ISO 21482:2007

ISO 21482:2007 specifies the symbol to warn of the presence of a dangerous level of ionizing radiation from a high-level sealed radioactive source that can cause death or serious injury if handled carelessly. This symbol is not intended to replace the basic ionizing radiation symbol (ISO 361), but to supplement it by providing further information on the danger associated with the source and the necessity for untrained or uninformed members of the public to stay away from it.

This symbol is recommended for use with International Atomic Energy Agency (IAEA) Category 1, 2, and 3 sealed radioactive sources. These sources are defined by the IAEA as having the ability to cause death or serious injuries.

X-Ray Tube

γ Gamma Ray

Gamma radiation, also known as gamma rays, and denoted by the Greek letter γ, refers to electromagnetic radiation of an extremely high frequency and are therefore high energy photons. Gamma rays are ionizing radiation, and are thus biologically hazardous. They are classically produced by the decay of atomic nuclei as they transition from a high energy state to a lower state known as gamma decay, but may also be produced by other processes. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900, while studying radiation emitted from radium. Villard's radiation was named "gamma rays" by Ernest Rutherford in 1903. Received Noble during 1908 for Chemistry.

Antoine Henri Becquerel

Antoine Henri Becquerel (15 December 1852 – 25 August 1908) was a French physicist, Nobel laureate, and the discoverer of radioactivity along with Marie Skłodowska-Curie and Pierre Curie, for which all three won the 1903 Nobel Prize in Physics. The SI unit for radioactivity, the becquerel (Bq), is named after him.

The discovery of radioactive elements

Subsequent to Roentgen's discovery of X-rays, in 1896 a French scientist Henri Becquerel was experimenting with a uranium compound. While investigating the properties of fluorescent minerals, it was Becquerel who discovered that certain types of atoms disintegrate by themselves. When working on the principles of fluorescence, he utilized photographic film to record fluorescence of various minerals when exposed to sunlight.

One of the minerals Becquerel worked with was a uranium compound. The experiment normally consisted of wrapping some photographic film in light proof paper, placing a piece of fluorescent uranium on top of the film, and leaving them in the sun. One day, after preparing the experiment, it was too cloudy to expose his samples to direct sunlight, so he stored the uranium compound and the film in a drawer. A couple of days later, he decided to develop this film anyway, and discovered an image of the uranium sample on the film. Becquerel questioned what would have caused this. He knew he had wrapped the film tightly in light proof paper, so the image was not due to stray light.

In addition, he noticed that only the film that was in the drawer with the uranium compound had an image on it. Becquerel concluded that the uranium compound gave off something invisible that could penetrate heavy paper and affect photographic film. Becquerel continued to test many samples of compounds and determined that the source of the invisible something was the element uranium. This invisible something was namedradiation, and it was determined that an element that gives off radiation is a radioactive element. Today, we know uranium as one of the radioactive elements. For his discovery of radioactivity, Becquerel was awarded the 1903 Nobel Prize for physics.

1. Henri Becquerel discovered the radioactive properties of uranium when he stored a piece with some film and notched an image on the film.

2. Uranium was named a radioactive element because if gives off something that is invisible to the human eye called radiation.