A Brief History of Radioactivity

More than one hundred years ago, Henri Becquerel discovered that uranium emitted penetrating rays similar to those used by Wilhelm Röntgen to take the first X-ray image (of his wife’s hand), starting a new era of far-reaching applications. There are of course many dangers that come with the use of radioactivity, but there are also many beneficial uses for our society.


An alpha particle is expelled from the nucleus.

The nucleus of an atom is made of protons and neutrons. Because protons have positive charge, they repel each other, so there must be a force that holds the nucleus together, and the neutrons don’t help, because they are neutral. This force is the strong nuclear force and the energy associated with it is called the binding energy.

For reasons that go beyond the scope of this article, atomic nuclei with more than 83 protons in it (bismuth) do not have enough binding energy to hold the nucleus together. In response, the nucleus tries to achieve balance by giving off a neutron or proton in the radioactive decay process, which emits radiation in the form of alpha particles, beta particles or gamma rays (among other more exotic processes). Alpha particles, for example, are composed of two protons and two neutrons that are expelled at high speed (some 5% of the speed of light) from the nucleus, and an atom of a different chemical element is created by the decay.


The first X-ray image from the hand of Anna Bertha Ludwig, Röntgen´s wife.

While conducting experiments with electricity and vacuum tubes in 1895, Wilhelm Röntgen discovered that his photographic plates were darkened, even when wrapped with black paper. He then concluded that some kind of yet unknown, penetrating rays were at play in his experimental setup. He was able to use this new “X-rays”, as he named them, to take the first X-ray image, using the hand of his wife Anna Bertha. A year later Henri Becquerel found that similar rays were produced naturally by uranium salts.

The phenomenon that produced the X-rays was named radioactivity by Marie Curie, Becquerel´s doctoral student. Marie and her husband Pierre, carried on much of the pioneering work on radioactivity. They discovered new elements with this property, such as radium, polonium, and thorium. Of the 48 women who have been awarded Nobel prizes, Marie Curie is the only one who won the distinction twice: first in physics for her work in radiation phenomena, and then in chemistry, for her discovery of radium and polonium. It is worth to mention that only four persons and two organizations have won multiple Nobel awards.

Marie Curie died in 1934, victim of her work with radiation, since it was not known at the time that radiation posed serious health issues. Her papers and even her cookbook are stored in shielded boxes as they are still highly radioactive and cannot be handed safely.


Advertisement for the Undark self-glowing paint.

Radium was found to be two million times as radioactive as uranium, the radium salts even glow visibly from radiation. This lead to a new industry that benefited from the new phenomenon (the Curies did not patent their discovery). The US Radium Corporation was a company that used a recipe that combined radium salts with glue and zinc sulfide, an element that glows in the presence of radiation. The result? Glow-in-the-dark paint, that was marketed with the name “undark”. It was used by the military in their wristwatches and instrument panels so they could be read at night. It was also used in house numbers, light switch plates, and even for the eyes of toy dolls.

The painting was done by a group of women, some as young as 14. They were known as the Radium Girls. When working with fine-tipped brushes to paint the numbers and hands of wristwatches, they used their lips and tongues to point the tips of the brushes. Unaware of the tremendous danger of the radiation, they even painted their fingernails and teeth in order to surprise their boyfriends. Of course they ingested huge amounts of radioactive material, and began to suffer from anemia, fallen teeth, stillborn babies, bone fractures and jaw necrosis.

The first legal suit against US Radium was filed in september 1925. With the help of doctors and dentists in their payroll, the company rejected all claims that the radium exposure was to blame. More than two years passed until one of the girls could find a lawyer that would take the case, and the trial dragged on for months. Four other girls also joined the suit and the case finally attracted the attention of the media.  The girls settled out the case for around $100,000 in today´s dollars, plus medical expenses and  $600 per year for as long as they lived. The last girl only survived for two years after the settlement. After the case was settled in 1928, US Radium continued operations under new safety laws until 1947.

There were similar histories, such as the Radiant Dial Corporation, which also employed women in the same conditions as US Radium, with similar unfortunate results.  Unfortunately, due to the initial lack of knowledge about the dangers of radiation, and the fact that everything atomic was terrifically fashionable at the time, radium was used in everything you can imagine: cosmetics, household cleaning products, toothpaste, suppositories, cigarettes and even virility boosters such as the Scrotal Radiendocrinator: place it under your scrotum and you’ll be atomic in the bedroom.

Despite the lawsuit won by the radium girls, the atomic products trend continued until the late 1950s. Fortunately, most of these products contained only tiny amounts of radium due to its high price.


There are many practical uses of radioactivity. Of course nuclear reactors for power generation are very well known. Tracers are radioisotopes whose pathway through a chemical reaction can be followed, and are used in chemistry and biochemistry to understand chemical reactions and their interactions. They can track the distribution of a substance in the tissue, and form the basis of several imaging systems such as positron emission tomography, and single-photon emission computed tomography. The location of fractures in hydraulic fracturing also makes use of tracers. Radiocarbon dating is used in archaeology to determine the ages of fossils. Irradiation of foods and medical equipment is used to kill germs without harming the substance that is being disinfected. Foods take much longer to spoil, and medical equipment can be sterilized without exposure to chemicals or extreme heat. Gauges containing radioactive substances are used to measure the thickness of paper products, fluid levels in oil and chemical tanks, and the moisture and density of soils.

Since its discovery, much has changed in our understanding of radioactivity. The knowledge of its properties has given humanity the power to use it in many fields that can be beneficial, but also a belated appreciation for the potential dangers.


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