What Is Radioactivity? The Basics

Chapter 1

Mysterious Rays

This symbol is universally recognized as a warning that ionizing radiation may be present. Today, it might be seen attached to buildings that were once designated as fallout shelters. In the 1950s and 60s these shelters were common.

Places such as basements and garages built with reinforced concrete were believed to offer some protection against immediate impact of an atomic bomb blast, if the explosion occurred far enough away. The shelters also were believed to offer protection against radioactive fallout that would follow an atomic bomb detonation.

In large cities, residents could look for these symbols to find a government-designated shelter. The shelters were sometimes stocked with food and water so that people could stay for the few critical days after an atomic bomb had been dropped on or near their city.

On December 22, 1895 William Conrad Roentgen called his wife, Anna Bertha, into the laboratory. He asked her to hold her hand out. He wanted to show her what would happen when he directed mysterious rays at her hand. In that moment, both Anna Bertha and William made history. The skeletal image of Anna Bertha's hand materialized under Roentgen's mysterious 'x-rays'.

William Roentgen

William Conrad Roentgen in his laboratory

When William Roentgen received the Nobel Prize in 1901, there may have been some very amazed teachers in the Dutch city of Utrecht, for William had been expelled from school there years before. At the time, it seemed the expulsion would threaten young William's academic future, but the determined student studied on his own. He was not going to let the expulsion derail his plans.

Eventually William was accepted at a technical institute in Zurich, Switzerland. It was here that he earned his PhD and began the laboratory work that would one day lead to the discovery of mysterious 'x-rays'.

The First X-Ray Ever Taken of the Human Body

Anna Bertha's hand, the first x-ray of the human body ever taken. Anna Bertha startled woman is reported to have been so impressed by the appearance of her hand that she exclaimed, I have seen my death.

Scientists all over the world were excited by Roentgen's discovery. Some of the greatest minds in the world investigated the properties of Roentgen’s x-rays.

In 1896, just months after Roentgen's discovery, Henri Becquerel began experimenting with uranium. He had been interested in phosphorescence. It was well known that certain substances, when exposed to sunlight, glowed. However, after a while the glow faded. Becquerel decided to investigate.

At first he surmised that uranium's glow came from exposure to sunlight. To his surprise, this turned out not to be true. He was amazed to learn that uranium glowed on its own. He realized that the glow came from something inside the material. He guessed that these 'rays' were similar to Roentgen's x-rays.

Becquerel understood correctly that the ability to produce rays was a property of the uranium itself and not from something that was affecting the uranium.

Phosphorescent Salts

Photo Demonstrations by Sparkla on Wikimedia Commons. In the public domain

The three jars in the picture above demonstrate the glowing quality of phosphorescence. On the left the salts are shown in full daylight. In the center the salts are shown under UV light and on the right the salts are shown in total darkness.

Becquere's Photographic Plate with the Image of a Coin Impressed on It