Useful Radiation Notes

8/6/2019 Useful Radiation Notes

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You can use a Geiger counter to show that nuclear

radiation is given off in all directions by something that's

radioactive. Irradiation doesn't make something

radioactive

When nuclear radiation hits something, like an apple, we say the apple has been irradiated.Irradiating things doesn't make them radioactive. The apple may absorb the energy of theradiation, making it a little warmer, but the apple doesn't start giving off nuclear radiation.

Irradiation can be used to kill bacteria in food so it will last longer.

Nuclear radiation can't be increased, decreased or turned

off

Non-nuclear radiation can normally be changed or even turned off.

But whatever we do we cant change how much nuclear radiation a radioactive source givesoff. The only thing we can do is wait.

We can cool it down, heat it up, blow it to bits or dissolve it in acid but we never destroy theatoms themselves so we never change the amount of radioactivity.

We call something that gives off nuclear radiation radioactive. So if something isradioactive we cant turn it off!

Nuclear radiation: difficult to detect, impossible to change

Nuclear radiation cant be seen, heard or felt and we cant do anything to change it. So thereare two major reasons for making sure radioactive substances are carefully controlled.

Without special instruments you cant tell that nuclear radiation is there until you notice theharm it is doing and this might be years later. And you cant change the amount of radiationgiven off so all you can do is keep the radioactive substance in a safe place.

Lesson 2: Alpha, Beta and GammaIntroduction

In this lesson we'll introduce the three most important kinds of nuclear radiation: alpha, betaand gamma. Well see how their different properties affect what they can be used for and inwhat ways they may be harmful.


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What is alpha, beta and gamma radiation?

We're not going to go into details about the exact origins of alpha, beta and gamma radiationin this lesson.

For the moment we'll say that alpha and beta radiation consist of tiny particles, much smallerthan an atom. They move incredibly fast, perhaps thousands ofkilometres per second.

Gamma radiation is a sort of invisible, very high-energy light.

Alpha, beta and gamma are the first three letters of the Greek alphabet. The types of radiationare named in the order that they were discovered.

Americium-241, an alpha source

Americium (pronounced a-meh-rees-ee-um) is a metal. It's radioactive and gives off alpharadiation so we call it an alpha source.

In school experiments we only use a tiny radioactive source the size of a grain of sand. It'snormally enclosed in a steel tube with a wire mesh covering one end. This means you can'ttouch the source directly and the radiation only escapes in one direction. There's often a

prong so you can pick up the source with pliers.

Alpha radiation doesn't go far but is very damaging

Alpha radiation gets stopped by a few centimetres of air or a thin sheet of paper. You maythink that this means alpha radiation is quite weak but in fact the opposite is the case.

Alpha radiation is like a big heavy ball rolled across a lawn. It doesn't go very far because it loses a lotof energy flattening out the bumps in the ground. In other words the heavy ball interacts strongly

with the ground.

This is what alpha radiation does to air. Each alpha particle loses its energy by ripping the airatoms to pieces as it flies past. Eventually it loses all its energy and just stops harmlessly.

The difference between irradiation and contamination

The best way to stay safe is to keep away from an alpha emitter, like americium-241. Youdon't have to be very far, half a metre is fine.

This is easy if the americium is a solid block but if its dissolved in a liquid or crushed intodust then you need to be much more careful. Dust can be blown long distances by the wind.If you inhaled some americium dust then your lung linings could be damaged as the alpharadiation tore up the molecules in your cells.

When radioactive dust lands on something we say that thing has been contaminated.Contamination is about the stuff thats emitting the radiation, like dust or water.Contamination can be a risk over long distances.


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Irradiation is about the radiation itself like alpha, beta or gamma. Radiation cant travel far sois not a risk over long distances.

Alpha particles cause lots of ionization in a short distance

Alpha radiation is up to twenty times more damaging than other kinds because it tears upatoms so much. This tearing up process is called ionization and well see what it means inmore detail later. The torn-up air particles (or ions) have an electric charge so they can be

part of an electric circuit.

Using americium-241 in a smoke detector

One use of americium-241 is in smoke detectors. The alpha particles tear up the neutral airmolecules.

The resulting positive and negative ions can be part of an electric circuit. In normal use thiscircuit is complete.

When there's a fire smoke particles enter the detector. The ions stick to the much biggersmoke particles because charged things are attracted to uncharged things. This breaks thecircuit. A different circuit senses the break and sets off the alarm.

Strontium-90, a beta source

Strontium-90 is a soft, highly reactive metal. It gives off beta radiation.

