Radiation Activity Fallout Measuremen
 

AIST measures energy spectra of the ionizing radiations from fallout using a Germanium semiconductor detector. The fallout sample is obtained by smearing on a vinyl sheet, which is the size of 1 m times 1.5 m and put on the ground at AIST. The following figure shows the energy spectra of the ionizing radiation from the fallout sample (red) and background (blue). We found radionuclides of Te-132, I-131, I-132, I-133, Cs-134, and Cs-137. These radionuclides are expected to be released from the nuclear power plants at Fukushima because these are not exist in the environment.

*AIST stopped the radio activity fallout measurements on April 8. This is due to the facts that the radiation dose in the air measured at AIST Tsukuba is decreasing constantly and that only trace amounts of radionuclides are detected for more than a week.


Photon energy spectra from the fallout sample smeared on the vinyl sheet on the ground at NMIJ measured on March 15, 2011 (red) and March 19, 2011 (green). The blue curve shows the background.

The following data show the change of the radioactivity of these radionuclides.

Radioactivity of the detected radionuclides
RadionuclideTe-132I-131I-132I-133Cs-134Cs-137
Half life3.2 day8.0 day2.3 hour21 hour2.1 year30 year
DateRadioactivity (Bq)
March 15, 9:20 - 10:2024124381644
March 15, 13:20 - 14:20183518432
March 16, 13:20 - 14:208237122
March 17, 13:20 - 14:20261000
March 18, 13:20 - 14:20010000
March 19, 13:20 - 14:20120000
March 20, 13:20 - 14:204516036
March 21No data is available due to rain.
March 22, 16:15 - 17:15794001
March 23, 12:20 - 13:20151001
March 24, 13:20 - 14:20141000
March 25, 13:20 - 14:20040001
March 26, 13:20 - 14:20191001
March 27, 13:20 - 14:20010000
March 28, 13:20 - 14:20010000
March 29, 13:20 - 14:20010000
March 30, 13:20 - 14:201500813
March 31, 13:20 - 14:20010000
April 1, 13:20 - 14:20010000
April 2, 13:20 - 14:20010000
April 3, 13:20 - 14:20000000
April 4, 13:20 - 14:20010000
April 5, 13:20 - 14:20000000
April 6, 13:20 - 14:20000000
April 7, 13:20 - 14:20000001
April 8, 13:20 - 14:20020012
(1) The sampling area is 1 m x 1.5 m on a vinyl sheet.
(2) The measured values change slightly due to sampling conditions.
(3) The sampling time changes due to rain.

Change of the radioactivity of the detected radionuclides


Germanium semiconductor detector system at NMIJ