Cosmic radiation, however, has nothing to do with radium. To get to that, let’s turn our attention again to the long-lived radioactive atoms: uranium-238, uranium-235, thorium-232, rubidium-87 and potassium-40.

  Rubidium-87 and potassium-40 break down simply. Each eliminates a beta particle and is done. Having rid itself of a beta particle, the rubidium-87 atom becomes a strontium-87 atom which is stable; the potassium-40 atom becomes a calcium-40 atom which is also stable. The breakdowns are ended.

  The breakdowns of uranium-238, uranium-235 and thorium-232, however, are more complicated affairs and in that complication rests the solution of our problem.

  Take uranium-238, for instance. It breaks down by ejecting an alpha particle. In doing so, it forms the atom thorium-234. But thorium-234 is not stable. In fact, it is much shorter-lived than uranium-238 and has a half-life of only 24 days.

  The thorium-234 atom breaks down by emitting a beta particle and becoming protactinium-234. But that is unstable, too, and has a half-life of less than seven hours. Protactinium-234 breaks down and so does the atom it becomes and the atom it becomes and so on. All told, uranium-238 breaks down through a total of 16 varieties of atoms before it finally becomes lead-206 (a stable atom) and comes to rest.

  Uranium-235 goes through a similar process, breaking down through 13 varieties of atoms before becoming lead-207, a stable atom. Thorium-232 breaks down through 11 varieties of atoms before becoming lead-208, a stable atom.

  These three series of atom varieties do not duplicate one another at any stage. Any variety of atom formed in one of the series is not formed in either of the other two. This means that a total of 40 different kinds of radioactive atoms are produced during the breakdown of uranium-238, uranium-235 and thorium-232.

  All 40 descendant atoms are continually breaking down but are also continually being produced, so all 40 exist on Earth wherever uranium and thorium are found, and will exist as long as uranium and thorium do. One of the 16 kinds of radioactive atoms formed from uranium-238 during its breakdown is radium-226 and that is why radium-226 still exists on Earth and will continue to exist unless mankind consumes all Earth’s uranium in nuclear power plants.

  The next question is, how much of these short-lived radioactive atoms exist on Earth as a result of uranium and thorium breakdown? It turns out that the ratio of quantity of a ‘descendant’ atom and its ‘parent’ is the same as the ratio of the half-lives.

  Let’s take an actual case. Uranium-238 has a half-life of four and a half billion years. Thorium-234, its first descendant atom, has a half-life of 24 days. The half-life of uranium-238 is thus sixty-eight billion times as long as that of thorium-234; therefore, there is one atom of thorium-234 present in the Earth for every sixty-eight billion atoms of uranium-238. It’s as straightforward as that.

  Once in a while, it happens that a radioactive atom can break down in two different ways. For instance, the radioactive bismuth-212 atom (which is one of the descendants of thorium-232) can lose an alpha particle to form thallium-208, or it can lose a beta particle to form polonium-212. For every three bismuth-212 atoms that break down, one polonium-212 atom and two thallium-208 atoms are formed. Whenever such ‘branching’ occurs, this must also be taken into account in determining the quantity of descendant atoms present in the Earth.

  When the total amounts of the various descendant atoms are calculated, it turns out that many are present in comparatively trifling amounts. Still, each of the three parent atoms, uranium-238, uranium-235 and thorium-232, has at least two descendants that do fairly well and are present in the ratio of at least one atom for every ten billion of the parent. These descendants are listed in Table VI.

  As you can see, uranium-234 is the most long-lived of these descendants. It is so long-lived (with a half-life of a quarter of a million years) that it piles up in uranium-238 to the point where there is one atom of uranium-234 for every 18,000 atoms of uranium-238. In other words, there is one atom of uranium-234 for every 130 atoms of the much longer-lived uranium-235.

