Experimental measurement of dose-rate distribution with scintillation fiber detector

Emoto, Takehiko; Torii, Tatsuo  ; Nozaki, Tatsuo ; Saito, Kei; Emori, Shuichi; Ando, Hideki

The technique has been developed to measure the dose-rate distribution of radiation easily. The detector is made of plastic scintillation fibers (of following PSFs). The technique is based on the time of flight method, that is to measure the time difference of scintillation reaching from a incidence position to both ends of fibers. Measuring devices were built as trials. The position resolution was measured with collimated ray. The dose-rate linearity and the energy response were measured with an irradiation equipment of ray. Then, the devices were applied to the dose-rate distribution measurements in facilities. The tests were carried out to turn the technique into practicable use. Main results are as follows; (1) The continuos dose-rate distribution of ray can be measured with a single detector. The result of a measurement is illustrated on the screen of a device immediately. (2) The upper limit of counting rate measuring range is 10 cps. The upper limit of ray dose-rate measuring range is 1 mSv/h (calculated value) for a detector of "0.25 mm 1 peace, 10 m length". (3) The detection efficiency does not depend on the ray energy between 500 keV and 1.5 MeV. (4) The practical length of PSFs is up to about 10 m for the dose-rate distribution measurement. (5) When the dose-rate distribution has sharp peaks, the output distribution of measurement is slightly flattened against the actual distribution based on the detector characteristic of position resolution. The unfolding method can correct this effect. (6) It is possible to discriminate the energy and type of radiation, if the pulse height output of a photomultiplire is corrected in each incidence position with the multi-parameter measuring method.