Beta particles can go through a few metres of air. They can pass through paper and thinaluminium easily but they get stopped by even a thin piece of lead.

Beta goes further than alpha but is less damaging

A beta particle can get through a few metres of air. It's like a golf ball rolled fast along ourgrassy lawn.

The ball jumps and bounces over the ground. You can see its path through the grass but itdoesnt flatten everything like alpha. The beta radiation ball breaks some of the blades ofgrass but most of them spring back unharmed.

We say that beta radiation is not so strongly ionizing as alpha because it doesnt rip atoms to

bits as much as it passes.

Does this mean beta radiation is safer? Yes, it does. Beta is safer than alpha.

Beta radiation will do less harm to a cell as it passes through. But it can reach more cells that

it can harm a bit. Radiation is most harmful if a cell is badly damaged but not killed.

Betas longer range in air means you have to be a few metres away from the radioactivesource in order to be safe. So you can protect yourself from exposure to beta radiation by


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keeping your distance. You could also use a thin lead shield but sometimes this can produceX-rays, which carry their own risk.

It's is much harder to keep your distance if the beta emitter is a dust or carried in water so itcan spread throughout the environment. Again, beta radiation is most dangerous if you breathin or swallow a substance that emits beta radiation. Remember its the radioactive substance

that gets breathed in. You cant breath in radiation.

Using beta particles to measure thickness

Imagine we want to manufacture some thin sheet aluminium. A good way of controlling thethickness is to shine beta radiation through the aluminium and measure how much getsthrough.

The less beta radiation that gets through, the thicker the sheet is.

Beta gauges are very sensitive but the real advantage is that you can measure the aluminium

without having to touch it as it races past. Often the system is computer controlled so therollers are moved automatically to keep the thickness the same.

Tiny beta capsules can be used to treat cancer

The capsules are injected around the cancer and the beta radiation kills the cancer cells.

Radiation is particularly damaging to cells that are in the process of dividing. Cancercells divide much more often than healthy cells. This means cancer cells tend to be killedwhile most of the healthy cells are unharmed.

Gamma radiation is often emitted with alpha and betaGamma radiation is a type of invisible, very high energy light. It's the same type of stuff aslight, infrared, radiowaves and X-rays. These are all types of electromagnetic radiation.

Gamma radiation isn't emitted by itself, only after another event like alpha or beta decay.Normally it's emitted at almost exactly the same time.

Gamma rays can pass through lead but aren't very

damaging

Gamma rays can pass through a thin sheet of lead with very little effect. You need about 10cm of lead to stop most gamma rays completely.

Gamma rays are like a wind blowing over our lawn. It occasionally blows down a blade ofgrass but mostly it just passes through undisturbed.

Gamma rays are weakly ionizing. They can rip an atom to pieces but they dont do it veryoften.


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Gamma radiation spreads out

All radiation spreads out as it gets further from the source. But alpha and beta radiation canbe absorbed by the surroundings quite easily so this spreading is more difficult to see.

Gamma radiation on the other hand passes through most things without really noticing sothe spreading out is much easier to detect.

So gamma radiation tends to pass through your body without interfering with the moleculesthat make up your cells too much. But you need to be quite a long way away from a gammasource in order not to receive much radiation.

One safety precaution is to keep gamma sources in lead containers. Wearing a lead apron alsohelps protect people whose job means they have to handle gamma sources regularly. Sincelead can itself be toxic another metal like titanium can be used instead for clothing.

Gamma rays are commonly used for tracers

Gamma can easily pass through solid materials unlike alpha and beta. If we use a source thatdoesnt give off very much gamma radiation then we can use it as a tracer in theenvironment.

For example, maybe we know an oil pipeline is probably leaking but we dont know where.First of all a gamma emitter is mixed with the oil. The oil carries the emitter to the leak.

The leaking oil mixes in with the earth around the pipe and ends up closer to the ground. Thegamma radiation can pass through the ground and be picked up by the gamma detector so youcan tell where the leak is.

Gamma radiation can sterilize medical equipment

Intense gamma radiation can kill bacteria and other microbes. This makes it useful forsterilizing medical equipment.

The gamma radiation can reach inside even the most complex shapes and it doesn't exposedelicate equipment to high temperatures. There's also no need to rinse off chemicalsafterwards.

Gamma radiation can be used to see inside a patient

In low concentrations gamma radiation is not very damaging to living cells because it tends topass straight through them.

Doctors can use gamma radiation to see inside a patient. But instead of shining gammaradiation at a patient from the outside they inject a gamma emitter into the patient and look atthe radiation that comes out.


