Ask Fuzzy: How do you trigger a nuclear weapon?

Emerging in a time of crisis during World War II, humanity harnessed the ability to obliterate itself through accident or the whim of a lunatic.

Well known is the fact that the Manhattan Project developed two atomic bombs using somewhat different approaches.

The Little Boy bomb dropped on Hiroshima used conventional explosives to drive two subcritical masses of uranium-235 into each other.

Exploding at 600 metres above the city with the force of approximately 15 kilotons of TNT, it released a tremendous blast wave. Combined with intense heat and ionising radiation, it immediately killed 70,000 to 80,000 people.

Three days later, Fat Man was dropped on Nagasaki. Employing a design that used conventional explosives to compress a subcritical mass of plutonium-239 into a supercritical state, it yielded a 20 kiloton TNT-equivalent explosion that killed 40,000 people.

Less well known is the role of polonium-210 and beryllium-9 as a triggering mechanism, probably the most complex facet of weapon design. In the Fat Man, this provided a neutron source to initiate nuclear detonation.

READ MORE:

Located in the centre of the bomb's plutonium shell, it was dubbed The Urchin due to its wedge-shaped latitudinal grooves. Coated with gold and nickel, the entire assembly weighed only seven grams and fitted inside the 2.5cm-diameter plutonium pit.

While the amount of polonium was tiny - 11mg - obtaining it for the Manhattan Project was an extremely difficult, industrialised process.

Although small amounts of polonium were available from lead residues, there was nowhere near enough with the necessary purity.

Instead they produced the polonium in nuclear piles at a plant in Dayton, Ohio. It involved bombarding large quantities of highly refined bismuth.

In all, it was an extraordinarily hazardous operation due to the extreme toxicity of polonium and other substances such as antimony.

Polonium is one of the most dangerous substances known. If swallowed, a dose of about 50 nanograms (ng) is lethal; if inhaled, a deadly dose is closer to 10ng. That theoretically means a single gram could poison 20 million people, of whom half would die.

Indeed, ex-KGB agent Alexander Litvinenko was murdered by being poisoned with polonium-210 in 2006, believed to have been administered by Russian agent Andrei Lugovoy.

Listen to the Fuzzy Logic Science Show at 11am every Sunday on 2XX 98.3FM.

Send your questions to AskFuzzy@Zoho.com Twitter@FuzzyLogicSci

We've made it a whole lot easier for you to have your say. Our new comment platform requires only one log-in to access articles and to join the discussion on The Canberra Times website. Find out how to register so you can enjoy civil, friendly and engaging discussions. See our moderation policy here.

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: