Ruby red grapefruit is a staple in the produce section of grocery stores. In cereal box ads that promote a “balanced breakfast,” it appears broken in half in a bowl and shiny. Its pink flesh is sweeter and smoother than that of a yellow grapefruit, and it has become a family favorite throughout the United States. In many fad diets of the 1970s and 1980s, pink grapefruits featured prominently and occasionally appeared in recipe books dusted with sugar and caramelized in the oven for a touch of sophistication.

The grapefruit, so called because it grows in clusters that vaguely resemble grapes on a vine, is actually an accidental hybrid. The first grapefruit seedling, a cross between a Jamaican sweet orange and an Indonesian grapefruit, sprouted on the island of Barbados in the 18th century. Early English settlers called the new citrus “forbidden fruit,” as the fragrant golden orbs hung seductively in the lush tropical forest. George Washington tried grapefruit during a visit to Barbados between 1750 and 1751 and recorded the experience in his diary.

The first pink grapefruit, a chance mutation of pale yellow-fleshed fruits, was discovered in 1906. Finding the color attractive, growers propagated more specimens. However, this pink grapefruit was not exactly the same as the varieties available in grocery stores today. In the case of ruby ​​red grapefruit and other registered varieties, we can thank radioactivity. But there is no need to panic! Today’s ruby ​​red grapefruits are not radioactive themselves. They are descendants of plants that were altered by radiation. The history of this popular fruit is intertwined with the fascinating and often tragic history of radioactivity.

The story behind your grocery store grapefruit begins in 1896, Bavaria

In 1896, Wilhelm Roentgen accidentally discovered X-ray fluorescence while researching ways to produce light using electromagnetic energy. During one of his experiments, Roentgen turned off the lights in his laboratory. As he did so, he noticed a faint glow coming from a chemical-coated screen on a table several meters away. The screen was too far away to reflect light, so Roentgen realized that some kind of invisible energy beams were emanating from his experimental setup instead.

Additional experiments showed that these energy beams could pass through most soft materials, but left behind dark traces of materials such as bone or metal that were too dense to penetrate. These x-rays, as they became known, quickly revolutionized medical science and became standard diagnostic equipment a couple of years after Roentgen’s initial experiments.

Invisible energy from chemical elements became an enormously exciting field of research. In 1898, Marie and Pierre Curie extracted uranium from a type of mineral called pitchblende and, in the process, discovered that they had also extracted a second chemical element that also gave off energy. They called this second element “radium” and called the type of energy it emitted “radioactivity.”

The radius is rad.

Radium was an absolute sensation in the years immediately following its discovery because it seemed to have miraculous energy-producing qualities. It was promoted as a vitality-increasing supplement and radium-infused water was sold as a health tonic.

Radium gave off so much energy that, in its pure form, it was hot enough to melt ice. When mixed with other elements, such as phosphorus, it emitted a greenish-yellow light. It was used to illuminate clock faces, and women employed to paint numbers on clock faces sometimes painted their teeth so they could amuse their friends with glow-in-the-dark smiles.

The radius transforms from rad to bad

Tragically, in the early decades of the 20th century, it became clear that radium and other radioactive elements that had been discovered around the same time were deeply harmful rather than the panacea people had hoped for. The “radium girls” who had painted their teeth and licked their brushes to give them the proper tip for painting clocks developed terrible debilitating diseases that ate away their bones and caused hundreds of premature deaths.

Marie Curie herself succumbed to cancer caused by radiation exposure. Today, his notebooks are still so impregnated with radiation that they must be handled with lead-coated protective equipment.

Radioactive energy: the wave of the future?

In the 1930s, scientists realized that radiation was dangerous, although that did not stop them from experimenting with radioactive elements in search of a way to harness their power.

The entire world witnessed that ferocious power in early August 1945. American pilots dropped two atomic bombs, the product of a collaboration between scientists called the Manhattan Project, on the Japanese cities of Hiroshima and Nagasaki. This first and only use of atomic weapons in an international war killed at least 200,000 people, most of whom were civilians. Thousands more suffered horrific injuries from the radiation blast, and in the decades after the war’s end, countless more casualties occurred from cancer and other diseases caused by radiation exposure.

The terrifying destructive power of atomic energy left its mark on public consciousness to such an extent that popular culture was filled with allusions to nuclear energy. Godzilla and other classic monsters Kaiju The genus had its origins in irradiated wildlife.

The Incredible Hulk and Spider-Man gained their powers from a gamma ray overdose and a radioactive spider bite, respectively. The backlash against nuclear bombs was so profound that, in the 1950s, the United States attempted to give nuclear energy a new name with a program titled “Atoms for Peace.”

Welcome to the gamma garden

Atoms for Peace supplied research equipment to hospitals, schools, and other institutions, and funded research aimed at developing more productive and less devastating uses of nuclear energy (such as using atomic bombs to bomb Alaska—no, really). One of these research programs was nicknamed the “gamma garden.” These were horticultural centers spread around the world specially designed to test the effects of radiation on plant life.

Gamma gardens were typically laid out on five-acre plots, a space roughly the size of five football fields packed together. The gardens were arranged in a circular shape with a retractable radiation source in the middle. Different species of plants were arranged in pieces, like slices of cake. The radiation source could be raised and lowered from a lead-shielded compartment, meaning researchers could control the duration of each exposure.

When the radioactive material left its chamber at timed intervals, each plant would receive a different amount of exposure, depending on its distance from the source. Radioactive energy directly affects the DNA of living things, primarily by breaking bonds within DNA molecules or causing mutations that can be passed on to future generations.

As expected, in gamma gardens the plants closest to the radioactive material tended to die. A little further afield, radioactive bombardments often caused strange growths, tumors and other abnormalities. However, beyond this dangerous radiation zone, there was a sweet spot where potentially beneficial genetic mutations could emerge.

One of these modified plants was the Rio Red grapefruit, originally developed at Texas A&M University in 1984. This grapefruit variant with a pleasingly vibrant pink flesh was also hardier and produced more fruit than other grapefruit varieties. Rio Reds now account for about 75 percent of all grapefruit produced in Texas.

Gamma gardening has for the most part fallen by the wayside, or at least morphed into a different form. Food products labeled as GMOs or genetically modified organisms have been modified using similar genetic alteration methods.

However, in 2017 there were still active gamma garden facilities, notably the Radiation Enhancement Institute in Hitachiohmiya, Japan.

Altering plants through radiation-induced mutations is essentially accelerating the types of genetic changes that occur naturally in a species over a much longer time scale. Descendants of irradiated plants include a variety of mint resistant to a pernicious fungal disease.

We also have research into radiation to thank for Calrose rice, a sticky, short-grain variety that is now the most common rice produced in California. Golden Promise, a high-yielding variety of barley, was extremely popular in the 1970s and 1980s, and some of that barley can still be enjoyed today in aged Scotch whiskey.

So the next time you wander through the citrus fruits at the supermarket or sip a glass of 45-year-old single malt, take a moment to consider the legacy of gamma gardens. They are a wonderful example of how seemingly unrelated things can connect to each other, and to specific moments in time, in unexpected ways.

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