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Say the doctor wants to get an image of a tumour in the patients brain. X-rays are no goodbecause X-rays only show bones and denser tissues. She selects a harmless chemical that willtend to accumulate in the brain tumour. Then she reacts the chemical with another chemicalthat emits gamma radiation.

This is called radioactive tagging. A common tag is called technetium-99m.

The tagged chemical is injected into the patients vein. It spreads around the body but tendsto build up in the brain tumour. So the brain tumour gives off gamma radiation.

The doctor then uses a special camera called a gamma camera', which is sensitive to thegamma radiation given off. The image is built up quite slowly because the gamma sourceused is not very bright for improved safety. So it takes a while for the camera to captureenough packets of gamma radiation.

The doctor may takes lots of images of the tumour from different angles. Sophisticatedcomputer software can then build a 3-D image of the tumour. The computer can then displayslices through the tumour. Displaying slices is called tomography.

Gamma radiation can be used as a 'knife'

Gamma radiation can also be used to treat some kinds of cancer. This is called externalradiotherapy because the radioactive source is not injected into the patient.

This machine is called a gamma knife. The gamma rays can pass through hundreds of holesin a lead ring. Its only in the middle of the ring that the gamma radiation is veryconcentrated.

The patient is moved round so that the gamma radiation kills the cancer cells.

Lesson 3: Half-life part 1

Introduction

In this lesson well see that radioactivity tends to decrease over time and that this hasproblems as well as benefits. Well see that for some jobs we want the radioactivity to stopquickly. For others we choose a substance thats radioactive for a long time.

We wont explain the exact meaning of half-life orwhy radioactivity decreases over time just

yet.

Half-life gives you an idea of how long a substance will be

radioactive for

Some substances lose their radioactivity quickly. Some take a long time. Radioactivityalways decreases with time but sometimes it appears to increase because other radioactivesubstances are produced.


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In theory the radioactivity of a source never reaches zero but in practise it does.

The longer the half-life the longer the material will be radioactive for. Well define half-lifemore precisely in lesson 15.

Radioactivity depends on half-life and how big the sample

is

The shorter the half-life the more radioactive a sample of radioactive material will be.

Also the bigger the sample the more radioactive it is. In absolute terms doubling the amountof radioactive material doubles the radioactivity but this is often not what you'd find if youtried to measure it.

The activity above uses a logarthmic scale for time so we

can fit very short and very long times on the same scale.

The most dangerous half-life is a few tens of years

After five half-lives only about 3% of the starting radioactivity will remain. This is 5 days ifthe half-life is 1 day, say, or 10 000 years if the half-life is 2000 years.

You'd think that the longer the half-life the more risk there'd be because it stays radioactivefor so long.

But you have to remember that long half-life means not very radioactive in the first place.

Radioactive materials with a short half-life are very radioactive but stop being radioactive

quite quickly. Those with a long half-life stay radioactive for hundreds or thousands ormillions of years but the radioactivity is low.

The most dangerous radioactive substances have a half-life of a few tens of years. They canbe dangerous in quite small quantities and stay radioactive for more than a human life-time.

Tracers are 'open' sources and have a short half-life

Sometimes radioactive sources are introduced directly into the environment. These are calledopen sources. For example, when used as a gamma tracer for finding leaks in an oil pipelineor when injected into a patient for medical imaging.

Because you dont have too much control over what happens to open sources you want themto have a short half-life. This means they stop emitting radiation quite quickly.

Short half-life means initially very radioactive so small quantities are normally enough to givethe the required amount of radioactivity.


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If you don't want radioactivity to change much you need a

long half-life

When the radioactive material stays in sealed container, we say the it's a 'closed' source. Wehave more control over what happens to a closed source so we dont mind if the half-life is

longer.

We do have to be extremely careful about disposing of closed sources after the machine theyare used in reaches the end of its life.

With ourthickness gauge example we need the half-life to be quite long so that the betaemissions dont change much from day to day. Similarly with the smoke detectorwe choosean alpha emitter that has a long half-life so the detector will work for a long time.

As well as thinking about the type of radiation and half-life, cost and availability are also important

when selecting a radioactive material.

Lesson 4: Background radiation

Introduction

In this short lesson well see that were bombarded with radiation all the time quite naturally this is called background radiation.

Radon gas comes from rocks and soil

Radon gas is an alpha emitter that comes from the radioactive decay of naturally occurringminerals in rocks and soil. The gas seeps out of the ground and is quickly diluted in the air.

