Strange Glow
Page 17
After the first wave of fatalities there was a lull in the storm of death at the hospital. Once the early deaths had culled out the most severely injured, a second wave of death arrived a week later. These patients suffered primarily from gastrointestinal (GI) problems, including severe diarrhea, but also hair loss and high fever. Some of the worst cases included combined symptoms of malnutrition due to poor absorption of nutrients from the intestines, abdominal bloating, dehydration, internal bleeding, and infection from bacteria entering the body through the damaged intestinal lining. There was little Sasaki could do to help these patients. By two weeks after the bombing, all were dead.
These GI symptoms can all be traced to complete shutdown of the small intestines. Although it may not be apparent at first, the small intestines share something in common with testicles. They both contain rapidly dividing cells; crypt cells and spermatogonia, respectively. We have seen how spermatogonia are preferentially sensitive to radiation damage, due to their rapid cell division. The same situation exists with the small intestine’s crypt cells. But while spermatogonia give rise to sperm, crypt cells give rise to structures called villi.
Villi are microscopic, fingerlike projections that line the inner surface of the small intestine and give it the appearance of a long-piled carpet. This carpet of villi increases the surface area of the intestines for the absorption of food, thereby facilitating the uptake of nutrients into the bloodstream. Since these villi wear down quickly as moving food rubs away their tops, cells need to be constantly replaced from below. At the base of the villi (between the fingers) are rapidly dividing crypt cells that constantly add newly made cells; these compensate for those cells lost at the top. In this way, the height of the villi remains constant as a growing cohort of recruits replaces the older cells that are swept away. The transit time for individual cells, from the base to the top of a villus, is about eight days. Thus, the maximum lifetime of a villus cell is eight days. So when crypt cells are killed by radiation and stop replenishing the villi, the villi waste away over this eight-day period. At its end, there are no villi left, so it’s not surprising that the average time to death from this syndrome is eight days.25
Patients suffering from villi failure are said to have the GI syndrome of radiation sickness. These patients received a whole-body radiation dose too low to severely damage the nondividing and, therefore, resistant brain cells. Consequently, they don’t develop the CNS syndrome. Still, their doses were high enough to kill the rapidly dividing crypt cells in their GI tract. It is important to appreciate that all tissues with rapidly dividing cells are affected the same way, and lose their population of dividing cells. GI symptoms appear first, however, because of the (1) short, eight-day lifetime of the cells of the villi, and (2) critical importance of the small intestine to survival due to absorption of nutrients and provision of a barrier between fecal matter in the intestines and the body’s internal organs.
As with CNS syndrome, there was no hope of recovery from GI syndrome. The GI syndrome patients soon succumbed to all of the medical problems one would expect to encounter in people who no longer had functioning small intestines. Patients who die from the GI syndrome have usually received whole-body doses less than 20,000, but more than 10,000 mSv.
After the GI syndrome patients had all passed away, Sasaki noticed another lull in deaths that lasted a couple of weeks. But then at around thirty days after the bombing, some of the surviving patients had a nearly complete loss of all types of blood cells (pancytopenia) and started to die from all of the medical complications associated with this condition. Sasaki and his colleagues soon learned that two important factors were critical to the prognosis of these patients. Either a very high and sustained fever, or a white-blood-cell count that dropped below 1,000 per microliter of blood, was bad news. One of these two symptoms meant death was highly likely, but having both spelled certain demise.
By the time the third syndrome arrived the doctors were well aware that they were dealing with radiation sickness. They treated patients with liver extracts, blood transfusions, and vitamins, all of which were thought to boost blood counts. They also found that penicillin was effective in these patients because loss of blood components made them vulnerable to infections which penicillin helped to fight.
FIGURE 7.2. ATOMIC BOMB VICTIM. A man, suffering the symptoms of radiation sickness, rests on a straw mat at a makeshift hospital in a Hiroshima bank building.
