Nuclear Fission for Dummies: Beta Radiation

Last time we talked about the basics of alpha radiation. If you remember, an alpha particle was basically a Helium atom. In much the same way, beta radiation is the emission of a high-energy electron or positron.

You could consider beta radiation to be a medium energy radiation; more energy than alpha radiation but far less than gamma. Beta particles are very small, but move at incredible speeds. The most high-energy betas travel at close the speed of light.

So what is a positron? Basically it is an anti-electron or the antimatter equivalent of an electron. In the unlikely event that a positron was to come into contact with an electron, the result would be annihilation. In annihilation, 100% of the mass of both particles is converted into energy (remember Einstein’s famous equation?).

There are two types of beta radiation or beta decay. They are beta minus (β−) and beta plus (β+). In β− an electron is emitted and in β+ a positron is emitted. β+ decay is one of the processes that occurs within stars and is a topic for another day. β− is the more common Beta radiation that is associated with the fission products commonly found in spent nuclear fuel.

During beta minus decay, an atom starts with an excess of neutrons causing it to become unstable. When the atom undergoes β− decay, the excess neutron becomes a proton. But remember the law of conservation of matter and energy? This also applies to the slight decrease in mass that occurs during transfer and also the change in electric charge. The electron emitted during the decay carries away the negative charge component of the neutron giving it a positive charge AKA a making it a proton. That electron carries off a small amount of mass.

But there is something missing from the equation. If you add up the sum of mass and energy in the before and after products of beta decay, there is still some missing energy. Where did that extra energy or mass go? Enter the antineutrino (v_e).

That missing energy and mass comes in the form of an extremely small particle moving at very near the speed of light. That missing mass particle is called an antineutrino and the missing energy is the kinetic energy of that tiny little particle. Antineutrinos are so small that they are said to have a “nonzero mass.” This means the laws of physics demand the particles have mass, but they are too small to measure. Antineutinos are the antimatter equivalent of a neutrino. Neutrinos are formed in the fusion process during β+ . Did you know that nearly 50 million solar neutrinos pass through your body every second? The reason you don’t notice boils down to the tiny nonzero mass of those particles. The science behind neutrinos and antineutrinos is still in its infancy and there is no limit to the possibilities these tiny, elusive little objects may hold.

Health Effects

Beta radiation dissipates quickly over distance, but if it comes into contact with DNA, it can cause health problems. The problems are called mutations. Although the product of these mutations certainly isn’t Godzilla, or the 100 ft killer Koala, the result can sometimes be cancer. Young children and especially unborn babies are more vulnerable to these mutations due to the rapid rate of cell division these children undergo. A mutated cell will divide into other damaged tissues amplifying the effects of beta radiation. A full grown person is far less susceptible.

There are some upsides however. Practice has shown that beta sources can be effective in targeting cancer cells in human bodies. Often there are side effects, but the effectiveness of the treatment cannot go unnoticed. Also, as technology advances, these treatments are becoming more and more targeted thus reducing the collateral damage to healthy tissue nearby.

Protection

Beta is a medium energy radiation. More powerful than alpha radiation, but far less so than gamma. Whereas alpha can be shielded by human skin or even a piece of paper, to protect against beta radiation, acrylic (usually about 10 mm thick) can stop a beta particle.

Beta Power Sources

By slowly but surely emitting electrons, a beta radiation source is essentially a very reliable, long lived battery.  There are several technologies currently under development that make use of a beta radiation source as a power supply for small devices. The benefit of this is that a beta radiation source can be relied on to emit a small but steady flow of electrons for several half-lives of the source material.  When applied in the field of Micro-Electro-Mechanical-System (MEMS) devices, a beta power source makes for a long lived microscopic machine that doesn’t need to recharge for several years.

Image Credit

Beta Radiaiton image courtesy of Wikimedia Commons published under the CC license.