50 Fun Facts About Radioactive Decay

An alpha particle, two protons and two neutrons bound together, is identical to the nucleus of which light element?

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.

Which former Russian agent died in London in 2006 after being poisoned with alpha-emitting polonium-210?

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.

Heat from the alpha decay of plutonium-238 has powered which pair of NASA probes since their launch in 1977?

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.

Which famous linen relic did three laboratories radiocarbon date in 1988, finding it was woven in the Middle Ages?

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.

A positron is the mirror-image twin of the electron, so positron decay naturally produces which exotic kind of matter?

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.

Hans Geiger and Ernest Marsden revealed the atomic nucleus by firing alpha particles at a thin foil of which metal?

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.

Which synthetic element, named after a continent, supplies the alpha particles inside many household smoke detectors?

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.

Which physicist's famous mass–energy equation is used to calculate the energy released when a nucleus decays?

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.

Tritium, which makes some exit signs glow without electricity, is a radioactive isotope of which element?

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.

Carbon-14, the isotope behind radiocarbon dating, beta decays into which gas found in every breath of air?

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.

Uranium-238 emits an alpha particle, moving two places back in the periodic table, to become which element?

Thorium-234 is only the first stop: it beta decays within weeks, the first of thirteen more decays before the atom finally becomes stable.

Radium-226 emits an alpha particle and turns into which radioactive gas that can build up in basements?

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.

Uranium-238's long decay chain of alpha and beta steps finally stops at a stable isotope of which heavy metal?

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.

Which Odessa-born physicist explained alpha decay in 1928 as a particle tunnelling through an energy barrier?

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.

Which Austrian physicist proposed the neutrino in 1930 to explain the energy that seemed to vanish in beta decay?

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.

Which Italian physicist, who later built the first nuclear reactor, wrote the first theory of beta decay in 1934?

Enrico Fermi's theory made room for the newly proposed neutrino and spread its name, which is Italian for little neutral one.

Which of the four fundamental forces of nature causes beta decay by turning a neutron into a proton?

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.

Beta-minus decay turns a neutron into a proton by changing one of its quarks into an up quark from which flavour?

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.

Caesium-137, a notorious fallout isotope, beta decays into which element that patients swallow before some X-rays?

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.

Cobalt-60, the gamma source in radiotherapy machines, beta decays into a stable isotope of which coin metal?

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.

Iodine-131, the fallout isotope that collects in the thyroid, beta decays into which element, one atomic number higher?

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.

Outside an atomic nucleus, a lone neutron beta decays into a proton after roughly how long on average?

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.

Beta particles pass easily through paper, but school demonstrations stop them with a thin sheet of which metal?

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.

Which hospital imaging technique, known by a three-letter abbreviation, follows tracers that emit positrons?

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.

Which element's isotope 18, built into a sugar-like molecule, emits the positrons in a common cancer-scan tracer?

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.

Which American physicist discovered the positron in 1932 while studying cosmic-ray tracks at Caltech?

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.

Which daughter of two Nobel laureates shared the 1935 chemistry prize for creating radioactive isotopes artificially?

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.

Beryllium-7 decays by electron capture, absorbing one of its own electrons to become which rechargeable-battery metal?

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.

Sodium-22 emits a positron and moves one place back in the periodic table to become which element?

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.

Potassium-40, the isotope that makes bananas faintly radioactive, usually beta decays into which element?

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.

Alpha and beta rays are fragments of matter, whereas a gamma ray is a very energetic example of which massless particle?

Photon is the name for a particle of light, and one from a gamma ray carries at least thousands of times the energy of a visible one, enough to pass straight through the body.

The m in technetium-99m, the most used medical radioisotope, stands for which word describing its excited nucleus?

Metastable nuclei are stuck in an excited state. Technetium-99m lingers for about six hours before relaxing with a single gamma ray, long enough to be injected and scanned.

Which French scientist discovered gamma rays in 1900 while studying the radiation given off by radium?

