that silicon detectors are much more expensive than these older technologies and require sophisticated cooling to reduce leakage currents (noise source). They also suffer degradation over time from radiation, however, this can be greatly reduced thanks to the Lazarus effect. Diamond detectors Diamond detectors have many similarities with silicon detectors, but are expected to offer significant advantages, in particular a high radiation hardness and very low drift currents. They are also suited to neutron detection. At present, however, they are much more expensive and more difficult to manufacture. Germanium detectors Germanium detectors are mostly used for gamma spectroscopy in nuclear physics, as well as x-ray spectroscopy. While silicon detectors cannot be thicker than a few millimeters, germanium can have a depleted, sensitive thickness of centimeters, and therefore can be used as a total absorption detector for gamma rays up to a few MeV. These detectors are also called high-purity germanium detectors (HPGe) or hyperpure germanium detectors. Before current purification techniques were refined, germanium crystals could not be produced with purity sufficient to enable their use as spectroscopy detectors. Impurities in the crystals trap electrons and holes, ruining the performance of the detectors. Consequently, germanium crystals were doped with lithium ions (Ge(Li)), in order to produce an intrinsic region in which the electrons and holes would be able to reach the contacts and produce a signal. When germanium detectors were first developed, only very small crystals were available. Low efficiency was the result, and germanium detector efficiency is still often quoted in relative terms to a "standard" 3″ x 3″ NaI(Tl) scintillation detector. Crystal growth techniques have since improved, allowing detectors to be manufactured that are as large as or larger than commonly available NaI crystals, although such detectors cost more than €100,000 (US$113,000). , HPGe detectors commonly use lithium diffusion to make an n+ ohmic contact, and boron implantation to make a p+ contact. Coaxial detectors with a central n+ contact are referred to as n-type detectors, while p-type detectors have a p+ central contact. The thickness of these contacts represents a dead layer around the surface of the crystal within which energy depositions do not result in detector signals. The central contact in these detectors is opposite to the surface contact, making the dead layer in n-type detectors smaller than the dead layer in p-type detectors. Typical dead layer thicknesses are several hundred micrometers for a Li diffusion layer