Mark Rodgers

What Are X Rays

At the end of 1895, Wilhelm Rontgen (there is a drawing of him in Figure 1.2) was experimenting using a vacuum tube (a glass tube from which the air has been removed) which had a positively-charged plate at one end and a negatively-charged plate at the other. It was well known at that time that in this setup, rays, then called cathode rays, would travel from one plate to the other. It was only later, in 1897, that Joseph John Thomson discovered that these rays were in fact electrons. Rontgen observed that, on hitting the positive plate, the electrons produced some penetrating radiation, which could be detected outside the glass tube by its ability to blacken a photographic film. He called these new rays “X rays”, with the “X” standing for something unknown.

What Are Radioactivity and Radiation

We and everything around us are made of atoms . The idea of the atom came out of ancient Greek philosophy: some philosophers (notably Aristotle ) thought that matter could be divided into ever smaller parts, and others (notably Democritus ) thought that at some point, there was a minimum size of object, which they called “atomos”, meaning “unsplittable”. With the techniques of modern science, it has become clear that these atoms do exist, and each one is about a ten-billionth of a metre across: the full stop at the end of this sentence is about a million atoms across.

How Can We Use Radioactivity Destructively

The discoveries that led to the development of nuclear weapons took place in the 1930s. In 1938, Otto Hahn and his assistant Fritz Strasmann were trying to produce transuranic elements —elements heavier than uranium, which is the heaviest in nature—by firing neutrons at uranium. To their surprise, they found that most of the products were lighter elements, like caesium and barium . This showed that, far from building up the nuclei to heavier elements, the neutrons had caused the uranium nuclei to break apart, in a process now called fission . Within a few months, Lise Meitner and her nephew Otto Frisch , a chemist, had explained correctly what had happened. Lise Meitner was not impressed by the physics expertise of Otto Hahn (whose surname means “chicken”), and she was reported to have said, “My little chicken, you understand nothing about physics!”.

What Does Radiation Do

Strictly speaking, radiation is never directly measured: it can only be detected via its interaction with matter. There are multiple different ways in which radiation can interact with matter: these interactions are characteristic for each radiation type – charged particles, neutrons, and photons (X and \(\gamma \) rays). Similarly, there are different ways of detecting these different radiation types, which are covered in detail in Appendix A.

How Can We Use Radioactivity Productively

Radioactive decay releases energy. As has been discussed in other chapters, the radiation which comes out of the decay deposits that energy in objects and in living beings in a way that can harm them: however, we can also use radiation to provide useful power.

How Can We Make Radiation

One might assume that radioisotopes are the only significant sources of radiation. Instead, thanks to rapid developments in both fundamental physics research and its technical applications, there is a variety of possibilities for producing nearly all sufficiently long-lived nuclei, elementary particles and photons in the form of radiation sources. These sources span a huge range of energy, from ultracold particles (25 meV) up to energies of 1 TeV. If, in addition, cosmic rays are considered, particles with energies even in excess of 1 TeV are available, albeit with very low intensity. In the following sections, the main methods of production of ionising radiation are described, along with their important applications in medicine and in batteries.

What About Non-Ionising Radiation?

Most of this book has concerned ionising radiation: chiefly \(\alpha \), \(\beta \), and \(\gamma \) rays and neutrons, but also X rays. \(\gamma \) radiation and X rays are electromagnetic waves: they differ from visible light or microwave radiation only by their energy (or, equivalently, by their frequency or wavelength ). It is only natural to ask to what extent electromagnetic radiation of other frequencies might be dangerous for humans.

What Happens When It Goes Wrong

Many radiation accidents in the fields of medicine and technology are caused by loss and careless disposal of radioactive material. The reason for unnecessary exposures is frequently improper storage of disused radioactive sources. Discarded sources have been found in scrapyards by children, who were pleased to find some pieces of (for example) nice-looking silver-coloured cobalt metal: tragically, this was highly radioactive and dangerous. Table 10.1 shows a number of examples of losses of radioactive sources and events of accidental irradiations.

Is Radioactivity Everywhere

Many people believe that radioactivity is all man-made, whether it be made in laboratories, nuclear power plants or nuclear explosions. This is entirely wrong. Since the Earth formed, along with the formation of the Sun and the other planets and moons about 4.6 billion years ago, both it and everything on it have been radioactive to a certain extent. In the distant geological past, the Earth was even more radioactive than it is today. The Sun and the Earth were made from the debris of supernova explosions, in which all the elements of the periodic table, including radioactive isotopes, were created. We are actually made of (slightly radioactive) star dust. Radioactivity is a natural ingredient of all life forms and also of the air that we breathe and the food that we eat. In addition, we are constantly being bombarded by cosmic-ray particles which mainly come either from the Sun or from other sources within our galaxy. These particles constitute a low-level radiation exposure. In the following chapter, the different natural sources of radioactivity will be presented in detail and compared with additional man-made radioactivity.

Why Should I Read This Book

Life on Earth has developed under constant exposure to radiation. In addition to ionising radiation from natural sources, a multitude of exposures from artificial sources produced by mankind came into play in the twentieth century. These radioactive sources were produced by some impressive developments in science and technology, and in turn they helped spur further developments, including of course in medical diagnostics and therapy .