Nuclear fusion or atomic fusion?

Most physicists would say that nuclear fusion and atomic fusion are the same thing.

At the high temperatures in the centre of a star (~ 15 million C in the Sun) there are no atoms.  Atoms are stripped of their electrons. This leaves bare nuclei in a swirling cloud of electrons. 

In physics, opposites attract, and likes repel. Two bare nuclei, with their positively charged protons, repel each other. It takes a lot of energy for those two bare nuclei to get close enough to each other so that the nuclear force can take over and allow them to fuse. 

Nuclear fusion takes place in the centres of stars, under conditions of high heat and pressure.

What about reactions at the far lower temperatures on Earth, where atoms have intact electron shells? Do atoms—not bare nuclei—undergo atomic reactions? Of course they do. Every time a radioactive atom decays, an atomic reaction occurs—often at room temperature. 

Take potassium-40 for example. A few potassium atoms here on Earth are radioactive. K-40 decays very slowly, with a half-life of 1.25 billion years. It’s a radioactive left-over from when Earth formed, 4.6 billion years ago. There’s still some around, but twelve and a half times less.

The earliest microbes evolved enzymes to deal with much higher radiation levels. We’re lucky to have inherited those enzymes. However, we’re now putting an extra workload on them by splitting uranium atoms in nuclear reactors, creating new radioactive atoms that increase the radiation burden on all living creatures, including ourselves.

Atomic reactions occur all the time at the ordinary temperatures on Earth—a lot more than a century ago, before humanity opened Pandora’s box and entered the nuclear age. 

Most physicists maintain that none of these atomic reactions involve fusion. Think again.

Radioactive K-40 can decay in either of two ways. Most often, one of the neutrons in the nucleus ejects an electron and transforms into a proton, creating calcium-40, the next element in the periodic table. But just over 10% of the time, one of the protons in the nucleus absorbs an electron from the electron shell and transforms into a neutron. This makes argon-40, the previous element in the periodic table.

Sure sounds like fusion, doesn’t it?

Then there’s neutron absorption. There aren’t many free neutrons around. They tend to eject electrons and transform into protons, lasting only around 15 minutes on average. But some free neutrons are released when high-energy particles from outer space strike the nitrogen and oxygen molecules in the atmosphere. These free neutrons—neither attracted nor repelled by electrons and protons—readily penetrate an atom’s electron shell and fuse with its nucleus.

This could be called “atomic fusion”— the absorption of an electron or a neutron by an atomic nucleus. It’s not nuclear fusion, because only one nucleus is involved, not two. Atomic fusion reactions occur at the ordinary temperatures here on Earth—“cold fusion.”

Cold fusion reactions in elements lighter than iron release large amounts of energy. My book, “The Sun Within,” suggests that organisms have learned how to put that energy to good use, doing things like making adenosine triphosphate (ATP), the “energy currency” of life. There’s a tradeoff—the energy released by atomic reactions can damage cells—but life evolved enzymes to repair that damage.