Restoring confidence in Japanese food safety, post-Fukushima

To help restore confidence in the safety of Japanese agricultural produce following the accident at the Fukushima nuclear plant in 2011, a team of researchers has used technology originally designed for use in outer space to create a system to inexpensively and non-destructively detect radioactive cesium contamination in food.

Measuring contamination in agricultural products was seen as a key to restoring public confidence; however, most monitoring is currently done with scintillation detectors that are located at the bottom of the testing container, requiring food to be ground into pieces so that it can be close enough to the detector to be accurately measured. Hence, the food put on store shelves cannot be the food that was actually measured.

The research team set out to develop a device with the scintillator set around the whole inner surface of the container, employing a lightweight plastic scintillator. However, they found that plastic scintillators were not sensitive enough to easily distinguish between the naturally occurring potassium 40 and the artificial cesium isotopes.

In response, they developed a mathematical algorithm to separate the two, taking advantage of the initial difference in photon energy, and were then able to develop a system, called LANFOS, to reliably detect the level of cesium in a large container, without harming the materials.

A key element to the device is a silicon photomultiplier, a type of device that was developed for use in space-based observatories.

According to Marco Casolino of the RIKEN Global Research Cluster's EUSO Team, "This type of photomultiplier has certain characteristics that make them good choices for use in space, such as low power consumption and low cost. These same characteristics made them good choices for our detector."

A prototype of the LANFOS device, which is large enough to test entire food samples, was fabricated and tested at a festival in Minamisoma City, Fukushima, one of the areas contaminated by the accident. The device was tested on samples including potatoes, cabbage and Japanese pears. According to Casolino, "The local people were impressed at the machine's ability to rapidly give them a readout of levels of radiation in the food, and this gave them hope that consumers might become more confident about buying their products."