Radar
See geophysics.

Radio-carbon dating
Until the development of dendrochronology, radio-carbon dating (or C14 dating) was the most precise type of dating in archaeology, and it is still used when not enough wood can be found to give a dendro date. It is based on the fact that all living things contain carbon, and that this consists of two sorts: ordinary carbon (carbon 12), and radioactive carbon 14, which occurs in small quantities. As soon as a living thing dies, the radioactive carbon begins to decay, shedding atomic particles to end up eventually as nitrogen. This rate of decay was worked out by Willard Frank Libby in the United States, who found that, after 5,730 years, half of the carbon 14 had gone. If the amount of radioactive carbon 14 can be measured in something that was once alive, be it wood, charcoal, bone, shell or whatever, then the year of its death can be discovered. There are a number of problems with the technique, but it is still very important and, over the last 20 years, has revolutionised our knowledge of the absolute, or calendar, dates of many of the sites and objects in archaeology.

Radiography
Radiography – the use of electromagnetic radiation such as X-rays – is a way of examining objects without damaging or destroying them. Developed for medical diagnosis, radiography is now widely used to look at archaeological objects, including human remains.

When X-rays are directed at an object, some are absorbed and some pass through the object to form an image on photographic film placed on the other side. Some substances absorb more radiation than others, and more rays will be absorbed by thick materials than thin, creating lighter and darker areas on the photographic film. In the case of human remains, X-rays can be used to show any damage to the skeleton, giving clues to how the person lived and died.

While X-rays provide a flat, two dimensional picture, CAT (Computerised Axial Tomography) scanning gives a three dimentional image. X-rays are directed at the object from all sides to create images of slices through it. A computer uses these to generate a three dimensional reconstruction of the inside of the object. Used in medicine to diagnose cancer and other conditions that affect soft tissue, CAT scanning is a valuable archaeological tool. It was used to examine the remains of 'Otzi', the neolithic hunter-gatherer whose frozen body was discovered in the Austro-Italian alps in 1991 and the baby ice mummy found in Greenland.

Raggle
A dialect term for the remains of a roof line preserved on the end of an adjacent building.

Recording
The most important aspect of archaeological work. Without proper recording of sites as fieldwork takes place or excavation is undertaken, it would not be possible to see what the context is of anything found. Since excavation, in particular, equals destruction, as complete a record of all layers, sections, features and finds is essential if the work is going to be understood by anyone after it has taken place. The same is true of most archaeological activities.

Rescue excavation
The term applied to excavations carried out in advance of any modern development such as roads, pipelines, housing schemes, town centre redevelopments and the like, which will destroy the archaeology lying under them, and where the information has to be 'rescued' before it is lost for ever. Often this takes place in areas that archaeologists themselves would not choose to dig, but opportunistically, they carry out excavations to answer questions or understand what was there. In Britain, most excavation since the 1960s has been rescue excavation.

Resistivity
See geophysics.

Roman occupation
The period from 43 AD, when Britain was invaded by the Roman army, to the 5th century, when links with the remains of the western Roman empire were severed. For about 400 years, Britain was part of the Roman empire, and this is reflected in the range of new aspects that appear in the archaeology of that time. These include: a greater variety of pottery, coins and metal goods; stone, tile, mortar and plaster as building materials; wall paintings; heating systems. Major industrial production of such items as pottery, and major engineering schemes for roads, bridges, drainage, town planning and so on, were also major innovations.

Rubbish heaps/middens
Much archaeological research is concerned with the rubbish of past societies and what we can learn of these people's lives from what they left behind. There are even modern garbage projects in the United States that analyse rubbish from different parts of American cities. What is in the rubbish provides a clear indication of the social and economic groups that have discarded the rubbish. The term 'midden' is often used interchangeably with 'rubbish heap', but strictly speaking it refers to the layer of soil containing the by-products of human activity from past ages where it has accumulated on an occupation surface. Stratified midden deposits can be invaluable for dating purposes.

Runes
Runes were used in a script formerly found in northern Europe and are particularly associated with Viking monuments. Like ogam, the script is based on a combination of vertical and diagonal cuts in wood or stone, although it was also applied to items such as swords. Most runes are associated with memorial stones.