Nuclear equations Revision Notes for Edexcel GCSE Physics

Nuclear equations

When an atom emits radiation, its nucleus changes, and it becomes a new element. This is because the number of protons in the nucleus determines which element it is.

The mass number (the top number) represents the total number of protons and neutrons in the nucleus.
The atomic number (the bottom number) represents the number of protons, which tells you which element the atom belongs to. In any nuclear reaction, the total mass number and atomic number must stay the same on both sides of the equation.

Alpha Decay Equations (α)

In alpha decay, an atom's nucleus loses 2 protons and 2 neutrons. Together, these particles form an alpha particle2:

\ce24He\ce{^4_2He}

As a result of this decay, the atom transforms into a new element with a lower atomic number, because it has lost protons.

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Example:

{^{238}_{92}U} \rightarrow \ce{^{234}_{90}Th} + \ce{^{4}_{2}He}

In this example, uranium-238 decays into thorium-234 by emitting an alpha particle $(\ce{^4_2He)}$

The mass number decreases by 4 (due to the loss of 2 protons and 2 neutrons).
The atomic number decreases by 2 (due to the loss of 2 protons).

Beta Decay Equations (β)

There are two types of beta decay: beta-minus (β-) decay and beta-plus (β+) decay. Both involve changes in the nucleus but in different ways.

Beta-minus Decay (β⁻)

In beta-minus decay, a neutron in the nucleus turns into a proton. During this process, the nucleus emits a beta particle (a high-energy electron, ${e^-}$ and an antineutrino $e\bar{\nu}$

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Example:

\ce{^{14}_6C -> ^{14}_7N + e^- + \bar{\nu}_e}

In this example, carbon-14 turns into nitrogen-14 by emitting a beta-minus particle.

The mass number stays the same (since a neutron turns into a proton, keeping the total count of protons + neutrons constant).
The atomic number increases by 1 (because a proton is gained).

Beta-plus Decay (β⁺)

In beta-plus decay, a proton in the nucleus turns into a neutron. During this process, the nucleus emits a positron (a positively charged beta particle, ${e^+}$ and a neutrino $(ν_e)$ .

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Example:

{^{18}_9F -> ^{18}_8O + e^+ + \nu_e}

In this example, fluorine-18 turns into oxygen-18 by emitting a positron.

The mass number stays the same (since a proton turns into a neutron).
The atomic number decreases by 1 (because a proton is lost).

Gamma Decay Equations (γ)

Gamma decay is different from other types of decay because it doesn't change the element. Instead, the atom loses energy in the form of gamma rays (high-energy electromagnetic radiation).

In gamma decay, both the mass number and the atomic number remain unchanged because gamma rays are pure energy, not particles.

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Example:

{^{60}_{27}Co^*}\rightarrow\ce{^{60}_{27}Co} + \gamma

In this example, cobalt-60 in an excited state $\ce{^{60}_{27}Co^*}$ releases gamma radiation (γ\gammaγ) and returns to its ground state, but remains the same element.

Summary of Changes in Nuclear Decay

Type of Decay	Particles Emitted	Change in Atomic Number	Change in Mass Number
Alpha (α)	2 protons + 2 neutrons (alpha particle)	-2	-4
Beta-minus (β⁻)	1 electron (beta particle)	+1	0
Beta-plus (β⁺)	1 positron	-1	0
Gamma (γ)	Energy (gamma rays)	0	0

Nuclear equations (Edexcel GCSE Physics): Revision Notes