Question

The phenomenon of nuclear fission can be carried out both in a controlled and in an uncontrolled way. Out of the following, the correct statements vis-avis these phenomena are

• A. the fission energy released per reaction is much more than conventional nuclear reactions and one of the products of the reaction is that very particle which initiates the reaction
• B. it is the "surface to volume" ratio of the sample of nuclear fuel used which determines whether or not the reaction would sustain itself as a "chain reaction"
• C. the "control rods" in a nuclear reactor must be made of a material that absorbs neutrons effectively
• D. the energy released per fission as well as energy released per unit mass of the fuel in nuclear fission are both greater than the corresponding quantities for nuclear fusion

Answer 1

Answer: (A), (B), (C)

the fission energy released per reaction is much more than conventional nuclear reactions and one of the products of the reaction is that very particle which initiates the reaction
the "control rods" in a nuclear reactor must be made of a material that absorbs neutrons effectively
it is the "surface to volume" ratio of the sample of nuclear fuel used which determines whether or not the reaction would sustain itself as a "chain reaction"

Statements (a), (b) and (c) are correct because of following reasons:

$1)$ If nuclear reactions are to be continued, it is necessary that one of the products works for initiating the reaction further.

For example, in the fission ${}^{235}U$, $3$ neutrons are released which cause fission of further three ${}^{235}U$ atoms.

$2)$ There are certain value of surface to volume ratio of the sample of nuclear fuel used which should be satisfied so as the fission can occur.

$3)$ Basically, the fission is continuously carried out due to production of neutrons.

In order to control the reaction, the neutrons should be absorbed.