Radon in your home depends on where you live and what

your house is like

But radon gas can collect in your home and become much more concentrated. It's in yourhouse thatbreathing in radon gas poses a health risk.

How much radon there is in your house depends on how easily radon can come up throughcracks in the floor and how easily it can escape.

Some rocks produce more radon than others. Granite produces lots of radon. So some partsof the country have naturally higher radon levels than others. But neighbouring houses canhave very different radon levels depending on how easily radon collects in them.

Radon emits alpha particles. Alpha radiation cant penetrate very deep into the body. Butradon is a gas so we can breathe it in. The alpha radiation from radon greatly increases therisk of lung cancer.


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The government sets maximum radon levels before you

ought to do something

If the radon level in your house is too high then the government advises you to reduce it. Youcan do this by sealing the floor to stop radon entering or by installing a fan system to help it to

leave.

Radon is much more dangerous if you smoke

Without any exposure to radon about one person in 200 would be expected to develop lungcancer by the age of 75. If you smoke the risk is TWENTY TIMES greater.

At just above the maximum safe level set by the government about one extra non-smoker in200 would be expected to get lung cancer. But seven extra smokers would get it.

Smoking makes radon exposure much more dangerous.

At six times the government 'action level' only one more non-smoker would get cancer but anadditional THIRTY smokers would get it.

If you dont smoke, radon exposure increases your risk of lung cancer from very low to a bithigher. If you smoke your risk of lung cancer goes from high to very high.

Cosmic rays from space

Cosmic rays consist ofmany different particles as well as gamma rays. Even though lots raindown on the Earth the whole time many of them can pass straight through people without anyeffect.

We only worry about particles that cause ionization in a persons body.

The higher you are the more more cosmic radiation you get. For example by flying or livingat high altitude.

Gamma radiation from rocks and soil

Almost all rocks contain natural radioactive compounds. These compounds emit alpha andbeta radiation. But most of this radiation gets absorbed by the rocks themselves and nevermakes it into the air.

Gamma radiation is often produced at the same time as alpha and beta radiation. Gammaradiation can pass through the rocks and so this is the type that we detect most of.

Bricks, cement and slate are made from stuff that comes from the ground so these also containradioactive compounds. Even though there is lots of natural gamma radiation about most of it

passes straight through people.


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Radiation emitted by the body

Naturally radioactive compounds are found in the air, soil and water. So the food we eat isslightly radioactive. Our bodies are made from the food we eat so we are also a little bitradioactive.

Most of the radioactivity comes from potassium-40 and carbon-14.

Most of this radiation is beta with a tiny amount of alpha so is absorbed in our body.Sometimes gamma rays are also emitted. These pass out of our body.

Nuclear power, weapons testing and Chernobyl

Chernobyl was the site of a nuclear power station in Ukraine where there was a majoraccident in 1986. Even though it was the worst nuclear accident in history its contributions to

background radiation are extremely small. The same is true of all the nuclear weapons tests.

Nuclear power stations if they are properly run add almost nothing to background radiation.

Medical, mainly X-rays

When we go to hospital or the dentist we may have an X-ray. X-rays do not come fromradioactive sources. They are made using a machine. But they can cause ionization which iswhy they are included with background radiation. If you dont have any X-rays or radiationexposure at a hospital then you dont receive any background radiation because of them.

Any X-rays that do escape through the hospital walls are so spread out that they are not animportant contributor to background radiation.

Jobs using radiation

X-rays and radioactive materials are used a lot in medicine. People who work with ionizingradiation receive more radiation than most people. This is carefully controlled by shieldingand keeping track of how much radiation they are exposed to.

A common way to do this is to use a badge with a strip of film. Radiation exposes the film.The film is developed at the end of each month. The darker the film the greater the overallexposure to ionizing radiation.

The government sets limits to the maximum exposure each year. This is typically about tentimes background.

If people who work with ionizing radiation receive so much more radiation why is the slice ofpie very thin? Its because the pie shows an average across the whole population and only asmall proportion of people work with ionizing radiation.


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Its important to realise that background radiation in some parts of the country might be tentimes higher than in other parts. So workers exposed to ionizing radiation dont really receivean unnaturally large amount.

Lesson 5: How radiation harms

Introduction

In this lesson well look at how nuclear radiation can harm us. We'll learn about radiationsickness and cancer risk and how the amount of radiation you're exposed to can be measured.

You only get large doses if something goes badly wrong

You only get large doses of radiation in an accident or nuclear explosion. Huge doses kill somany cells that you die quickly. If the radiation itself doesnt kill you it still makes you veryill. You can catch infections more easily and these can kill you.

