Aluminum stops beta radiation mainly because beta particles can be stopped by any significant thickness of matter, even half an inch of skin. However, only a thin sheet of aluminum is required to stop beta-radiation because the metalloid properties of aluminum cause an electrostatic interaction with the charged beta particle, which is generally an electron but can be a positron in the case of beta-plus decay. As a metalloid, aluminum does not have the same conductive properties as a transition metal, but rather it is a semiconductor. Electrostatic interactions help dissipate excess energy from the electron, slowing its progress and limiting its penetrating capabilities.
Beta particles are much smaller than alpha particles and therefore have much less ionizing power (less ability to damage tissue), but their small size gives them much greater penetrating power. Most resources say beta particles can be stopped with quarter-inch thick aluminum foil. However, once again, the greatest danger occurs when the beta emitting source gets inside of you. Due to its very short half-life of approximately 770,000 years, aluminum-26 must have formed or mixed in the surrounding planet-forming disk of the young Sun shortly before the condensation of the first solid matter in our solar system.
It plays an important role in the formation of planets such as Earth, as it can provide enough heat through radioactive decay to produce planetary bodies with stratified interiors (such as the Earth's solid core covered by a rock mantle and, above, a thin crust). The radioactive decay of aluminum-26 also helps dry out the first planetesimals to produce rocky, water-poor planets. Practically all of the nuclear reactions in this chapter also emit gamma rays, but for simplicity, gamma rays are generally not shown. The half-life of uranium-238 is 4.5 billion years, which means that during that immense period of time half of the nuclei in a sample of uranium-238 will decay (in the next 4.5 billion years, half of what remains will disintegrate, leaving a quarter of the original, and so on).
These types of equations are called nuclear equations and are similar to the chemical equivalent discussed in the previous chapters. Nuclear reactions release some of the binding energy and can convert small amounts of matter into energy. A common example is nuclear reactors, which operate for long periods, producing very high fluences of neutrons, some of which can irradiate metal components and cause possible harmful effects. In a nuclear explosion or some type of nuclear accident, in which radioactive emitters are dispersed throughout the environment, the emitters can be inhaled or ingested with food or water, and once the alpha emitter is inside you, you have no protection whatsoever.
Therefore, it is acceptable to ignore the load on the equilibrium of nuclear reactions and to focus only on balancing mass and atomic numbers. To insert an electron into a nuclear equation and make the numbers add up correctly, you had to assign an atomic number and a mass number to an electron. When studying nuclear reactions in general, there is usually little information or concern about the chemical status of radioactive isotopes, because electrons in the electron cloud are not directly involved in the nuclear reaction (unlike chemical reactions). The atomic number assigned to an electron is a negative one (-), because it allows a nuclear equation containing an electron to balance atomic numbers.