Edexcel iGCSE Physics -7.7 Nuclear Changes During Radioactive Emission- Study Notes- New Syllabus
Edexcel iGCSE Physics -7.7 Nuclear Changes During Radioactive Emission- Study Notes- New syllabus
Edexcel iGCSE Physics -7.7 Nuclear Changes During Radioactive Emission- Study Notes -Edexcel iGCSE Physics – per latest Syllabus.
Key Concepts:
update
Effects of Nuclear Radiation on Atomic and Mass Numbers
When an unstable nucleus emits radiation, the composition of the nucleus may change. Each type of radiation affects the atomic (proton) number and mass (nucleon) number in a specific way.
Key Reminder
- Atomic number (Z): number of protons
- Mass number (A): number of protons + neutrons
Alpha (α) Radiation
Nature: An alpha particle consists of two protons and two neutrons.
Effect on the nucleus:
- Atomic number decreases by 2.
- Mass number decreases by 4.
Reason: Two protons and two neutrons leave the nucleus.
\( \mathrm{^{A}_{Z}X \rightarrow ^{A-4}_{Z-2}Y + ^4_2\alpha} \)
Beta (β⁻) Radiation
Nature: A beta particle is a fast-moving electron.
Effect on the nucleus:
- Atomic number increases by 1.
- Mass number remains unchanged.
Reason: A neutron changes into a proton and an electron.
\( \mathrm{^{A}_{Z}X \rightarrow ^{A}_{Z+1}Y + \beta^-} \)
Gamma (γ) Radiation
Nature: Gamma radiation is electromagnetic energy.
Effect on the nucleus:
- Atomic number remains unchanged.
- Mass number remains unchanged.
Reason: No particles leave the nucleus — excess energy is released.
Key idea: Gamma emission often follows alpha or beta decay.
Neutron Radiation
Nature: A neutron is emitted from the nucleus.
Effect on the nucleus:
- Atomic number remains unchanged.
- Mass number decreases by 1.
Reason: A neutron leaves the nucleus, but no protons are lost.
\( \mathrm{^{A}_{Z}X \rightarrow ^{A-1}_{Z}Y + n} \)
Comparison Summary
| Type of radiation | Change in atomic number (Z) | Change in mass number (A) |
|---|---|---|
| Alpha (α) | Decreases by 2 | Decreases by 4 |
| Beta (β⁻) | Increases by 1 | No change |
| Gamma (γ) | No change | No change |
| Neutron | No change | Decreases by 1 |
Example
A nucleus is represented by \( \mathrm{^{238}_{92}U} \). It emits an alpha particle followed by a gamma ray. State the atomic and mass numbers of the final nucleus.
▶️ Answer / Explanation
After alpha emission:
\( \mathrm{Z = 92 – 2 = 90} \)
\( \mathrm{A = 238 – 4 = 234} \)
Gamma emission causes no further change.
\( \mathrm{Final\ nucleus = ^{234}_{90}} \)
Example
A nucleus undergoes beta decay followed by neutron emission. Describe the overall effect on its atomic number and mass number.
▶️ Answer / Explanation
- Beta decay increases atomic number by 1.
- Mass number remains unchanged after beta decay.
- Neutron emission reduces mass number by 1.
- Overall: Z increases by 1, A decreases by 1.