What is radioactivity and how is it related to the Edexcel IGCSE Physics syllabus?

Radioactivity refers to the process by which unstable atomic nuclei lose energy by emitting radiation. In the Edexcel IGCSE Physics syllabus, students learn about the types of radiation, their properties, and their effects on matter. Understanding radioactivity is crucial for grasping concepts related to atomic structure and nuclear reactions.

What are the three main types of radioactive decay covered in the Edexcel IGCSE curriculum?

The three main types of radioactive decay are alpha decay, beta decay, and gamma decay. Alpha decay involves the emission of an alpha particle, which consists of two protons and two neutrons. Beta decay involves the transformation of a neutron into a proton with the emission of a beta particle (electron or positron). Gamma decay involves the emission of gamma rays, which are high-energy photons. Each type of decay has distinct properties and effects, which are studied in the Edexcel IGCSE Physics course.

How is the concept of half-life important in understanding radioactivity for IGCSE Physics students?

Half-life is the time required for half of the radioactive nuclei in a sample to decay. It is a crucial concept in radioactivity because it helps predict how long a radioactive substance will remain active. In the Edexcel IGCSE Physics syllabus, students learn to calculate half-life and understand its implications for radioactive dating, medical applications, and nuclear power.

What safety precautions are necessary when handling radioactive materials, according to the Edexcel IGCSE guidelines?

When handling radioactive materials, it is essential to follow safety precautions to minimize exposure to radiation. The Edexcel IGCSE guidelines recommend using shielding (such as lead aprons), maintaining a safe distance, minimizing exposure time, and using proper detection equipment. Understanding these precautions helps students appreciate the importance of safety in environments where radioactivity is present.

How do detectors measure radioactivity, and what role do they play in the Edexcel IGCSE Physics curriculum?

Detectors measure radioactivity by detecting the particles or energy emitted during radioactive decay. Common detectors include Geiger-Müller tubes, scintillation counters, and cloud chambers. In the Edexcel IGCSE Physics curriculum, students learn how these detectors work and their applications in measuring radiation levels, which is essential for experiments and understanding the practical aspects of radioactivity.

Why is "Confusing 'isotope' with 'ion'" a common mistake in Radioactivity ?

Why it happens: Both alter atoms. How to avoid it: Isotopes differ in NEUTRON number (same Z, different A — same element). Ions differ in ELECTRON number (same nucleus, different charge). Source: 4PH1 Examiner Reports 2022-2024

Why is "Saying half-life is the time for HALF the SAMPLE to decay" a common mistake in Radioactivity ?

Why it happens: Looks the same as 'half the ACTIVITY'. How to avoid it: Half-life is the time for the NUMBER OF UNDECAYED NUCLEI (or the ACTIVITY) to fall to HALF its initial value. Because activity is proportional to undecayed nuclei, both definitions give the same value.

Why is "Confusing contamination and irradiation" a common mistake in Radioactivity ?

Why it happens: Both involve being exposed to radiation. How to avoid it: Contamination = source IS ON or IN you. Irradiation = source is NEXT TO you. Mnemonic: contamination CONTACTS; irradiation IRRADIATES from a distance. Source: 4PH1 Examiner Reports 2022-2024

Why is "Saying alpha 'travels' through paper at low speed" a common mistake in Radioactivity ?

Why it happens: Confusing 'stopped' with 'slowed'. How to avoid it: Alpha is STOPPED by paper — its energy is fully absorbed within a few mm. It does not pass through 'more slowly'.

Radioactivity and ParticlesEdexcel IGCSE Physics (4PH1)

Radioactivity

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Radioactivity — Pearson Edexcel International GCSE Physics 4PH1 Study Notes (2026 onwards, Spec Issue 4)

Atomic structure, isotopes, the three main ionising radiations (α, β⁻, γ) and neutron emission. Decay equations balancing nucleon and proton numbers. Half-life. Detection, background radiation, uses, dangers, and the contamination-vs-irradiation distinction.

What you’ll learn

Mapped to the Cambridge IGCSE 4PH1 syllabus (2026 onwards).

