In a recent post, Japanese blog writer Mitsui Wanaka criticizes my book Hiroshima Revisited, which makes the case that no nuclear bombs were detonated in Hiroshima and Nagasaki. Mr. Wanaka focuses in particular on the sixth chapter, in which I discuss physical studies on the neutron radiation that was supposedly released by the Hiroshima bomb. The rationale of such studies is as follows:

  1. Neutrons from the bomb that strike the ground will be taken up at random by atomic nuclei there.
  2. Some of the nuclei that took up a neutron will thereby become radioactive.
  3. We can measure, at some later time, the radioactivity of such nuclei in order to determine how much neutron radiation was released by the detonation.

The radioactive nuclei in question will belong to different chemical elements and isotopes, each with their own characteristic half-lives and other properties. From the relative abundance of those isotopes, we can draw some conclusions regarding the energy spectrum of the bomb neutrons. Furthermore, by comparing samples collected at different distances from the detonation, we can determine how far the bomb neutrons had traveled.

Thus far the theory. Now, the entire premise of such studies is obviously incompatible with the central thesis of my book. If indeed no atomic bombs were detonated, then where does the neutron-induced radiation come from? I posit that all of the neutron-irradiated samples were forged for the sake of these very studies. And here I must emphasize a crucial point:

I ruled the neutron studies to be fake not because of their internal contradictions, but based on evidence entirely out of their own scope.1

A straightforward piece of such evidence is the considerable number of people who survived supposedly unsurvivable radiation near the hypocenter. My own book contains some relevant statistics, but Chikatsu Hayashi’s more recent book (in Japanese) has more compelling detail and first-hand testimony. For further evidence, and for the reasons to prefer it to studies on neutron radiation etc., please see my own book or its Japanese translation.

Because Mr. Wanaka ignores this background, he starts his entire analysis from a mistaken premise. He writes:

In the 1990s, the “DS86 neutron problem” was discussed, in which samples far from the epicenter in Hiroshima had radiation measurements that exceeded calculations. This is a real academic debate. Palmer uses this discrepancy as a starting point for his claim that the data was fabricated.2

Mr. Wanaka, taking my book chapter out of context, assumes that its purpose is to prove that the neutron data were faked. However, its real purpose is merely to examine how skilfully they were faked. The entire chapter thus is merely a footnote to the central thesis of the book.

Focusing now on the substance of the neutron studies, the difference between my own arguments and Mr. Wanaka’s can be summed up as follows:

  • I argue that the collective studies on neutron radiation contain numerous contradictions that cannot be resolved.
  • Mr. Wanaka argues that these contradictions do not matter—only the most recent studies on neutron radiation should be considered valid, and all previous ones should be ignored.

Again: the only thing at stake here is the cleverness of the fraud. I posit that it is transparent. If Mr. Wanaka could prove his point, this would mean that the studies had been faked rather more proficiently. However, he has not proved his point. This will become clear below.

One central parameter in the studies on neutron radiation is the relaxation length, which determines how far, on average, the neutrons can travel through the air before being “swallowed up” by some atomic nuclei in their path. Experimental studies begun in Nevada during the 1950s had yielded a relaxation length of 235 meters. Under the different atmospheric conditions in Hiroshima and Nagasaki, a value of 198 meters was assumed. Subsequent measurements on neutron-induced radioactivity in samples from both cities confirmed this value. Nevertheless, in the early 1980s, a new theoretic model was introduced, according to which the relaxation length should be reduced to 155 meters. The new theory thus contradicted the available measurements. What is more, the measurements conducted after its introduction continued to support the old theory but not the new one.

What would a real scientist do in such a situation? He would admit defeat—accept that his theory is rejected by the evidence and look for a better one. And in this case, he would not even have to look at all, since he could simply go back to the old theory!

