Nuclear (Physics) Part-I

Total Questions: 50

11. Source of Energy from the Sun is: [Uttrakhand U.D.A./L.D.A. (Mains) 2006]

Correct Answer: (b) Nuclear fusion
Solution:

The Sun produces energy by the nuclear fusion in its core. Since there is a huge amount of hydrogen in the core, these atoms stick together and fuse into a helium atom. This energy is then radiated out from the core and moves across the solar system.

This is the main source of energy for the Sun and stars. Besides that the gravitational contraction in stars is also the source of their energy.

12. Consider the following statements: In a nuclear reactor, self-sustained chain reaction is possible, because: [I.A.S. (Pre) 2001]

1. More neutrons are released in each of the fission reactions.

2. The neutrons immediately take part in the fission process.

3. The fast neutrons are slowed down by graphite.

4. Every neutron released in the fission reaction initiates further fission.

Which of these statements are correct ?

Correct Answer: (b) 1 and 3
Solution:

Nuclear reactor, formerly known as atomic pile (molecular furnace) uses Uranium - 235 or Plutonium-239 as fuel. When this fissile atomic nucleus absorbs a neutron, it may undergo nuclear fission.

The heavy nucleus splits into two or more lighter nuclei, releasing kinetic energy, gamma radiation, and free neutrons. To reduce the speed of neutrons in this reaction H₂O (light water), D₂O (heavy water), graphite or beryllium oxide are used as the moderator.

This whole process is called self-sustained chain reaction, so statement 1 and 3 are correct.

13. What is a Nuclear Reactor? [U.P.P.C.S. (Pre) 1992]

Correct Answer: (d) Molecular furnace
Solution:

Nuclear reactor, formerly known as atomic pile (molecular furnace) uses Uranium - 235 or Plutonium-239 as fuel. When this fissile atomic nucleus absorbs a neutron, it may undergo nuclear fission.

The heavy nucleus splits into two or more lighter nuclei, releasing kinetic energy, gamma radiation, and free neutrons. To reduce the speed of neutrons in this reaction H₂O (light water), D₂O (heavy water), graphite or beryllium oxide are used as the moderator.

This whole process is called self-sustained chain reaction, so statement 1 and 3 are correct.

14. Which statement is not associated with nuclear fission: [Uttarakhand P.C.S. (Pre) 2016]

Correct Answer: (b) Energy generation in stars.
Solution:

Nuclear fission is a type of reaction in which a heavy atomic nucleus splits into fragments of roughly equal mass releasing huge amount of energy. In contrast, nuclear fusion occurs when two or more smaller atoms fuse together to form a heavier atom releasing large amount of energy.

Neutron induced nuclear reaction, nuclear reactors producing electricity and atom bomb are based on the nuclear fission reactions whereas energy generation in stars is due to nuclear fusion.

15. Consider the following statements about nuclear fusion reactors: [U.P.R.O./A.R.O. (Pre) 2016]

i. They work on the principle of fission of heavy nuclei.

ii. They usually have Tokamak design.

iii. They operate at very high temperature.

Of these

Correct Answer: (c) Only ii and iii are correct
Solution:

Nuclear fusion reactors work on the principle of fusion of two light nuclei. So, statement (i) is incorrect. Nuclear fusion reactions are also called "Thermonuclear reactions' because they operate at very high temperature. Usually, nuclear fusion reactors have Tokamak design.

16. The difference between nuclear reactor and atom bomb is that: [U.P.P.C.S. (Pre) 1999, I.A.S. (Pre) 1995]

Correct Answer: (b) The chain reaction in nuclear reactor is controlled.
Solution:

The chain reaction process used in nuclear reactors and atom bombs both release vast amount of energy, but the manner in which the energy is controlled and utilized is different in both the cases.

In nuclear reactors, the reaction is moderated and controlled for peaceful purpose, while in nuclear bombs the reaction is uncontrolled.

17. With reference to the radioactivity, which of the following statements is/are correct? [U.P.P.C.S. (Pre) 2021, U.P.R.O./A.R.O. (Mains) 2016]

1. Radioactivity is a nuclear property.

2. Hydrogen bomb is prepared on the principle of nuclear fission.

Select the correct answer using the codes given below.

Codes:

Correct Answer: (a) Only 1
Solution:

Radioactivity is a nuclear phenomenon in which an unstable atomic nucleus undergoes a decay. In this process, unstable atomic nucleus loses energy by radiation. It is the process of spontaneous emission of alpha, beta and gamma radiations from the nuclei of an atom.

Hence, statement 1 is correct. Statement 2 is incorrect as hydrogen bomb is prepared on the principle of nuclear fusion in which nuclei of isotopes of hydrogen combine under extremely high temperature to form helium nucleus.

18. With reference to India, consider the following statements: [I.A.S. (Pre) 2022]

1. Monazite is a source of rare earths.

2. Monazite contains thorium.

3. Monazite occurs naturally in the entire Indias coastal sands in India.

4. In India, Government bodies only can process or export monazite.

Which of the statements given above are correct?

Correct Answer: (b) 1, 2 and 4 only
Solution:

Monazite is a complex reddish-brown phosphate of thorium and rare earth minerals [(Ce, La, Nd, Th, Y) PO₄] and this is radioactive in nature. In India, monazite is the principal source of rare earths and thorium.

Monazite bearing economic heavy mineral deposits are found along the coastal and inland placer sands of the country. However, monazite is not found in entire Indian coastal sands.

Atomic Minerals Directorate for Exploration and Research (AMD), a constituent unit of Department of Atomic Energy (DAE) has so far established 12.73 million tonnes (as per 2020 estimates) of monazite contained in 130 deposits in the coastal beach placer sands in parts of Kerala, Tamil Nadu, Odisha, Andhra Pradesh, Maharashtra and Gujarat and in the inland alluvium in parts of Jharkhand, West Bengal and Tamil Nadu.

These deposits have been formed naturally due to littoral action of sea waves coupled with wind action. In India, private firms are restricted from processing or exporting monazite. Monazite is a strategic mineral and cannot be sold in commercial market.

It is a prescribed substance to be handled by the DAE. IREL (Indian Rare Earths Limited), a Government of India Undertaking under the DAE and KMML (The Kerala Minerals and Metals Ltd.), a Kerala State Government Undertaking, are actively engaged in mining and processing of beach sand minerals from placer deposits.

IREL is the only entity processing monazite to produce thorium and rare earth (RE) compounds.

19. The important nuclear fuel available in India in abundance is: [U.P. Lower Sub. (Pre) 2003, R.A.S./R.T.S. (Pre) 1992]

Correct Answer: (b) Thorium
Solution:

India is one country that has an abundance of an important nuclear fuel thorium. According to the Department of Atomic Energy, the resource estimates of monazite (principal source of thorium in India) are at 12.73 million tonnes in 2020.

20. Radioactive element which has been found to have large reserves in India is: [Uttarakhand P.C.S. (Pre) 2006]

Correct Answer: (c) Thorium
Solution:

India is one country that has an abundance of an important nuclear fuel thorium. According to the Department of Atomic Energy, the resource estimates of monazite (principal source of thorium in India) are at 12.73 million tonnes in 2020.