GCSE · Physics · Edexcel · Spec 1PH0

Contamination vs irradiation

Food zapped with gamma rays stays fresher for longer, and it isn't radioactive at all. So what is the difference between being hit by radiation and being radioactive?

Physics · Radiation

Irradiated or contaminated?

For each case, ask: did radiation pass through it, or did radioactive particles end up on or in it? Then sort it.

Still to sort

Irradiation (0)

Exposed to radiation. Nothing radioactive is left behind.

Where the line is: The object is exposed to radiation, but it does not become radioactive.

Contamination (0)

Radioactive particles are on or in it.

Where the line is: Radioactive particles have been transferred, so the object or place is radioactive.

7 of 7 still to sort.

Seven cases. One question for each.

Watch out: Being hit by radiation does not make something radioactive. Only radioactive particles on or in it do.

Why irradiated is not radioactive

Atoms in an irradiated objectvsAtoms in a radioactive material

Look inside the atoms. What does each situation change?

Focus

Ionising radiation

Atoms in an irradiated object

Passes through, and parts of the material may be ionised: the number of electrons changes

Atoms in a radioactive material

Is released as its unstable nuclei decay

The insight

Ionising radiation can turn atoms into ions by changing electrons. Releasing that radiation is what a radioactive material does.

The nuclei

Atoms in an irradiated object

Not made unstable by the irradiation

Atoms in a radioactive material

Unstable, so they decay over time

Is the object radioactive?

Atoms in an irradiated object

No. The object is only exposed to radiation

Atoms in a radioactive material

Yes. It contains isotopes with unstable nuclei

Irradiated food

?

Reason it through

Why is gamma-irradiated food not radioactive, even though it stays fresher for longer?

Link 1 of 4

First link · your turn

Gamma radiation is shone at the food. What happens to the microbes on it?

2
Locked — reveal the link above first
3
Locked — reveal the link above first
4
Locked — reveal the link above first

Predict, then check

Gamma radiation is used to irradiate food and sealed medical equipment such as a scalpel.

Which properties of gamma radiation make it suitable for this job?

Physics · Radiation

Which idea is closest to yours?

Three friends are arguing about radiation. Each of them says something slightly different.

Which of these is closest to what you think right now?
How sure are you?

What you need to know

  • Radioactive materials contain isotopes with unstable nuclei, which decay over time and release ionising radiation.
  • Ionising radiation can turn atoms into ions by changing the number of electrons.
  • Have a goIonising radiation hits an atom and the number of electrons in that atom changes. What has the atom turned into?

    An ion.

    Changing the number of electrons is exactly how ionising radiation turns an atom into an ion. The change is to the electrons.

  • Irradiation means exposing an object to radiation. The object is irradiated, but it does not become radioactive.
  • Have a goSam says: 'That apple went through a radiation machine, so it must glow with radioactivity now.' What do you tell Sam?

    Being irradiated is not the same as being radioactive. The apple was exposed to radiation, so it is not radioactive.

    Sam has swapped 'exposed to radiation' for 'giving out radiation'. Irradiation does not make an object radioactive.

  • Contamination means radioactive particles have been transferred to an object or place, so unwanted radioactive atoms are there.
  • Particles can stick to skin after touching a radioactive material, or a radioactive gas such as radon can be breathed in.
  • Have a goWhich one doesn't belong: touching a radioactive material, breathing in radon, or standing in a beam of radiation that passes through you?

    Standing in the beam. That is irradiation.

    The other two leave radioactive particles on or in you. The beam only passes through, so no particles are left behind.

  • Fallout from nuclear accidents and nuclear weapons testing can contaminate large regions for very long periods.
  • Gamma-irradiated food is not radioactive and stays fresher for longer, because the radiation kills microbes.
  • Gamma radiation is highly penetrating and ionising enough to kill microbes, so it can also sterilise sealed medical equipment.
  • Irradiation can damage living organisms and sensitive materials such as electronics.

The big picture

Irradiation is exposing an object to radiation, and the object does not become radioactive. Contamination is radioactive particles ending up on or in an object or place, and that does make it radioactive. For any case, ask: did radiation pass through it, or did radioactive particles end up on or in it?

Key points

1Irradiation is exposure to radiation. The irradiated object does not become radioactive.
2Contamination is radioactive particles on or in an object or place. A contaminated object is radioactive.
3Gamma-irradiated food and sterilised sealed equipment are not radioactive.
4Contamination can come from touching a radioactive material, breathing in radon, or fallout.

Worked example

Problem

Radioactive dust settles on a workbench in a laboratory. Decide whether the workbench has been irradiated or contaminated, and say whether it is radioactive.

⚠ Watch out

Thinking that anything exposed to radiation becomes radioactive. It doesn't. Irradiated food and sterilised equipment are not radioactive. Only radioactive particles on or in something make it radioactive.

🧠

Memory hook

Rays pass through, particles stay behind. Irradiation is the rays. Contamination is the particles.

✓

Check yourself

Without looking back: give two different ways a person can become contaminated, then say what those two ways have in common.

Flashcards

(14)
What is irradiation?
Exposing an object to radiation. The irradiated object does not become radioactive.
What is radioactive contamination?
The transfer of radioactive particles to an object or place, so unwanted radioactive atoms are there.
A contaminated object is radioactive. Why?
Radioactive particles in it or on its surface are emitting radiation.
What do radioactive materials contain?
Isotopes with unstable nuclei, which decay over time and release ionising radiation.
How can ionising radiation turn atoms into ions?
By changing the number of electrons.
Is gamma-irradiated food radioactive? Why or why not?
No. Irradiation does not introduce radioactive particles and does not make the nuclei of atoms in the food unstable.
Why does gamma-irradiated food stay fresher for longer?
The radiation kills the microbes on the food, and microbes are what make food rot.
Which two properties of gamma radiation make it suitable for irradiating food?
It is highly penetrating, so it reaches every part of the food, and it is ionising enough to kill microbes.
Name a piece of medical equipment that can be sterilised by irradiation.
A sealed scalpel. Gamma radiation can irradiate sealed medical equipment to sterilise it.
Give three ways contamination can happen.
Particles stick to skin after touching a radioactive material, a radioactive gas such as radon is breathed in, or fallout from nuclear accidents and weapons testing.
How far and for how long can fallout contaminate?
It can contaminate large regions for very long periods.
Is gamma radiation shone through the body to kill cancer cells irradiation or contamination?
Irradiation. It does not put radioactive material into the tissue.
What can irradiation damage?
Living organisms and sensitive materials such as electronics.
Which question separates irradiation from contamination?
Did radiation pass through it, or did radioactive particles end up on or in it?

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

Learning with Lightbulb is opening soon

You can use this lesson now. Join the waitlist and we'll let you know when the full Lightbulb experience is ready.

Keep me posted

More Edexcel GCSE Physics topics

See the full Edexcel Physics curriculum →

How this lesson was checked. This Edexcel GCSE Physics (specification 1PH0)lesson was published through Lightbulb Learning's human-designed editorial process — the educational standards, accuracy rules and publication checks it must pass were authored and approved by Philip Halpin. It passed subject-specific assessment, automated educational checks and technical publication verification before going live (publication checks completed 9 October 2026). Published pages are monitored, human spot-checking is ongoing across the lesson library, and anything found wrong is corrected or withdrawn. How our lessons are made and checked. Spotted a mistake? Email hello@lightbulblearning.co and we'll review it.