Natural Radioactivity Applet

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Discovery of radioactivity

In November 1895 Wilhelm Conrad Röntgen discovered X-rays. In a meeting of the French Academy of Science, the following January in Paris, Henri Becquerel heard Poincaré report the recent discovery. The X-rays discovered by Röntgen were the result of fluorescence produced by cathode rays in a cathode ray tube. Becquerel wondered if luminescence was a precondition for the observation of X-rays – he had already studied phosphorescence of uranium compounds.

© R. Oldenbourg Verlag

In one of his early attempts, Becquerel exposed uranium-containing minerals to sunlight to cause the material to glow (phosphorescence). The sample was placed on top of a photographic plate wrapped in black paper. Following development of the plate he could observe if radiation had penetrated the paper. This was indeed the case. By placing various objects (coins etc.) between the mineral and the photographic plate, he could reproduce the shapes of the objects. From his detailed records, it is known that Becquerel decided to develop plates that had been in his drawer together with the uranium mineral. These had not been exposed to sunlight. Remarkably, the plates had been “fogged” by the uranium without activation by sunlight. The uranium was emitting rays by itself. Becquerel had discovered radioactivity. Shortly after this event, Pierre and Marie Curie showed that thorium also acted like uranium. In an effort to try to isolate the source of the rays, they discovered the elements polonium and radium. Rutherford started working with these newly discovered uranium rays believing that they were similar to the X-rays discovered by Röntgen. In 1899, he discovered that these “rays” could be bent by a magnetic field and that there were two types of rays: alpha and beta. Today we know that the alpha particle is a nucleus of helium and the beta particle is an electron. In later experiments, Rutherford would use these alpha particles to probe the structure of atoms.

The radioactivity of a material is given in becquerel (Bq) where 1 becquerel is one atomic decay per second. Formerly, the (radio) activity was measured in Curie (Ci) where 1 Ci = 3.7x10¹⁰ Bq.

Background Radioactivity

Ionising radiation in our direct environment arises from natural processes (e.g. cosmic radiation, radioactivity in the body, inhalation of radon gas, radionuclides in food and drink) and from artificial process (such as medical X-rays, fallout from nuclear weapons tests, and discharges of radioactive waste).The average annual dose in the U.K. is approximately 2.6 mSv. The table below gives a breakdown of the sources of ionising radiation.

Source: Living with Radiation, NRPB, 1998

About the applet

This applet is based on the “Radioactivity Carousel” (photo below) which was constructed by Matjaz Kozelj of the Jozef Stefan Institute, in Llubljana, Slovenia, to demonstrate the natural radioactivity of everyday materials. The applet was written by Christin Auerbach during her practical course at the Institute for Transuranium Elements in Karlsruhe, an Institute of the Joint Research Centre of the European Commission. She is a twenty-year-old computer science in economics student of the Berufsakademie Karlsruhe. She started the study in October 2004 and has courses in business economics, economics, law, maths, information systems, computer systems and system development. We would like to thank Matjaz Kozelj (JSI), Volkmar Ernst, Jean Galy, and David Hamilton (ITU), for the many discussions which took place during this development.

Radioactivity Carousel at Jozef Stefan Institute (Courtesy Matjaz Kozel).

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