Tag Archives: Internal Exposure

Initial Survey of Fukushima Children Finds No Detectable Internal 137-Cesium

by Jay T. Cullen


The purpose of this blog is to bring to the attention of interested readers a recent peer-reviewed, open-access study published in the Journal or Radiological Protection . The investigators describe the design and manufacture of a whole body sensor whose purpose is the detection of 137-Cs (half-life ~30 years) in children who were proximate to radionuclide releases after the triple meltdowns at the Fukushima-Daiichi nuclear power plant which began in March 2011. Health impacts of the disaster are likely to be most acute in Japan given that levels of radionuclides in air, soil and water resulting from the disaster were higher compared to levels measured and expected on the west coast of North America. The detector in question (called BABYSCAN) is demonstrated to have a detection limit of better than 50 Bq/body and has been installed in a hospital in Fukushima. Because children are most vulnerable to the impacts of ionizing radiation, 100 Fukushima children were scanned for the presence of 137-Cs and none were found to have detectable levels of the isotope in their bodies. Larger scale measurements of the population will be reported as the long term impacts of low levels of ionizing radiation present owing to the Fukushima disaster warrant further study.

As a result of the radionuclides released to the atmosphere after the meltdowns in March 2011 at the Fukushima-Daiichi nuclear power plant, Fukushima Prefecture was contaminated with radioactive cesium (134-Cs and 137-Cs) and other isotopes, which pose radiological health risks to the resident population.  As would be expected for parents around the world, parents of small children in Fukushima Prefecture have great concern about the internal exposure experienced by their offspring.
The paper by Hayano and colleagues describes the design and manufacture of a whole body scanner designed specifically for the purpose of detecting gamma-emitting isotopes that have been internalized by children. The instrument was first installed at the Hirata Central Hospital in Fukushima Prefecture in December 2013. The design principles, implementation and the initial operating experience are reported in the paper.


The age distribution of the first 100 children who were selected for isotope counting are given in the figure below:

Age distribution of the subjects.
Radioactive 134-Cs and 137-Cs was not detected in any of the 100 subjects. Naturally occurring radioactive 40-Potassium (40-K) was detected in all subjects. Typical gamma-ray energy spectra are are shown in the figure below with black dots indicating data collected with a subject in the instrument (4 min of counting), and those shown in grey dots were taken without subject (blank measurement taken over 5 hours and normalized to 4 min).


Typical gamma-ray energy spectra measured with the BABYSCAN. Left: 8-month-old girl, right: 8-year-old boy. The spectra shown in black dots were taken with subjects (4 min), and those in grey dots were taken without subject (measured for 5 h, normalized to 4 min). The background-subtracted spectra are shown in open circles.

Given the experimental conditions the minimum detectable activity (MDA) for 137-Cs (Bq/body), was calculated for each subject and plotted against weight for each child as shown below.

The minimum detectable activity (MDA) for 137-Cs (Bq/body) versus subjects’ weight.

The detection limit of BABYSCAN for 137-Cs, one of the most significant isotopes with respect to radiological health risks released from Fukushima, is better than 50 Bq/body. Despite this low detection limit, 137-Cs was not detected in any of the first 100 children scanned from the most contaminated areas of Japan in Fukushima Prefecture. Ongoing analyses will be carried out on a larger-scale with BABYSCAN and reported in publications by the investigators in the future. I will report on data as it becomes available.