Hello, my name's Dr.

George.

This lesson is called, "Uses of Radiation" and is part of the unit, "Nuclear Physics." The outcome of the lesson is, "I can describe some uses of radiation and how it can be used safely." Here are the key words for this lesson, which I'll explain as they come up.

You can come back to this slide anytime if you need a reminder of the meanings.

The lesson has two parts.

They're called, "Using radiation," and "Using radiation safely." So let's start.

Radioactive materials contain isotopes, particular types of atom that have unstable nuclei.

These nuclei decay over time and release ionising radiation.

That's radiation that can turn atoms into ions by changing the numbers of electrons.

Many radioactive materials occur naturally.

They can be found underground.

But some radioactive materials are produced in nuclear power stations or by nuclear weapons.

Now when an object is exposed to ionising radiation, we say that it's being irradiated.

Here's what that might look like.

Radioactive source emitting ionising radiation and that radiation hitting a non-radioactive object.

The radiation will cause parts of the material to be ionised, which could cause damage, for example, to something like sensitive electronics.

But the exposed material does not become radioactive itself.

So an object doesn't become radioactive by being exposed to radiation.

Irradiation will cause damage to living organisms. And a useful aspect of this is that the bacteria on food can be killed by irradiating the food with gamma radiation.

The irradiated food doesn't become radioactive when this happens, but, because the microbes on it have been killed, it stays fresher for longer.

Now here's a question for you.

True or false? Strawberries that have been irradiated with gamma radiation are radioactive.

And I'd also like you to explain your answer.

Press pause while you do this and press play when you're ready.

And the answer is false.

The strawberries won't be radioactive because the irradiation doesn't introduce radioactive particles into the strawberries.

It doesn't make the nuclei of atoms in the strawberries become unstable.

When radioactive particles are transmitted to an object, then we say the object has been contaminated.

This could happen to a person if they touch a radioactive material.

Small amounts of the material might stick to their skin.

A contaminated object now is radioactive because now it contains, or has on its surface, radioactive particles that will emit radiation.

Some radioactive materials, like the radioactive gas radon, can be breathed in.

Radon gas is an invisible natural gas, which is found in regions that have igneous rock.

It's a dense gas so it sinks, and so it will sink into caves, mines and cellars.

Any underground spaces that it can get into.

Breathing in the gas will cause contamination because there are now radioactive particles inside the person's body and it can cause lung cancer to develop.

Nuclear accidents and nuclear weapons testing have, in the past, produced radioactive fallout, radioactive material that ends up in the atmosphere and then on the ground.

Radioactive fallout contains particles of many radioactive isotopes.

Fallout can contaminate large regions and it can remain for very long periods of time.

The region around the Chernobyl nuclear power plant has been contaminated since an accident happened there in 1986.

The nearby city of Pripyat is still abandoned because it's not safe for people to live there.

Which of the following are examples of radioactive contamination? Press pause while you read these and press play when you've chosen your answers.

A and B are both examples of contamination.

Radon being trapped inside a room means the room has now radioactive particles in it.

And radioactive material in the air spread out by the wind, this is actual radioactive material that's present, so this is contamination.

But in C, beta particles, it's the type of radiation, are absorbed by the wing of an aircraft which is used to detect tiny cracks.

That isn't contamination, that's irradiation.

It doesn't make the aircraft wing radioactive.

And gamma radiation absorbed by cancer cells when it's shone through to kill them, again, that's irradiation.

It's not actually putting radioactive material into the tissue.

Well done if you've picked A and B.

Now onto the different types of radiation.

Gamma radiation is weakly ionising compared to alpha or beta radiation, but it is highly penetrating, so that means it can pass through a human body and most solids.

That doesn't mean that it's safe because if enough gamma radiation passes into your body, that could add up to a lot of ionisation.

To stop, or mostly stop, gamma radiation requires sheets of lead, which is a dense metal or several metres of concrete.

People in hospitals who work with gamma radiation or X-rays, which are also ionising radiation, can wear aprons with thick sheets of lead in them and that protects them.

And when a patient receives an X-ray to part of their body, they may be given a sheet of lead to cover other sensitive parts of their body that aren't being x-rayed.

And often medical staff leave the room during treatment involving gamma rays or x-rays, as another way to protect themselves.

That doesn't mean that it's highly dangerous for a patient to receive an X-ray or gamma ray treatment, but if someone's working with these types of radiation every day, it would add up to a lot of irradiation over time if the worker didn't protect themselves.

The properties of gamma radiation make it very useful.

As we've already seen, it can be used to irradiate food because it can pass through it and reach every part of the food, and it's ionising enough to be able to kill microbes in the food.

And it's microbes that cause food to rot, so food that's been irradiated will last longer.

