Radioactivity, Uses & Dangers (Edexcel IGCSE Physics (Modular): Unit 2)

There are two sources of alpha radiation in some houses:

• Radon gas in the air

• Solid americium in a smoke alarm

The alpha particles from radon are a greater risk to health then the alpha particles from americium.

Explain why.

The graph shows how the activity of a sample of radon-220 changes with time.

(i) Complete the graph by adding the missing unit for activity.

(1)

(ii) Explain what is meant by the term half-life.

(2)

(iii) Use the graph to find a value for the half-life of radon-220.

(2)

Half-life = .................................................... s

A smoke alarm contains a source of alpha particles and a detector.

The alpha particles reach the detector through a sample of air from the room.

The alarm sounds if there is a sudden drop in the detector reading.

This graph shows changes in the detector reading.

(i) Why is the detector reading never zero?  

(1)

(ii) Why is the detector reading never constant?

(1)

Suggest why fewer alpha particles reach the detector if there is a fire.

A teacher shows his class how to investigate the half-life of a radioactive source.

The readings from the counter need to be corrected for background radiation.

(i) State one source of background radiation.

(1)

(ii) Describe the method the teacher should use to correct for background radiation.

(3)

Every half a minute, the teacher records the count rate. He corrects for background radiation and produces this results table.  

(i) Draw a graph of corrected count rate against time for these results. 

(5)

(ii) Use your graph to estimate the half-life for this material. 

(1)

Half-life = .................................................. minutes

The isotope technetium-99 is a gamma emitter with a half-life of 6 hours. It is used as a radioactive tracer in medicine.

The technetium-99 is injected into a patient’s bloodstream and carried around the body by the blood. The radiation it emits is detected outside the body.

Explain why technetium-99 is suitable for use as a tracer in this way.

The photograph shows an old camera lens that contains several pieces of glass. 

One of the pieces of glass includes a radioactive isotope, thorium-232. 

Thorium-232 undergoes alpha decay and produces an isotope of radium, Ra.  

Complete the equation for this decay. 

The radioactive glass also emits beta particles from a different isotope. The diagram shows the position of the radioactive glass in the camera. 

Amateur astronomers sometimes remove an old camera lens to use as a lens in a homemade telescope.

(i) Suggest why it is safe to use radioactive glass in the camera as shown. 

(1)

(ii) Suggest why an astronomer should not use a lens with radioactive glass close to their eye.  

(2)

A teacher investigates the half-life of a radioactive isotope that decays quickly. 

The teacher measures the background activity.

Explain how this value should be used in the investigation.

Explain what is meant by the term half-life.

The graph shows how the activity of a sample of the radioactive isotope changes with time.

(i) Use the graph to find the half-life of the isotope. 

(2)

Half-life = ................................... s

(ii) The teacher takes a new reading every 20s. Suggest why the teacher measures the activity so frequently. 

(1)

An unstable isotope of strontium has a half-life of 28.8 years.

It is a beta emitter and can be represented by this symbol. 

(i) What is the mass number of this isotope? 

(1)

(ii) Explain the meaning of the term half-life.

(2)

(iii) A person can absorb strontium atoms, which stay in their bones.

Explain why strontium-90 in the bones is a serious health hazard.

(2)

When a strontium-90 nucleus emits a beta particle, it decays to form yttrium-90. 

(i) Complete the equation for this decay. 

(2)

(ii) Yttrium-90 is also an unstable isotope.

Explain why strontium-90 and yttrium-90 can both be described as isotopes, even though they have different numbers of protons. 

(2)

lodine-131 is used to treat thyroid cancer. This radioactive isotope is allowed to enter the tumour.

Explain why iodine-131 is suitable for this treatment. 

The diagram shows a machine which makes aluminium foil.

The machine uses a radioactive source to measure the thickness of the foil.  

The radioactive source emits beta particles. The output from the detector indicates the thickness of the foil.

Explain why beta particles are used, rather than alpha particles or gamma rays.

Carbon-14 has a half-life of 5700 years. A sample of cloth contains 6.0 g of carbon-14.

What mass of carbon-14 will remain in the cloth after 11 400 years?

The graph shows how the activity of tritium in a luminous sign varies with time.

(i) Explain what is meant by the term half-life.

(2)

(ii) Use the graph to estimate the half-life of tritium. Show your working. 

(2)

The manufacturer of the luminous sign claims that the sign will work for more than 20 years. The minimum activity required for the tubes to emit sufficient light is 400 counts per minute.

Evaluate the manufacturer’s claim.

What is meant by the term half-life?

A doctor uses gamma radiation to produce an image of a person's brain.

A radioactive isotope called technetium-99m is used in this process. Technetium-99m emits gamma rays and has a short half-life.

The doctor injects a solution of technetium-99m into the patient. A detector outside the patient received gamma radiation to form the image.

Suggest why isotopes that emit alpha particles or beta particles are not suitable for this use.

Technitium-99m has a half-life of 6 hours. A sample of technitium-99 has an activity of 420 MBq.

(i) Explain why the activity of a radioactive sample reduces with time.

(2)

(ii) Calculate the activity of the technitium-99m sample after 24 hours.

(3) 

Activity = ..............................................MBq

A sample of sodium-24 has an activity of 1400 Bq. The half-life of sodium-24 is 15 hours.

On the axes, sketch a graph to show how the activity of this sample changes over the next 40 hours.

Granite is a rock. It contains a radioactive isotope of uranium that decays very slowly.

(i) Explain how scientists can use this radioactivity to find the age of a piece of granite.

(4)

(ii) Suggest why the age of a piece of granite could not be found using a uranium isotope with a half-life of 15 hours.

(2)

A scientist placed a radioactive source in front of a Geiger-Muller detector and measured the count rate every 20 minutes.

The table shows her data.

The scientist corrects the count rate readings to allow for background radiation.

(i) State two sources of background radiation. 

(2)

(ii) Describe how the scientist should measure the background radiation and correct the count rate readings.

(3)

(i) Plot a graph of the corrected count rate against time and draw the curve of best fit.

(5)

(ii) Use your graph to find the half-life of the radioactive source.

(2)

half-life = ...................................................... minutes

The scientist needs to reduce the risks when working with radioactive sources.

(i) Explain why radioactive sources can be dangerous.

(2)

(ii)  Describe how the risks of working with radioactive sources can be reduced.

(3)