There's a place in the New Mexico desert open to the public for just two days out of the year, but I got to visit by myself with only a small film crew.

This is the Trinity bomb test site, where on July 16th, 1945, at exactly 5:29 and 45 seconds in the morning, the first nuclear bomb was exploded.

The test was called Trinity; there was actually a tower here that stood 100 feet or about 30 meters.

The list of people who witnessed the test reads like a who's who of 20th-century physics: Fermi, Feynman, Oppenheimer, von Neumann.

But the test was top secret; the general public weren't to know.

But how do you hide a huge nuclear explosion?

Well, the Albuquerque Tribune published a statement claiming it was a large but accidental conventional explosion.

It wasn't just the general public who were kept in the dark; the governor of New Mexico was not even aware that Trinity was a nuclear test until after the bombing of Hiroshima.

Even then, details about the blast were scarce.

But Kodak, the film company based on the other side of the country in New York state, well, they figured out what was happening.

It all started with some defective x-ray film.

Kodak found when they developed unused film it showed tens or even a hundred little dark spots; the film had been exposed to radiation even though it had never been taken out of its packaging.

This was actually not a new problem.

During World War II, radium was used extensively to make glow-in-the-dark dials, flight instruments, and watches.

Radium glows because it is radioactive; it gives off alpha particles.

Now, some of this radium ended up on paper and cardboard at these factories, and because supplies were scarce, leftover paper products were salvaged and recycled, leading small amounts of radium to end up in the general paper supply.

And when this paper was used to package up Kodak film, radiation from radium would expose the film before it was ever used.

And it was such a problem that Kodak altered their supply chain, carefully selecting just a few paper mills where they could strictly control the raw materials.

One of the mills was in Vincennes, Indiana, on the Wabash River.

It made strawboard, which was inserted between sheets of x-ray film.

Now, for months, this strawboard was working perfectly until a batch manufactured on August 6, 1945, started to cause spots to appear on the x-ray film.

So Julian Webb, a scientist at Kodak, was tasked with solving the problem.

So he punched out little holes of strawboard behind where the film had been exposed, and then he measured the alpha particles coming off that material.

But the level was not appreciably higher than background, and this ruled out radium and the other naturally occurring isotopes of uranium, thorium, and actinium, all alpha emitters.

But when he measured beta radiation, he found significant activity; this matched what he saw on the film.

The radiation penetrated several layers, something beta particles can do but not alpha.

And over a period of months, he measured the half-life of the radioactive substance, finding it was only about 30 days.

This half-life, combined with the energy of the beta particles, led Webb to conclude that the radioactive contaminant was most likely Cerium-141, an isotope that could only have come from a nuclear fission explosion.

What's more, the same contaminant appeared in paper from another of Kodak's mills, this one hundreds of kilometers away in Tama, Iowa.

So how did Cerium-141 end up in that strawboard?

Well, when that first atomic bomb exploded in the New Mexico desert, the plutonium core underwent a fission chain reaction.

Plutonium nuclei ripped in two, releasing energy and more neutrons to continue the chain reaction.

But fission is a messy process; it doesn't always split the nucleus into the same products.

Instead, hundreds of different nuclei are produced, virtually all of them radioactive, and they are carried up into the stratosphere with the mushroom cloud and dispersed on air currents whichever way the wind blows.

In this case, they traveled over a thousand kilometers, ending up over Iowa and Indiana.

Here, rain captured some of these radioactive particles, causing them to fall out of the sky, hence the term radioactive fallout.

This radioactive material ended up in rivers like the ones that run beside the two Kodak paper mills, which used that river water to make their paper.

So that's how Cerium-141 ended up fogging Kodak's x-ray film and exposing the U.S. nuclear secret.

Now, word of Kodak's detection made it back to scientists at Los Alamos, who were intrigued and wanted to know more.

A consultant wrote to Webb to find out how much radioactivity per square mile he detected, and the size of the particles which fell, and the half-life of the activity.

Although Webb completed his experiments by the end of 1945, he only published them in Physical Review in 1949, and that's because I'm sure he recognized just how sensitive his findings were.

After all, he himself had worked on the Manhattan Project at Berkeley and Oak Ridge, using electromagnetic techniques to separate uranium isotopes.

What was clear to Kodak was that they needed to take steps to protect their film, and so they installed air samplers to monitor for fallout in the air intakes of their buildings.

Fallout is a vitally important subject; bombs are being tested which to some extent contaminate the atmosphere.

Now, the U.S. government was aware they needed to carefully consider where to test nuclear bombs.

What we need is a site closer to our stateside laboratories and available air support, somewhere in the continental United States, but where?

After Trinity, the Manhattan Project's chief of radiological safety, Stafford Warren, recommended tests be conducted at least 150 miles from civilian populations.

In 1948, an Air Force meteorologist, Colonel Holzman, told the site selection committee that a location on the East Coast would be best because otherwise the prevailing westerly winds across the U.S. would spread the fallout across the country.

The site they chose was Nevada, almost as far west as you can go and just 100 miles from Las Vegas.

The rationale was this site was closer to weapons labs so it would accelerate their development.

After the first bomb test there in 1951, Kodak detected fallout at their headquarters in Rochester, New York.

