleus gives the information about the probability that a nuclear reaction will occur in the nucleus of an atom.
If the nuclear cross section is more then the probability of the nuclear reaction to occur in the nucleus increases.
The nuclear cross section of a nucleus gives the area of the nucleus.
We know that the radius of the nucleus is $${10}^{-14}\text{m}$$. Therefore, the area of the nucleus should be of the order of $${10}^{-28}{\text{m}}^2$$.

Note:
The students may get confused between the value of one barn or area of nucleus in an atom in the SI system of units and CGS system of units. The value of one barn in the SI system on units is $${10}^{-28}{\text{m}}^2$$ and the value of one barn in the CGS system of units is $${10}^{-24}\text{c}{\text{m}}^2$$. Hence, the students should perfectly keep in mind the value of one barn in different systems of units.