50 Fun Facts About Radioactivity

Which scientist coined the word radioactivity and is the only person to win Nobel Prizes in two different sciences?

Marie Curie took the physics prize in 1903 and the chemistry prize in 1911. Her notebooks, and even her cookbooks, are still radioactive.

Which glowing element did American factory women paint onto watch dials in the 1920s before suing over their poisoning?

Radium was in the luminous paint, and the women were told to sharpen their brushes on their lips. Their lawsuits brought major improvements in industrial safety.

Which fruit gives its name to an informal unit of radiation dose because of the potassium it naturally contains?

Banana equivalent dose compares an exposure to eating one banana, whose potassium-40 is very slightly radioactive. The body sheds surplus potassium, so the dose never builds up.

Which isotope, with a half-life of about 5,730 years, lets archaeologists date ancient wood, bone and cloth?

Carbon-14 is taken up by every living thing until it dies, and then the clock starts ticking. Willard Libby won the 1960 Nobel Prize in Chemistry for the method.

Which nuclear power plant's 1986 reactor explosion forced the permanent evacuation of the nearby city of Pripyat?

Chernobyl's reactor 4 exploded on 26 April 1986. Pripyat's 49,000 or so residents were bussed out the next day, and the city has stood empty ever since.

A speck of radioactive americium-241 ionises the air inside which common household safety device?

A smoke detector of the ionisation type relies on alpha particles to keep a tiny current flowing through its chamber. Smoke drifting in disturbs the current and trips the alarm.

Which famous thought experiment uses one radioactive atom's random decay to trigger a flask of poison in a sealed box?

Schrödinger's cat is, in theory, both alive and dead until someone opens the box. Erwin Schrödinger devised the puzzle in 1935 while debating quantum mechanics with Albert Einstein.

What colour is the Cherenkov glow that surrounds highly radioactive fuel rods stored underwater in a reactor pool?

Blue light appears because charged particles from the fuel move through the water faster than light does there. Pavel Cherenkov shared the 1958 Nobel Prize in Physics for detecting it.

Which radioactive gas seeps from rock into basements and ranks second only to smoking as a cause of lung cancer?

Radon has no colour or smell, so only a test kit reveals it. It is denser than air, which is why it collects in basements and crawl spaces.

Which element, named after its discoverer's homeland, killed former Russian agent Alexander Litvinenko in London?

Polonium-210 killed him three weeks after he fell ill, the first confirmed death of its kind. The element honours Poland, birthplace of the scientist who found it in 1898.

The three classic types of nuclear radiation are named after the first three letters of which alphabet?

Greek letters alpha, beta and gamma were handed out in rising order of penetrating power. Alpha rays are the easiest to block and gamma rays the hardest.

An alpha particle carries a charge of plus two and is identical to the nucleus of which light element?

Helium nuclei are what alpha particles really are, and most of the helium on Earth began that way. It builds up underground as heavy elements decay and collects in natural gas fields.

A beta-minus particle, which a few millimetres of aluminium will stop, is identical to which subatomic particle?

Electron is the everyday name for a beta-minus particle, but it is not waiting inside the nucleus beforehand. It is created at the instant of decay and leaves at tremendous speed.

Which dense metal is the standard shield against gamma rays and also the stable end point of uranium's decay chain?

Lead is where all three natural decay chains finish, each at its own stable isotope. Its density also makes it the usual lining for containers of radioactive material.

Which part of the human body is enough to stop alpha particles, which is why they mainly harm when swallowed or inhaled?

Skin stops them within about 40 micrometres, only a few cells deep. Inside the lungs or gut there is no such barrier, so the same particles strike living tissue directly.

Which radiation detector clicks faster as a radioactive source gets closer?

Geiger counter clicks each mark one ionising event inside a gas-filled tube. The principle dates from 1908, but a practical instrument had to wait for an improved tube in 1928.

Wilhelm Röntgen's 1895 discovery of which radiation prompted the experiments that revealed radioactivity months later?

