@misc{oai:repo.qst.go.jp:00067762,
 author = {Shirakawa, Yoshiyuki and 白川 芳幸},
 month = {Oct},
 note = {A new type of detector, which positively raises directional dependence for coming gamma-rays, has been studied to measure directions and energies of coming gamma rays emitted from radioactive materials. In the detector, a cylindrical NaI(Tl) scintillator, the same-sized BGO or CsI(Tl) scintillator, and a photomultiplier tube are combined optically in this order. A spectrum obtained by this detector has two dominant photopeaks for a Cs137 source. One is derived from the front scintillator, and the other is caused by the back scintilltor. Since the lengths of crossing each scintillator are changed dependent on a coming direction of gamma rays, both photopeak counts are also altered. A typical case is shown in Fig.1. This characteristic shows the possibility of measuring the direction by obtaining the ratio of both photopeak counts, which id defined by:
    R(X)= peak counts by the back scintillator / peak counts by the front scintillator          (1)
where X is a coming direction from 0 to 90 degrees. Experiments were carried out using the detector with the 2.5 cm in diameter x 5.0 cm in length of NaI(Tl) and the same-sized BGO or CsI(Tl) scintillator: (1) to confirm the measurement principle and (2) to the performance. A Cs137 source of 3.7 MBq was put in front 100 cm of the detector(X=0). Coming gamma rays were counted for 300 seconds, and R(X) was calculated. The source was moved from 0 degree in the front direction to 90degrees in side direction by 10 degrees interval. Then the similar experiments were repeated using other shaped detectors, which had the 5.0 cm in diameter x 2.5 cm in length and the 5.0 cm in diameter x 5.0 cm in length scintillator. This means that the coming direction can be decided when the counting ratio is known. At the same time, it was confirmed that the energy characteristics of the tandem detector were the same as those of  conventional  NaI(Tl) and BGO scintillators. As observed in Fig.2, the best response was gained by the combination of NaI(Tl) and BGO scintillators of 2.5 cm in diameter x 5.0 cm in length. At the same time, it was confirmed that the energy characteristics of the detector were the same as those of an NaI(Tl) and a BGO detector. As a result, it has been shown that the proposed detector has a possibility of measuring the coming directions and the energies of gamma rays simultaneously., 1st International Meeting on Applied Physics},
 title = {GAMMA RAY DIRECTIONAL DETECTORS FOR SEARCHING RADIOACTIVE MATERIALS},
 year = {2003}
}