  The total number of atoms in the Earth’s crust is, as I said earlier, 6 x 1047. From that and from other data given earlier, we can calculate the total number of atoms of uranium-238, uranium-235 and thorium-232 in the Earth’s crust. Having got so far, we can then determine the number of atoms present for any of the descendants. What’s more, knowing the number of atoms of any substance, it is possible to calculate the corresponding weight and that is given in Table VII.

  As you see from Table VII, it turns out that through the normal processes of the radioactive breakdown of uranium-238, the supply of radium-226 in the Earth’s crust amounts to over twenty-eight million tons. A ton of radium-226 (assuming it to be five times as dense as water) takes up about six and a half cubic feet. The total quantity of radium in the Earth’s crust is therefore 184 million cubic feet. If this were spread evenly over an area the size of Manhattan Island (which is 22 square miles in area), it would cover it 3½ inches deep.

  Of course, far less radium is actually available to mankind. We can only dig through the topmost layers of the crust and only in certain parts of Earth’s land area. At most, only one or two per cent of the crust is available to us and even there the radium-226 is spread so thinly that it is a Herculean task to scrape even a small fraction of an ounce together.

  In Table VII, I considered only the long-lived parent atoms and their comparatively long-lived descendants. Even the least of the atom varieties mentioned is present in the Earth’s crust in the thousands of tons. However, there are 31 varieties of descendant atoms that are not mentioned in Table VII. What of them?

  To get the other end of the picture, I’ll begin by listing descendant atoms with very short half-lives in Table VIII.

  The half-lives of some of these atoms are so short that the second becomes an inconveniently long time interval to use as a measure. The microsecond (one-millionth of a second) is handier. It seems much more casual and neat to say that the half-life of astatine-215 is 100 microseconds than to say that it is one ten-thousandth of a second. Even a microsecond is none too small. Polonium-212 has a half-life that is only about a third of a microsecond and it isn’t a record-breaking example by any means.

  The short half-lives are not the only things that make the atoms listed in Table VIII rare. Most of them are formed through branched breakdowns of their parent atom, usually on the short side of the branch. For instance, thallium-206 is formed through the breakdown of bismuth-210. Bismuth-210, however, also breaks down to form polonium-210. But out of every 10,000,000 bismuth-210 atoms that break down, 9,999,999 turn into polonium-210 and only 1, just 1, becomes thallium-206.

  If the short half-life is taken into account and also whatever short-changing the various atoms may have had in the way of branched breakdowns, it is possible to calculate the weight of each variety of atom present in the Earth’s crust. This is done in Table IX.

  You can see it is no longer a question of tons at all. Except for two of the atom varieties, it isn’t even a question of ounces, but of fractions of ounces. Astatine-215 is worst off. Not only has it a short half-life (100 microseconds), but it is formed from uranium-235, which is the least common of the three parent atoms. To top it off, astatine-215 is at the short end of a 200,000 to 1 branching breakdown. The result is that in the entire crust of the Earth, there is less than a billionth of an ounce of astatine-215. If it were all gathered together in one spot, it wouldn’t be enough to see with the naked eye.

  Consider once again the acre of land ten feet deep I mentioned earlier in this chapter. That amount of soil would contain something like 1033 atoms (a billion trillion trillion). If all the various atoms in the Earth’s crust were spread evenly throughout, you would find in your acre of land, three hundred trillion trillion atoms of uranium and one trillion trillion atoms of gold. (That’s right, gold is much rarer than uranium.) There would be a little over a billion atoms even of francium-223.

  The chances, however, would be 30 to 1 against there being even a single atom of astatine-215 present.

  CHAPTER TWO—THE EXPLOSIONS WITHIN US

  It is all very well to speak of radioactive atoms that occur in the soil, as I have been doing in the previous chapter. There is something objective and detached about atoms exploding within rocks and soil. But plants grow in the soil and animals live on plants. Is it possible that radioactive atoms may find their way into living tissue and even into our own bodies?

