Nuclear Physics

Nuclear Physics is the shortest major topic in Cambridge IGCSE 0625, yet it appears on every paper. Expect 8-12 marks on Paper 4 and two to four multiple-choice questions on Paper 2. Students who learn its small set of rules score faster here than anywhere else in the syllabus.

What does this topic cover in 0625?

Five areas: the nuclear model of the atom, isotopes and nuclide notation, the three types of radioactive emission, detection and safety, and half-life calculations. The content is mostly descriptive. There is only one routine calculation type, half-life, and it never needs more than repeated halving at IGCSE level.

Why do students lose marks in Nuclear Physics?

Examiner reports flag the same three errors each session. First, nuclide notation. Students write the proton number and nucleon number the wrong way round in decay equations, so the equation does not balance. In alpha decay the nucleon number drops by 4 and the proton number by 2; in beta-minus decay the proton number rises by 1. Second, vague property answers. “Alpha is dangerous” earns nothing; “alpha is the most ionising but is stopped by paper or a few centimetres of air” earns the mark. Third, half-life questions with background radiation. Extended papers expect you to subtract background count rate before halving. Miss that step and the final answer mark goes.

Think a descriptive topic means easy marks? Only with precise wording. Cambridge mark schemes for radioactivity accept specific phrases and reject paraphrases, so learn the accepted forms.

How should you revise it?

Build one summary table for alpha, beta and gamma: nature, charge, mass, ionising power, penetration, deflection in fields. That single table answers roughly half of all Nuclear Physics questions since 2017. Then balance 10 decay equations until nucleon and proton numbers check automatically. Finish with half-life practice: table-of-halvings questions, graph questions where you read the time to fall to half the original count, and Extended questions with background correction.

This is the best marks-per-hour topic in 0625. Want it locked down fast? Book a free 1-hour taught trial and ask us to cover the full alpha-beta-gamma table in that lesson. 1-to-1, online, RM80/hr after the trial. WhatsApp us to book.

How Nuclear Physics Is Assessed Across the Papers

Nuclear Physics is small but it appears every session, which is why the marks-per-hour payoff is so high. Papers 1 (Core) and 2 (Extended) carry two to four multiple-choice items: properties of alpha, beta and gamma, penetration and ionising power, and a quick half-life read-off. Papers 3 (Core) and 4 (Extended) give a structured question worth 8 to 12 marks, usually a balanced decay equation, a properties comparison, and a half-life calculation. The Core and Extended split is narrow because the topic is mostly descriptive, but the Supplement tier expects the harder half-life work: subtracting background count rate before halving, and reading non-integer numbers of half-lives from a decay graph. Papers 5 (Practical) and 6 (Alternative to Practical) test the safe handling of sources, the absorber experiment that identifies a radiation type, and the correction of a measured count rate for background. Because the calculations are so few, the marks here come mostly from precise wording, so practise the accepted phrases for penetration, ionising power and the random nature of decay until they are automatic.

A Worked Example That Shows the Method

A radioactive source has a half-life of $15\ \text{minutes}$. The measured count rate is $6420\ \text{counts/min}$ and the background count rate is $20\ \text{counts/min}$. Calculate the measured count rate $1.0\ \text{hour}$ later. [4]

Worked solution:

$\text{corrected count rate} = 6420 - 20 = 6400\ \text{counts/min}$

In $1.0\ \text{hour}$ there are $\dfrac{60}{15} = 4$ half-lives, so the corrected rate halves four times:

$6400 \rightarrow 3200 \rightarrow 1600 \rightarrow 800 \rightarrow 400\ \text{counts/min}$

Add the background back to predict the meter reading:

$\text{measured count rate} = 400 + 20 = 420\ \text{counts/min}$

Mark scheme:

• M1: correct background subtraction, $6420 - 20 = 6400$
• M1: $4$ half-lives in $60\ \text{minutes}$, corrected rate $= 400\ \text{counts/min}$
• A1: measured rate $= 420\ \text{counts/min}$
• B1: background added back at the end (not left subtracted)

The two background steps frame the calculation: subtract it before halving, then add it back to predict the meter reading. Candidates who skip the final addition give the corrected rate of $400$ and lose the last mark, even though every halving was correct.

Once the rules are fixed, keep our physics equations list and the calculation-question method guide beside you while you work through the subtopics below.