How does a nuclear weapon initiator function?

A nuclear weapon initiator, sometimes called a neutron initiator, functions by producing a burst of neutrons at the precise moment that the fissile material reaches its most supercritical state. This injection of neutrons starts the chain reaction uniformly and rapidly throughout the compressed core, ensuring a more efficient and powerful explosion. One common type of initiator, known as a polonium-beryllium initiator, consists of two separate materials: polonium-210 and beryllium. Polonium-210 is an alpha emitter, meaning it decays by emitting alpha particles (helium nuclei). The polonium and beryllium are kept physically separated until the moment of detonation. When the high explosives detonate and compress the fissile core, they also force the polonium and beryllium together. When alpha particles from the polonium strike the beryllium, they induce a nuclear reaction that releases neutrons. This reaction is: alpha particle + Beryllium-9 -> Carbon-12 + neutron. The sudden release of neutrons ensures that the chain reaction starts promptly and uniformly throughout the compressed fissile material. Without an initiator, the chain reaction might start spontaneously due to naturally occurring background neutrons, but this would be unpredictable and likely inefficient, leading to a lower yield or a 'fizzle yield.' The initiator ensures that the chain reaction starts at the optimal moment for maximum efficiency.