Radiation detectors include indirect conversion type detectors, and direct conversion type detectors. The indirect conversion type detectors are adapted to first convert radiation into light and then perform photoelectric conversion of the converted light into electric signals. The direct conversion type detectors are adapted to convert incident radiation directly into electrical signals, such as a radiation sensitive type semiconductor film. Generally, a radiation detector is constructed in such a manner that the electromagnetic radiation is incident on a converter arrangement. Depending on the specific construction of the radiation detector, either a directly converting converter layer in the converter arrangement converts the radiation into electric charge carriers which are subsequently read out, or the radiation is first converted into visible light by means of two converter layers and subsequently. Radiation detectors are based on the principle that the thermal radiation emitted from a subject is proportional to the temperature of the subject raised to the fourth power. The radiation emitted is also a function of the emissivity of the subject and of background radiation, but can be calibrated out for applications in which the target has consistent properties. Radiation detectors may be designed and constructed to be sensitive to particular regions of the electromagnetic spectrum. For example, infrared detectors are radiation detectors that are sensitive to radiation in the infrared region of the electromagnetic spectrum. Radiation measurement requires a high energy resolution and a high detection efficiency. A high energy resolution means a small variation in signals obtained from radiation having a certain energy. A high detection efficiency means a high probability that the radiation is irradiated to the detection area of a detector and extracted as signals. Radiation sensor devices are used to detect radiation and provide spatial mapping of radiation intensity in radiation-based imaging systems. In the medical, industrial, and other fields, there are increasing needs for radiation detectors capable of quickly and accurately detecting and picking up radiation images. For meeting such needs, there are known radiation detectors provided with a scintillator for converting a radiation image into an optical image, an image pickup device for picking up such an optical image, and a lightguide optical member for guiding the optical image from the scintillator to the image pickup device. A variety of imaging sensors may be constructed using an array of radiation detectors. Such sensors may be used in an imaging system that produces an image based on radiation impinging on the imaging sensor. Based on the type of detectors used, the imaging sensor may be responsive to a particular region of spectrum. Basically, a radiation source generates a beam in the direction of an object to be examined and a detector measures the intensity of the beam after it has passed through the object. The sensor device detects and measures the information required to produce an image representing the attenuation of the radiation resulting from absorption and scattering by the structure through which the beam traveled.

Semiconductor solid state radiation detectors have long been used in nuclear medicine, science and industry. Such devices are useful in detecting radiation such as X-rays, gamma rays, electron beams, or neutron beams. Present radiation-detection technology is based on the fact that ionizing radiation, as it passes through matter, creates electrical charges. These electrical charges can be collected by applying an electrical field to the matter such that an electrical signal is derived. Ionizing radiation includes both particulate radiation, such as alpha or beta particles, and electromagnetic radiation, such as gamma or x rays. A semiconductor radiation detector is a device in which an electric charge produced therein due to ionization effect of incident radiation is swept and collected to produce a signal under an electric field applied between both electrodes. Semiconductor radiation detectors generally operate by absorbing a quantum of gamma-ray or x-ray radiation and by converting the radiation energy into a number of electron-hole pairs that is proportional to the absorbed energy. After the conversion, the motion of the electrons and holes induce electrical signals on the detector electrodes. The electrical signals are also proportional to the energy of the absorbed radiation. Semiconductor radiation detectors typically have an active volume, which is depleted of free charge carriers, and is used to absorb at least some of the radiation to generate charges. Semiconductor radiation detectors typically have an entrance window electrode to receive impinging radiation. X-ray and light photon detection efficiency of semiconductor radiation detectors is often limited by a dead layer at the entrance window electrode of the radiation detector, in which photons are absorbed but not detected. A typical gaseous-based ionizing radiation detector comprises a planar cathode and anode arrangement, respectively, and an ionizable gas arranged between the cathode and anode arrangements. The detector is arranged such that a radiation beam from a radiation source can enter the detector for ionizing the ionizable gas. Further, a voltage is typically applied for drifting electrons created during ionization of the ionizable gas towards the anode. High-resistivity semiconductor radiation detectors are widely used for detecting ionizing radiation due to their ability to operate at room temperature, their small size and durability. Such detectors are used in a wide variety of applications, including medical diagnostic imaging, nuclear waste monitoring, industrial process monitoring, and space astronomy.