Radioactivity lingering in Hiroshima and Nagasaki

'Long-lived neutron activation products,Co-60, Eu-152, Eu-154 and Cl-36 ... are still detectable today [in Hiroshima and Nagasaki] using modern analytical techniques...' - Nezahat Hunter and Monty W Charles, An update on the discrepancy between calculated and measured neutron-induced radioactivity levels in Hiroshima, J. Radiol. Prot. , v. 22 (2002), pp. 345-356.

In a previous post I mentioned the long-term effects of neutron radiation:

'In a controlled sample of 36,500 survivors, 89 people got leukemia over a 40 year period, above the number in the unexposed control group. (Published in Radiation Research volume 146:1-27, 1996.)

'Over 40 years, in 36,500 survivors monitored, there were 176 leukemia deaths which is 89 more than the control (unexposed) group got naturally. There were 4,687 other cancer deaths, but that was merely 339 above the number in the control (unexposed) group, so this is statistically a much smaller rise than the leukemia result.'Natural leukemia rates, which are very low in any case, were increased by 51 % in the irradiated survivors, but other cancers were merely increased by just 7 %.

'Adding all the cancers together, the total was 4,863 cancers (mainly natural), which is just 428 more than the unexposed control group. Hence, the total increase over the natural cancer rate was 9 %, spread over 40 years.'

All the 89 leukemia victims of Hiroshima and Nagasaki (leukemia is important since it is generally considered the worst type of cancer, the hardest to treat effectively), were caused by the initial nuclear radiation which lasted for a few seconds. The residual doses were completely trivial by comparison. But people don't accept this without seeing the evidence that air bursts don't produce significant residual radioactivity on the Earth. So this post presents the evidence.

Hiroshima and Nagasaki are still radioactive! Why aren't they evacuated? Well, the chief problem with detecting the nuclear bomb radiation using conventional equipment for the past 60 years has been the problem that it is swamped with something called natural background radiation, which stems from the supernova that created the matter - including potassium-40 which 'pollutes' the oceans, uranium which 'pollutes' the land, and many other nuclides like radon-222 which 'pollutes' the air naturally - found on a planet called Earth some 4,540 million years ago, not to mention the continuing short-lived induced activity in the atmosphere caused by nuclear radiation from the sun and from other nuclear reactors in space.

Should I even mention natural nuclear reactors that 1,700 million years ago emitted an average of 100 kW of power over 150 million years, and safely stored the resulting massive quantities of 'hazardous' fission products in the uranium ore seams of Gabon, Africa: 'Fifteen natural fission reactors have been found in three different ore deposits at the Oklo mine in Gabon, West Africa. These are collectively known as the Oklo Fossil Reactors. ... The radioactive remains of natural nuclear fission chain reactions that happened 1.7 billion years ago in Gabon, West Africa, never moved far beyond their place of origin. They remain contained in the sedimentary rocks that kept them from being dissolved or spread by groundwater.' Just notice the lies from the anti-nuclear lobby which thinks radioactive waste is somehow unnatural and 'polluting nature' and that 'nobody knows how to safely store the waste for 24,000 years because the 'nuclear age' is just over 60 years old.' Also notice that the nuclear industry has gone from spewing out pathetic pro-nuclear propaganda to 'working with' these nutters, and cannot present to the public the facts about radiation without either being condescending and patronising with authority, or on the other hand being so over-technical that nobody wants to listen. Those people are all 'professional wallies', like string theorists. More on Earth's natural nuclear reactors here, here, here, here, here, here, here, here, here, here, and here.

Tadashi Hashizume and others in a paper published in Health Physics, v. 17, (1969), p. 761, found that the total neutron-induced gamma dose (from Na-24 and Mn-56) at ground zero in Hiroshima and Nagasaki were 80 and 30 R, respectively (falling to 18% of this at 0.5 km from ground zero, and to 0.07% at 1 km). This is measured data, you simply measure the remaining activity in the soil from the few very long-lived nuclides, then you irradiate the soil sample with neutrons in a laboratory to replicate that activity, and you can then measure the short-term Na-24 and Mn-56 hazards accurately.