7.1 — Use the units Bq, cm, h, min, s.
7.2 — Describe atomic structure (protons, neutrons, electrons); use notation $^{14}_6 C$ .
7.3 — Know the terms atomic (proton) number, mass (nucleon) number, isotope.
7.4 — Know α, β⁻ and γ are ionising radiations emitted from unstable nuclei in a random process.
7.5 — Describe nature of α, β, γ and distinguish by penetrating power and ionising ability.
7.6 — Required practical: investigate penetration powers of different types of radiation (sources or simulations).
7.7 — Describe effects on atomic and mass numbers of α, β, γ and neutron emission.
7.8 — Understand how to balance nuclear equations in terms of mass and charge.
7.9 — Know that photographic film or a Geiger-Müller detector can detect ionising radiation.
7.10 — Explain sources of background radiation from Earth and space.
7.11 — Know that activity decreases over time and is measured in becquerels.
7.12 — Know the definition of half-life and that it is different for different radioactive isotopes.
7.13 — Use half-life concept to carry out simple calculations on activity, including graphical methods.
7.14 — Describe uses of radioactivity in industry and medicine.
7.15 — Describe the difference between contamination and irradiation.
7.16 — Describe the dangers of ionising radiations including mutations, cell/tissue damage, and disposal of radioactive waste.

Atomic structure and isotopes (spec 7.2, 7.3)

Nucleus + electrons; $^A_Z X$ .

Atoms consist of a tiny, dense central NUCLEUS surrounded by electrons in orbits.

Particle	Charge	Relative mass	Location
Proton	+1	1	Nucleus
Neutron	0	1	Nucleus
Electron	−1	1/1836	Orbiting nucleus

Notation $^A_Z X$ . $X$ is the chemical symbol, $Z$ the proton number, $A$ the nucleon number.

$Z$ = number of protons = number of electrons in a neutral atom. Determines the ELEMENT.
$A$ = total number of protons + neutrons.
Neutron number $N = A - Z$ .

Isotopes. Atoms with the SAME proton number $Z$ but DIFFERENT mass number $A$ . Same element, different mass.

Example: $^{12}_6 C$ , $^{13}_6 C$ , $^{14}_6 C$ are three isotopes of carbon — all 6 protons, but 6, 7 and 8 neutrons respectively. Carbon-14 is radioactive and used in radiocarbon dating.

Nucleus = protons + neutrons; electrons orbit.
$Z$ = proton number = element identity.
Isotopes: same Z, different A.

α, β⁻, γ and neutron emission (spec 7.4-7.8)

Three (or four) types — properties and equation balancing.

Unstable nuclei emit ionising radiation as they decay. The 4PH1 spec covers FOUR types:

Radiation	Nature	Charge	Penetration	Ionising power	Stopped by
Alpha (α)	He-4 nucleus (2p + 2n)	+2	Low	Highest	Paper / few cm air
Beta-minus (β⁻)	Fast electron from nucleus	−1	Medium	Medium	A few mm aluminium
Gamma (γ)	High-energy EM photon	0	High	Least	Several cm lead / thick concrete
Neutron (n)	Free neutron (rare)	0	High	Low (indirect)	Water / hydrocarbon material

Note the trade-off. Larger charge and mass → easier to lose energy via ionisation → fewer atoms reached. So highest-ionising = lowest-penetrating.

Required practical (spec 7.6). Sources or simulations: place each source in turn in front of a Geiger-Müller counter. Insert paper, then aluminium, then lead between source and counter. Record count rate. The radiation type that no longer reaches the counter has been stopped by that absorber.

Effects on $A$ and $Z$ (spec 7.7).

Emission	$\Delta A$	$\Delta Z$	Note
α	−4	−2	Nucleus loses 2p + 2n
β⁻	0	+1	Neutron → proton + electron (electron emitted)
γ	0	0	Energy emitted only
Neutron	−1	0	Free neutron ejected

Balancing nuclear equations (spec 7.8). Conservation of NUCLEON number on both sides; conservation of PROTON number on both sides.

Examples:

$^{226}_{\;88}\text{Ra} \to {}^{222}_{\;86}\text{Rn} + {}^4_2\alpha$ (alpha decay)

$^{14}_{\;6}\text{C} \to {}^{14}_{\;7}\text{N} + {}^{\;0}_{-1}e$ (beta-minus decay)

α stopped by paper; β by Al; γ by lead.
α: A −4, Z −2. β⁻: A 0, Z +1. γ: no change.
Equations balance nucleon AND proton number.

