Research was led by Marco Casolino of the RIKEN Global Research Cluster's EUSO Team and Masayuki Goto of G-Tech Corporation, a private company which develops radiation measurement equipment.
The system, called LANFOS (Large Food Non-destructive Area Sampler), can separate cesium from the background of radiation caused by natural levels of radioactive potassium.
It uses a silicon photomultiplier, a device that was developed for use in space-based observatories.
System presentation
The research was funded under the JST Development of Advanced Measurement and Analysis program and will be presented on March 24 at the 70th Annual Meeting of the Physical Society of Japan.
Work was done in response to the accident at the Fukushima Daiichi Nuclear Power Plant in 2011 following the Great East Japan Earthquake and tsunami.
To ensure public safety and ease concerns, the limits of maximum amount of admissible radiation was reduced first to 500 Bq/kg and then to 100 Bq/kg.
Farmers have been affected due to consumer fears and measuring contamination in agricultural products was seen as key to restoring public confidence.
The team developed a device with the scintillator set around the whole inner surface of the container, employing a lightweight plastic scintillator.
Current method
At the moment most monitoring is done with scintillation detectors at the bottom of the testing container, requiring food to be ground into pieces so it can be close enough to the detector to be accurately measured.
So the food put on store shelves cannot be that which was actually measured.
Using the device food samples do not have to be pre-processed prior to a test and can be consumed after measurements.
Casolino said plastic scintillators are not sensitive enough to easily distinguish between the naturally occurring potassium 40 and the artificial cesium isotopes.
“This is a problem because official regulations set the maximum level of cesium at near the level of natural potassium 40.
“Fortunately, we were able to develop a mathematical algorithm to separate the two taking advantage of the initial difference in photon energy, and now we are able to reliably detect the level of cesium in a large container, without harming the materials."
A prototype of the LANFOS device which was made by G-Tech was tested in Minamisoma City, Fukushima, one of the areas contaminated, on samples including potatoes, cabbage, and Japanese pears with positive results.