Nevertheless, these doctors had some crude ideas about the mechanism by which radiation was unleashing its health effects on the blood. They thought that gamma rays had penetrated the victims’ bodies at the time of the blast and made the phosphorus in their bones radioactive.26 The radioactive phosphorus supposedly started irradiating the bone marrow—the blood-forming tissue of the body—by emitting beta particles, which slowly started to break the marrow down. The doctors apparently had some knowledge of the radium girls and the problems they experienced due to radium substituting for calcium in their bones, and they also knew that the health effects of overexposed x-ray workers included delayed anemia. So they likely conflated these two entirely different circumstances into a unifying hypothesis, with a common causal mechanism involving radioactive bones. Although phosphorus is a major constituent of bone, and radioactive phosphorus-32 does, in fact, emit beta particles, gamma irradiation of phosphorus does not make it radioactive. A bone biopsy and a Geiger counter—a handheld instrument that identifies radioactive contamination and produces an audible “click” for each atomic decay (disintegration) detected—could have easily shown that their hypothesis was flawed. But, apparently, the wrongheaded idea went unchallenged.
We now have the correct explanation of why these blood problems appeared so late. Bone marrow cells—the cells that make all of the blood components—divide rapidly, just like the crypt cells. Additionally, the bone marrow cells are prone to an accelerated type of cell death,27 making them even more sensitive to radiation than the crypt cells. Nevertheless, this syndrome doesn’t precede the GI syndrome because the mature blood cells have longer average lifetimes in the blood’s circulation than do the villi cells; thirty versus eight days, respectively. Thus, the blood can continue its functions much longer before the lack of new recruits is noticed. Nevertheless, by thirty days, the mature cells are old and starting to die off, and the absence of replacements results in severe anemia. The symptoms Sasaki witnessed included everything that would be expected for patients with no blood cells in their circulation. Without medical intervention, death usually followed. This scenario of acute anemia caused by radiation is called the hematopoietic (Latin for “blood forming”) syndrome of radiation sickness. People who suffer from this syndrome received whole-body doses insufficient to wipe out crypt cells but high enough to kill some or all of blood-forming cells residing in bone marrow (1,000 to 10,000 mSv).
The probability of dying from hematopoietic syndrome is decidedly dose dependent. Those with whole-body doses greater than 5,000 mSv will likely die within thirty days. Those with doses near, but still below, 5,000 mSv will probably recover because they usually have enough surviving cells squirreled away somewhere in their marrow to ultimately grow back and start making blood cells again. Recall that Marie Curie and her staff frequently suffered bouts of anemia, followed by apparent full recovery, suggesting that their whole-body doses were somewhere in the 1,000 to 4,000 mSv range.
Unlike CNS and GI syndromes, hematopoietic syndrome is sometimes amenable to treatment, including blood transfusions and antibiotics. The blood transfusions, in particular, may buy these patients the time they need for their own blood-producing capabilities to grow back, in about 60 to 90 days. But the prospects are again highly linked to dose. Patients receiving 4,000 to 8,000 mSv may be helped by such transfusions, but those above 8,000 mSv are not likely to recover because at the higher end of the range, the more lethal GI syndrome starts to predominate.28 In contrast, those receiving substantially less than 4,000 mSv are highly likely to su
rvive even without medical interventions, because normal individuals are generally able to tolerate a modest level of cell loss, and are fully capable of regenerating all or most of the lost cells.
What about Sasaki’s own health? His location at 1,650 yards (1,509 meters) from ground zero, plus the fortuitous fact that he was shielded by the hallway’s brick walls rather than being in front of a hallway window, likely resulted in minimizing his dose. He probably received a radiation dose well below 1,000 mSv. At doses less than 1,000 mSv, the potential for developing radiation sickness drops drastically, and below 500 mSv radiation sickness is not possible. This is because doses below 500 mSv are typically not very toxic to cells, whether rapidly dividing or not. Radiation sickness is a disease caused by the killing of large numbers of cells in vital body tissues. In the absence of cell killing, radiation sickness cannot occur. In fact, most tissues can tolerate significant losses of cells before health problems ensue. For this reason, radiation sickness has a practical starting point at about 1,000 mSv.29
Fortunately, it takes a lot of radiation to kill significant numbers of body cells. In addition, partial body irradiations, even in great excess of these threshold doses, are not likely to produce radiation sickness. This is because surviving cells in the nonexposed body areas can come to the rescue of the overdosed region. For example, dividing blood stem cells can enter the circulation and recolonize radiation-depleted bone marrow. Thus, the survivable doses for partial body irradiations are much higher than for a whole-body irradiation.
