A particle with the same mass as an electron but a positive charge

How does gamma emission change the nucleus?

No change to mass number or atomic number; the nucleus loses energy

Beta-plus decay, neutrons and nuclear equations

Unstable nuclei can give out alpha particles, beta-minus particles (electrons), beta-plus particles (positrons), gamma rays or neutrons. Each changes the nucleus in a different way.

GCSE · 1PH0 · 6.5, 6.15, 6.18, 6.19, 6.20, 6.21, 6.22
About 16 minutes

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What each emission is

Emission	What it is	Relative mass	Charge
Alpha (α)	2 protons + 2 neutrons (a helium nucleus)	4	+2
Beta-minus (β⁻)	A fast electron from the nucleus	about 0.0005	−1
Beta-plus (β⁺)	A fast positron (the antiparticle of the electron)	about 0.0005	+1
Gamma (γ)	High-frequency EM radiation	0	0
Neutron (n)	A neutron	1	0

How the nucleus changes

Alpha: mass number −4, atomic number −2.
Beta-minus: a neutron turns into a proton and an electron. Mass number unchanged, atomic number +1.
Beta-plus: a proton turns into a neutron and a positron. Mass number unchanged, atomic number −1.
Gamma: the nucleus rearranges and loses energy. No change to either number. Gamma is often given out after alpha or beta decay.
Neutron emission: mass number −1, atomic number unchanged.

Balancing nuclear equations

The mass numbers must add up to the same total on both sides, and so must the atomic numbers (charges).
Beta-minus: carbon-14 (6 protons) → nitrogen-14 (7 protons) + electron
Beta-plus: carbon-11 (6 protons) → boron-11 (5 protons) + positron
Alpha: uranium-238 (92 protons) → thorium-234 (90 protons) + alpha particle

Worked example

Fluorine-18 (atomic number 9) decays by beta-plus emission. Find the mass number and atomic number of the new nucleus.

Beta-plus: a proton becomes a neutron.
Mass number stays 18.
Atomic number goes down by 1: 9 − 1 = 8 (oxygen).

Answer: Mass number 18, atomic number 8 (oxygen-18)

Key idea

Alpha: −4 mass, −2 atomic number. Beta-minus: neutron → proton, atomic number +1. Beta-plus: proton → neutron, atomic number −1. Gamma: no change. Neutron emission: mass number −1. Balance mass numbers and atomic numbers in nuclear equations.

Key words

Atomic number: The number of protons in the nucleus of an atom.
Mass number: The total number of protons and neutrons in a nucleus.
Alpha particle: Two protons and two neutrons (a helium nucleus). Strongly ionising, stopped by paper or a few cm of air.

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Quick check

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Extra practice

2 more questions

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Carbon-11 (atomic number 6) decays by beta-plus emission. What is the atomic number of the new nucleus?
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Answer: 5
A proton changes into a neutron, so the atomic number falls by 1: 6 − 1 = 5.
Carbon-14 (atomic number 6) decays by beta-minus emission. What is the atomic number of the new nucleus?
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Answer: 7
A neutron changes into a proton, so the atomic number rises by 1: 6 + 1 = 7.

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Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

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