Nuclear Fission and Radioactive Fallout
Fukushima samples retested 2 years later.
By George Dowell
Fission:
n. noun
1. The act or process of splitting into parts.
2.A nuclear reaction in which an atomic nucleus, especially a heavy nucleus such as an isotope of uranium,
splits into fragments, usually two fragments of comparable mass, releasing from 100 million to several
hundred million electron volts of energy.
A nuclear power reactor relies on fission to produce the heat that makes the steam that drives the electric
generators.
Consider the most common nuclear fuel, Uranium 235 (U-235). When a stray neutron is absorbed into a
U-235 nucleus, U-236 is
formed, which is a highly unstable atom. U-236 will usually split or fission into at least two smaller
fragments called Fission Products,
which themselves can be radioactive and decay by releasing nuclear fragments (alpha particles and
electrons)
Of the many possible fission products possible, the ones of main concern in analyzing fallout are Cesium
137 (Cs-137),
and Strontium 90 (Sr-90) due to their long persistence (Half-Life). Cs-137 and Sr-90 also occur in fallout
from nuclear weapons detonations.
Another version of radioactive cesium is peculiar only to fallout from a nuclear reactor, not a bomb:
Cesium 134. The reason for this is that Cs-134 is formed over a period of time in a reactor by neutron
activation, not fission.
The Fukushima situation was unique is another respect, we believe now that the hydrogen chemical
explosion vented large quantities of cesium in its gaseous form, but not strontium. Cesium is very much
more volatile than strontium, therefore gasifies much easier, and transports on the wind to greater
distances. Our tests are only on small environmental samples i.e. soil and vegetation, taken at a distance
from the reactor site.
Sr-90 was tested using a magnetic beta spectrograph and found to be missing. Those tests are the subject
of another article.
About Cesium Radioisotopes:
Cs-137 has a half-life of over 30 years. Its presence can still be detected in Trinitite from the first nuclear
explosion at Trinity site, and is the main contaminant left in Chernobyl fallout.
Cs-134 has a half-life of about 2 years. By rule-of-thumb it will only 1/64th as active after 12 years (6 halflives) and be virtually
undetectable after 20 years (10 half-lives).
Fig. 1: The Home Rad Lab with SPECTECH UCS-20 MCA and ST-150 Nuclear Lab Station
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Fig. 2:
SPECTECH UCS-20 MCA, RAS-20 Calibrated Absorber Set and a variety of shielded probes.
The UCS-20 will work with a wide variety of probes, with some, additional adaptors
may be required, see text for details.
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Fig. 3:
Soil samples from 4 locations 25 miles west of the Nuclear Power Plant in Fukushima, Japan
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Fig.4:
Location of the collection sites of the 4 soil samples, Fukushima, Japan, 2011.
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Fig. 5:
Drying and preparing soil samples into test tubes for Gamma Analysis in the UCS-20.
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Fig.6:
Weighing the soil sample of interest. This sample, #F4, is grassy, leafy and other vegetation.
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Fig.7:
Gamma spectrum analysis on the SPECTECH UCS-20 shows clear signatures of Cs-134 and Cs-137,
fission products from the reactors at Fukushima after the 3/11/2011 accident.
Analysis accomplished on 26 Oct 2011.
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Fig 7A:
Same data as Fig. 7 but in linear display mode.
Fig.8:
Test tube and results showing on computer screen after background subtraction and 3 point smoothing,
features
included in the UCS-20's free software. This is that latest edition of the software, available on the
SPECTECH site at:
www.spectrumtechniques.com.
PART II
Two Years Later
Fig.2-1: Comparing the 2011 scan to a 2103 scan of sample tube Site2. The present, less active sample has
been mathematically subtracted from the original more active version, leaving the difference displayed.
Shown in yellow are the components of Cs-134 that were originally present in 2011 but absent in 2013.
Fig.2-2: Site F4 sample tube- 2013 scan in yellow with 2011 scan in red overlaid.
Fig.2-3: Close-up of important peaks and my interpretation. Non labeled peak at 212 keV is the normal
backscatter
peak, it does not represent radiation directly from the fallout.
Fig.2-4: Similar methodology applied to samples taken at undisclosed Tokyo location in 2011, tested 2011
and 2013.
Fig.2-5 Fukushima soil superimposed over Trinitite sample.
Fig.2-6:Japan rice contaminated with Fukushima fallout.
Fig.2-7: Scan showing Fukushima contaminants in/on rice.
Conclusions:
Gamma spectrum analysis with simple equipment can differentiate fallout from weapons vs. reactors;
tell if the fission was via uranium or by plutonium; tell the relative age of the sample; determine certain
environmental
conditions at the time of release.
Remnants of nuclear events leave different traces, some uniqueTrinitite has Cs-137, Sr-90 but also types of radioactive europium, a prompt activation product, formed
at Trinity in the soil
by the moderating action of rainwater from a very recent storm (said storm that actually delayed the
shot). Plutonium and
Pu byproducts are present.
Chernobyl contaminated vegetation is presently showing only Cs-137, as any Cs-134 is long decayed
away. Furthermore
Vegetable contamination is primarily Cs due to the preferential biological disposition of elemental cesium
in plants. Closer to the NPP, solid debris can be found, including fuel fleas (tiny pieces of actual nuclear
fuel)
Fukushima contaminated samples are showing both Cs-134 and Cs-137. In time only the Cs-137 will
remain.
George Dowell
© 2013
GEOelectronics@netscape.com