Radioactive Decay
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50 free Radioactive Decay trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Radioactive decay is nature's own alchemy. An unstable nucleus cannot be told when to change, and nothing we do to it in everyday life hurries it along, yet a large enough crowd of such nuclei keeps time so reliably that we use them to date ancient cloth, power spacecraft and find tumours. This quiz works through the main kinds of decay the way a physics course does: what an alpha particle is and what it leaves behind, how beta and positron emission shift an atom one square along the periodic table, where gamma rays fit in, and how half-lives and decay chains are worked out. Alongside the equations you will meet the people who pieced the story together and some of the places decay turns up, from hospital scanners to the smoke alarm on the ceiling. It suits students revising nuclear physics or chemistry, teachers looking for a ready-made review, and anyone curious about why some atoms simply refuse to stay as they are. Most questions reward clear thinking over memorised numbers, with a few harder ones for readers who know their isotopes.
30 of 50 questions with answers and explanations. Play the quiz
Q 01An alpha particle, two protons and two neutrons bound together, is identical to the nucleus of which light element?
Helium
Helium on Earth is mostly made this way: alpha particles shot out of decaying rock lose speed, pick up two electrons and collect underground in natural gas.
Q 02Which former Russian agent died in London in 2006 after being poisoned with alpha-emitting polonium-210?
Alexander Litvinenko
Alexander Litvinenko's doctors were baffled for three weeks: polonium-210 gives off almost no gamma rays, and its alpha particles are hard to pick up with ordinary radiation detectors.
Q 03Heat from the alpha decay of plutonium-238 has powered which pair of NASA probes since their launch in 1977?
Voyager
Voyager 1 and 2 each carry three generators that turn the warmth of decaying plutonium into electricity, which kept them reporting home for decades, all the way into interstellar space.
Q 04Which famous linen relic did three laboratories radiocarbon date in 1988, finding it was woven in the Middle Ages?
Shroud of Turin
The Shroud of Turin's flax stopped taking in carbon-14 the day it was harvested, and the decay since then dated it to 1260–1390, the very period in which the cloth first appears in records.
Q 05A positron is the mirror-image twin of the electron, so positron decay naturally produces which exotic kind of matter?
Antimatter
Antimatter was first seen in the form of a positron. When one meets an electron, the pair vanish in a flash of gamma rays, so positrons from a decay never travel far.
Q 06Hans Geiger and Ernest Marsden revealed the atomic nucleus by firing alpha particles at a thin foil of which metal?
Gold
Gold is the most malleable metal, so the foil could be beaten extremely thin. Most alpha particles sailed straight through, but a few bounced back off something tiny and dense.
Q 07Which synthetic element, named after a continent, supplies the alpha particles inside many household smoke detectors?
Americium
Americium-241's alpha particles let a trickle of electricity flow through the air inside the detector. Smoke drifting in cuts it off and trips the alarm.
Q 08Which physicist's famous mass–energy equation is used to calculate the energy released when a nucleus decays?
Albert Einstein
Albert Einstein's E = mc² does the sum: the products of a decay weigh slightly less than the original nucleus, and the missing mass is the energy carried away.
Q 09Tritium, which makes some exit signs glow without electricity, is a radioactive isotope of which element?
Hydrogen
Hydrogen usually has no neutrons at all, but tritium has two. It beta decays with a half-life of about 12 years, and the particles it throws out make the sign's coating glow.
Q 10Carbon-14, the isotope behind radiocarbon dating, beta decays into which gas found in every breath of air?
Nitrogen
Nitrogen is also where carbon-14 comes from: cosmic rays turn atoms of it high in the atmosphere into carbon-14, which slowly decays back over thousands of years.
Q 11Uranium-238 emits an alpha particle, moving two places back in the periodic table, to become which element?
Thorium
Thorium-234 is only the first stop: it beta decays within weeks, the first of thirteen more decays before the atom finally becomes stable.
Q 12Radium-226 emits an alpha particle and turns into which radioactive gas that can build up in basements?
Radon
Radon is a gas while everything else in uranium's decay chain is a solid, so it alone can seep out of rock and soil and collect indoors, where breathing it can cause lung cancer.
Q 13Uranium-238's long decay chain of alpha and beta steps finally stops at a stable isotope of which heavy metal?
Lead
Lead-206 is where the chain stops, so the lead that has built up in a uranium-bearing mineral shows how long ago it formed, a clock that has dated the oldest rocks on Earth.