Gumma radiation can be used in a similar way to irradiate medical equipment, to sterilise it.

Medical equipment, such as a scalpel, can be put into sealed packaging, irradiated with gamma rays, and that destroys the microbes that are on the equipment.

And because no microbes can get into the sealed packaging, the equipment remains sterile, free of microbes, until the packaging is opened when it's needed.

And now a question for you.

Which of the following properties of gamma radiation makes it suitable for the irradiation of food? I'll wait for five seconds, but if you need longer, press pause and press play when you have your answer ready.

And the correct answer is C.

It's the most penetrating of the common types of radiation, so it can get to every part of the food.

Moving on to beta radiation, it's moderately ionising and moderately penetrating.

It can pass through the outer layer of a person's skin so it can get through the dead layer of skin, and into the living tissue.

It can be stopped by a sheet of aluminium and it can only travel a few metres through the air.

A useful property of beta radiation is that it passes through solid materials, but not that easily.

And that means that the amount passing through a solid changes by an amount that could be measured when the properties of the solid change.

I'll show you a way that that can be useful.

It can be used to control the thickness of materials that are produced in sheets like paper or aluminium foil.

The foil passes between rollers and as you can seem, after the rollers, there's a radioactive source of beta radiation on one side of the foil and a detector of beta radiation on the other side.

More beta radiation is detected if the foil is too thin and less is detected if it gets too thick.

The amount of radiation getting through is constantly monitored and the result is sent to the computer that adjusts the pressure between the rollers.

And so the correct thickness of foil can be consistently made.

And now alpha radiation, is strongly ionising and not very penetrating.

It is actually stopped by the outer layer of a person's skin and it can be stopped by just a sheet of paper and only travels a few centimetres in air.

Alpha radiation harms living cells very easily, but only if the radioactive isotope that's emitting the alpha radiation is in contact with the cells.

If it's outside the body, the alpha radiation can't get to living cells.

Alpha radiation also has uses, and one of them is in smoke alarms. Inside a certain type of smoke alarm, there's an alpha source which ionises the air near it.

That enables a current to flow, so there's a small current flowing in the smoke detector all the time.

If smoke gets into the sensor, which it can through holes in the outside of the detector, it will block the alpha particles from ionising the air as much, and that reduces the electric current that can get through.

And the electric circuit is set up so that when the current drops an alarm goes off.

Which type of radiation is used to detect the thickness of thin sheets of a material? And that was beta radiation.

The one that can get through a sheet of say, aluminium foil, but the amount that gets through is significantly affected by the exact thickness of the foil.

Now here's a longer task for you.

Gamma radiation is sometimes used to irradiate food, killing bacteria and making it last longer.

Describe the difference between an object being irradiated and one that's been radioactively contaminated.

And then explain why food that's been irradiated is safe to eat.

But food that's been radioactively contaminated is not.

And finally, can you suggest a reason why some people won't eat irradiated food? Press pause when you write your answers and press play when you're ready and I'll show you some example answers.

Let's take a look at ways you could have answered this.

So the difference between an object being irradiated and one that has radioactive contamination.

You could say something like this.

When it's irradiated, an object is bombarded by radiation.

Atoms in it may be ionised, but it won't become radioactive.

If it's contaminated, some radioactive particles have been transferred to the object.

It's radioactive because it contains these particles.

And now explaining why food that's been irradiated is safe to eat, but food that has radioactive contamination is not.

Irradiated food is not radioactive as it does not contain radioactive particles.

Contaminated food will contain radioactive particles which will emit radiation and may harm you if you eat it or are near to it.

And then finally suggest why some people won't eat irradiated food.

There's different things you could say here.

One example is they may be afraid that the food is contaminated, radioactive, or that somehow the radiation has changed the food to make it unsafe.

Well done if you came up with suitable answers to these.

And now let's move on to the second part of the lesson.

Using radiation safely.

The half-life of a radioactive isotope affects how harmful it could be.

Radioactive isotopes with shorter half lives decay more quickly, and so they have a higher activity.

A larger number of decays per second.

Carbon-15, for example, has a short half-life.

So if you were able to obtain a pure sample of carbon-15, it would have a high activity, although that activity would fall quite quickly over time.

Carbon-14 happens to have a long half life, and so if you obtained a pure sample of that, it would have a low activity, although that low activity would take a long time to fall much further.

If the activity of a sample is greater, then in a given time, more radiation's emitted that can cause damage to living cells that it passes through.

The type of radiation emitted is also relevant to the amount of damage it could cause.

Beta radiation is more ionising than gamma radiation when it passes through living cells and it's the ionisation that leads to cell damage.

Skin can actually stop alpha radiation from entering any living cells, although if an alpha radiation source got into the bloodstream, that would be highly dangerous because that would bring it very close to living cells and it could cause a lot of ionisation.

