A traditional scintillation counter has its scintillator directly attached to the photomultiplier tube (PMT) which amplifies the scintillation light signal and converts it to an electric pulse signal. There have been some attempts to separate the scintillator and PMT and to use optical fiber to transmit the light signal. However, these attempts have not yet resulted in a practical application because of the large transmission losses which are caused by the short wave length of the scintillation light (350～400 nm).
We have developed a new detector system using a wave length shift technique. This is called LITTRA (Light Transmission Type Radiation Monitor). The new detector system, which has a long optical fiber between the scintillator and PMT, has been found to be practicable.
From the preliminary experiments of LITTRA, it was concluded that the newly developed LITTRA is a very useful and a unique radiation counter. LITTRA has a wide dynamic range of sensitivity, from dose rates as low as natural radioactivity to high dose rates. Moreover, because electric power is not needed in the detector probe section, it has a higher S/N ratio as power supply noise is eliminated. Also, this advantage makes it possible to apply it to underwater measurements which are difficult with a traditional detector.