See the full worked example for radioactivity →

Detection and background radiation (spec 7.9, 7.10)

GM tubes; everyday radioactive sources.

Detection (spec 7.9). Two main methods:

Geiger-Müller (GM) tube. A sealed tube of gas with a thin window. Incoming radiation ionises gas atoms, producing a current pulse that is counted. Count rate (in Bq) is displayed.
Photographic film. Radiation darkens the film when developed (the basis of radiation badges worn by lab workers and dental technicians to monitor cumulative dose).

Background radiation (spec 7.10). Low-level ionising radiation that is ALWAYS present in the environment. Sources include:

Cosmic rays from the Sun and outer space (more at higher altitudes — pilots get bigger doses).
Rocks and soil containing natural uranium, thorium, potassium — especially RADON gas emitted from granite (a major contributor in some regions).
Food and drink contain small amounts of natural radioactive isotopes (e.g. potassium-40 in bananas).
Medical procedures (X-rays, CT scans, radiotherapy) add to cumulative dose.
Nuclear weapons fallout and nuclear power account for very small contributions.

When measuring a sample's activity, ALWAYS subtract the background count rate first to get the true activity from the source alone.

GM tube ionises gas → current pulse → counter.
Film badges = dose monitoring.
Background sources: cosmic, rocks (radon), food, medical.

Half-life (spec 7.11-7.13)

Activity halves every half-life.

Activity (spec 7.11) = number of decays per second in a sample. Units: becquerels (Bq) = 1 decay/s. Activity DECREASES with time as undecayed nuclei deplete.

Half-life $t_{1/2}$ (spec 7.12) = the average time taken for HALF the undecayed nuclei in a sample to decay, or equivalently for the activity to fall to half its initial value.

Different isotopes have different half-lives — from MICROSECONDS to BILLIONS of years.

Isotope	$t_{1/2}$
Polonium-214	0.16 ms
Iodine-131	8 days
Cobalt-60	5.3 years
Radium-226	1600 years
Carbon-14	5700 years
Uranium-238	4.5 × 10⁹ years

Calculations (spec 7.13). For whole numbers of half-lives:

$A = A_0 \times \left(\tfrac{1}{2}\right)^n$

where $n$ is the number of half-lives elapsed.

Graphical method. Plot activity vs time. Read off the time when activity falls from $A_0$ to $A_0/2$ — that's the half-life. Check by reading off the time to fall from $A_0/2$ to $A_0/4$ ; should give the same value.

Subtract BACKGROUND count rate from your measured count rate before any half-life analysis.

Half-life = time for activity to halve.
Different for different isotopes.
After $n$ half-lives: $A = A_0 (1/2)^n$ .

See the full worked example for radioactivity →

Uses of radioactivity (spec 7.14)

Industry + medicine.

Industry.

Tracers. Inject a short-half-life radioactive isotope into a pipe / oil flow / blood stream and follow it with a detector. Used to find leaks in pipes underground.
Smoke alarms. Tiny amount of Americium-241 emits α-particles inside the chamber; smoke disrupts the ion current and triggers the alarm.
Thickness gauging. Sheet metal or paper passes between a β source and a detector; thicker material absorbs more radiation → controls the rolling machine.

Medicine.

Medical tracers (e.g. iodine-131 for thyroid imaging, technetium-99m for general imaging). Inject and image with a gamma camera.
Radiotherapy for cancer. Targeted external gamma beams (cobalt-60 source) or internal seeds destroy tumour cells.
Sterilisation of surgical equipment with gamma radiation kills bacteria without heat damage.

Spec wording note. Spec 7.14 wants "industry AND medicine" — give at least one example of each.

Tracers: short half-life for safety.
Smoke alarm: α-particle disruption.
Radiotherapy: targeted γ destroys tumours.

Contamination vs irradiation; dangers (spec 7.15, 7.16)

Critical distinction; mutations and waste.

