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What Are Nuclear Isomers?
Nuclear Isomers Defy Common Sense
Imagine using batteries that are smaller than the eye can see. Imagine shooting laser beams like in the movies. Nuclear batteries and gamma ray lasers are just two potential applications for nuclear isomers. Typically, detailed physics knowledge is needed to understand the intricacies of such machines; however, their essential operation can be communicated with a few simple analogies.
What Are Nuclear Isomers?
If you take droplet of water and keep separating it into smaller and smaller droplets, you eventually end up with a molecule of water, also known as H2O. If you take a saucepan filled with water and place it on a hot stove, it will begin to boil. By heating the water you are causing the water molecules to smash into each other, which is why the water appears to be moving and bubbling. When the stove is turned off the water returns to a state of calm. Indeed, it is common sense to expect hot objects cool down. Now imagine turning off the stove and seeing the water remain hot. Impossible right? Yes, but not for a nuclear isomer! The key thing to understand about nuclear isomers is they stay hot.
Water molecules are called H2O, which means they contain two hydrogen atoms and one oxygen atom. There are many types of atom, some of which will be familiar, such as silicon, iron, gold and silver. A gold bar is essentially trillions of gold atoms lined up and bonded together. When a gold bar is melted, these bonds break down. At the centre of each of the atoms is what we call a nucleus. Buzzing around the outside of the nucleus are electrons. Together, the nucleus and the electrons make up the atom (see picture).
You’ll notice that the central nucleus contains lots of smaller lumps. For simplicity we’ll call these nucleons. Like the saucepan of water, when the nucleus is heated up, the individual nucleons move about. However, once the heat is removed, one or several of the nucleons may stay “hot” without cooling down. When this happens, we say that the atom has become an isomer. For example, a silver atom can become an isomer that stays hot for 438 years before cooling down to become a normal silver atom again.
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We can heat up a nucleus by smashing things into it. If you shoot a bullet into a tank of water, the water will heat up. The same principle is true for atoms; by firing one atom into another you cause both to heat up. When this occurs, at least one of the nucleons will jump-up from its position in the nucleus. Usually it will fall back to its original position soon afterwards, but there are particular positions where the nucleon will stay for a very long time! This is what occurs in all nuclear isomers.
In the silver isomer one of those nucleons is sitting high above its normal position for 438 years. When it finally does fall back to its normal position, it will release the heat energy it has stored up. Nuclear isomers release heat energy in the form of light. This light may be described as gamma rays or X-rays, which are impossible to see with the naked eye, but which can be detected using specialised equipment.
The laws of quantum mechanics determine why some nucleons hold onto their energy while others do not. These laws are difficult to explain to non-physicists, but if you imagine throwing a Frisbee into a tree, sometimes it will become snagged on a branch, and sometimes it will fall to the ground. Depending on the angle of the branch, a very strong wind may be needed to dislodge a snagged Frisbee. For nucleons, a very strong emission of gamma rays may be needed to dislodge it from particular positions in the nucleus. In the same way hurricanes are rare compared to breezes; a strong emission will not occur as often as weaker emissions, meaning the nucleon will remain in its position for a very long time.
Nuclear isomers are atoms with at least one of their nucleons stuck in an energetic position. This means that isomers are essentially tiny energy storage devices, or nuclear batteries. If a silver isomer remains hot for 438 years then it has stored energy for that period of time. However, this energy is useless unless it can be released in a controlled way. Currently, there is no easy way to do this.
Theoretically, it should be possible to release an isomer’s energy by knocking the nucleon out of its "hot" position. In our analogy, this would involve throwing something up into the tree to dislodge the Frisbee. By giving the nucleon extra energy, it can be forced into higher positions where it will remain hot for much shorter periods of time. Essentially, a light would be shone onto the isomer, heating it up slightly before a complete release of all the isomer's energy. This is exactly like focusing the sun's rays onto a piece of paper with a magnifying glass, and watching it burst into flame. It would work like a switch, releasing the stored energy in a cascade of gamma rays. This nuclear process could be achieved without any radioactive waste.
In practice, however, the release of an isomer’s energy has only been possible by shining a very high intensity of light onto the isomer, which is not ideal. Nevertheless, it may only be a matter of time before someone discovers the conditions required to release the energy of nuclear isomers in an efficient way. This could lead to the manufacture of nuclear batteries that are smaller than the eye can see, revolutionizing phones, computers, and opening the door for technology that is integrated with the human body.
Gamma Ray Laser
With an understanding of stimulated energy release, it should become possible to release a great deal of an isomer's energy in a controlled burst of gamma rays. One could construct a gamma ray laser by arranging the isomer material in a narrow tube so that emission is focused towards the end of the tube. By using a crystalline material with some of the crystal's atoms replaced by the isomer, any recoil resulting from the emission of gamma rays would be experienced by the whole crystal, preventing any re-absorption of the gamma rays, thereby maximising energy output (Mossbauer Effect).
This and other considerations could lead to the creation of a gamma ray laser with manifold applications. One could create a handhold weapon like those in the movies. Unlike Star Wars, you wouldn’t be able to see or hear the laser burst, although it could certainly be signalled in some way! A gamma ray laser could also be used to heat up air, powering the jet engines on planes. This is known as a quantum nucleonic reactor. Furthermore, a gamma ray laser could compress fuel capsules for nuclear fusion reactors or bombs.
Nuclear Isomers Are Already Used In Medicine
Isomers already have a number of applications, some of which may be familiar. An isomer of the Technetium atom is used in medical imaging. Once ingested by a patient, it binds chemically with a number of biomolecules. The isomer emits gamma rays which can be detected by a doctor, highlighting health problems. For example, when the technetium isomer is combined with a tin compound it will easily bind to red blood cells, identifying problems with a patient’s circulatory system, such as bleeding sites. The gamma rays emitted by the isomer are sufficiently low in energy to avoid harm to the patient.
Nuclear isomers promise to provide the human race with a clean use for nuclear energy. Whether this is through the invention of nuclear batteries, or the initiation of nuclear fusion reactions with gamma ray lasers, we have only scratched the surface of what is possible.