The amount of radiation exposure is called a radiation dose, and that's a measure of the risk of harm from a person's exposure to radiation.

It takes into account not only the amount of radiation the person's exposed to, but which type it is.

And the unit for radiation dose is the sievert.

Symbol capital S, small V.

But typical doses are usually smaller and measured in millisieverts.

One sievert is a thousand millisieverts.

One millisievert is 0.

001 sieverts, because milli means thousandth, just as it does in millimetre or millilitre.

Radiation exposure to humans is mainly from things that occur naturally or also from procedures used for medical diagnosis or treatment.

Here are some examples of typical doses.

You get a tiny amount of exposure from eating a banana because food is very slightly radioactive.

X-rays are not a type of nuclear radiation, but they are ionising radiation.

So we also measure exposure to X-rays in sieverts.

If you work as a flight attendant, you spend a lot of time at a higher altitude and then you're exposed more to radiation from cosmic rays.

And 2.

4 millisieverts is a typical annual dose that a person will get, although it does depend on where in the world you live because different types of rock under our feet are more or less radioactive.

A CT scan is a type of X-ray scan that gives 3D images and that involves a lot of exposure to X-rays.

And a lethal dose, a dose that's likely to kill a person over a short period, is something in the region of 5,000 to 10,000 millisieverts.

So can you remember what is the unit of radiation dose? And of course it's the sievert.

Now, cancerous cells are living cells that are multiplying too rapidly and they can cause harm to the organisms that they're in.

Cancerous cells can form lumps called tumours.

Radiation can be used to kill cancer cells, but care must be taken to minimise damage to healthy cells around them.

And cancer treatments include radiotherapy and radioactive implants.

I'll explain what those are.

In radiotherapy, beams of x-ray or gamma radiation can be used to kill cancerous cells.

If this person has a brain tumour, for example, here, a single intense radiation beam could be directed towards that tumour, but it would also pass through healthy cells along the way and damage or kill those too.

So what happens instead, is that weak beams of gamma radiation are fired from a range of different angles towards the tumour.

That means that none of the healthy cells get a heavy dose of radiation, but only the tumour does.

So that can destroy the tumour while the healthy cells only get a small dose and survive.

Another way of exposing a tumour to radiation is to use a radioactive implant.

The implant can actually be placed inside the tumour and it contains a source that emits alpha radiation.

Alpha radiation kills the cancer cells around the implant, due to the high level of ionisation that it causes.

But healthy cells further away from the implant are undamaged as alpha particles aren't very penetrating, so cannot reach them.

Why does gamma radiation not kill healthy cells during radiotherapy treatment? The answer, it's not very ionising.

And also, the amount passing through any one cell is not enough to be very harmful.

And now another written task for you.

Radioactive substances are sometimes injected in parts of the body so that the radiation they emit can be detected from outside the body, helping to form detailed images of organs or tissues inside the body.

So there is a device called a gamma camera, and the person's been injected with a radioactive substance, which is sending out gamma rays.

The gamma camera positioned outside the body can detect the gamma rays coming out.

And from the different amounts that penetrate through the body to the outside in different places, images of organs or tissues can be made.

Two questions for you to think about.

Why are radioactive isotopes used that emit only gamma radiation? And why are radioactive isotopes used that have short half lives of just a few minutes? Now, I haven't given you the answers to these questions during this lesson, but you know enough now that you can deduce the answers yourself.

Press pause while you write the answers and press play when you're finished.

So here are the answers, although you don't have to have written yours in exactly the same way.

Why are radioactive isotopes used that emit only gamma radiation? Gamma radiation moves easily through the body so it can be detected on the outside.

It's also not very ionising and will cause much less damage to living cells than alpha or beta radiation.

And why are radioactive isotopes used that have short half lives? If the isotopes decay quickly, a small amount will emit lots of radiation for a short time to form the images.

After a short time, its activity will fall to very low levels, so the risk of harm to living cells quickly goes away.

Well done if you've got the answers to those right.

And now we've reached the end of the lesson.

So here's a summary of it.

Gamma radiation passing through objects irradiates them.

It kills microbes in food but does not make the food radioactive.

Beta radiation is less penetrating than gamma and can be used to control the thickness of materials like paper or aluminium foil during production.

Alpha radiation is least penetrating and is used in smoke alarms. Objects are contaminated if radioactive particles are transferred to them and they become radioactive themselves.

An isotope with a high activity has a short half-life.

Radioactive dose is a measure of the risk from exposure to radiation.

Radioactive isotopes are used in medical diagnoses and treatments.

The risk of use is balanced against the benefits of use.

Well done for working through this lesson.

I hope you found it interesting and useful to know, and I hope to see you again in a future lesson.

Bye for now.