Contamination (spec 7.15) = the unwanted PRESENCE of radioactive material on or in an object. As long as the radioactive material remains, it continues to irradiate the surrounding tissue. Worse for ALPHA emitters because their short range means all the energy is deposited locally inside the body.

Irradiation = exposure to radiation from an EXTERNAL source WITHOUT the source touching you. Exposure stops as soon as you move away or the source is shielded.

Protection methods.

Hazard	Protection
Contamination	Gloves, protective clothing, fume cupboards, washing, sealed containers, food-handling protocols
Irradiation	Distance (1/r²-style fall-off), shielding (lead, concrete, water), time (minimise exposure duration)

Dangers of ionising radiation (spec 7.16).

Cell damage — radiation can kill cells or damage their DNA, leading to MUTATIONS, cancer or radiation sickness.
Mutations are inheritable changes in DNA that may pass to offspring.
Tissue damage especially in rapidly dividing tissues (gut lining, bone marrow, foetus).
Disposal of radioactive waste is a major societal problem. High-level waste (spent nuclear fuel) remains dangerous for thousands of years. It is currently stored in deep geological repositories or in cooling ponds at the plant. Risk reduction: VITRIFY into glass blocks, encase in concrete, bury in stable rock formations far from groundwater.

Contamination = source ON/IN you (worse for α).
Irradiation = source near you (mitigated by distance, shielding, time).
Dangers: cell damage, mutation, cancer; waste disposal is long-term.

See the full worked example for radioactivity →

How it’s examined

Radioactivity is a high-yield topic for 4PH1 Paper 1 — typically 10-15 marks total. Common items: α/β/γ comparison table (5-6 marks), balancing decay equations (4-5 marks), half-life calculations (4-5 marks), contamination vs irradiation (4 marks). Spec 7.6 required practical and spec 7.14 uses appear in roughly half of recent papers.

Sources: Pearson Edexcel International GCSE Physics 4PH1 specification — Issue 4, September 2024 (valid for 2026 onwards); Pearson Edexcel 4PH1 Examiner Reports 2022-2024; 4PH1/1P May/Jun 2024 question paper and mark scheme; 4PH1/1P January 2024 question paper and mark scheme. Last reviewed 2026-05-12.

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Step-by-step worked examples — Radioactivity

Step-by-step solutions to past-paper-style questions on radioactivity , written exactly the way a tutor would explain them at the board.