  It is not only possible; it is certain.

  In general, living tissue is made up of the common elements of the environment it lives in, but there are exceptions. Some very common elements play no part in the machinery of life. For instance, silicon, which is the second most common element, and aluminum, which is third, do not occur in the body. On the other hand, small quantities of moderately rare elements do occur.

  In order to make some decisions about the nature of the radioactivity within the human body, then, we can’t use figures based on the composition of the soil. We must know the composition of living tissue. I will therefore begin with a list of the elements that occur in living tissue and give the best estimates I can find or calculate as to the quantity of each present. You will find this in Table X.

  We can leave the other elements out of consideration. The other elements do occur, of course. We cannot help but swallow extraneous matter with our food and are bound to get elements such as silicon and aluminum into our intestines that way. Some even manages to get absorbed into our body proper.

  In fact, if we went over the body, atom by atom, we would probably find at least one atom of every variety known to exist in the soil, ocean and atmosphere of Earth. Knowledge concerning the concentration of these ‘accidental’ elements in the human body is still very slim, however. For the purposes of this discussion, I’ll forget about them.

  You might wonder, by the way, about the elements at the bottom of the table, the ones that occur only to the extent of a few atoms per billion. They are usually referred to as the ‘trace elements’ because they are present only in traces. Does the body really need them? It certainly does. With the exception of fluorine, they are absolutely essential to human life and even fluorine is necessary for healthy teeth.

  Does it seem strange to you that the body can do with so little and yet not be able to get along with none at all? From five atoms per billion to zero atoms per billion seems such a small step.

  Well, it’s all in the way you look at it. Suppose we count the atoms involved.

  Start with a hundred and Fifty pound human being. He is made up mostly, but not entirely, of microscopic cells, which are the individual chemical factories of the body. The ‘not entirely’ part comes about as follows: In the blood and in the spaces between the cells there is a total of some 30 pounds of fluid (mostly water) which does not form part of any cell and is called ‘extracellular fluid’. In the bones and teeth there are some 15 pounds of mineral matter which is also extracellular. This leaves 105 pounds of cells.

  The average liver cell weighs about one fourteenth-billionth of an ounce. Let’s assume that this is about average for the weight of a cell. In that case, there are some twenty-five trillion (25,000,000,000,000) cells in the body.

  The material outside the cells does not contain the same elements in the same proportion as the material inside the cells. For instance, the extracellular fluid is richer in sodium and poorer in potassium than the material inside the cells. The mineral matter in the bones is richer in calcium and phosphorus and poorer in carbon and nitrogen than the material inside the cells.

  Furthermore, the cells of various tissues differ among themselves. For instance, liver cells have at least two or three times as high a concentration of copper and cobalt as do most other types of cells; red blood cells are particularly rich in iron, and so on.

  Nevertheless, to begin with, I am going to suppose that the material of the body is divided up perfectly evenly among the cells and the extracellular material. Well, then, each cell contains about ninety trillion (90,000,000,000,000) atoms. Using Table X, it is easy to calculate how much of each trace element is present in each cell. The figures are given in Table XI. (I leave out fluorine in that table since it is not essential to life and in its case we know for sure that it occurs only in the mineral matter of the bones and teeth and hardly at all in the cells themselves.)

  So you see, even in the case of the least of these trace elements, cobalt, each individual cell, each of the little factories of the body, has nearly half a million atoms at its disposal. Actually, this is a conservative estimate for the chances are that the trace elements are more highly concentrated in the cells than in the extracellular material. If all the cobalt were in the cells, then each one would have about 650,000 cobalt atoms. Liver cells, with a higher-than-average concentration of cobalt, might even have up to a million or two cobalt atoms apiece.

  Now, then, the difference between five per billion and zero per billion may not seem much; but certainly there is a vast difference between a cell having a few hundred thousand atoms and its having none at all.

