What is an alpha particle?

A helium nucleus: 2 protons and 2 neutrons, with charge +2.

What is a beta particle?

A fast electron emitted from the nucleus, with charge −1.

What is gamma radiation?

Electromagnetic radiation from the nucleus, with no mass or charge.

How does alpha decay change the mass number and atomic number?

Mass number falls by 4 and atomic number falls by 2.

How does beta decay change the mass number and atomic number?

Mass number stays the same and atomic number rises by 1.

Give two sources of natural background radiation.

Rocks (radon gas) and cosmic rays.

The time taken for the activity of a sample to fall to half its starting value.

A sample has activity 64 and a half-life of 2 hours. What is the activity after 6 hours?

6 ÷ 2 = 3 half-lives: 64 → 32 → 16 → 8, so the activity is 8.

Why is a gamma emitter with a short half-life used as a medical tracer?

Gamma rays pass out of the body to be detected, and the activity falls quickly so exposure is short.

What is the difference between fission and fusion?

Fission splits a large nucleus; fusion joins two small nuclei.

Radioactivity and half-lifeIB MYP Chemistry: Flashcards

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What is an unstable nucleus?

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What is an unstable nucleus?: A nucleus that emits radiation to become more stable.
What is an alpha particle?: A helium nucleus: 2 protons and 2 neutrons, with charge +2.
What is a beta particle?: A fast electron emitted from the nucleus, with charge −1.
What is gamma radiation?: Electromagnetic radiation from the nucleus, with no mass or charge.
Which radiation is stopped by paper?: Alpha.
Which radiation needs thick lead or concrete to reduce it?: Gamma.
Which radiation is most ionising?: Alpha.
How does alpha decay change the mass number and atomic number?: Mass number falls by 4 and atomic number falls by 2.
How does beta decay change the mass number and atomic number?: Mass number stays the same and atomic number rises by 1.
Give two sources of natural background radiation.: Rocks (radon gas) and cosmic rays.
Define half-life.: The time taken for the activity of a sample to fall to half its starting value.
A sample has activity 64 and a half-life of 2 hours. What is the activity after 6 hours?: 6 ÷ 2 = 3 half-lives: 64 → 32 → 16 → 8, so the activity is 8.
Why is a gamma emitter with a short half-life used as a medical tracer?: Gamma rays pass out of the body to be detected, and the activity falls quickly so exposure is short.
What is the difference between fission and fusion?: Fission splits a large nucleus; fusion joins two small nuclei.

Exam questions on Radioactivity and half-life

A smoke detector in a school contains a tiny sample of americium-241, which emits alpha particles. The alpha particles ionise the air between two metal plates, so a small current flows. When smoke enters the detector, the current falls and the alarm sounds.
Explain why the alpha source inside the detector is safe for people in the room.2 marks
A nucleus of uranium-238, which has atomic number 92, is unstable and decays by emitting an alpha particle. The new nucleus is an atom of thorium.
The thorium nucleus, with mass number 234 and atomic number 90, then decays by beta emission. Give the mass number and atomic number of the nucleus formed, and explain why the atomic number changes.2 marks
A hospital in Dubai uses the radioactive tracer technetium-99m to check how well a patient's kidneys work. The tracer emits gamma rays and has a half-life of 6 hours. It is injected into the patient, and a detector outside the body picks up the gamma rays.
A patient is given a dose of the tracer with an activity of 800 counts per minute. Calculate the activity of the tracer after 18 hours.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).