X-rays made physicists wonder whether glowing minerals gave off something similar. Tests with uranium salts in early 1896 showed they darkened photographic plates with no sunlight at all.

Which French physicist, namesake of the SI unit of radioactivity, found that uranium salts fog photographic plates?

Henri Becquerel owed the discovery to bad weather: on two overcast days he left his plates in a dark cabinet, and they fogged anyway. One becquerel is one decay per second.

Which New Zealand-born physicist named alpha and beta rays and later showed that atoms have a tiny, dense nucleus?

Ernest Rutherford coined the two names in 1899 and proposed the nucleus in 1911, after alpha particles were seen bouncing off thin gold foil. He is called the father of nuclear physics.

After a reactor accident, tablets of stable iodine are handed out to protect which gland from radioactive iodine?

Thyroid tissue soaks up iodine to make hormones and cannot tell the stable kind from the radioactive kind. Filling it with harmless iodide first means iodine-131 is flushed away instead.

Uranium-238 emits an alpha particle and becomes which element, named after a Norse god?

Thorium honours Thor, the god of thunder. The thorium-234 made this way is unstable too, the first of many steps in a long decay chain.

Potassium-40 decays into which noble gas, a clock geologists use to date ancient volcanic rock?

Argon escapes from molten rock but starts to build up once the rock hardens, so the clock starts at zero. Nearly all the argon in the air came from this decay.

In beta-minus decay, which particle in the nucleus transforms, moving the atom one place up the periodic table?

Neutron becomes proton in this decay, and a beta particle flies out to balance the charge. The atom's mass barely changes, yet it is now a different element.

Wolfgang Pauli proposed which almost massless particle to explain energy that seemed to vanish during beta decay?

Neutrino means little neutral one in Italian. About 65 billion of them from the Sun pass through every square centimetre of you each second.

PET scanners detect the gamma rays released when which particle, emitted in beta-plus decay, is annihilated?

Positron is the P in PET. Each one meets its ordinary-matter twin almost at once, and the pair vanish into two gamma rays flying in opposite directions.

School demonstrations block alpha particles with a single sheet of which material, saving aluminium for beta rays?

Paper is enough because an alpha particle is heavy and doubly charged, so it gives up its energy quickly. Even in air it travels only a few centimetres.

Which quantity, written as a superscript to the left of an element's symbol, falls by four in alpha decay?

Mass number counts every particle in the nucleus, and an alpha particle carries off four of them. The atomic number falls by only two, so the atom moves two places down the periodic table.

Physicists call a decaying radioactive nucleus the parent, so which family word names the new nuclide it becomes?

Daughter nuclides are often radioactive themselves, and what they decay into is called a granddaughter. A long run of such generations makes up a decay chain.

Which of the four fundamental forces of nature is responsible for the beta decay of radioactive atoms?

Weak force is the only one of the four that can change one type of quark into another. That swap is what turns a decaying atom into a different element.

George Gamow explained how alpha particles escape a nucleus with which quantum effect, also vital to fusion in stars?

Tunnelling gives a trapped alpha particle a tiny chance of turning up outside an energy barrier it could never climb. Gamow's theory also showed why faster particles mean shorter half-lives.

Which Austrian-born physicist explained how uranium nuclei split, yet was left off Otto Hahn's Nobel Prize?

Lise Meitner worked out the physics in exile after fleeing Nazi Germany in 1938. Element 109, meitnerium, was later named in her honour.

Which Italian-born physicist led the team that started the first nuclear reactor, under a Chicago sports stand?

Enrico Fermi's reactor first ran on 2 December 1942 at about half a watt, too feeble to light a bulb. It had no shielding or cooling system at all.

Which process, first proved in a Berlin laboratory in 1938, releases the heat that drives nuclear power stations?

Fission got its name from physicist Otto Frisch, who borrowed the word biologists use for a dividing cell. Splitting one heavy nucleus can set off others, creating a chain reaction.

