Question

Which of the following is the major reason of a self-sustained chain reaction of U-235 fission?

• A. High instability of U-235 isotope.
• B. High instability of U-236 isotope
• C. A neutron is required to trigger the fission of U-235 and after each fission neutrons are created, which trigger another reaction.
• D. A neutron is required to trigger the fission of U-235 and we continuously bombard the neutron on the fuel sample.

Answer 1

Answer: (B), (C)

The correct options are
B High instability of U-236 isotope
C A neutron is required to trigger the fission of U-235 and after each fission neutrons are created, which trigger another reaction.

Let's understand the meaning of a self-sustained chain reaction. It means that we don't need to supply any ingredient for the reaction to continue in a sample once we have started it.
It's like a good investment in financial terms!! Invest at a right place and then there is a self-sustained income, you just relax after that!!

This is what happens here.

We have already discussed why we bombard a neutron to trigger the nuclear reaction for U-235 fission.

From our previous discussions we also know that in each fission reaction of U-236 certain neutrons are emitted (2 or 3 mostly) the average being 2.4

Now to trigger the second reaction what do we need? Another neutron. Right!!

But we got 2 or 3 neutrons as the product of the first reaction itself. So do we need to supply any more neutrons? No.

These "Product neutrons" will themselves trigger another one. And so on my friend!!

So, you bombarded one neutron, just one and then relax….!!