After a snowstorm, Geiger counters read 25 times the normal background.

So Kodak threatened to sue the U.S. government for the considerable amount of damage to our products resulting from the Nevada tests or from any further atomic energy tests.

But instead of a lawsuit, the two sides came to an agreement: the Atomic Energy Commission would give Kodak, and indeed the entire photographic industry, advanced warning about upcoming tests and where the fallout was likely to end up given meteorological models.

In return, the company agreed to keep quiet about radioactive fallout.

And from 1951 until 1963, the U.S. conducted a hundred above-ground nuclear tests in Nevada; the resulting mixture of radioactive nuclei was blown, as predicted, across most of the country.

When these atoms fell on agricultural land, they were eaten by livestock or taken up in crops, and they became part of the food supply.

Radioactive Iodine-131 eaten by cows is passed on to humans through their milk, and this is particularly problematic because iodine is concentrated by the body in the thyroid gland.

And children with small, developing thyroids drink the most milk; it's estimated that the nuclear tests led to tens of thousands of extra cases of thyroid cancer.

The Atomic Energy Commission wasn't too worried about Iodine-131 because it has a radioactive half-life of only eight days; it decays quickly.

They were more concerned about Strontium-90, which has a half-life of almost 30 years.

Strontium-90, because of a unique combination of properties, probably represents the greatest danger.

Strontium-90 behaves biochemically like calcium, so when ingested, it ends up in our teeth and bones.

And as it emits ionizing beta radiation, it can cause bone cancer, cancer in the surrounding tissues, or leukemia.

In what's become known as the baby tooth survey, scientists in St. Louis collected up 320,000 teeth between 1950 and 1970.

They found that kids born in 1963 had 50 times more strontium in their baby teeth than those born in 1950.

Presently existing evidence indicates that fallout has caused only a small increase in background radiation and correspondingly only a minute increase in mutations.

In reality, both Iodine-131 and Strontium-90, plus other radioactive isotopes in the fallout, almost certainly increased rates of cancer and other diseases in the U.S. population.

This is borne out by studies showing correlations between rates of disease and radioactive isotope uptake.

The graph shows a peak in 1964, just after the Partial Nuclear Test Ban Treaty was signed in 1963; it banned nuclear tests in the atmosphere, underwater, and in outer space, leaving only underground tests.

A central aim of the treaty was to address growing public concern over the scale of nuclear tests and the resulting radioactive fallout.

When the U.S. Senate finally held a hearing on the matter almost 50 years later in 1997, the agreement with Kodak was sharply criticized, especially by Senator Tom Harkin.

He said the government warned the entire photographic industry and provided maps and forecasts of potential contamination. Where, I asked, were the maps for dairy farmers? Where were the warnings to parents of children in these areas?

The government protected rolls of film but not the lives of our kids; there's something wrong with this picture.

And I think the main problem was that in the 40s and 50s, not enough was known about the biological effects of radioactive fallout.

Every so often, a gene changes or mutates, and a characteristic of the organism is altered.

We do not know the exact process by which mutations occur.

Cancers took years or even decades to appear, and fallout models predicted a more uniform and therefore less concentrated spread of contaminants.

When students in Albany, New York, measured a thousand times background levels after a heavy rainstorm, well, the Atomic Energy Commission's report about the event called it an interesting example of a small area of very intense fallout.

Now, concerned with alarming people unnecessarily in downwind communities, the Atomic Energy Commission's approach was to limit as much as possible the information that was shared.

Their conclusion, it seems, was that people are less sensitive to radiation than film is.

So the studies of radioactive fallout remain inconclusive.

What is certain is that 1945 marked the start of a new era: no radioactive fallout before then, and lots after it.

And scientists have shown you can use this to detect wine forgeries.

Any wine made in the last 75 years will give off distinctive gamma rays from Cesium-137, whereas none before that date will.

Plus, the level of activity can be used to estimate the vintage, at least between 1952 and 1980.

A similar technique can be used to detect art forgeries because old paint contains no radioactive cesium or strontium.

You can even use Strontium-90 to determine the age of a skeleton, how long ago that person died, given it's in the past 75 years or so.

This technique has been employed in dozens of forensic cases where there previously was no reliable method of estimating the year of death if it was within the last 50 years.

This method works because while we're alive, we are ingesting Strontium-90, something that stops when we die.

To this day, we all have some Strontium-90 in our bones, albeit at lower levels.

It's been about two half-lives since the peak of radioactive contamination, so three-quarters of it have decayed, and the rest has dispersed throughout the environment.

So these days, it's no longer much of a health concern.

Still, it is there inside every one of us, a signal that can't be covered up or faked: we are of this modern age.

In your bones are the literal atomic fragments of atomic bombs that exploded decades ago.

The series comes from Ridley Scott, and it's about a post-apocalyptic future in which they're trying to restart humanity on an exoplanet, and the young children, the future of our species, are being raised by androids.

Now I've watched the first few episodes, which are out, and there are some extraordinary performances in there, particularly by a couple of Aussie actors, Travis Fimmel and Winter McGrath.

So you should go check it out; you can stream Raised by Wolves on HBO Max.