Whole body and local doses

A large dose is most dangerous if its spread over your whole body because it damages somany cells. The same dose concentrated in a small area may produce local burns but wontkill you. You wouldnt even notice a small dose but it will increase your risk of gettingcancer in later life.

Radiation damages cells that are dividing

Radiation is most damaging to cells that are dividing rapidly. This is why it kills cancer cellsbut also makes your hair fall out.

Which type of nuclear radiation is most dangerous?

Alpha radiation is most dangerous inside the body because it causes so much ionization in asmall volume. Remember you can't breath in radiation but you can breath in a substance thatemits radiation. If you breath in an alpha emitter, the alpha radiation can damage your lungs.

Outside the body gamma radiation is most dangerous because its difficult to shield, eventhough it causes little ionization when it hits you.

How radiation damages our cells

Radiation harms us because it transfers its energy to our cells, damaging them. The particlesthemselves are not poisonous. Alpha and beta particles give up their energy and then stay inour body like harmless sub-atomic dust.

Gamma radiation disappears when we absorb it. Its energy remains and this can causeelectrons in our cells to move quickly.


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The amounts of energy involved are very small. A teaspoon of boiling water will give you anasty scald.

But the same amount of energy delivered by gamma radiation is enough to kill you. Nuclearradiation is so dangerous because it can damage the most sensitive parts of cells deep in your

body.

What does the energy of a radiation dose depend on?

The harm that radiation does depends on the type of radiation but the amount of energyabsorbed doesn't.

You absorb more energy if you're exposed for longer or if the source is bigger so it emitsmore radiation per second. You'll also absorb more energy the higher the energy of each

particle.

A beta particle is much faster than an alpha of the same

energy

An alpha particle has about 7000 times the mass of a beta particle. This means it needs to begoing much slower to have the same kinetic energy as a beta particle of the same energy.

A gamma ray is a type of high-energy invisible light so it travels at the speed of light. Thehigher the energy of the gamma ray, the shorter its wavelength and the higher its frequency

but its speed doesn't change.

But it's the energy of the particles that's important when working out your energy dose nothow fast they're moving.

The energy of alpha and beta particles

Alpha particles from the same source all have the same energy. In other words they all travelat the same speed. Some sources produce alphas of higher energy than others.

Beta particles from a given source come with a continuous spectrum of energies. Inother words the speed is random, from very low up to a maximum speed that depends on thesource. Different beta sources have different peak energies.

This was a real puzzle for scientists at the start of the twentieth century but was solved by

some brilliant creative thinking by one of the founders of quantum theory, Wolfgang Pauli.

DNA damage with alpha, beta and gamma

If you are exposed to the same energy dose by gamma or beta radiation then they causeroughly the same amount of harm. But this amount of energy delivered by alpha particles can

be up to 20 times more damaging.


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Radiation sickness is certain, cancer is completely random

Radiation sickness happens quickly, often within hours of exposure. Cancer happens manymonths, years or decades after.

There is another important difference. The effects of radiation sickness are certain. Above 3sieverts everyone feels ill. The higher the dose, the worse you feel.

Cancer is not certain: it is random. You can be exposed to a very high dose and not getcancer. The higher the dose the more LIKELY you are to get cancer. But a higher dosedoesnt give you worse cancer.

There are some more controversial ways in which radiation can cause you harm.

Protecting yourself from nuclear radiation: distance,

shielding, time

Weve seen how radiation can harm us. Now lets look briefly at how we can protectourselves from being harmed by radiation.

Unless you are near a serious nuclear accident or a nuclear explosion you will never getradiation sickness. In the extremely unlikely case that you are near one of these events thenthere are some things you can do to reduce your risk.

The first thing to remember is that radiation does not travel far but radioactive dust does. Sokeep indoors away from the dust.

The second is that even gamma rays are stopped to some extent by brick and earth. So stay in

the cellar if you have one.

The third thing is that the most radioactive substances are around for the shortest period oftime. Waiting several days before leaving your house will allow these to stop beingradioactive.

Radioactive iodine and thyroid cancer

A nuclear accident or explosion may produce lots of radioactive iodine which cancontaminate your food and so enter your body. Iodine accumulates in your thyroid gland,which can give you thyroid cancer.

You can fill up your thyroid gland with non-radioactive iodine by taking potassium iodidepills. This will stop your thyroid taking up radioactive iodine because it has already absorbedas much as it can.

Radiation protection for lower doses


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These precautions are for severe accidents only. Most radiation protection is designed forpeople who work with it every day. or example, doctors and patients need to be protectedfrom radiation used in medicine.

