A bit of casual reading for the Easter holidays is offered here:
There are now a few scientific articles available from the arXiv preprint server. We may put some more detailed comments on them as soon as we have had the time to look at them closer ourselves, but they may be of interest to a broader audience.
The articles are (click on the link for each article in order to reach the arXiv page, then download the article as pdf or other format from the box in the upper right corner):
- 30 March 2011: Observations of Fallout from the Fukushima Reactor Accident in San Francisco Bay Area Rainwater, by Eric B. Norman, Christopher T. Angell, Perry A. Chodash, Department of Nuclear Engineering, University of California, Berkeley, USA.
- 15 April 2011: Arrival time and magnitude of airborne fission products from the Fukushima, Japan,reactor incident as measured in Seattle, WA, USA, by J. Diaz Leon, D. A. Jaffe, J. Kaspar, A. Knecht, M. L. Miller, R. G. H. Robertson, A. G. Schubert, Department of Physics and Center for Experimental Nuclear Physics and Astrophysics, University of Washington, Seattle, USA, and Department of Interdisciplinary Arts and Sciences, University of Washington, Bothell, USA.
- 19 April 2011: Measurement of airborne radioactivity from the Fukushima reactoraccident in Tokushima, Japan, by K. Fushimi, S. Nakayama, M. Sakama, Y. Sakaguchi, Institute of Socio Arts and Sciences, The University of Tokushima, Japan, Department of Radiological Science, Division of Biomedical Sciences, Institute of Health Biosciences, The University of Tokushima, Japan, and Faculty of Integrated Arts and Sciences, The University of Tokushima, Japan.
In an earlier blog post there were discussions in the comments regarding the difficulties in correctly identifying which isotopes that are found in the releases. These articles show some nice examples of pulse-height spectra from gamma spectroscopy measurements (incidentally, it is Figure 1 in all three papers). Figure 1 in the paper about analysis of rainwater in the San Franciso Bay area (page 6) clearly illustrates how difficult it can be to correctly identify relatively small peaks on a large background. The samples taken in the water pools at the Fukushima power plant have an even more complicated mix of radioactive nuclides, so this is part of the explanation to why there have been some strange reports regarding identified isotopes.
The last paper surprised me first due to the low levels of Iodine-131 detected, there was a peak value of 2.5 milli-Becquerel per cubic meter of air observed on 6 April, only slightly higher than the peak value observed in Stockholm on 30-31 March (2.15 milli-Becquerel per cubic meter, a tiny amount as explained here (in Swedish only)) and the other data are much lower, around 0.1-0.2 milli-Becquerel per cubic meter. The reason is due to the geography, Tokushima is located on the island Shikoku far to the south-west of Fukushima. Due to the dominating wind pattern, the detected radioactive nuclides have mainly traveled around the entire planet before reaching Tokushima, and therefore have much lower activity. However, the peak around 6 April is due to a temporary change in the wind pattern. Calculations from the Central Institute for Meteorology and Geodynamics (ZAMG) in Austria show examples of the wind patterns. Here is an example from 6-7 April for Iodine-131.
If anybody has any questions related to the articles, you are welcome to post them here and we will try to answer.