Paul Villard never gave his rays a name. That came three years later, once the labels alpha and beta had already been handed out in order of penetrating power.

A radioactive sample has a half-life of ten days, so what fraction of the original atoms remains after twenty days?

One-quarter remains, because each half-life halves whatever is left: a half after ten days, then half of that. In theory the amount never quite reaches zero.

Which Greek letter do physicists use for the decay constant, the chance that a given nucleus decays each second?

Lambda is the decay constant, and dividing 0.693 by it gives the half-life, so a large value means an isotope that disappears quickly.

Which New Zealand-born physicist named alpha and beta rays in 1899 and later introduced the idea of half-life?

Ernest Rutherford ranked the rays by how deeply they penetrate. His 1908 Nobel Prize came in chemistry, not physics, for showing that radioactive atoms break up into other elements.

Which English chemist introduced the word isotope and won the 1921 Nobel Prize for his work on radioactive elements?

Frederick Soddy took the word, which means same place, from a suggestion by Margaret Todd: atoms of different mass can share one square of the periodic table.

Which SI unit of radioactivity, named after a French physicist, equals one nuclear decay per second?

Becquerels are tiny: the potassium naturally present in one human body produces roughly 4,000 decays every second.

Which detector, invented by Scottish physicist Charles Wilson, makes the tracks of alpha and beta particles visible?

A cloud chamber shows an alpha particle as a thick, straight streak and a beta particle as a thin, wandering thread, each a line of droplets forming along the particle's path.

Which American chemist won the 1960 Nobel Prize for developing radiocarbon dating at the University of Chicago?

Willard Libby had spent the war enriching uranium for the Manhattan Project. His dating method, worked out in the late 1940s, went on to transform archaeology.

Which element named after a US state has an isotope, mass 252, that works as a powerful portable source of neutrons?

Californium-252 owes its neutrons to spontaneous fission: about 3 percent of its nuclei split apart unprompted instead of emitting an alpha particle.

Uranium-239 beta decays into which element, the first one beyond uranium in the periodic table?

Neptunium-239 lasts only a couple of days before a second beta decay turns it into plutonium-239, which is how reactors breed that fuel from ordinary uranium.

Which Chinese-American physicist showed in 1956 that the beta decay of cobalt-60 does not respect mirror symmetry?

Chien-Shiung Wu's result won the 1957 Nobel Prize for the two theorists who had proposed the test, but not for her; she was honoured with the first Wolf Prize in 1978.

Which English physicist discovered the neutron in 1932 in the radiation that alpha particles knock out of beryllium?

James Chadwick realised that a mystery radiation other researchers had taken for gamma rays was really a stream of neutral particles about as heavy as protons.

Which word, borrowed from alchemy, describes one element changing into another, as happens in alpha and beta decay?

Transmutation by chemical means, the alchemists' old goal, is impossible, yet unstable nuclei manage it all by themselves, with no outside help.

Which collective name covers both protons and neutrons, the particles counted in an atom's mass number?

Nucleon numbers are what alpha decay changes most: the nucleus loses four at a stroke, while beta decay swaps one kind for the other and leaves the total alone.

Which word describes radiation able to strip electrons from atoms, the property that lets Geiger counters work?

Ionising radiation leaves a trail of charged atoms behind it, which is how it damages the DNA in living cells and why even small doses are tracked carefully.

Which letter, taken from the German word for number, do scientists use as the symbol for atomic number?

Z stands for Zahl, and it is the number that decay rewrites: alpha decay lowers it by two, beta decay raises it by one and positron emission lowers it by one.

Roughly how long is the half-life of uranium-238, the isotope that makes up over 99 percent of natural uranium?

4.5 billion years is about the age of the Earth, so roughly half of the uranium-238 the planet was born with has yet to decay.

Which rare-earth metal, element 61, has no stable isotopes even though both its neighbours in the periodic table do?

Promethium shares that oddity only with technetium, and is so scarce that Earth's entire crust holds little more than half a kilogram of it at any moment.