1Comparing α, β and γ (6 marks, Paper 1)
Core• Adapted from 4PH1/1P May/Jun 2024• alpha-beta-gamma, spec-7.5
Question
Compare alpha, beta-minus and gamma radiations in terms of their nature, charge, penetrating power and ionising ability. (6 marks)
Step-by-step solution
1. Step 1
  Alpha (α). A HELIUM-4 NUCLEUS (2 protons + 2 neutrons). Charge +2. Stopped by a sheet of PAPER (or a few cm of air). HIGHLY ionising.
2. Step 2
  Beta-minus (β⁻). A high-energy ELECTRON emitted from the nucleus. Charge −1. Stopped by a few mm of ALUMINIUM. MEDIUM ionising.
3. Step 3
  Gamma (γ). A high-frequency ELECTROMAGNETIC WAVE (photon). NO charge, NO mass. Stopped by several cm of LEAD or thick concrete. LEAST ionising.
4. Step 4
  Inverse trend. Highest-ionising = lowest-penetrating (α). Lowest-ionising = highest-penetrating (γ).
Answer
α = He-4, +2, paper-stopped, most ionising. β⁻ = electron, −1, Al-stopped, medium. γ = EM wave, 0, lead-stopped, least ionising.
Examiner tip
Edexcel mark schemes commonly award 1 mark for each row in a 'compare' table. Use a clear table or labelled bullet structure rather than running prose. Penetration AND ionising ability must both be quoted.
2Balancing a decay equation (5 marks, Paper 1)
Core• Adapted from 4PH1/1P January 2024• nuclear equation, spec-7.7, spec-7.8
Question
Complete this beta-minus decay equation, identifying the daughter element: $^{14}_{\;6}\text{C} \to \text{X} + {}^{\;0}_{-1}e$ . Show how nucleon and proton numbers are conserved. (5 marks)
Step-by-step solution
1. Step 1
  Conservation of nucleon number. $14 = A + 0 \Rightarrow A = 14$ .
2. Step 2
  Conservation of proton number. $6 = Z + (-1) \Rightarrow Z = 7$ .
3. Step 3
  Identify X. $Z = 7$ → NITROGEN.
  $^{14}_{\;6}\text{C} \to {}^{14}_{\;7}\text{N} + {}^{\;0}_{-1}e$
4. Step 4
  Physics (spec 7.7). In β⁻ decay, a NEUTRON in the nucleus changes to a PROTON, releasing an electron. So nucleon number stays the same, proton number INCREASES by 1.
Answer
X = $^{14}_{\;7}\text{N}$ . Nucleon: 14 = 14 + 0 ✓. Proton: 6 = 7 + (−1) ✓.
Examiner tip
Edexcel mark scheme awards a mark for nucleon balance, a mark for proton balance and a mark for identifying the daughter. Always state BOTH conservation laws explicitly.
3Half-life calculation (5 marks, Paper 1)
Core• half-life, spec-7.12, spec-7.13
Question
A radioactive isotope has a half-life of 8 days. The initial activity of a sample is 6400 Bq. (a) Calculate the activity after 24 days. (b) After what time will the activity fall to 200 Bq? (5 marks)
Step-by-step solution
1. Step 1
  (a) 24 days / 8 days = 3 half-lives. Each halves the activity.
  $A = 6400 \times \left(\tfrac{1}{2}\right)^3 = 6400/8 = 800\ \text{Bq}$
2. Step 2
  (b) $200 = 6400 / 2^n$ → $2^n = 32$ → $n = 5$ half-lives.
3. Step 3
  Time $= 5 \times 8 = 40$ days.
Answer
(a) 800 Bq. (b) 40 days (5 half-lives).
Examiner tip
Edexcel half-life problems usually use whole numbers of half-lives. If the answer doesn't land on a nice multiple, you may have set up wrong — check the ratio of initial to final activity is a power of 2.
4Contamination vs irradiation (4 marks, Paper 1)
Core• Adapted from 4PH1/1P May/Jun 2024• spec-7.15
Question
Explain the difference between contamination and irradiation, and state a precaution to reduce the risk from each. (4 marks)
Step-by-step solution
1. Step 1
  Contamination. Radioactive material gets ONTO or INSIDE the body. Continues to irradiate the body from inside or on the skin for as long as the source remains.
2. Step 2
  Irradiation. Exposure to radiation from an EXTERNAL source WITHOUT the source touching the body. Exposure stops as soon as you move away (or the source is shielded/removed).
3. Step 3
  Precaution against contamination. Wear protective clothing/gloves, work in fume cupboards, wash thoroughly after handling, store sources in sealed containers.
4. Step 4
  Precaution against irradiation. Increase distance from source, shield with lead/concrete, limit exposure time.
Answer
Contamination = source ON or IN body (continues to irradiate). Irradiation = exposure WITHOUT contact. Precautions: gloves/clothing for contamination; distance/shielding/time for irradiation.
Examiner tip
Spec 7.15 is a frequent Paper 1 question. Edexcel marks BOTH definitions AND a matching precaution for each. Vague 'be careful' precautions earn nothing — name the specific mitigation.

Key Definitions and Keywords — Radioactivity

Definitions to memorise and the exact keywords mark schemes credit for radioactivity answers — sharpened from recent examiner reports for the 2026 Pearson Edexcel IGCSE 4PH1 sitting.