'The residual radiation levels in Hiroshima and Nagasaki about the time of occupation troop arrival are fairly well-documented. As discussed in more detail subsequently in Section 3, a scientific group organized by the Manhattan Engineer District conducted radiological surveys in Nagasaki from 20 September to 6 October 1945, and in Hiroshima from 3 to 7 October 1945. Later surveys were conducted in Nagasaki (15-27 October 1945) and Hiroshima (1-2 November 1945) by a team from the Naval Medical Research Institute (NMRI). The NMRI surveys were supplemented by measurements made by Japanese scientists at even later dates.' - DNATR805512F.

That report contains residual radiation contours for neutron-induced activity (concentrated on ground zero, as in all air bursts) and fallout (trivial deposits occurring some distance downwind). For Hiroshima, the measured neutron-induced activity gamma dose rate of 0.1 mR/hr on 3-7 October 1945 had an average radius of 230 m from ground zero. This does not include natural background radiation (generally 0.01-0.02 mR/hr). Fallout produced a small 'hotspot' of 0.045 mR/hr (not including natural background) at a distance of 3.6 km west of ground zero (downwind) in Hiroshima, measured on 3-7 October 1945.

In Nagasaki, although the bomb had a higher yield the high explosive around the core absorbed more of the neutrons so the neutron induced activity was less extensive: 0.03 mR/hr out to an average radius of 210 m from ground zero was measured in surveys between 21 September and 4 October 1945 (not including natural background). However, the fallout was more heavy downwind from Nagasaki than from Hiroshima; the fallout 2.6 km east (downwind) of ground zero in Nagasaki that these times was about 1 mR/hr (not including natural background).

Because the neutron induced activity peaks something like 6-7 cm deep in the soil, there is a lot of self-shielding by the topsoil which reduces the dose rate, that must be taken into account in converting from the activity in the soil to the dose rates in the air above it.

From a previous post on this blog:

Above: typical composition of representative soil types for calculating neutron induced activity, given in Philip J. Dolan's originally secret manual Capabilities of Nuclear Weapons, DNA-EM-1, U.S. Department of Defense, Chapter 5, Nuclear Radiation Phenomena, August 1981 revision.Above: decay rates of the different soil neutron induced activities, given in Philip J. Dolan's originally secret manual Capabilities of Nuclear Weapons, DNA-EM-1, U.S. Department of Defense, Chapter 5, Nuclear Radiation Phenomena, August 1981 revision.
Above: neutron induced activity dose rates, decay rates, and doses for Hiroshima and Nagasaki air bursts where fallout was negligible at ground zero ("DS02" indicates 2002 dosimetry system, the latest data).

'Some related field manuals with data are publically available, however, like chapters 1 and 7 of FM 3-3-1 also on line here as a better quality PDF file (this reproduces the table of neutron induced activities in soil from TM 23-200 and DNA-EM-1). Note that the various FM 3-3-1 neutron induced activity illustrations of the dose rates for a given weapon and soil type are contradictory and useless; Dolan's manual makes it clear that the gamma dose rate at 1 hour after burst due to neutron induced activity can vary by a factor of 4,540 depending on the amounts of manganese and sodium in the soil.

'The minimum rate corresponds to clean Pensacola sand (99.982% pure silicate) which is 0.001% sodium, 0% manganese, and 46.65% silicon by mass. For such almost pure silicate sand, silicon-31 becomes a significant gamma contributor although it is trivial in all other soils (containing higher manganese or soldium levels). Because there is so little sodium-24 in this soil, Si-31 stands out initially (at 1 hour after burst, 52% of the gamma dose rate would be due to Si-31 with a 2.62 hr half life, and 48% to Na-24 with a 15.0 hr half life).

'The worst danger, 4,540 times more intense, would come from Hawaiian lava clay soil, since that is 2.94% manganese by mass resulting in a massive amount of Mn-56 (2.58 hr half life), although no other significant gamma emitters. The hazards from most soils and also from sea water fall between these two extremes. The dose rate variations due to the type of soil far outweigh possible variations due to the design of the nuclear weapon used. Hence a reasonable prediction is possible provided that the target is known. The peak neutron induced activity generally occurs at a depth of 6-7 cm so there is considerable self-shielding by the soil which makes the hazard far less than you would naively expect if assuming the activity is in the top surface layer of soil.'