Report of the British Mission to Japan

RADlO-ACTIVE EFFECTS

69. The process of atomic fission gives rise to radio-activity in three ways :

• First is the release of penetrating particles (neutrons) and radiation, which are directly harmful to human beings.
• Second are the new products into which fission breaks the constituent material, either Uranium 235 or Plutonium 239. These fission products are themselves radio-active.
• Third are materials which, penetrated by the released neutrons, become radio-active in their turn.

70. Of these effects, as they were produced by the bombs on Hiroshima and Nagasaki, those due to the action of neutrons, either directly or indirectly, were probably the least important. Neutrons did affect human beings, for Japanese scientists found induced radio-activity in the phosphorus of their bones ; but the scale of the effect does not appear to have been comparable with that produced by penetrating radiation. Similarly, 'such radio-activity as was detected in the ground was probably in the main not induced by neutrons.

71. At the time of the visit of the Mission, three months after the bombing, there were areas which remained radio-active both in Hiroshima and in Nagasaki. But the amount of radio-activity was trivial then, and had been so soon after the bomb exploded. For example, cases are known of people in both cities who worked near the centre of damage from the afternoon of the bombing without ill effect. And in spite of stories to the contrary, plant life was flourishing in both cities. Thus residual radio-activity is not a danger from these bombs exploded at such heights. The small amounts of radio-activity which remained in both cities were the result of the fall of a small fraction of the radio-active fission products. In fact, the radio-active areas in each city lie downwind from the explosion ; and Japanese physicists had identified three known fission products in deposits in Hiroshima. It was foreseen that, from bombs exploded at these heists, the amount of fission products which would faH on the cities would be insignificant. From bombs burst at lower heights, however, the ground, and particularly rough ground, would receive markedly greater, amounts of these products, in quantities which might leave it dangerously radio-active for days or longer.

72. The most important radio-active action at Hiroshima and Nagasaki appears to have been that from penetrating radiation. The exact make-up of this is unknown, and for convenience all this radiation will be summarily called gamma rays. Its effect is to cause injuries which, so far as can yet be judged, are analogous to but more severe than those caused by over-exposure to X-rays. For the description of these effects, and the bulk of kindred material in this report, the Mission is indebted to the Medical Section of the Joint Commission for the Investigation of the Effects of the Atomic Bomb, which will ultimately publish a more detailed and more accurate report than this interim statenent

73. The gamma rays were very penetrating, and passed through the skin without affecting it. As a result, those exposed to gamma rays, if they were protected from flashburn and from indirect injury, showed no immediate ill-effect. Even those severely irradiated probably did not show the characteristic symptoms, nausea, vomiting and fever, for 24 hours, and rarely died in less than one week. These first symptoms were followed by bloody diarrhea, occurring most frequently in the second week, at which time loss of appetite and general malaise also became marked. Patients began to lose their hair after the first week.

74. Thereafter, in the severe cases, the clinical picture came to be dominated by signs of deficient blood formation. This effect on the blood is indirect, and therefore delayed : the gamma rays do not attack the cells in the blood-stream, but the primitive cells in tibe bone marrow, from which most of the different types of cells in the blood are formed. Therefore serious effects begin to appear only as the fully-formed cells already in the blood die off gradually and naturally, and are not replaced as they would be normally by new cells formed in the bone marrow. In severe cases, it was apparent that the gamma rays had virtually killed the entire bone marrow. In such cases, all three types of ceDs formed in the marrow became de&ieat: red cells, platelets, and white cells (granulocytes). As red cell formation ceased, the patient began to suffer from progressive anemia. As platelet formation ceased, the thin blood seeped in small and large hemorrhages into the skin and the retina of the eye, and sometimes into the intestines and the kidneys. The fall in the number of white cells, which was useful in diagnosing mild cases because it could be detected by taking blood counts, in severe cases lowered resistance, so that the patient inevitably fell prey to some infection, usually spreading from the mouth and accompanied by gangrene of the lips, the tongue, and sometimes the throat. Death in these cases was the result of a combination of anemia, internal bleeding, and infection. Deaths probably began in about a week after the explosion, reached a peak in about three weeks, and had for the most part ceased after six to eight weeks.

75. The distances at which these effects were felt are not easy to determine. It is thought that gamma rays ultimately caused the death of nearly everyone who was fully exposed to them up to a distance of ½ mile from the centre of damage. A figure can be obtained for the 50 per cent, chance of survival, from the evidence of two groups of workers who had been brought into Hiroshima from an outlying village, and who were working in the open but screened by wooden buildings at 1,200 yards from the centre of damage. Of the total of 198 men, 6 were killed immediately by debris and 95 of the survivors subsequently died, it is believed all from the effects of gamma rays. Allowing for some small protection afforded by the wooden buildings, it is estimated that people in the open have a 50 per cent, chance of surviving the effects of gamma rays at ½ mile from the centre of damage. As regards lesser effects, loss of hair was recorded up to 1 ¼ miles from the centre of damage, and some doctors felt that the milder forms of radiation sickness, more difficult to diagnose, may have extended to 2 miles.

76. The gamma rays are capable of penetrating considerable thicknesses of building and other material. They thereby pose new problems of protection, the scope of which is not yet fully understood, and is best illustrated by examples.

• An unusually strong three-storey reinforced concrete building at Hiroshima, less than 250 yards from the centre of damage, contained 23 people whose fate can be traced. The building remained structurally undamaged, and none of these people was killed immediately ; nearly all had some lesser injuries from debris and fire, but were able to walk to hospital for treatment. Subsequently,between the sixth and the seventeenth day after the explosion, 21 of these people died, probably all from the effects of gamma rays. The two survivors were in the telephone room on the ground floor, where they were shielded by all the floors and possibly by adjacent buildings.
• In a five-storey reinforced concrete building 700 yards from the centre of damage, gamma rays caused many deaths on the fourth and fifth floors and a few on the third, but killed no one below this who was screened by all the higher floors.
• A partly underground concrete shelter less than i mile from the centre of damage had no gamma ray casualties, or indeed any but minor debris * injuries.
• At distances approaching 1 mile from the centre of damage, less massive buildings began to protect from gamma rays. For example in the City Hall of Hiroshima, at this distance, there were no deaths from gamma rays and at most 6 mild cases of radiation sickness.

Only tentative conclusions can yet be drawn from this and similar information.

77. The effects of gamma rays on human reproduction necessarily form a long-term study, which will continue for some years. Of the effects already detected, the most striking are those on pregnancies at all stages from two months onwards. At distances up to 1,000 yards from the centre of damage, pregnant women who survived have had miscarriages. At distances up to 1¼ miles from the centre of damage, pregnant women who survived have had either miscarriages or premature infants who died very soon. Even beyond this range, up to nearly 2 miles, only about one-third of pregnant women have given birth to what appear to be normal children. Two months after the explosion miscarriages, abortions, and premature births throughout Hiroshima were nearly five times as frequent as in normal times, and formed more than one quarter of all deliveries.

78. Sperm counts made in Hiroshima show that a high proportion of men exposed to gamma rays, up to perhaps f mile from the centre of damage, have reduced powers of reproduction. Gamma rays also stopped menstruation in women ; but this condition was so common throughout Japan, it is thought as a result of war-time diet and overwork, that no conclusions regarding its permanence can yet be drawn.

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