Britain's Prince Harry checking out an Apache helicopter in Afghanistan. (John Stillwell/AFP/Getty Images)

Annoyed, perhaps a bit frightened by that low-flying helicopter that’s been buzzing your neighborhood at 80 mph?

Is the United Nations flying exploratory missions, preparing for that massive black helicopter attack it’s been planning to take away our freedoms?

Relax. It’s the National Nuclear Security Administration (NNSA), measuring what it says is “naturally occurring radiation” in this area.

The agency says its helicopter, “equipped with remote gamma radiation sensing technology” and flying as low as 150 feet above the ground, is measuring radiation “to determine baseline levels.”

It’s likely that once you know what those levels are, you can figure out when something unusual — and maybe nasty — might be going on.

The two-week operation began just after Christmas and ends Friday, according to an agency announcement — which preceded the flights — that was put out “so that citizens . . . are not alarmed.”

The flights have been only in daylight, said the agency, which is part of the Department of Energy. So if you’re hearing low-flying helicopters at night, that might be the U.N. folks.