The principles are similar: keep your distance, use shielding and limit your time of exposure.

Everyone who might be exposed to radiation as part of their job is monitored carefully tocheck they dont get too much.

Lesson 6: Science and risk

Introduction

In this lesson well look at how scientists investigate how much harm radiation does. Thiswill help us begin to understand something of how science works.

Well look at how scientific discoveries are reported in the media and how people use thisinformation to work out the risk to their own health.

It's unethical to do experiments on people that might

seriously harm them

Scientists often do experiments but its wrong to do experiments on people that will harmthem, such as exposing them to radiation.

So when scientists are investigating radiation and health they have to study people who havebeen exposed anyway. For example, because of the atomic bombs dropped on Hiroshima and

Nagasaki or the Chernobyl nuclear accident. Scientists may also study people who areexposed to radiation as part of their job, like uranium miners and hospital workers.

The Chernobyl accident helped scientists understand more

about radiation and health

Were going to use an imaginary accident which is partly based on the worlds only majornuclear accident, at Chernobyl in 1986.

In this accident operators at a nuclear power station shut down some of the safety systems toconduct tests. They lost control of the reactor and there was a series of conventional (non-

nuclear) explosions.

These spread radioactive fall-out over a large part of Europe and eventually over much of theNorthern Hemisphere.

Science can only answer some types of question

There are some questions that science can answer and some that science cant.


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Science cant answer questions about human values in the same way that you cant use ideasabout football to explain opera. Science CAN tell us whether something is possible, like

building a nuclear reactor but it CANT tell us whether we should do it or not.

The land of scientific knowledge

Imagine science as being like exploring an unknown land.

Around the land is space that is unknowable by science. This space contains questions like:Is there a God? ; How do we get the most out of life?; Is research on animals wrong?.

The scientific land that we want to explore contains answers to questions that can be observedor measured. How old is the universe?, How can we reduce heart disease, How similarare rat and human organs?.

How scientists develop theories

But scientists dont just go round observing and measuring things and thenpulling theoriesout of thin air.

Scientists have developed core theories that they treat as being fact even though they knowthat later theories might replace them. One example would be the idea that everyday stuff ismade up of particles which change their motion because of the forces between them.

Most science involves trying to describe precisely how one or more of these core theoriesapply to what is being studied. For example a chemist might make a new crystal that makes avery pure note when its tapped.

She might try and explain this by describing exactly what the particles are like, theirseparation and how they move. She might use this minor theory to make a prediction that shecan test with an experiment. If the experiment doesnt confirm the prediction shell assumetheres a problem with the details of her particular theory or experiment.

She wont say that this crystal isnt made of particles.

How theories change over time

Core theories can change over time. But scientists are very reluctant to take on a new oneuntil theyre sure its better. The theory that the planets orbited the Sun not the Earth took150 years to develop before it was much better at explaining the night sky.

To be accepted, a new core theory must explain everything the old core could plus muchmore.

What makes a good scientific theory?


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A good scientific theory will suggest what to investigate next, though it takes the imaginationof a scientist to work out the details. A core theory in biology is that DNA controls what our

body does. This leads scientists to look for genes that might cause certain diseases.

Another sign of a good theory is that it predicts the existence of something that has never beenseen. Scientists can then hunt for it.

For example the existence of the neutrino waspredicted 20 years before it was finallydetected.

Scientists increase scientific knowledge by using existing theories to gradually push out theboundaries of the known into the unknown. It takes time for the community of scientists toaccept new research as knowledge.

The scientific community

So what is the scientific community and how does it work to do science?

Most scientists work for universities, government research departments, or companies that usescience to develop new products. A group of scientists may have an idea about a questionthey want to answer.

For example: How has the nuclear accident affected the number of people who get braincancer?

Research grants

Theyll need money to buy equipment and to pay themselves while theyre doing the researchso they apply for a research grant.

Their application explains why the work is new and important and how it relates to what isalready known. It explains what they want to find out, how theyre going to do it, how longthey think it will take and what they will spend the money on.

This is essentially what youre doing when you write a plan for your investigation. You justdont get paid for it.

The university may have a fund of money to award as research grants or the scientists mayapply to a government department, private company or maybe even a charity.

Lets say our scientists get their money. How do they go about planning their research?

Getting valid data

Our scientists want to see whether the number of people with brain cancer after the accident isgreater than before. This type of research is called an epidemiological study.

If their research shows an increase then it will be more convincing if it shows that moreradiation exposure means a bigger risk of cancer.