Q 21Iodine-131, the fallout isotope that collects in the thyroid, beta decays into which element, one atomic number higher?
Xenon
Xenon-131 is stable and almost completely unreactive, so an atom that began by homing in on the thyroid ends its career as a harmless noble gas.
Q 22Outside an atomic nucleus, a lone neutron beta decays into a proton after roughly how long on average?
About 15 minutes
About 15 minutes is the average life of a free neutron, yet locked inside a stable nucleus the very same particle can last for billions of years.
Q 23Beta particles pass easily through paper, but school demonstrations stop them with a thin sheet of which metal?
Aluminium
Q 14Which Odessa-born physicist explained alpha decay in 1928 as a particle tunnelling through an energy barrier?
George Gamow
George Gamow showed that an alpha particle with too little energy to climb out of the nucleus can still leak through the wall. He later became a leading champion of the Big Bang.
Q 15Which Austrian physicist proposed the neutrino in 1930 to explain the energy that seemed to vanish in beta decay?
Wolfgang Pauli
Wolfgang Pauli's particle interacts so rarely that it can cross the whole Earth untouched, and none was caught until 1956, twenty-six years after he suggested it.
Q 16Which Italian physicist, who later built the first nuclear reactor, wrote the first theory of beta decay in 1934?
Enrico Fermi
Enrico Fermi's theory made room for the newly proposed neutrino and spread its name, which is Italian for little neutral one.
Q 17Which of the four fundamental forces of nature causes beta decay by turning a neutron into a proton?
Weak interaction
The weak interaction is the only force that can change one flavour of quark into another, and that swap is what converts a neutron into a proton.
Q 18Beta-minus decay turns a neutron into a proton by changing one of its quarks into an up quark from which flavour?
Down
Down becomes up, leaving two up quarks and one down, which is the recipe for a proton. The change also throws out an electron and an antineutrino.
Q 19Caesium-137, a notorious fallout isotope, beta decays into which element that patients swallow before some X-rays?
Barium
Barium-137m is what forms first, and this short-lived product, not the caesium itself, fires off the gamma rays that detectors pick up from fallout.
Q 20Cobalt-60, the gamma source in radiotherapy machines, beta decays into a stable isotope of which coin metal?
Nickel
Nickel-60 is born in an excited state and sheds the surplus energy as two gamma rays. Those rays, not the beta particle, are what radiotherapy puts to use.
Aluminium a few millimetres thick stops most beta particles, though as they brake they can give off X-rays of their own, known as bremsstrahlung, German for braking radiation.
Q 24Which hospital imaging technique, known by a three-letter abbreviation, follows tracers that emit positrons?
PET scan
A PET scan never sees the positrons themselves: each one soon meets an electron, and the pair turn into two gamma rays flying in opposite directions, which the scanner traces back.
Q 25Which element's isotope 18, built into a sugar-like molecule, emits the positrons in a common cancer-scan tracer?
Fluorine
Fluorine-18 has a half-life of under two hours, so it is made to order in a particle accelerator and hurried to the scanner before it fades away.
Q 26Which American physicist discovered the positron in 1932 while studying cosmic-ray tracks at Caltech?
Carl Anderson
Carl Anderson noticed tracks left by something with the mass of an electron but the opposite charge. The find won him a Nobel Prize just four years later.
Q 27Which daughter of two Nobel laureates shared the 1935 chemistry prize for creating radioactive isotopes artificially?
Irène Joliot-Curie
Irène Joliot-Curie and her husband Frédéric fired alpha particles at boron and found it went on emitting positrons after the bombardment stopped: radioactivity made to order.
Q 28Beryllium-7 decays by electron capture, absorbing one of its own electrons to become which rechargeable-battery metal?
Lithium
Lithium-7 is the result. Because the nucleus has to grab one of the atom's own electrons, this is one of the few decays whose pace shifts, very slightly, with the atom's chemical surroundings.
Q 29Sodium-22 emits a positron and moves one place back in the periodic table to become which element?
Neon
Neon-22 is stable, and the swap happens because a proton in the nucleus turns into a neutron: the mirror image of what happens in ordinary beta decay.
Q 30Potassium-40, the isotope that makes bananas faintly radioactive, usually beta decays into which element?
Calcium
Calcium-40 is the result about nine times in ten. The rarer route, in which the nucleus captures an electron and becomes argon, is the one geologists use to date volcanic rock.