Since “An Inconvenient Truth” came out in 2006, Participant Media has become a brand name for creating documentaries expertly machined to educate, terrify and galvanize. And the formula works again in “Countdown to Zero,” Lucy Walker’s alternately edifying and alarming film about nuclear proliferation.

As a template, Walker uses John F. Kennedy’s 1961 speech to the United Nations — in which he described a “nuclear sword of Damocles, hanging by the slenderest of threads, capable of being cut at any moment by accident or miscalculation or by madness” — then proceeds to give examples of how close we’ve come to having the sword lowered.

Using archival images of mushroom clouds and imploding houses, street interviews with everyday citizens who have no idea who has nukes or how many, and a plethora of wise talking heads, Walker makes a clear, cogent and irrefutable case for the total elimination of nuclear weapons.

Skeptics need only sit in on a chilling conversation with a Russian smuggler who was arrested before selling highly enriched uranium to agents posing as al-Qaida, all so that he could afford some kitchen appliances.

Or listen as former U.S. launch control officer Bruce Blair (an executive producer of the film) explains how as a young lieutenant he could have brought on nuclear Armageddon with the numbingly simple code of 12 zeros.

Or witness the sobering litany of near-misses we never heard about during the Cold War, when the rising moon and a flock of geese were both mistaken for incoming missiles in Russia. (“Thank God Yeltsin wasn’t drunk,” one witness recalls of another episode.)

The most chilling passage might belong to nonproliferation policy expert Joseph Cirincione, who explains that the most dangerous place on Earth is probably Pakistan, where an unstable government, nuclear weapons and Osama bin Laden coexist in perilous proximity.

The world that emerges in “Countdown to Zero” is a lawless place of porous borders and amoral, anarchic forces, where a cache of HEU or plutonium can enter the country as easily as a shipment of kitty litter or marijuana.

Educating? Check. Terrifying? Check. Galvanizing? We can only hope.