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It will be even more convincing if they can show that this agrees with other research showing HOW

radiation causes brain cancer. So where are they going to get their data from? Hospital records,

death certificates, newspapers?

Probably the best approach is to look at hospital records but how many do they need to see, all of

them or just a sample? If its just a sample, how big does the sample have to be? You could do lots

of random surveys and take an average but it probably makes more sense just to look at all the

records.

Finding trends

So our scientists are going to look at all the tens of thousands of hospital records. But howmany years do they need to look at? The problem is that the incidence of brain cancerchanges every year. This is called scatter.

They have to use a branch of mathematics called statistics to see if they can spot any trends.One technique is to use a moving average to flatten out the scatter.

Say our data showed that the rate suddenly increased in 1990, four years after the accident.

Confounding factors

As well as removing scatter, scientists need to check that the incidence of cancer wasntchanging anyway. The number of brain cancer cases might be changing for lots of differentreasons. These are called confounding factors.

It might be that the number of cases is rising or it might just be that the hospital is gettingbetter at detecting them. Perhaps a new technique for detecting brain cancer has been

discovered, which would tend to show an increase in cases. Or maybe there was less moneyso fewer cases were being diagnosed, which would show up as a decrease.

Lets assume that our scientists manage to adjust the data for all these effects and are sure thatthere HAS been an increase in brain cancer.

Drawing conclusions

How do they know that this increase was caused by radiation from the nuclear accident?

Remember that the problem with cancer caused by radiation is that it looks just like any other

cancer. The cancer isnt radioactive and there arent any tests you can do to find out whatcaused it.

It would help if the scientists could show that an increase in radiation exposure increased therisk of getting brain cancer. This is much more difficult. The accident happened twenty yearsago and all they have is some hospital records.


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If someone shows up with brain cancer fifteen years after the accident youll know from thehospital records where they live now. But how do you know where they lived at the time ofthe accident? The only way to be sure is to follow up every brain cancer case.

If they do this then the scientists can plot a graph of relative risk of brain cancer againstcontamination. Here relative means relative to your risk with no exposure to

contamination. So with zero exposure your relative risk is 1. So the graph seems to confirmthat increased radiation gave increased risk of brain cancer.

Publishing research in a scientific journal

So our scientists have done some research but nobody else knows about it.

Nobody has had a chance to look carefully at their work to check they havent made anymistakes. And other scientists cant yet use it as a starting point for research of their own.

Our team will write up their research in a paper. It will be detailed and technical so that other

scientists could try and duplicate their work if they wanted to check it.

There are around 10 000 scientific journals worldwide, most specialising in a tiny part ofscience. The scientists choose one that specialises in their area and send their paper to theeditor. The editor will decide whether the work is original and important enough to merit

publication.

Peer review: review by your equals

If she decides to accept it in principle then she sends copies of the paper to two or threeworking scientists, who act as referees. She will choose referees who specialise in the samearea of science as the reports authors. Only the editor knows the identity of all the referees.They dont communicate with each other or the scientists who wrote the paper.

This use of referees is called peer review. Here peer means someone who is an equal.So peer review means review by your equals because science is not about who you are butthe work that you do.

The referees may spend many weeks reading the paper to check it for mistakes or sometimessuggest improvements. Each referee then sends a brief recommendation to the editor whetherto publish. She makes the final decision. If the editor decides not to publish she may suggestchanges to be made to the paper if the scientists wanted to have another go.

Published work is there for the scientific community to use

So what does it mean if our scientists are successful in having their paper published in thejournal?

Specialist scientific journals tend to be bought by universities and other institutions ratherthan individual scientists. Papers that have been published in peer-reviewed journals areconsidered to be part of the permanent scientific record.


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But it doesnt mean that their conclusions are true.

What it means is that the data and conclusions are now available for anyone to look at. Otherscientists can draw different conclusions from the same data or they may use the conclusionsto support their own.

Our research showed that brain cancer went up when radiation went up. This is called acorrelation. But a correlation does not mean that one thing CAUSED another.

Our scientists concluded that radiation did cause the increase because other research showed amechanism. Radiation damages DNA and damaged DNA can cause cancer.

But another scientist might have a theory that what causes brain cancer is fear. The peoplewho were contaminated were afraid and this made them more likely to get brain cancer.

Notice that this theory leads to predictions that can be tested. For example: people who worryless should be less at risk of brain cancer.

However our fear causes cancer theory would not replace the radiation causes cancer

theory unless it could explain more things.

If a leading scientist was asked Did the radiation from the accident cause brain cancer? thenthey might reply something like Most research shows that it does and we know radiationdamages DNA but some scientists have linked the increase to fear.