Atomic structure (spec 7.2, 7.3)
Examiner keyword
A central NUCLEUS containing PROTONS (positive) and NEUTRONS (neutral), surrounded by orbital ELECTRONS (negative). Notation $^A_Z X$ where Z = proton number (number of protons), A = nucleon (mass) number (protons + neutrons). ISOTOPES have same Z but different A.
Ionising radiation (spec 7.4)
Examiner keyword
Radiation that has enough energy to remove an electron from an atom, leaving an ION. Includes α, β⁻ and γ from unstable nuclei. Emission is a RANDOM process — no way to predict when a given nucleus will decay.
Alpha particle (α) (spec 7.5)
Examiner keyword
A helium-4 nucleus ( $^4_2\text{He}$ ): 2 protons + 2 neutrons, charge +2. Most ionising (large mass, double charge); least penetrating (stopped by paper or a few cm of air).
Beta-minus particle (β⁻) (spec 7.5)
Examiner keyword
A high-energy electron emitted from the nucleus when a neutron converts to a proton. Charge −1, negligible mass. Medium ionising; stopped by a few mm of aluminium.
Gamma ray (γ) (spec 7.5)
Examiner keyword
A high-frequency electromagnetic wave (photon) emitted from an excited nucleus. No charge, no mass. Least ionising; only stopped by thick lead or concrete.
Half-life (spec 7.12)
Examiner keyword
The AVERAGE time taken for half the unstable nuclei in a sample to decay, or for the activity to fall to half its initial value. Different for different isotopes — ranging from microseconds to billions of years.
Activity (spec 7.11)
Examiner keyword
The number of nuclear decays per second in a radioactive sample. Measured in becquerels (Bq). 1 Bq = 1 decay per second.
Background radiation (spec 7.10)
Examiner keyword
Low-level ionising radiation that is always present in the environment. Sources: cosmic rays from space, naturally occurring radioactive isotopes in rocks and soil (e.g. radon gas), food and drink, medical procedures.
Contamination (spec 7.15)
Examiner keyword
The UNWANTED PRESENCE of radioactive material on or inside an object. As long as the radioactive material remains, it continues to irradiate the surrounding tissue.
Irradiation (spec 7.15)
Examiner keyword
The EXPOSURE of an object to radiation from a SOURCE WITHOUT the source actually touching the object. Exposure ends when the source is removed or shielded.

Common Mistakes and Misconceptions — Radioactivity

The traps other students keep falling into on radioactivity questions — taken from recent Pearson Edexcel IGCSE 4PH1 examiner reports and mark schemes — and how to avoid them.

✕Confusing 'isotope' with 'ion'
4PH1 Examiner Reports 2022-2024
Why it happens
Both alter atoms.
How to avoid it
Isotopes differ in NEUTRON number (same Z, different A — same element). Ions differ in ELECTRON number (same nucleus, different charge).
✕Saying half-life is the time for HALF the SAMPLE to decay
Why it happens
Looks the same as 'half the ACTIVITY'.
How to avoid it
Half-life is the time for the NUMBER OF UNDECAYED NUCLEI (or the ACTIVITY) to fall to HALF its initial value. Because activity is proportional to undecayed nuclei, both definitions give the same value.
✕Confusing contamination and irradiation
4PH1 Examiner Reports 2022-2024
Why it happens
Both involve being exposed to radiation.
How to avoid it
Contamination = source IS ON or IN you. Irradiation = source is NEXT TO you. Mnemonic: contamination CONTACTS; irradiation IRRADIATES from a distance.
✕Saying alpha 'travels' through paper at low speed
Why it happens
Confusing 'stopped' with 'slowed'.
How to avoid it
Alpha is STOPPED by paper — its energy is fully absorbed within a few mm. It does not pass through 'more slowly'.

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Radioactivity — frequently asked questions

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Radioactivity

Short Study Notes in the form of Slides

Detailed Study Notes

What you’ll learn

How it’s examined

1Comparing α, β and γ (6 marks, Paper 1)

2Balancing a decay equation (5 marks, Paper 1)

3Half-life calculation (5 marks, Paper 1)

4Contamination vs irradiation (4 marks, Paper 1)

Atomic structure (spec 7.2, 7.3)

Ionising radiation (spec 7.4)

Alpha particle (α) (spec 7.5)

Beta-minus particle (β⁻) (spec 7.5)

Gamma ray (γ) (spec 7.5)

Half-life (spec 7.12)

Activity (spec 7.11)

Background radiation (spec 7.10)

Contamination (spec 7.15)

Irradiation (spec 7.15)

✕Confusing 'isotope' with 'ion'

✕Saying half-life is the time for HALF the SAMPLE to decay

✕Confusing contamination and irradiation

✕Saying alpha 'travels' through paper at low speed

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Radioactivity — frequently asked questions