Radioactivity

Question 1

Define nuclear fission.

Answer 1

When large, unstable nuclei split into smaller nuclei, releasing energy in the form of radiation. This normally happens when the nucleus absorbs a neutron.

Question 2

Define nuclear fusion.

Answer 2

Two light nuclei are joined together to form a heavier nucleus. Some of the mass of the nuclei is converted into energy, which is released as radiation.

Question 3

Which process releases the energy in stars?

Answer 3

Nuclear fusion.

Question 4

What causes nuclear fission?

Answer 4

Nuclear fission is triggered when a neutron is absorbed by a nucleus. It can also happen spontaneously, but this is incredibly rare.

Question 5

What does a nucleus release during nuclear fission?

Answer 5

Gamma radiation, two or three neutrons and two identical daughter nuclei are formed. Energy is also released by the reaction. All of the fission products have kinetic energy.

Question 6

How is nuclear fission a chain reaction?

Answer 6

For nuclear fission to occur, a nucleus must absorb a neutron. When a nucleus splits during nuclear fission, alongside forming two identical daughter nuclei, it releases gamma radiation and two or three neutrons. These neutrons go on to be absorbed by other nuclei, which then undergo nuclear fission and repeat this process. This is a continuous chain reaction.

Question 7

Why does fusion produce so much energy?

Answer 7

Some of the mass of the original nuclei is being transferred to energy instead of the new nucleus.

Question 8

What is controlled nuclear fission used for, and why?

Answer 8

Controlled nuclear fission is used to generate electricity in nuclear reactors, as the chain reaction releases a lot of energy very quickly. Controlling this chain reaction allows us to convert the kinetic energy released to electricity.

Question 9

Give two uses of nuclear fission.

Answer 9

Nuclear weapons (uncontrolled)
Generating electricity (controlled)

Question 10

Why would nuclear fusion be beneficial as an alternative energy source?

Answer 10

It produces great amounts of energy quickly. The hydrogen required for it to occur is easy to obtain. But most importantly, it does not produce any radioactive waste.

Question 11

Why can’t nuclear fusion happen on earth?

Answer 11

It can only occur at extreme temperatures and pressures, the likes of which cannot be achieved on Earth. (10 000 000°C)

Question 12

How can we work out the energy released by nuclear fusion?

Answer 12

With Einstein’s E=mc^2 formula.

Question 13

Define an isotope.

Answer 13

Atoms of the same element with the same number of protons and electrons, but different numbers of neutrons.

Question 14

What is radioactive decay? Is it controlled or random?

Answer 14

Radioactive decay is when some isotopes’ nuclei are unstable, so they release forms of radiation to become stable. It is a completely random process.

Question 15

What are the three forms of radiation?

Answer 15

Alpha, Beta, Gamma.

Question 16

What does Alpha radiation consist of?

Answer 16

Alpha particles are two protons and two neutrons - the same as a helium nucleus.

Question 17

What does a beta particle consist of?

Answer 17

A beta oarticle is a single electron ejected from the nucleus at very high speed.

Question 18

How is a beta particle formed?

Answer 18

It is formed when a neutron changes into a proton and an electron.

Question 19

What is gamma radiation?

Answer 19

It is an electromagnetic wave.

Question 20

State the properties of an Alpha particle.

Answer 20

• Large
• Can travel up to 5cm in air before they collide with particles and stop
• Very high ionising power
• Very low penetrative power. Can be stopped by a sheet of paper.

Question 21

State the properties of a Beta particle.

Answer 21

• Can travel up to 15cm in air.
• Quite strongly ionising, but not very.
• Relatively strong penetrative power, stopped by a few millimeters of aluminium.

Question 22

State the properties of Gamma rays.

Answer 22

• Weakly ionising.
• Can travel several metres in air before stopping.
• Highest penetrative power, stopped by a few centimeters of lead.

Question 23

What can each form of radiation be stopped by?

Answer 23

Alpha particles- at sheet of paper.
Beta particles- a few millimeters of aluminium.
Gamma rays - a few centimeters of lead.

Question 24

What is the change to the element’s atomic number and mass number if it decays and releases gamma radiation?

Answer 24

There is no change. They are just an electromagnetic wave.

