some way, creating an unstable configuration, which then decays, releasing the extra energy in radiation of wavelengths characteristic of the atom. A device to read the wavelengths and radiational intensities at those wavelengths then identifies the element and concentration present. Of the three general types of activation, the mass spectrometer bombards the sample with a stream of electrons, or electrical current, until it reaches temperatures high enough to dissociate the atoms into a plasma, or cloud of superenergized ions, in which the electrons have acquired the energy to expand into unstable orbits. As the electrons fall back they lose energy as visible light. Diffraction of the light produces a spectrum that can be read electronically or captured on film. The bands of light identify the elements. Specrometers are used less frequently in archaeology as they destroy the sample; in fact, Law 3028 forbids destructive tests of artifacts. In a second type, Neutron activation analysis (NAA), a stream of neutrons generated in a particle accelerator is directed onto the sample, forcing some of its atoms to acquire additional neutrons, generating unstable isotopes, which decay immediately, releasing gamma radiation. As in electron bombardment, the radiation emitted is of wavelengths characteristic of the element. The gamma photons are diffracted for a spectrum read-out; in addition, the half-life of the decaying isotope can be calculated, which also is characteristic and serves as an identifier. This is a popular method in ceramic elemental analysis because it is non-destructive of the sample. As it requires larger facilities, such as a particle accelerator, not present at most laboratories, the samples must be sent out. The third method, X-ray fluorescence. a type of fluorescence, analyzes the elemental composition of solids without dissociating the atoms from the solid state. It is generally employed on the solids of art and archaeology, such as ceramics, metallic objects, paintings, and so on. In this type the sample is bombarded with x-rays or gamma rays. The electrons are energized in place without breaking up the solid matrix. Moving from the inner orbits to the outer, they fall back to the inner, giving up the induced energy as x-rays of wavelengths characteristic of the element. These are diffracted and read. In 1960, Sinclair Hood, director of the British School, in the process of attempting to determine whether some pottery was Minoan or Mycenaean, contacted the new laboratory for Archaeology and the History of Art