Radioactivity

Question 1

In nuclear notation, what is the top number and what is the bottom number?

Answer 1

• Top number is the mass number (no. of protons + no. of neutrons)
• Bottom number is the atomic number which determines the element (no. of protons)

Unless it is an ion, the number of protons will be equal to the number of electrons

Question 2

What does ionisation mean?

Answer 2

The gain or loss of electron(s) in order to form an ion

Question 3

What is an isotope?

Answer 3

An atom with the same number of protons but a different number of neutrons

Isotopes occur naturally, but some are more rare than others

Question 4

Why do some nuclei emit radiation?

Answer 4

• Because they are unstable as they are isotopes which are too big and/or have too many or too few neutrons
• They emit radiation to become more stable

Radioactive decay is a random (unpredictable) process

Question 5

What are the three types of nuclear radiation that can be emitted from unstable nuclei?

Answer 5

• Alpha
• Beta
• Gamma

Question 6

What does an alpha particle released from an unstable nucleus consist of?

Answer 6

Two protons, and two neutrons (+2 charge)

It is the same as a helium nucleus

Question 7

What does a beta particle released from an unstable nucleus consist of?

Answer 7

One electron (-1 charge)

Question 8

What does gamma radiation released from an unstable nucleus consist of?

Answer 8

High energy electromagnetic waves (gamma rays)

Gamma rays have no charge so cannot be affected by electromagnetic fields

Question 9

What is the order of penetrating power between the three types of radiation?

Answer 9

Gamma - High (Stopped by 1m of concrete)
Beta - Medium (Stopped by 1cm of Aluminium)
Alpha - Low (Stopped by paper)

Same goes for range and speed

Question 10

What is the order is ionising ability between the three types of radiation?

Answer 10

Alpha - High
Beta - Medium
Gamma - Low

Because alpha radiation has the highest mass, size charge etv. This obviously ties in with penetrating power too

Question 11

What is the order of mass and size between the three types of radiation?

Answer 11

Alpha - High
Beta - Low
Gamma - N/A

Question 12

When measuring the radioactivity of a source, what property should it have for reliable results?

Answer 12

Long half life

Question 13

What must you take into consideration when measuring the count rate of a source?

Answer 13

The background radiation

Question 14

When is the effect on a nucleus when it emits an alpha particle?

Answer 14

• The mass number decreases by four
• The atomic number decreases by two, so a new element will be formed
• The charge decreases by two

Question 15

What is the effect on a nucleus when it emits a beta particle?

Answer 15

• A neutron is turned into a proton and an electron, the proton is kept and the electron is emitted
• The mass number stays the same, but the atomic number increases by 1, forming a new element
• The charge increases by 1

Question 16

What is the effect on a nucleus when it emits gamma radiation?

Answer 16

There is no effect on the nucleus, however it does become less energetic

Question 17

What are the two devices you can use to measure radiation?

Answer 17

• Geiger-Muller Tube/Detector
• Photographic film

Question 18

What are the natural sources of background radiation?

Answer 18

• Radon gas from radioactive rocks like granite
• Other rocks and soil which emit radiation
• Radioactive cosmic rays from the sun
• Radioactive material in food and drink like potassium-40 in bananas
• Radiation from carbon-14 in all living materials

Question 19

What are the man-made sources of background radiation?

Answer 19

• Medical uses, like x-rays and radiation therapy
• Fallout from nuclear weapon testing
• Nuclear waste and nuclear accidents from power stations

Question 20

What unit is radioactivity measured in?

(The rate at which unstable nuclei decay)

Answer 20

Bequerels (Bq)

Question 21

What happens to the activity of a radioactive source overtime and why?

Answer 21

• It decreases
• This is because each decay reduces the overall number of radioactive particles in the source

Question 22

What is the definition of half life?

Answer 22

The time it takes for the number of nuclei/actvity in a sample of a rdioactive sample to decrease by half

• Half life is different for every isotope because the rate of decay (actvity) is different
• Sources with short half lives tend to have higher activities

Question 23

How does a smoke detector work?

Answer 23

• A source is placed in the detector, usually alpha and with a long half life as it cannot penetrate the casing of the detector and will ionise the air
• There will be a current detector as well
• If smoke enters the detector, the alpha particles will no longer ionise the air as it will be blocked and there will no longer be a current present
• The drop in current will sound the alarm

It might also be done with a radiation detector, and if a drop in count rate is detected due to the blocking smoke, an alarm will sound

Question 24

How can radiation be used to measure thickness of paper/foil in industry?

Answer 24

• Beta should be used, as it will penetrate the paper, but not penetrate everything including the counter
• If the thickness of the paper changes, the count rate changes
• The source should have a long half life to achieve a constant reading

Question 25

How are radioactive sources used in medical tracers?

Answer 25

* A radioactive source will be injected into a patient * A radiation detector can measure the activity of the source when inside the body, finding diagnostics like the location of tumours * It should be gamma so it can penetrate the body and does not ionise, and should have a short half life so the patient suffers little exposure

Question 26

How can radiation be used in radiotherapy?

Answer 26

* Precise beams of gamma radiation are fired at cancerous tumours, while minimising damage to healthy cells * Gamma rays are used as they can penetrate the whole body

Question 27

How can radiation be used to sterilise food and medical equipment?

Answer 27

* The item is irradiated with gamma radiation to kill bacteria * It is gamma so that it penetrates the whole item including its packaging and still kills the bacteria

Question 28

What is contamination?

Answer 28

* The unwanted presence of materials containing radioactive atoms * This will make the material itself radioactive

Question 29

What is irradiation?

Answer 29

* The process of exposing a material to a specific source of radiation * The material itself does not become radioactive, but it can kill living cells on the material

Question 30

What are the dangers of radiation?

Answer 30

* DNA damage/mutation from ionisation, causing cancers and tumours * Cell and tissue damage, like skin burns, white blood cell damage etc.

Question 31

What are the problems with disposing of nuclear waste and how can the risks be reduced?

Answer 31

* The radioactive sources can have a long half life and can contaminate areas around it * They should be buried deep undergroud, sealed by lead or concrete

Question 32

How can you reduce the risk to your health from radiation?

Answer 32

* Store sources in a lead-lined container with shielding * Increase the distance from you and the source by using tongs * Reduce time exposed to the source * Avoid contact with bare skin and wash yourself after being around it * Protective clothing should be worn, like lead-lined apron