In summary, for any whole-body irradiation incident, whether from an atomic bombing or an accident, those coming down with radiation sickness experience one of three possible syndromes, depending upon the dose they receive. And the dose that they receive is highly dependent upon their exact location relative to the radiation’s source (i.e., ground zero). Radiation dose drops off rapidly with distance.30 For this reason, nearly all of the radiation sickness patients in Sasaki’s hospital were likely to have been between 1,000 yards (915 meters) and 1,800 yards (1,645 meters) from ground zero when the bomb was dropped. Any closer than 1,000 yards, they probably would have died from the percussive effects (i.e., the 5 psi rule), and further than 1,800 yards away, they wouldn’t have experienced enough radiation-induced cell death to have any radiation symptoms at all. Thus, at 1,650 yards (1,509 meters), the hospital was ideally located to witness large numbers of patients suffering from the complete spectrum of radiation syndromes.
WAGES OF WAR
By November 1945, the radiation syndromes in Hiroshima had run their course. Those destined to die had done so, and those fated to survive were on their way to recovery. It isn’t clear how much influence medical intervention had in determining these outcomes, but it definitely wasn’t much. There were very few medical services available to the victims since only 3 of the city’s civilian hospitals out of 45 were seeing patients and both military hospitals were destroyed. It is estimated that 90% of the city’s doctors and nurses had been killed or injured.31
Recovery from radiation sickness would not be complete for every survivor, as there were lingering side effects, including chronic and debilitating fatigue. Still, these side effects paled in comparison to the horrific disfigurements suffered by the burn survivors. So those who had survived radiation sickness without any obvious physical deformities tended to suffer in silence, thankful that they were not among the burned or dead. Nevertheless, their problems weren’t over. Some of them would go on to experience radiation’s late health effects, as we shall soon see. But, for the moment, they were simply glad to be alive.
No one is really sure how many people were killed in the atomic bombing of Hiroshima. The exact casualty numbers for the city are elusive, because many people left no corpses and it is always hard to account for the missing, particularly in wartime. Estimates range from 90,000 to 165,000 deaths. Although the numbers are fuzzy, it’s thought that of those killed by the bomb, about 75% died from fire and trauma and 25% from radiation effects.32 Not all were Japanese. About 50,000 inhabitants of the city (20% of the population) were Korean conscripts performing forced labor,33 and there were even a couple of dozen American prisoners of war held in downtown Hiroshima.34 None of these Americans survived.35
THE PROBLEM WITH NEUTRONS
When the Japanese government failed to immediately surrender in the wake of the Hiroshima bombing, the United States dropped another atomic bomb, this time on the city of Nagasaki. While the Hiroshima bomb employed uranium-235 as the fissionable material, and had a yield of 15 kilotons (equivalent to the detonation of 15,000 tons of TNT), the Nagasaki weapon used plutonium-239 and had a yield of 21 kilotons. Plutonium-239, a man-made radioactive element, was included in the bomb production plans of the Manhattan Project when it became apparent that it would not be possible to purify enough uranium-235 to satisfy the United States’ atomic bomb requirements. The plutonium bomb used a different detonation device than the uranium bomb (implosion rather than gun-assembly triggering36), but otherwise they worked on the same fundamental principle. In each case, detonation of a conventional explosive device within a confined space propels subcritical masses of fissionable material together with sufficient force and speed to instantaneously create a single supercritical mass. This supercriticality of fissionable material results in nearly simultaneous fission of large numbers of atomic nuclei, thereby releasing massive amounts of energy all at once.
