Ultra-compact KURAMA-II

A nuclear disaster is a very special kind of disaster because it is the first disaster that can be recognized by visualizing radiation, which cannot be sensed by the five human senses. Therefore, it is extremely important to establish an appropriate monitoring system to respond to the development of events. Based on the experience of the accident at the TEPCO's Fukushima Daiichi NPS following the Great East Japan Earthquake, it is considered extremely important to conduct precise and continuous radiation monitoring activities within about 10 days after the occurrence of a disaster to obtain data on short-lived nuclear species such as iodine-131, which are extremely important for determining the scale of the disaster, the extent of damage and the initial exposure dose to the residents.
However, when a nuclear disaster occurs, the environment can be harsh not only because of the release of radioactive materials, but also because of damage to infrastructures, such as damage to monitoring posts, power outages, and disruption of roads and communication networks. Amid this situation, it is expected to be extremely difficult to assess the situation with limited personnel, equipment, and materials, and to take necessary protective measures and medical treatment for radiation exposure.

Therefore, we developed the ultra-compact KURAMA-II, which combines Sony Spresense and LPWA, as a tool that enables flexible deployment of radiation monitoring immediately after a disaster based on the knowledge and know-how gained through KURAMA-II. With not only low power consumption but also GNSS reception capability (500 kS/s high-speed ADC for high-resolution, supporting MICHIBIKI, GPS, GLONASS, etc.), "SPRESENSE" is the best single-board computer platform for the ultra-compact "KURAMA-II".

About Ultra-conpact KURAMA-II

The ultra-compact KURAMA-II uses a radiation detector that combines a CsI(Tl) scintillator and MPPC. This is the same as the C12137 manufactured by Hamamatsu Photonics, which has a proven track record in the conventional KURAMA-II. Compared to the conventional photodiode and scintillator combination, the C12137 is extremely superior in terms of S/N and sensitivity and can realize stable radiation measurement.
One of the features of this ultra-compact KURAMA-II is that while the conventional C12137 uses a built-in amplifier to shape the pulse signal from the MPPC, then uses a built-in ADC to perform AD conversion and output via USB, this time the waveform-shaped analog signal is input to Spresense's 500 kS/s high-speed ADC (HPADC), which measures the wave height for each pulse. This simplification of the configuration has resulted in lower costs and smaller equipment, as well as a significant reduction in power consumption. Since this wave height is proportional to the energy of the radiation, the radiation spectrum can be obtained by histogramming the detected wave heights and their numbers. They are converted internally into radiation doses and further tagged with location information obtained from the SPRESENCE's GNSS receiver function. The implementation of the wave height measurement algorithm and other algorithms in Spresense was done by S2 Factory, Inc.(Japanese)
Acquired data is transmitted via mesh-type LPWA. The current ultra-compact KURAMA-II uses ZETA.Since ZETA automatically configures a mesh network among relay stations, the optimal communication path is automatically selected and data is sent to the base station when connecting to one of the relay stations. It also consumes very little power and can be operated for a long period even with batteries, thus solving the problem of maintaining communications during power outages, which is a serious issue in emergencies.

How to use

The ultra-compact KURAMA-II maintains the capabilities of the conventional KURAMA-II but is smaller and less expensive. This gives a highly mobile and detailed means of response to conventional radiation monitoring, which is based on high reliability.
For example, in the living sphere, ultra-compact KURAMA-II will be deployed in large numbers at various locations such as hospitals, schools, evacuation centers, government offices, and companies in the event of a nuclear disaster. By connecting these sites with ZETA, an LPWA capable of building an agile and autonomous mesh network, detailed and continuous radiation monitoring that is not affected by local damage conditions can be achieved. By deploying the ultra-compact "KURAMA-II", which can acquire spectral data, to every corner of the region to achieve continuous monitoring, it will be possible to collect the information necessary to assess the diffusion of short-lived nuclear species such as iodine-131 and their effects on the human body.
If an event occurs in the vicinity of a nuclear facility and forces a withdrawal from the front line, withdrawal routes and sequential deployment by drone are possible. The ultra-compact KURAMA-II deployed in the area will continue to acquire and transmit radiation data as long as the battery lasts. This ultra-compact KURAMA-II monitoring not only provides continuous monitoring of the event's progress, but also allows time to set up a full-scale monitoring system for the event while this monitoring continues.

This research was supported by a grant from the Nuclear Regulation Authority of Japan (JPJ007057) for the Strategic Promotion of Radiation Safety Research. The development was supported by Sony Corporation, TOPPAN PRINTING CORPORATION, and Shimane Nuclear Environmental Center.