To find unknown point gamma sources in large areas, we proposed a source direction estimation method based on self-shielding profiles of 3D multi-pixel array detectors. A convolutional neural network model was investigated to estimate the direction of the gamma-ray source in 4π directions to the detector. The estimation of source direction for a single ¹³⁷Cs point source was demonstrated both computationally and experimentally using a multi-pixel CdTe array detector. The validation results showed that 59.2% of the estimated results were within 10 degrees of the true incident direction.

  Large amounts of radioactive materials were spread over the surrounding environment caused by the accident of the Fukushima Daiichi Nuclear Power Plant. Since some areas are still in the difficult-to-return zone, it is important to understand the radiation distribution in these areas. We measured the radiation distribution by using a Compton camera and an optical camera in these areas. As a result of the actual measurement, we were able to identify the radiation source location and its spatial extension by filming the high-dose area from various positions and angles.

  A radiation detector consisting of a scintillator and optical fiber has been proposed for the decommissioning of nuclear power plants to determine the dose rate in real-time. Inside the plant, gamma-ray and neutron emitting debris can remain, and the scintillator is required to have gamma-ray and neutron sensitivity. Moreover, red or near-infrared emission scintillators have the advantage to obtain higher sensitivity. In such demand, we have developed Li₂Hf(Br, I)₆ scintillator with an emission wavelength of around 650 nm under visible light excitation and X-ray excitation. The light outputs of this material excited by thermal neutron and 662-keV gamma-ray excitation were evaluated to be 18,000 photons/(thermal neutron) and 16,000 photons/MeV, respectively. Therefore, we found this material has a potential to apply such a real-time monitor.

  Electron accelerators have greatly contributed to advanced research in fields such as high energy physics and radiation physics for about a century. They are also contributing to the medical and industrial field s in the form of applications such as radiation therapy and non-destructive testing. Recently, electron acceleration techniques have been improved with regard to the acceleration efficiency and the maximum electric fields in order to realize the required beam parameters for higher performance of these applications . This paper describes the recent trends in electron acceleration technology, focusing on various accelerating structures.

  The threat of nuclear and radiological terrorism (RN terrorism) using nuclear materials and other radioactive materials out of regulatory control (MORC) has been widely recognized by the international community, and many countries have been developing nuclear security capabilities to counter the RM terrorism. In nuclear security, it is important not only to enhance physical protection measures for nuclear facilities possessing nuclear and other radioactive materials, but also to develop technical measures such as nuclear detection including recovery of the materials, and nuclear forensics for initial response and criminal investigations to the incidents involving MORC. In this paper, technical challenges regarding nuclear forensics and detection, mainly in the field of radiation measurement, will be discussed, and the development of radiation technology at the Integrated Support Center for Nuclear Nonproliferation and Nuclear Security (ISCN) of JAEA will be introduced.

  As a summary of my second half research activity, the energy-resolved computed tomography (CT) with a new detector system called a transXend detector and a low-noise current preamplifier VIEC are described. The transXend detector consists of several segmented detectors which measure X-rays as electric current and gives energy spectrum of X-rays after analysis. The operation principle and some applications of the transXend detector are explained. For the purpose of the decrease of dose exposure in CT, the VIEC was developed with modifying a charge preamplifier. The comparisons of the VIEC with a conventional current preamplifier is under study. The results obtained so far are shown.