The year was 1966, the height of the cold war and the final years of the Franco dictatorship, when an American B-52 bomber carrying four thermonuclear bombs collided with a supply plane above the village of Palomares in south-eastern Spain.
Two bombs landed intact, one just outside the village of 1,200 people in the province of Almería, the other salvaged, unscathed, by a fisherman five miles offshore in the Mediterranean, at a depth of 760 metres (2,500 feet). The third and fourth bombs were damaged by a chemical explosion on impact, releasing about 20kg (44lb) of plutonium into the centre of Palomares and surrounding hills.
Nobody died or is known to have developed cancer, but Spain's worst nuclear accident took three months and the work of 1,600 US specialists to clean up before it was promptly forgotten outside of Spain. The amnesia was helped along with a now legendary stunt by the former minister of tourism under Franco, Manuel Fraga, who took a much-photographed swim in the Mediterranean with the American ambassador to prove the waters - and budding tourist industry - were safe.
More than 40 years later, the Spanish nuclear regulatory agency and a national research centre on the environment, energy and technology, CIEMAT, have concluded the first large-scale study of the extent of radioactive contamination around the village, now perched in the middle of the nationwide building frenzy.
It found that the area of soil contaminated with americium, a radioactive metal derived from plutonium, is more than three times larger than was previously thought: 300,000 square metres.
The largest pocket of contamination was discovered to the east of Palomares in the Almagrera hills, where one of the bombs released a cloud of smoke and radioactive particles that was spread by the winds.
The nuclear regulatory agency is expected to prohibit building or selling produce grown inside the contaminated area at its meeting today, according to El País. "There is no health risk," Teresa Mendiz bal, director of environmental studies for CIEMAT, told El País. "The dose of radiation is very low, and we are only restricting use of the land where there is americium, but only as a precaution."
Experts sampled a total of 6.6m square metres, and only about 4.5% showed radiation above accepted limits. "We've looked at an enormous area in detail and the results are reassuring," she said.
The €200,000 (£135,000) study, subsidised partly by the US government, was belatedly commissioned when it became clear that this arid and once sparsely populated slice of southern Spanish coastline was being engulfed by housing developments and golf courses.
Palomares is located next to the growing resort areas of Vera and Cuevas de Almanzores. As plans for holiday villas spread to Palomares, environmental experts feared that moving the soil during construction could release dangerous particles into the air.