Which code name was given to the first nuclear weapon test, held in the New Mexico desert in July 1945?

Trinity is a name often credited to J. Robert Oppenheimer, though its true origin is unknown. The blast melted the desert sand into a pale green glass now called trinitite.

Which Marvel superhero does physicist Bruce Banner become after being caught in a blast of gamma rays?

The Hulk was grey in his first issue in 1962, but the shade printed so unevenly that Stan Lee switched him to green.

Which three-bladed shape, usually black on a yellow background, is the international warning symbol for radiation?

Trefoil signs were first drawn in 1946 at the University of California's Radiation Laboratory in Berkeley. The earliest versions were magenta instead of black.

Which radioactive form of hydrogen makes emergency exit signs and watch hands glow for years without any electricity?

Tritium gives off beta particles that strike a phosphor coating and make it shine. Its half-life is about 12 years, so the glow fades slowly over a decade or two.

Which element, the first ever made artificially, provides the tracer used in millions of hospital scans each year?

Technetium is the lightest element whose every form is radioactive, so almost none survives in nature. Its name comes from a word meaning artificial.

Gamma rays from which reactor-made isotope sterilise medical equipment and treat tumours in radiotherapy machines?

Cobalt-60 barely exists in nature, so it is bred by leaving ordinary cobalt inside a reactor. Its rays have also been used to sterilise insect pests such as the screwworm fly.

Which element's isotope 238 supplies the heat that has kept both Voyager spacecraft running for decades?

Plutonium-238 has a half-life of nearly 88 years, so its warmth fades slowly. Thermocouples on board turn that heat straight into electricity.

Which SI unit, named after a Swedish medical physicist, measures the health risk of a dose of radiation?

Sievert doses are usually quoted in thousandths: the recommended yearly limit for the public is one millisievert on top of natural background, not counting medical exposure.

Which metal, used in upset-stomach remedies, was thought stable until its very slow alpha decay was detected in 2003?

Bismuth has a half-life roughly a billion times longer than the age of the universe. For every practical purpose it still counts as stable.

Which radioactive isotope from nuclear bomb tests is nicknamed a bone seeker because the body mistakes it for calcium?

Strontium-90 behaves so much like calcium that the body builds it into bones and teeth. A survey that collected 320,000 baby teeth found levels rising in children born in the 1950s.

Scrap dealers in Goiânia spread which radioactive element in 1987 after opening an abandoned hospital machine?

Caesium-137 salt from the machine glowed in the dark, so the finders passed it around family and friends. Four people died, and about 112,000 were checked for contamination.

Which nut is more radioactive than most common foods because its tree's vast roots concentrate elements from the soil?

Brazil nut trees have very extensive root systems that gather naturally radioactive material from the soil. The dose from eating the nuts is small, though higher than from everyday foods.

Which rock, popular for kitchen worktops, is mildly radioactive because it holds far more uranium than limestone?

Granite can hold 10 to 20 parts per million of uranium, several times the level in most other rocks. The potassium in its feldspar crystals is faintly radioactive too.

Which mineral from Australia's Jack Hills, dated by its trapped uranium, is the oldest known material formed on Earth?

Zircon crystals from the site formed about 4.4 billion years ago, not long after the planet itself. Their chemistry suggests liquid water was already present on the surface.

In which African country did a natural nuclear reactor run by itself at Oklo, nearly two billion years ago?

Gabon's ore gave the secret away in 1972, when French chemists found it oddly short of uranium-235. The reactions had flickered on and off for a few hundred thousand years.

Power stations burning which fuel give the public a bigger radiation dose than a nuclear plant of the same size?

Coal holds traces of uranium that end up in its ash and fumes. One estimate puts the dose from a coal-fired plant at more than three times that of an equivalent nuclear one.

Which element is the rarest found naturally in Earth's crust, with less than a gram existing at any one moment?

Astatine forms only when heavier elements decay, and it soon decays in turn. Its name comes from a word meaning unstable.