Many kinds of devices are available for measuring radiation in food, and it is important to be sure
that they will give similar results. When an independent radioactivity measurement laboratory asks
to participate in the site, MDS conducts accuracy checks by using standardized brown rice samples.
This check helps determine whether the numerical measurement values given by the equipment at that laboratory
are accurate enough to be included.
◎About Standardized Brown Rice Samples:
We selected brown rice as a basic sample for establishing standards as it can be stored for a long time and is easy to handle.
We use brown rice that has been measured by an extremely sensitive germanium semiconductor nuclide analysis detector.
The rice is carefully graded into four degrees of Cesium contamination. C-lab is responsible for this analysis.
A）High concentration （100Bq/kg）
D）Very low concentration（3Bq/kg）
◎ Accuracy Check Method:
・The four types of samples (3, 10, 50, 100 Bq/kg) are measured with each measuring instrument intended to be included
in the MDS database.
・The measurement time is set to allow a numerical Cesium concentration value to be identified.
・The measured concentration value is compared with a corrected value that reflects the expected attenuation
on the day the measurements are carried out, and evaluated to see whether the value is within the acceptable range.
・When the values of all samples are determined to be within the range, accuracy is judged to be adequate.
・If values outside the range are found, the samples are re-measuring.
Each sample is removed from the Marinelli container and the container is refilled.
・If the value is still outside the range, the measuring instrument is adjusted using efficiency calibration at the standard source.
・After adequate accuracy is ensured, the laboratory is registered at MDS as a participant organization.
The data of the laboratory is also registered at MDS.
・After the registration, a package including a table for calculating correction values for Cesium attenuation,
an oxygen absorber, and instruction manuals, is sent to the laboratory.
・Water content is checked by entering the gross weight measurement into the table each time.