Scientists try not to see peer-reviewed research that contradicts their own ideas as a threat butas an opportunity to learn more.

The people who pay the research grants may influence

scientists' conclusions

It might be that the scientists feel under pressure to come to a conclusion that agrees with thegroup that funded them. Thats why some journals insist on knowing where the money camefrom. Was it the nuclear industry or perhaps an environmental group?

Even though science is about ideas, scientists themselves are still just people with beliefs andprejudices just like everyone else.

Open discussion of ideas is encouraged

So journals and conferences allow scientists to discuss their ideas both in writing and face to

face.

How scientific research is reported in the media

So how do the public ever get to hear about scientific research? The simple answer is thatthey dont, unless newspaper journalists think the research will make an interesting story.

Two articles can use the same figures but present very different points of view.


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One article might emphasize the fact that 200 000 people may die. It doesnt tell us that theseare people who may die far in the future, not people who have died already in one great biggroup. It might show a graph that shows a big proportional increase in certain type ofcancer but it doesnt say that the risk is still very small. It wants to convince us that nuclearaccidents are very bad because they affect a large number of people.

Another article might emphasize the fact that the overall cancer rate has increased by less than1%. It doesnt tell us that this still amounts to a lot of people in a big population. It mightshow a graph that shows that the risk of all cancers has stayed pretty much the same but itdoesnt tell us about the human effects of each extra case. It wants to convince us that nuclearaccidents are not so bad because your risk of getting cancer hasnt increased very much.

So if you were asked How bad was the nuclear accident? your answer may depend on whicharticle you happened to read.

Nothing is 100% safe

Both articles would acknowledge that the research shows about 3000 extra people a yearwould die of cancer. Can this possibly be justified? One way to consider this figure is inrelation to other risks that people take.

Over 100 000 people die each year in the UK because of heart disease. If the governmentbanned smoking, high fat food and extra salt and made everyone take regular exercise thisfigure could be reduced to almost zero!

What would you want to see prohibited to save lives? Shouldn't people be able to take risks ifthey want to?

Almost everything we do carries some risk. Nothing is ever safe.

It's easy to spend lots of money without decreasing risk

much

It also costs money to make things safe.

Say it costs $1 million to make a steel surround for a nuclear reactor that will stop a leak for90% of all possible accidents. It might cost another $1 million to make it stop a leak for 95%of all possible accidents. The next 5% of protection costs as much as the first 90%.

The ALARA principleSo people and governments have to work out what level of risk is As Low As ReasonablyAchievable. This means you dont waste millions reducing one risk a tiny amount when youcould spend it reducing another risk by a lot.

The Precautionary Principle


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Of course one way to reduce a risk to zero is to avoid it altogether. For example you dontneed to go parachuting. Perhaps we should avoid doing things where the result might beserious and irreversible harm.

This is called the precautionary principle and was first widely adopted by governments inthe 1980s.

It makes sense to avoid doing something if you don't know whether serious and irreversible

harm might result from it.

An example might be We dont know the long-term risks of burying nuclear waste so weshould avoid doing it.

One problem with the precautionary principle is that its never possible to prove thatsomething wont cause harm. Another is that it ignores both the potential benefits and thecost of doing nothing. The precautionary principle seems simple but people disagree on themeanings of know, serious, might and harm.

Do the benefits outweigh the costs?

A more common way of working out whether or how to adopt a new technology is to add upthe costs and benefits. A cost of nuclear power is the risks posed by nuclear waste. A benefitis the electricity produced.

People accept a risk if they think it is outweighed by the benefits. For example if you valueelectricity more than the risk of nuclear waste.

Assessing risk

But how do we know how big a risk is?

The worst type of risk is likely to happen and the consequences are very bad. Getting lungcancer from smoking would be a good example.

There has only ever been one nuclear accident, Chernobyl, where people outside a plantdied. How would you rate the risk of a nuclear power station accident?

Why people overestimate risk

Nuclear radiation is not a big risk factor for cancer compared with smoking, poor diet and

lack of exercise. Nuclear accidents are extremely rare but still many people rate nuclearenergy as being extremely risky.

Why is this? A possible reason is that when people think about taking a risk they dont justthink about numbers. In fact the actual numerical size of the risk may not feature at all in how

people rate it.

For example people rate risks that are forced on them higher than risks they decide to take bychoice.


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Science cant answer questions about whether there should be nuclear power. It can only provide

the numbers. It is up to each person to decide the risks they are prepared to take themselves or pass

on to other people.

Useful Radiation Notes

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