[♪ INTRO]In July 1945, a group of scientists gathered in New Mexico and began a new age of science by detonating a nuclear bomb.

It was called the Trinity test and was part of the larger Manhattan Project, which successfully developed nuclear technology for World War II. But there were also some unexpected consequences.

For example, the radioactive particles from the bomb test went into places no one had thought of. Like into the rainwater more than 1600 kilometers away in Indiana. Almost no one knew about this until years later in the 1990s, when the National Cancer Institutes started releasing reports about it.

No one, that is, except the Kodak camera company. It all started when Kodak customers began returning their X-Ray films because they were unusable. The films had been fogged; that is, they looked like they had already been exposed.

Which isn’t helpful if you’re trying to diagnose a patient. First, people guessed that the fogging was caused by the radioactive element radium,since it could trigger and expose X-Ray films if it managed to get into the package. And, since radium was a lot more common back then, it seemed like an easy target.

At the time, we didn’t really understand how bad playing with radioactive material was. So radium appeared in all kinds of stuff, like radium paint, which was used to make glow in the dark watches up until the 1960s. Kodak was already taking precautions to keep contamination down, but just in case, a company researcher named Julian Webb started looking into it.

And he found that the radiation wasn’t from anything inside the package,it was in the packaging itself. The kind of radiation didn’t even match radium, or anything else in nature. Which was probably not that comforting.

For one, it was made of the wrong kind of particles. Radium mainly emits what’s called alpha radiation,which are clumps of two neutrons and two protons. Meanwhile, the radiation from the packaging was mostly beta radiation,which is made up of single electrons.

Also, the half-life of the radiation was wrong. Half-life is a measure of how long it takes half of something radioactive to decay into something else. It can vary from milliseconds to thousands of years,and it’s different for every isotope of every element.

The radiation Webb measured did not have radium’s half-life, which is about 1600 years. The half-life in the packaging was roughly 31 days, which is a little different. So, whatever was in the packaging definitely wasn’t radium.

By comparing his measurements to other sources of radiation, Webb eventually linked it to an isotope of cerium, called cerium-141, which has one more neutron than normal. He then traced that to a specific paper mill in Indiana,and to a specific production run from that August. Since the raw materials in the mill were stored indoors and away from any source of radioactivity,Webb knew that couldn’t be the problem.

But, he did notice the paper mill was right next to a river,and that contamination was worse after heavy rain. Eventually, Webb made the connection: The radioactive particles were in the rain, and were being deposited into the river. And ultimately, he connected that to the Trinity test in New Mexico.

He didn’t actually publish his findings until four years later, in 1949 in the journal Physical Review, so it isn’t clear how long it took him to make the connection. But once he realized the rain was radioactive,and that the film problems started just a few weeks after the Trinity test,it couldn’t have taken him that long to put two and two together. And we know he was right.

When a nuclear bomb goes off, it throws a huge number of particles into the air, a lot of which are radioactive, like cerium-141. They’re also small and light enough to be carried on the wind. There, they mix with water vapor and get caught in clouds.

When it rains, down go the radioactive particles, and your umbrella just won’t cut it. Since it falls out of the air, this kind of radiation is called fallout, and it’s the same thing happened in Hiroshima, Japan, after World War II. There, some called it the “Black Rain” because of all the soot that also fell in the rainwater.

Now, even though Webb kept his discovery from the public for years, and no one’s positive why, he was still one of the first citizens to find evidence of it. Which isn’t what usually comes to mind when you think of a camera company. Of course, because we didn’t understand how dangerous radiation was, and because people thought nuclear bombs were really important, his paper didn’t do much to slow testing.

Several years later, in 1951, the American government detonated more test bombs in Nevada. And in New York, more than 3200 kilometers away, a Geiger counter in the Kodak office detected the fallout after a big snowstorm. Which is… concerning.

And unfortunately, those storms came with consequences. The National Cancer Institute estimated that the fallout from those tests could have caused tens of thousands of cases of lung and thyroid cancer from molecules like cerium-141 andiodine-131, another radioactive particle from the bombs. Thankfully, the United States hasn’t conducted above-ground nuclear tests like that since the 1960s, so these days, you only have to look out for regular rain.

But these nuclear tests are also an important reminder that, as we’re exploring new kinds of science, it’s important that we understand the consequences as best we can,and that we take them seriously. Thanks for watching this episode of SciShow! If you’d like to learn more about the early nuclear tests, you can watch our video all about the Manhattan Project.[♪ OUTRO]