The Energy of Radioactivity
It eventually became clear that radioactivity involved the giving off of energy. Uranium emitted gamma rays that we now know to be a hundred thousand times as energetic as ordinary light rays. What’s more, alpha particles were being emitted at velocities of perhaps 30,000 kilometers per second, while the lighter beta particles were being shot off at velocities of up to 250,000 kilometers per second (about 0.8 times the velocity of light).
At first, the total energy given off by radioactive substances seemed so small that there was no use worrying about it. The amount of energy liberated by a gram of uranium in 1 second of radioactivity was an insignificant fraction of the energy released by a burning candle.
In a few years, however, something became apparent. A lump of uranium might give off very little energy in a second, but it kept on for second after second, day after day, month after month, and year after year with no perceptible decrease. The energy released by the uranium over a very long time grew to be enormous. It eventually turned out that while the rate at which uranium delivered energy did decline, it did so with such unbelievable slowness that it took 4.5 billion years (!) for that rate to decrease to half what it was to begin with.
If all the energy delivered by a gram of uranium in the course of its radioactivity over many billions of years was totalled, it was enormously greater than the energy produced by the burning of a candle with a mass equal to that of uranium.
Let’s put it another way. We might think of a single uranium atom breaking down and shooting off an alpha particle. We might also think of a single carbon atom combining with 2 oxygen atoms to form carbon dioxide. The uranium atom would give off 2,000,000 times as much energy in breaking down, as the carbon atom would in combining.
The energy of radioactivity is millions of times as intense as the energy released by chemical reactions. The reason mankind had remained unaware of radioactivity and very aware of chemical reactions was, first, that the most common radioactive processes are so slow that their great energies were stretched over such enormous blocks of time as to be insignificant on a per second basis.
Secondly, chemical reactions are easily controlled by changing quantities, concentrations, temperatures, pressures, states of mixtures, and so on, and this makes them easy to take note of and to study. The rate of radioactive changes, however, could not apparently be altered. The early investigators quickly found that the breakdown of uranium-238, for instance, could not be hastened by heat, pressure, changes in chemical combination, or, indeed, anything else they could think of. It remained incredibly slow.
But despite all this, radioactivity had at last been discovered and the intensity of its energies was recognized and pointed out in 1902 by Marie Curie and her husband Pierre Curie (1859-1906).
Where, then, did the energy come from? Could it come from the outside? Could the radioactive atoms somehow collect energy from their surroundings, concentrate it several million-fold, and then let it out all at once?