Question 25

What is the change to an element's atomic number and mass number if it decays and releases a beta particle?

Answer 25

Nothing is added to the mass number as a neutron forms a protons and an electron, so the number of protons and neutrons hasn't changed. However, 1 is added to the atomic number as another proton has been formed.

Question 26

What happens to an element's atomic number and mass number is it decays and releases an alpha particle?

Answer 26

Atomic number - decreases by 2 Mass number - decreases by 4

Question 27

State the two definitions of half-life.

Answer 27

The half-life of a radioactive isotope is the time taken for the number of nuclei of the isotope in a sample to halve. The half-life of a radioactive isotope is also the time taken for the count rate (activity) to fall to half its initial reading.

Question 28

A radioactive isotope has a half-life of 15 days and an initial count rate of 200 counts for second. Determine the count rate after 45 days.

Answer 28

Half-life = 15 days 45 ÷ 15 = 3, so 3 half-lives have been spent. 200 ÷ 2 = 100 100 ÷ 2 = 50 50 ÷ 2 = 25 The count rate will be 25.

Question 29

Why are sources with longer half-lives more dangerous?

Answer 29

A longer half-life will mean that the source will be able to ionise its surroundings for longer, as its activity (count rate) will take much longer to fall.

Question 30

Define contamination.

Answer 30

When unwanted radioactive isotopes end up on other materials.

Question 31

Define irradiation.

Answer 31

Irradiation - when an object is exposed to nuclear radiation.

Question 32

Which type of radiation would be best for sterilising medical tools?

Answer 32

Gamma rays. They have the highest penetrative power, so would kill the most bacteria present on the tool.

Question 33

How are workers kept safe from radiation?

Answer 33

When tools are sterilised, workers are kept safe with lead shields. Radiation monitors will measure how much radiation a person has received, and can tell us if someone has received too much. If this is the case, then that person will stop working with radiation.

Question 34

Why don't objects become radioactive if they are irradiated?

Answer 34

They don't become radioactive if they are irradiated because they only come into contact with the radiation and not the radioactive isotope itself.

Question 35

Why must precautions be taken if people regularly work with radioactive isotopes?

Answer 35

Radioactive isotopes can emit ionising radiation. Ionising radiation increases the risk of cancer in humans, which is highly dangerous. This means that workers must be protected if they regularly work with radioactive substances to prevent the accumulation of ionising radiation in their body over time and by extension the risk of cancer.

Question 36

Which kinds of radiation can penetrate into the body?

Answer 36

Beta and Gamma. Gamma rays are able to pass straight through. Alpha particles are too large, and are blocked by dead cells on the skin's surface.

Question 37

How does ionising radiation cause cancer?

Answer 37

Alpha particles are extremely ionising. This is because they can crash into living cells and damage their DNA - which can cause mutations and, from that, cancer.

Question 38

Give two natural sources of radiation.

Answer 38

- Cosmic rays from space. These are very high-energy particles that trav from space and crash into the Earth's atmosphere. They come from supernovae. - Certain rocks, such as granite, are radioactive.

Question 39

Give two man-made sources of background radiation.

Answer 39

- Fall out from nuclear weapons. - Nuclear accidents.

Question 40

What is used to measure count rate?

Answer 40

A Geiger-Muller tube.

Question 41

How would nuclear radiation be used to explore internal tissue?

Answer 41

They would be able to explore internal organs using a tracer. The patient would swallow the tracer and a radiation monitor would be used to measure how much radiation from the radioactive isotope ingested the afflicted area absorbs. A diagnosis would be produced from this.

Question 42

How would nuclear radiation be used to control or destroy unwanted tissue, e.g. in cancer?

Answer 42

In radiotherapy, certains cancers are destroyed using ionising radiation. Gamma rays are passed through the body and destroy the tumour.

Question 43

What is a disadvantage to radiotherapy?

Answer 43

The gamma rays passed through the patient could also damage healthy tissue. This is amended, however, by the radiation being targeted precisely to the tumour.

Question 45

Explain why some atoms emit radiation.

Answer 45

Most isotopes are unstable, meaning that over time they decay into atoms of other elements to become stable.They emit radiation as this happens.