(1) Field of the Invention
The present invention relates to a radiation detector that is used for medical field, industrial field, nuclear field, etc., and the present invention particularly relates to a technique of a scintillator array having a plurality of three dimensionally disposed scintillator elements.
(2) Description of the Related Art
Radiation detectors have scintillators that convert radioactive rays into a light using an emitted light generated by incidence of radioactive rays; light guides that guide the light converted by the scintillator; and photo multiplier tubes that multiply the guided light to convert into electrical signals (for example, refer to Japan Patent No. 2602287 specification (page 4, FIG. 1). Radiation detectors used for nuclear medicine diagnosis apparatuses, such as PET (Positron Emission Tomography) apparatuses need high discriminating ability for discriminating positions of incidence of radioactive rays in the scintillator. Therefore, adopted are measures for improving the discriminating ability by increasing the number of scintillator elements that constitute the scintillator arrays. In recent years, DOI detectors enabling discrimination of the position of the light source (DOI: Depth of Interaction) that has given interaction, in particular, in a depth direction are developed by laminating scintillator elements also in a depth direction. (For example, refer to JP-A No. 2004-279057 (pages 1 to 13, FIG. 1).)
Here, disclosed is a radiation detector that disposes the first light guide on a side face of a scintillator, that disposes a photo detection means (that is, photoelectric conversion element) for detecting a light in the first light guide, that disposes the second light guide on a surface opposite to a plane of incidence of the scintillator into which radioactive rays enter, and that disposes a photo detection means to the second light guide (for example, refer to JP-A No. 2000-346947 official report (page 1 to 10, FIGS. 1 to 18)). This radiation detector has outstanding discriminating ability of a position in a large area, and enables background compensation.
However, the precision of separation of a position calculation map at an end area will drop in a two-dimensional position calculation map of the radiation detector of the above-described JP-A No. 2004-279057 official report, and as a result the position discriminating ability at the end area also reduces.