8 Nuclear

Question 1

What is fission and how is it induced in uranium-235?

Answer 1

Fission is the process of splitting the nucleus of an atom into two smaller nuclei, releasing a large amount of energy. Fission is induced in uranium-235 by firing a thermal neutron into the nucleus.

Question 2

What is the critical mass in nuclear reactions?

Answer 2

The critical mass is the minimum amount of fuel required to maintain a steady chain reaction. Using less than the critical mass would lead the reaction to eventually stop.

Question 3

What are the key features of a nuclear reactor?

Answer 3

The key features of a nuclear reactor include a moderator to slow down neutrons released in fission reactions, control rods to absorb neutrons and control the rate of fission reactions, and a coolant to absorb heat and generate steam for electricity production.

Question 4

What is the role of the moderator in a nuclear reactor?

Answer 4

The moderator slows down the neutrons released in fission reactions to thermal speeds through elastic collisions. This is necessary for the neutrons to induce further fission reactions.

Question 5

What is the role of control rods in a nuclear reactor?

Answer 5

Control rods absorb neutrons in the reactor to control chain reactions. They are made of materials that absorb neutrons without undergoing fission, such as boron and cadmium.

Question 6

What is the role of the coolant in a nuclear reactor?

Answer 6

The coolant absorbs the heat released during fission reactions in the core of the reactor. This heat is then used to make steam which powers electricity-generating turbines.

Question 7

What is the fuel used in nuclear reactors called?

Answer 7

Enriched uranium.

Question 8

What does U-238 do in a nuclear reactor?

Answer 8

U-238 absorbs fission neutrons and helps to control the rate of fission reactions.

Question 9

How is enriched uranium formed?

Answer 9

Through the enrichment of mined uranium which consists of around 99% U-238, which does not experience fission in order to increase the percentage of U-235 to around 5%.

Question 10

How are fuel rods inserted into a nuclear reactor?

Answer 10

Remotely to limit worker’s exposure to radiation.

Question 11

What is the purpose of the thick concrete shielding around a nuclear reactor?

Answer 11

To block radiation from escaping from the reactor and affecting the workers in the power station.

Question 12

Why might the shielding become radioactive after long-term use?

Answer 12

Neutrons which escape the reactor may enter the shielding nuclei causing them to become unstable and start experiencing beta-minus decay.

Question 13

What is an emergency shutdown in a nuclear reactor?

Answer 13

When control rods are dropped into the reactor core entirely in order to stop fission reactions from occurring as soon as possible by absorbing all the free neutrons in the core.

Question 14

Why are spent fuel rods dangerous?

Answer 14

Because two daughter nuclei are produced during a fission reaction which are usually extremely unstable and have a very high activity, so need to be disposed of responsibly

Question 15

What is high-level nuclear waste?

Answer 15

Spent fuel rods, which contain long-lived radioactivity.

Question 16

What is low-level nuclear waste?

Answer 16

Waste that contains only short-lived radioactivity, such as tools and gloves.

Question 17

How is low-level nuclear waste disposed of?

Answer 17

Close to the surface as it will not take very long to stop being radioactive.

Question 18

How is high-level nuclear waste disposed of?

Answer 18

placed in cooling ponds for up to a year, any plutonium or usable uranium is removed, vitrified (encased in glass) and placed in thick steel casks, then stored in deep caverns in geologically stable locations.

Question 19

What are the risks and benefits of nuclear power stations?

Answer 19

Nuclear power stations produce no polluting gases, are reliable for power production, and need far less fuel than other power sources. However, they produce radioactive waste and a nuclear meltdown could have catastrophic consequences.

Question 20

How are the risks of nuclear power stations minimized?

Answer 20

Through safety aspects such as remote handling, cooling ponds, vitrification, and deep cavern storage in geologically stable locations.

Question 21

What is the mass defect / mass difference?

Answer 21

The mass defect / mass difference is the difference between the mass of a nucleus and the mass of its nucleons. This difference is converted into energy and released when the nucleons fuse to form a nucleus.

Question 22

What is binding energy of a nucleus?

Answer 22

The binding energy of a nucleus is the energy required to separate the nucleus into its nucleons

Question 23

What is nuclear fission?

Answer 23

Nuclear fission is the splitting of a large nucleus into two daughter nuclei. It occurs in very large, unstable nuclei such as uranium and can occur spontaneously or be induced

Question 24

What is nuclear fusion?

Answer 24

Nuclear fusion is the joining of two smaller nuclei to form a larger nucleus. It occurs in fairly small nuclei and releases more energy than fission, but requires extremely high temperatures to overcome the electrostatic force of repulsion between nuclei.

Question 25

What are the four reasons why a nucleus might become unstable?

Answer 25

• It has too many neutrons
• It has too many protons
• It has too many nucleons
• It has too much energy.

Question 26

How does a nucleus decay through beta-minus emission?

Answer 26

One of the neutrons in the nucleus changes into a proton and a beta-minus particle and antineutrino is released. The nucleon number is constant, while the proton number increases by 1.

Question 27

How does a nucleus decay through beta-plus emission or electron capture?

Answer 27

In beta-plus decay, a proton changes into a neutron and a beta-plus particle and neutrino is released. In electron capture, an orbiting electron is taken in by the nucleus and combined with a proton causing the formation of a neutron and neutrino.

Question 28

What is gamma emission?

Answer 28

Gamma emission is the decay of an excited nucleus that has excess energy

Question 29

What is radioactive decay?

Answer 29

a random process meaning you can’t predict when the next decay will
occur

Question 30

What is radiation?

Answer 30

Radiation is where an unstable nucleus emits energy in the form of EM waves or subatomic particles in order to become more stable.

Question 31

How are the properties of the three types of radiation summarized?

Answer 31

Question 32

How can radiation from a source be identified using a simple experiment?

Answer 32

By using a geiger-muller (GM) tube and counter to measure the count rate of radiation emitted from a source, placing a sheet of paper, aluminum foil, or lead block between the source and GM tube, and observing any significant decrease in count rate to identify the type of radiation being emitted.

Question 33

What are some uses of gamma radiation in medicine?

Answer 33

Gamma radiation is used as a detector, to sterilize surgical equipment, and in radiation therapy to kill cancerous cells. However, there are risks involved and safety measures are put in place to reduce exposure times and use shielding.

Question 34

What did Rutherford’s experiment demonstrate about the atom?

Answer 34

Rutherford’s experiment demonstrated that the atom has a small, dense, positively charged nucleus at its centre.

Question 35

What was the plum pudding model?

Answer 35

states that the atom was made up of a sphere of positive charge, with small areas of negative charge evenly distributed throughout like plums in a plum pudding.

Question 36

What was Rutherford’s experimental setup for the scattering experiment?

Answer 36

Rutherford used an alpha source and a gold foil in an evacuated chamber, covered in a fluorescent coating. He used a microscope to observe the path of the alpha particles around the outside of the chamber.

Question 37

What were the results of Rutherford’s experiment?

Answer 37

most alpha particles passed straight through the foil with no deflection, a small amount of particles were deflected by a large angle, and very few particles were deflected back by more than 90°. This suggested that the atom is mostly empty space, has a small, dense, positively charged nucleus at its centre, and that the centre of the atom is very small and very dense.