But this is not what the scientific institutions in charge of the Hiroshima data did. Instead, they stubbornly clung to the new theory, even though for more than a decade no supporting evidence was forthcoming. They obviously were not pursuing scientific truth but rather a political agenda.3

Relief came only in the early 2000s with an updated official report that contained “new and improved” versions of both the theoretical calculations and the experimental data. This was the DS02 report,4 which Mr. Wanaka highlights in his post. The new calculations in this report can be described as a “nothing-burger.” The changes from the previous theory are so minor, and the accuracy of the experimental data available to distinguish between the two versions is so low, that one wonders why anyone found it worthwhile to prepare and publish these new calculations. I suspect that they were only a pretext for unveiling the “new and improved” evidence.

Let us now take a look at the evidence. In his post, Mr. Wanaka deals with measurements on three radioactive isotopes induced by neutron radiation: chlorine-36, europium-152, and cobalt-60. In each case, he argues that we should discard the old measurements, which agreed with the old theory, and accept the new ones, which fit the new theory. The basic argument is the same in each case—namely, that the old studies had overlooked the contribution of some kind of natural background radiation to the measured signals, which they had mistakenly included in the bomb radiation. Because the proportion of such background radiation will be greater at larger distances from the detonation, these will appear too high relative to samples obtained nearer the detonation. The result will be an inflated estimate of the relaxation length, i.e. of the neutrons’ reach.

To decide if Mr. Wanaka’s claim has merit, we must ask: did the authors of those earlier studies fail to account for background radiation, or did they not? Before we go into details, two general remarks are in order:

  1. The whole idea that researchers—and not just single researchers, but multiple groups of them, throughout decades of research work—would commit such a blunder is absurd. Nobody with any training and experience in experimental research would believe it for a minute.
  2. To verify whether or not those studies accounted for background radiation, one would obviously have to read them in their entirety. However, Mr. Wanaka notes: “For the 1992, 2005, and 2008 papers, the abstracts were reviewed. The full texts of the papers were not reviewed.” This pertains to the papers he cites in his own blog post. I assume that he did not read any of the research papers cited in my book either.

If we do trouble to actually examine some of the early papers before dismissing them, we quickly see that the authors were fully aware of the background radiation problem. The very first paper on cobalt-60 radiation was published by Hashizume et al. in 1967. There, we read:5

The background of the spectrometer is thus restricted by that of the GM tube, and discrimination against a cosmic ray particle background (muons) is made by pulse height selection. The detailed performance of a detector of this type has already been reported.16-18

We can assume that all later investigators who examined cobalt-60 radiation were familiar with this early study and, trying to improve on it, would likewise have done their best to account and correct for background radiation. While these early investigators had to make do with less sophisticated instruments than were available at the time of the DS02 report, they did have the benefit of a higher signal-to-noise ratio. For example, between the years 1967 and 2000, the activity of bomb-induced cobalt-60 would have decayed by a factor of about 75.

Early measurements of chlorine-36 were reported by Straume et al. in 1992.6 Mr. Wanaka makes much of the natural background of chlorine-36 that was allegedly not accounted for by these authors. However, Table 1 of Straume’s study lists four samples that were obtained at a “slant range” of exactly 1708 meters. This corresponds to a ground distance of 1606 meters—the largest distance of all samples examined, and therefore the most relevant to the alleged neglect of background radiation. All four samples came from the same building. Two samples are described as exposed to the bomb radiation. With these samples, the measured abundance of chlorine-36, relative to the stable isotope chlorine-35, is given as 579×10-15 and 310×10-15, respectively. The two other samples are described as “totally shielded”, and the table explicitly lists them as “background.” The measured values are 120×10-15 and 125×10-15, respectively. Evidently, Straume and his co-authors, too, were familiar with the background problem and dealt with it.

