The two smaller nuclei which result from the fission of the heavy uranium give atoms which have normal chemical reactions and are in most respects no different from atoms found in the world about us. But their birth is somewhat unnatural and they are slightly unbalanced in their construction. They have more neutrons in them than is proper. This makes them unstable and most of them keep on shooting out electrons until they are stable. This is called radioactivity. The fast electrons shot out of the nucleus are called beta rays, in the process several penetrating kind of X-rays called gamma rays are also produced.

Rays and Cells

These rays have energies which on our scale of ray energies are far above those of heat and light rays and they have effects on matter which are far greater than those of the common rays. They consequently have effects on the cells of animals and plants and this makes them a considerable embarrassment to anyone using nuclear energy for war or peace.

The rays are produced in great numbers at the time of the original fission. But because in a bomb test this is soon over and in a reactor may be shielded by thick walls of concrete etc., this is not so serious. The unstable atoms (called radioactive isotopes) produced in fission take different times to shoot out their electrons and become stable. The time depends on the structure of the particular nucleus. Most of them go through most of the steps towards stability in seconds but when they are very nearly stable and only have one or so rays to shoot out the nucleus may wait years to do it. These are the fission products which are potentially the most dangerous.

The most dangerous ones of all are those whose chemistry is like that of some element common in animal bodies. A radioactive element with such a chemistry when absorbed in the body may substitute for the stable element which it is chemically similar to, and so is accumulated in the body rather than eliminated. The natural radioactive element radium has always been a particular menace because it is taken up by the bones in place of calcium. Now in fusion reactions we are producing a radio isotope strontium-90 which has a chemistry similar to calcium.

If a radioactive element accumulates in any part of the body the tissue around is bombarded by the rays given off as the isotope decays to a stable nucleus. The cells may be damaged and cease to function properly, if the bones contain much radioactive material the marrow is damaged by radiation and leukemia starts and the patient has little chance of living. Many famous physicists who due to the ignorance of the danger were careless with radium have died of leukemia. The picture has one saving feature, cancer cells in the body may be killed in preference to healthy ones by radiation and several other kinds of growth may be killed by rays. Sometimes it is simply stated that radiations produce cancer. This may have to be reviewed in the light of present work on this disease but we definitely know that radiation sometimes does produce cancer, but a fair amount of radiation is required.

Mutation Rate

At present the effect of radioactivity in the body which is regarded as most serious is its effect on the mutation rate. It is thought that in this only small increases in radioactivity may produce large results over a period and so we must be immediately concerned. A mutant is an offspring of an animal which has characteristics not normal in the species to which its parents belong. It is thought to occur when certain special parts of those cells most directly concerned in reproduction are damaged. Experimentally we find that radiations produce mutations in plants and animals. Only in very rare cases can a mutation be regarded as an improvement. In nearly all cases the mutant is definitely defective and inferior to its parents.

Exactly how much cancer and how many mutations are caused by the radiation which the body receives from natural sources of radioactivity and cosmic rays is uncertain. Biochemical irregularities and other factors may also cause cell damage. [unclear: Experimentally] we can obtain a measure of the amount of radiation required to give twice the natural mutation rate in insects, mice, etc. And we can roughly say that if humans are subjected to similar doses there will be more genetic mutants born than at present. Perhaps many more as man is a more complex organism.

The explosion of atomic bombs has increased the amount of radioactivity in the world around us. So far the test explosions have only produced an increase which is small compared to natural radio-activity (radium in the earth, cosmic rays etc.). But already there are indications that special processes which [unclear: are] not well understood are causing localised danger from strontium-90. There is probably a greater danger in the increasing use [unclear: of] radioactive isotopes and X-rays. However, these are carefully controlled by legislation in most countries.

A nuclear war in which many atomic weapons were used would have an aftermath in which the world would be more radioactive than at present and the whole of humanity would be exposed to the consequences of this. I hope every one who has control over modern nuclear weapons views this with the same horror, as I do.

There is almost as great a problem in the increasing use of nuclear power. If all the world's power is produced by reactors collossal quantities of radioactivo material will be produced each year. Their disposal will be a serious problem. Also, more and more of the population, will be exposed to increased radiation while they attend our power plants.

The hydrogen bomb obtains most of its power from a different nuclear reaction from that of fission, in it there is fusion of light elements to make heavier ones, in this reaction very little dangerous radioactive material is produced, if a hydrogen bomb is exploded well clear of the ground it should produce no more radioactivity than an ordinary atomic bomb in spite of its far greater power.

Cannot Control

The physicist cannot yet control the fusion reaction so that it produces power slowly but he thinks that he will be able to in time. If such controlled light element [unclear: fusion] is possible we will have a power source which has far less radiation hazard than uranium reactors and a virtually inexhaustible fuel supply.

To sum up. Using nuclear power sources produces radioactive material. This is dangerous to life. So far bomb tests have not produced significant increases in the total radiation but we are already exposing a few people to more radiation than is desirable. A large scale use of uranium bombs would over a long period afterwards be a real menace to life. Tests of hydrogen bombs are not a radiation hazard in proportion to their size. Our hope for the future is in the control of the hydrogen bomb reaction. We must carry on experimenting towards this, even carefully testing hydrogen bombs if this is going to help. But no one should seriously contemplate going to war with them.

Peter Andrews