Question 1

What is the difference between nuclear fission and fusion?

Accepted Answer

**Fission splits heavy atoms. Fusion joins light ones.** Both release energy, and both do so for the same underlying reason.

**Why either releases energy.** The **binding energy per nucleon** — how tightly protons and neutrons are held — varies across the periodic table, peaking around **iron-56**. Moving toward iron from either direction releases energy. So splitting elements heavier than iron releases energy, and fusing elements lighter than iron releases energy. Iron is the floor of the valley, which is why stars cannot generate energy by fusing it.

**Fission.** A heavy nucleus — typically uranium-235 or plutonium-239 — absorbs a neutron and splits into lighter fragments, releasing energy and **more neutrons**. Those neutrons can trigger further fissions, producing a **chain reaction**. Controlling that chain reaction with neutron-absorbing control rods is what a reactor does.

Fission is the basis of all current nuclear power. It works, it is proven, and it produces long-lived radioactive waste.

**Fusion.** Light nuclei — usually deuterium and tritium, isotopes of hydrogen — combine to form helium, releasing considerably more energy per unit mass than fission. This is what powers stars.

**Why fusion is so difficult.** Nuclei are positively charged and repel each other fiercely. Overcoming that repulsion requires temperatures around **100 million degrees** — far hotter than the Sun's core, because we cannot replicate the Sun's immense gravitational confinement. The plasma must be held at that temperature, at sufficient density, for long enough to produce net energy, and it cannot touch any container. Magnetic confinement (tokamaks such as ITER) and inertial confinement (laser compression, as at the National Ignition Facility, which achieved target energy gain in 2022) are the two main approaches.

**Fusion's appeal:** abundant fuel, no chain reaction to run away, no long-lived high-level waste, and no CO₂. Commercial viability remains unproven.

Question 2

Why is nuclear fusion so hard?

Accepted Answer

Because you must force atomic nuclei — all positively charged and therefore violently repelling each other — close enough to fuse, which requires conditions comparable to the inside of a star, and

Question 3

What is an isotope, and why do isotopes matter?

Accepted Answer

Atoms of the same element with different numbers of neutrons — so they share chemical behaviour but differ in mass and, crucially, in nuclear stability. The distinction that defines it. An element is

Question 4

How do stars form, and what happens when they die?

Accepted Answer

Stars form when gravity overcomes pressure in a cloud of gas and dust, and they die when they run out of fuel to resist gravity with. The entire life of a star is a standoff between those two forces,

Question 5

Why is the Earth's core still hot after billions of years?

Accepted Answer

Two reasons: heat left over from the planet's formation, and heat still being generated now by radioactive decay. Together they account for the roughly 5,000–6,000°C at the inner core — comparable to

Question 6

Why does iron rust but aluminium doesn't?

Accepted Answer

Both metals do react with oxygen. The difference is entirely in what the resulting oxide does — and it is one of the most consequential differences in materials science. Iron. Iron reacts with oxygen

Question 7

What does a catalyst actually do?

Accepted Answer

A catalyst speeds up a chemical reaction without being consumed by it — and the mechanism is more specific and more interesting than "it helps the reaction along". The core idea: activation energy.

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