  Looking over the list of elements in the human body, we see at once that we can forget about uranium, thorium or any of the long-lived varieties of unstable atoms I mentioned in the previous chapter. All, that is, but one! That one is potassium-40.

  The body contains 570,000 atoms of potassium in every billion of atoms generally. One out of every nine thousand atoms of potassium is potassium-40, the radioactive variety. This means that out of every billion atoms in the body, 63 are potassium-40.

  This is no small amount. There is more than three times as much potassium-40 in the body as there is iodine. If potassium is considered to be spread evenly through the body, there would be, on the average, about five and a half million atoms of potassium-40 per cell. Actually, it is worse than that. Ninety-eight per cent of the body’s potassium is within the cells and only two per cent is in the extracellular material. That raises the number to an even eight million atoms of potassium-40 per cell.

  Fortunately, all those atoms of potassium-40 aren’t breaking down simultaneously. At any time, only a comparatively small number are breaking down since potassium-40 is a long-lived atom with a half-life of over a billion years. In fact only one atom out of every fifty-three thousand trillion (53,000,000,000,000,000) atoms of potassium-40 breaks down each second.

  Don’t heave a sigh of relief too soon, however. In the body as a whole there is so much potassium-40 that even at this incredibly low rate of breakdown, 38,000 atoms of potassium-40 are exploding each second. In nine-tenths of the breakdowns, a beta particle is emitted. (The remaining 10 per cent of the breakdowns take another form which need not concern us here.) This means that during the course of each second, we are subjected to the effects of 35,000 beta particles crisscrossing within us. Things may seem a little better, though, if we consider the explosions in a single cell rather than in the body as a whole. Each particular cell undergoes one of these explosions, on the average, only once every two hundred years.

  Or, to put it still more comfortingly, if you live for seventy years, then the odds are two to one that any particular cell of your body will never know what it is to have a potassium-40 atom explode within it.

  Well, how do these explosions affect us? Obviously, they don’t kill us outright. We’re not even aware of them.

  Yet they have the capacity for damage. Enough radioactivity can kill and has killed, but 35,000 explosions per second are far from enough to do that. What about milder effects, though? A beta particle, as it darts out of a breaking down potassium-40 atom usually hits a water molecule (which is by far the most common molecule in the body) and knocks off a piece of it. What is left of the water molecule is called a ‘free radical’. Free radicals are reactive substances that will tear into any molecule they come across.

  There is always a chance, then, that the unfortunate molecule that finds itself in the path of a free radical may be one of the nucleo-protein molecules called ‘genes’. There are several thousand genes in each cell, each gene controlling some particular facet of the cell’s chemistry. If one of those genes is damaged or altered as a result of a collision with a free radical, the cell’s chemistry is also altered to some extent. The same thing happens, of course, if the beta particle should happen to hit the gene directly.

  If the cells whose chemistry is altered happen to be germ cells (that is, cells which eventually give rise to ova or spermatozoa—as the case may be), it is quite possible that the offspring of the organism exposed will end up with a chemical organization different from that of its parents. The change may be so small and unimportant as to be completely unnoticeable, or sufficiently great as to cause physical deformity or early death. In either case the change is referred to as a ‘mutation’.

  If a gene is changed in a cell other than a germ cell, the cell may be altered with no permanent hardship to the body as a whole, or Gust possibly) it may be converted to a cancerous cell with very drastic results.

  This is not just speculation. Animals exposed to high-energy radioactive particles, or to radiation energetic enough to be capable of manhandling genes, may be damaged to the extent of developing radiation sickness and dying. At lower doses, the animals will show an increased incidence of cancer and of mutations.

  Nor are human beings immune. Radioactive radiations and X-rays have caused cancer in human beings and killed them, too. Some skin cancers have been attributed to over-exposure to the sun’s ultra-violet radiation.

  But when all known causes of cancer and mutations are eliminated there always remain a certain number that seem ‘spontaneous’; that arise from no known cause.