Regarding the studies on europium-152, let me cite one of the authors that were accused later on of having neglected background radiation. Kiyoshi Shizuma, together with three colleagues, published a study whose very purpose was the minimization of background radiation.7 The abstract of this study reads:

Low-background gamma-ray spectrometers were constructed for the measurement of residual 152Eu activity induced by the atomic-bomb neutrons. Optimum thickness of lead shielding, inner linings and background characteristics were investigated for an ordinary coaxial- and a well-type Ge detector. In addition, an anticoincidence shielding was installed for the well-type detector. As a result, the background counting rate due to cosmic rays was greatly reduced. It was also shown that a sample preparation to enrich the objective activity and eliminate background activities was important in the case of the 152Eu measurement.

A German researcher in this field whom I had contacted to clarify some technical points volunteered that “Shizuma’s work was always extremely careful and accurate.” This is precisely the impression one gets when reading Shizuma’s papers. In summary, the allegations that Shizuma and all those other earlier researchers had neglected background radiation are nonsensical and scurrilous. Mr. Wanaka should have known better than to repeat such allegations without vetting them first.

Mr. Wanaka also claims that the gamma radiation of europium-152 cannot be distinguished from that of actinium-227, which is similar in energy. However,

  1. detectors that can discriminate the two isotopes’ signatures have been available for a long time,
  2. actinium-227 is a short-lived isotope that occurs only as part of the uranium-235 and the thorium-232 decay chains, and thus is always accompanied by the other members of those chains. Therefore, even if its own activity were obscured by that of europium-152, it could be calculated and corrected for based on the signatures of those other isotopes.

Another option is to chemically extract europium from the sample before determining its isotopic composition. This was indeed done in the study by Shizuma et al. (see quote above). The difficulty raised by Mr. Wanaka therefore can and has been dealt with.

The above points address the major bone of contention. Since the older studies did in fact account for background radiation, the reason given by Mr. Wanaka for dismissing them is invalid. We are thus left with unresolved contradictions between the older and the newer experimental data sets. My book chapter cites several other, even more glaring contradictions than those discussed by Mr. Wanaka. Strictly speaking, these contradictions prove only that some of the data were faked; they cannot prove that all of them were. As pointed out above, the latter assertion rests on evidence outside the scope of these measurements themselves.

Mr. Wanaka alleges several other supposed errors on my part which, just like the ones discussed above, result from errors and misunderstandings of his own. I do not consider it worth the time of my readers to address them in detail. I will therefore close with the recommendation to Mr. Wanaka to first do his homework next time.

Notes

  1. For a somewhat trite analogy, consider a policeman listening to Mr. X accusing Mr. Y of robbing a bank on the same day. Since the same policeman had arrested Mr. Y on the day before for robbing another bank, he does not need to consider the details of Mr. X’s testimony to know that Mr. X is lying. (back)
  2. All literal quotes from Mr. Wanaka’s post were translated using DeepL. (back)
  3. I deal with the likely motive for this maneuver in Chapter 11 of my book. (back)
  4. Young, R.W. and Kerr, G.D. (2002) Reassessment of the atomic bomb radiation dosimetry for Hiroshima and Nagasaki: dosimetry system 2002 https://www.rerf.or.jp/library/scidata/scids/ds02/ (back)
  5. Hashizume, T. et al. (1967) Estimation of the air dose from the atomic bombs in Hiroshima and Nagasaki. Health Phys. 13:149-61 https://www.ncbi.nlm.nih.gov/pubmed/?term=6029426 (back)
  6. Straume, T. et al. (1992) Neutron discrepancies in the {DS}86 Hiroshima dosimetry system. Health Phys. 63:421-6 https://www.ncbi.nlm.nih.gov/pubmed/?term=1526783 (back)
  7. Shizuma, K. et al. (1992) Low-background shielding of Ge detectors for the measurement of residual 152Eu radioactivity induced by neutrons from the Hiroshima atomic bomb. Nucl. Instrum. Methods Phys. Res. B 66:459464 http://www.sciencedirect.com/science/article/pii/0168583X9295419R (back)