Radioactivity - Radioactive Substances
From outside the body, beta and gamma radiation are the most harmful to humans.

Radioactivity - Radioactive Substances

This GCSE Physics quiz on radioactivity takes a look at radioactive substances. Radioactive substances emit hazardous particles which can damage the structure of materials and molecules including those in our own bodies. It is released as the nucleus of an unstable atom decays, breaking down into new materials. It only happens to unstable isotopes of element, for example, carbon-12 atoms are stable isotopes and their nuclei never change. Carbon-14 is an unstable isotope and sooner or later, its nucleus will change to a nitrogen-14 nucleus by emitting radiation. Radioactive decay is spontaneous, in other words, it happens at random and for no apparent reason.

As time progresses, the level of radioactivity emitted from a sample will drop as the nuclei of the atoms break down into new, more stable isotopes.

This is measured by the half-life. The half-life is the time taken for the level of radioactivity to drop to half of its original level. The shorter the half life, the more rapidly radioactivity levels will decrease to a safe level. The half life can be followed using a Geiger-Muller tube. Readings of the radiation level are taken at set intervals and can be plotted on a graph. You can then find the time it takes for the level to decrease by one-half from the curve of best fit. The half life of carbon-14 is 5,730 years. In other words, if you started with a sample of carbon that contained 1g of carbon-14 atoms, after 5,730 years, there would be 0.5g left.

Radioactivity can cause a wide range of health issues including cancer and mutations in unborn animals, including humans. Following the dropping of the atomic bomb on the Japanese cities of Hiroshima and Nagasaki, people who were not killed in the blast suffered terrible burns and radiation sickness. One of the first signs of radiation sickness is vomiting, which can start within a few minutes of receiving a deadly dose. Later, other symptoms appear like headaches, hair falling out and diarrhoea. It is therefore important for people handling radioactive materials to use the proper equipment and wear protective clothing to keep them safe.

On the other hand, radioactive materials can be very useful. Radioactive tracers are short half-life isotopes of radioactive elements that are injected into the body so that doctors can find out what needs to be done to treat a patient. Radioactive isotopes can also be used to treat some types of cancer. In industry, radioactive isotopes are used to control the thickness of materials such as paper.

There are three types of radiation - alpha, beta and gamma. Alpha radiation is made up from helium nuclei (two protons and two neutrons). Since these are relatively large, they can be easily stopped by paper, cloth and a few centimetres of air. They are the most dangerous to humans when inside the body as they have no chance of passing through body cells without being absorbed. Beta particles are fast-moving electrons, these can't be stopped using paper or cloth, it requires a thin sheet of metal to absorb them. Inside the body, they are still dangerous but it is possible that some of the beta particles could pass through body cells and escape from the body. Gamma is the highest energy type of radiation, it is an electromagnetic wave and therefore travels at the speed of light. It takes several cm of lead or several metres of concrete to stop it. It is the least harmful inside the body as most of it will pass straight through the cells and out of the body.

If a particle is radioactive and emits electromagnetic waves, what kind of decay is taking place?
Alpha decay
Beta decay
Gamma decay
Water decay
Gamma has the highest energy of all of the waves of the electromagnetic spectrum
Which material found in nature is a naturally-occurring fissile isotope?
Fissile means that the nucleus can be made to split. Uranium-235 is the only naturally-occurring substance that can sustain a chain reaction of nuclear fission
What type of radiation is the most harmful to humans?
They are all dangerous
Inside the body, alpha is the most dangerous as it can't get out of the body and will damage cells. However, outside the body, beta and gamma sources are extremely dangerous as they can penetrate the body
Which of the following instruments can be used to measure the amount of radiation being emitted by a source?
Geiger-Muller tube
A ticker tape timer
A mercury thermometer
An orrery
It is usually connected to some sort of counter to register the intensity of the radiaoctivity
How do we dispose of nuclear waste from our nuclear reactors?
Burn it
Bury it
Freeze it
Feed it to animals
At present we don't have a good way to dispose of nuclear waste so we encase it in a thick layer of concrete and bury it in the ground. This stops the radiation from being harmful to objects near it, however the radiation produced in nuclear reactors has a very long half-life so the material will need to remain buried for a very long time
Which of the following materials is the most-used fuel within nuclear reactors?
There are reactors that use plutonium but the majority of nuclear power stations use uranium
A certain radioactive material emits two protons and two neutrons to become stable. What kind of radiation has been emitted by this material?
An alpha particle is the nucleus of a helium atom
Which of the following conditions could be caused by exposure to radiation?
Hair loss
All of the above
Varying amounts of exposure to different types of radiation can cause a wide range of ailments, with prolonged exposure causing death. This is why it is very important to ensure safety procedures are adhered to when dealing with radioactive substances
Radioactive substances can be harmful to humans. Which of the following materials could be used to block all types of radiation?
Thin sheet of aluminium
A tennis ball strategically placed between the source of radiation and a person
A very thick piece of paper
A very thick piece of lead
In nuclear reactors, lead would be too expensive so they use concrete that is several metres thick
What is emitted from a particle if beta decay occurs?
A helium atom
An electron
A burst of electromagnetic radiation
A small Russian doll
Like alpha radiation, beta can be deflected by electrical and magnetic fields as they are both charged particles
You can find more about this topic by visiting BBC Bitesize - Radioactive decay and half-life

Author:  Martin Moore

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