In nature, almost all heavy elements disintegrate themselves, a phenomenon known as alpha decay. During this radioactive decay process, the nucleus releases an alpha particle, a helium nucleus, which transforms into another type of nucleus. The mystery of this process is closely related to nuclear force, electromagnetic force and quantum tunneling. This article will gradually reveal the secrets of alpha decay and explore its applications in nature and technology.
Alpha decay is the most common form of cluster decay because alpha particles have extremely high nuclear binding energy and small mass.
The alpha particle is composed of two protons and two neutrons, which gives it a mass of about 4 Da and a charge of +2. When a heavy element like thorium-238 decays, it turns into uranium-234. This decay process is the result of nature's self-regulation. The presence of heavy elements often means that the energy balance of these elements within the nucleus is about to be broken, which provides a catalyst for the occurrence of alpha decay.
As early as 1899, Ernest Rutherford first described the alpha particle, and in 1907 he determined it to be the He2+ ion. Subsequently, George Gamow solved the tunneling theory of alpha decay in 1928, laying the foundation for understanding this mysterious phenomenon. Gamow's model introduced the concept of quantum mechanics to the study of nuclear decay for the first time, and found that even if alpha particles are theoretically trapped in the nuclear potential well, there is still a slight chance of tunneling through the barrier and escaping from the nucleus.
The essence of alpha decay lies in the delicate balance between nuclear and electromagnetic forces. The nuclear force ensures the stability of atomic nuclei, while the electromagnetic repulsive force makes massive nuclei unstable. When the mass of the nucleus exceeds 210 nucleons, the nuclear force will not be able to completely resist the electromagnetic repulsion between protons, leading to alpha decay. Key to this process is the high binding energy of the alpha particle, which makes it much more likely to be released from the nucleus.
Quantum tunneling theory allows us to understand that alpha particles escape from the nucleus not through obtaining enough energy to break through the barrier, but through the tunneling effect.
It is this tunneling effect that makes alpha decay a low-energy, long-lived form of decay. For some heavy elements, the emission of alpha particles can even release energy of several MeV, making the decay process spontaneous and efficient.
Alpha decay has many applications in science and industry. For example, in smoke detectors, aluminum magnesium manganese 241 is used as an alpha emitter to help detect and alert; and thorium-223 is used in the treatment of bone metastasis cancer played an important role. Because the energy and radioactivity of alpha particles are more easily shielded than other forms, this also makes them an ideal energy source for radioactive thermoelectric generators used to explore the universe.
Although alpha particles have a strong barrier to the outside world, once they enter the human body, they can cause severe damage to the gastrointestinal tract or lungs. The probability of double-strand breaks in DNA caused by alpha particles is much higher than that of other types of radiation. So while it may appear harmless on the outside, the potential for harm can be devastating if exposed internally. This type of alpha particles that enter the lungs through inhalation or ingestion can cause severe damage to cells, leading to the occurrence of cancer and other diseases.
For many scientists, alpha decay provides a critical look at how matter changes at a microscopic level. And this change is not limited to the laboratory, it also has a deeper meaning. Why do heavy elements choose to disintegrate themselves? Is it a self-defense mechanism in nature, or part of a deeper energy conversion process?