Although the Nagasaki bomb had 40% greater explosive power, the Hiroshima bomb’s radiation was potentially more lethal because a higher proportion of its radiation energy was emitted in the form of neutrons, rather than gamma rays. This was due to differences in the underlying physical properties between their nuclear fuels—plutonium-239 fission (Nagasaki) and uranium-235 fission (Hiroshima).37 Although these differences are of no consequence to the shock waves or the firestorm generated, neutrons can enhance the lethality of the bomb’s radiation to humans, since fast neutrons are ten to twenty times more damaging to human tissue than gamma rays. Thus, bombs with high neutron yields can be particularly lethal.
At first it might seem strange that neutrons—those “ghost particles” that cause no direct ionization themselves and, thus, eluded discovery by ionizing radiation detectors for so many years—might be among the most lethal types of ionizing radiation. But a fast neutron’s biological effects are delivered through an emissary—a fast moving proton. Neutrons are highly penetrating to most matter because they have no electric charge and, therefore, plow blindly through all the vacant space that constitutes atoms, unperturbed by the electrical forces that push and pull other types of particulate radiation. (Recall the empty baseball stadium analogy in chapter 4.) When neutrons ultimately do happen to collide with the much larger mass of a typical atomic nucleus, most bounce back; an example is how Rutherford’s alpha particles bounced back from gold nuclei, leaving the neutron-impacted nucleus unfazed by the experience. Still, not all nuclei are as large as gold’s. In fact, hydrogen’s nucleus consists of just a single proton. Remember, a proton has exactly the same mass as the neutron, albeit positively charged; herein lies the explanation for a neutron’s lethal powers.
If a neutron were the size of a ping-pong ball (i.e., a table tennis ball), the nucleus of a typical element would be about baseball size or larger. Try throwing a ping-pong ball at a baseball and see how much you can move it. Not much, eh? But hydrogen looks just like another ping-pong ball to the colliding neutron, and the high-speed neutron collision can send the sedentary proton off on its own high-speed journey; a journey that now involves a positive electrical charge ripping electrons from the molecules it encounters along the way. (Recall that it was the reported interaction of a yet unidentified type of radiation with the hydrogen atoms in paraffin that had betrayed the very existence of neutrons to Chadwick; see chapter 4.) Dislodged electrons cause ionization damage. So neutrons can indirectly ionize and damage molecules with the cooperation of hydrogen nuclei.
Biol
ogical tissues are loaded with hydrogen. Not only is the body composed mostly of water (about 55%), which has two hydrogen nuclei for every oxygen nuclei (H2O), but also all biological molecules are comprised largely of hydrogen, and a few other elements. The bottom line is that about 65% of the atoms in the human body are hydrogen. What does this mean for the human body in terms of sensitivity to neutrons? Ironically, the human body, because of its high hydrogen content, is better at absorbing neutrons than a slab of lead. And those absorbed neutrons conspire with the proton nuclei of the hydrogen atoms to produce a tremendous amount of cellular damage. For living tissue, neutrons are bad news indeed. This was another salient fact that did not go unnoticed by nuclear bomb physicists.
After suffering two atomic bombs, and potentially facing more, the Japanese had had enough. On August 15, 1945, in a recorded radio address broadcast simultaneously to the entire nation, Emperor Hirohito (1901–1989) announced unconditional surrender and officially ended World War II. He explained to his people:
The enemy has begun to employ a new and most cruel bomb, the power of which to do damage is, indeed, incalculable, taking the toll of many innocent lives. Should we continue to fight, it would not only result in an ultimate collapse and obliteration of the Japanese nation, but also it would lead to the total extinction of human civilization.
It was the first time the entire Japanese population had heard the broadcast voice of their emperor, and it gave them pause. They would not hear another national broadcast from their emperor for 66 more years, when still another nuclear catastrophe would once again necessitate an imperial address.
THE FIRST CASUALTY