Topic 5 - Nuclear Fission and Nuclear Fusion

Question 1

What does the mass (nucleon) number of an atom show?

Answer 1

-The total number of protons and neutrons

Question 2

What does the atomic (proton) number of an atom show?

Answer 2

-The number of protons

Question 3

What is an isotope?

Answer 3

-Atoms with the same number of protons in their nucleus but a different number of neutrons

Question 4

In an isotope, are the mass number and the atomic number the same?

Answer 4

• Atomic number=same

- Mass number=different

Question 5

Using carbon-12 and carbon-14 as an example, explain how the radioactivity of an atom differs between different isotopes.

Answer 5

• Most elements have different isotopes but only 1/2 stable (carbon-12)
• Others tend to be radioactive (carbon-14)

Question 6

What happens when an unstable isotope become radioactive?

Answer 6

-Decays into other elements & gives out radiation

Question 7

Where does radioactivity come from?

Answer 7

-Unstable radioactive isotopes undergoing nuclear decay & spitting out high-energy particles or waves

Question 8

What part of the atom does ionising radiation come from?

Answer 8

-Nucleus (when unstable)

Question 9

What are the three types of radiation that can come from a nucleus when it decays (the ionising radiation)?

Answer 9

• Alpha
• Beat
• Gamma

Question 10

Is there a pattern to when an unstable nuclei starts to decay?

Answer 10

• No, it is random

- Nothing can be done to force decay to happen

Question 11

What is meant by ionisation?

Answer 11

-When an atom (with no overall charge) gains or loses an electron to turn it into an ion (with an overall charge)

Question 12

What charge does an alpha particle have and what effect does it have on atoms?

Answer 12

• Strong positive charge
• When an alpha particle passes close to an atom, it pulls a negatively charged electron out of orbit (as like forces attract)

Question 13

What charge does a beta particle have and what effect does it have on atoms?

Answer 13

• Negative charge

- Pushes an electron out of an atom’s orbit (like charges repel)

Question 14

What effect does a gamma particle have on an atom?

Answer 14

• Transfers energy to the electron in atom’s orbit

- If electron gets enough energy, it can break free from atom

Question 15

What is an alpha particle and what is it made up of?

Answer 15

• Helium nuclei

- Two protons and two neutrons

Question 16

How ionising is an alpha particle and why?

Answer 16

• Strongly ionising
• Due to their big mass and charge (also makes them slow)
• Able to remove electrons from lots of atoms creating lots of ions

Question 17

How penetrative is an alpha particle?

Answer 17

-Don’t penetrate far into material and are stopped easily

Question 18

How ionising and how penetrative is a beta particle?

Answer 18

-Moderately ionising and moderately penetrative (quite fast and quite small being an electron)

Question 19

What change goes on in the nucleus when a beta particle is emitted?

Answer 19

-A neutron turns into a proton

Question 20

What is a beta particle?

Answer 20

-Electrons emitted from a nucleus

Question 21

What is gamma radiation?

Answer 21

-Electromagnetic radiation (wave)

Question 22

How ionising and how penetrative is gamma?

Answer 22

• Weakly ionising

- Penetrates a long way

Question 23

What materials block each type of ionising radiation?

Answer 23

• Alpha particles are blocked by paper and cardboard
• Beta particles are blocked by thin aluminium
• Gamma rays are blocked by thick lead

Question 24

What is nuclear fission?

Answer 24

A type of nuclear nuclear reaction that is used to release energy from uranium (or plutonium) atoms (i.e. in a nuclear reactor). Huge amounts of energy can be released in this way through a chain reaction.

Question 25

Explain how nuclear fission works in terms of chain reactions.

Answer 25

• Slow moving neutron fired at isotope uranium-235. Neutron absorbed by nucleus making it unstable and causing it to split
• When U-235 splits, forms 2 new, lighter elements (daughter nuclei) & thermal energy is released
• Can make a large number of new nuclei but are all radioactive as not correct number of neutrons
• Each time uranium atoms slit, spits out 2-3 neutrons which can hit other uranium nuclei, so they split, causing a chain reaction

Question 26

How are nuclear power stations powered?

Answer 26

Nuclear reactors

Question 27

What happens in a nuclear reactor?

Answer 27

-Controlled chain reaction where uranium atoms split up
-Heat energy released by nuclear fission boils water to drive steam turbine, turning generator to generate electrical energy
Nuclear energy->heat energy->kinetic energy->electrical energy

Question 28

How are chain reactions controlled in nuclear reactors?

Answer 28

• Fuel rods placed in a moderator - slow down fast moving electrons, creating steady rate of nuclear fission, where one new neutron produces another fission
• Control rods (often made of boron) limit rate of fission by absorbing excess neutrons. Placed between fuel rods & raised & lowered in reactor to control chain reaction

Question 29

Why must chain reactions be controlled in nuclear reactors?

Answer 29

• If left to continue unchecked, large amounts of energy are released in a short time
• Many new fissions will follow each fission, causing a runaway reaction which could lead to an explosion

Question 30

What is the opposite of nuclear fission?

Answer 30

Nuclear fusion

Question 31

What is nuclear fusion?

Answer 31

• 2 light nuclei collide at high speed & join (fuse) to create a larger nucleus
• Releases lots of energy - all energy released from stars comes from fusion
• Doesn’t leave behind a lot of radioactive waste & plenty of hydrogen to use as fuel so people are trying to use it to make fusion reactors to make electricity

Question 32

What temperature and pressure does fusion work best at and why?

Answer 32

• Very high pressures and temperatures

- Doesn’t happen at low temps/press due to electrostatic repulsion of protons (like charges repel etc)

Question 33

Why is it hard to make the right conditions for nuclear fusion?

Answer 33

• No materials can withstand the temperature as it just gets vaporized so hard & expensive to build
• Have to contain the hot hydrogen in a magnetic field and not a physical container

Question 34

Who claimed to have discovered cold fusion?

Answer 34

-Stanley Pons and Martin Feischmann, 1989

Question 35

Why would cold fusion be so advantageous?

Answer 35

-Could generate lots of energy easily & cheaply