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Chapter 9: Alpha Particles: A Closer Look at These Fascinating Ionizing Radiation Particles

...the inspector's keen mind explored the untapped potential of harnessing the energy within alpha particles...


Ionizing radiation encompasses three primary types: alpha particles, beta particles, and gamma rays/x-rays. Among these, alpha particles hold a special intrigue due to their ability to be halted by a simple sheet of paper, effectively releasing their energy. Let's delve deeper into the world of alpha particles, particularly in relation to radon.


Alpha particles, composed of two protons and two neutrons, are energetic, positively charged particles. They are frequently emitted during the radioactive decay of heavy elements such as uranium-238, radium-226, and polonium-210. Despite their high energy, their substantial mass causes alpha particles to move slowly through the air.


The impact of alpha particles on human health largely depends on the mode of exposure. External exposure, such as contact with the skin, is far less concerning than internal exposure. This is because alpha particles lack the necessary energy to penetrate the outer layer of the skin or even a thin sheet of paper. However, if alpha emitters are inhaled, ingested, or absorbed into the bloodstream through a cut in the skin, for instance, they can pose a significant risk to sensitive living tissues.


Alpha decay, a form of radioactive decay, involves the release of alpha particles from atomic nuclei. In this process, the atomic nucleus emits an alpha particle, resulting in the transformation or decay of the atom into a new atom with a mass number four units lower and an atomic number two units lower.


Due to their relatively large mass, a positive charge of +2, and comparatively low velocity, alpha particles are highly likely to interact with other atoms, losing their energy in the process. Consequently, their forward motion is effectively stopped within a few centimeters of air. Being heavy and positively charged, alpha particles possess a short "mean free path" - the average distance traveled between collisions with other particles - quickly dissipating kinetic energy close to their source. This concentrated deposition of several million electronvolts (MeV) within a small volume enhances the likelihood of cellular damage in cases of internal contamination.


External exposure to alpha radiation is generally harmless, as these particles are effectively shielded by a few centimeters of air, a sheet of paper, or the thin layer of dead skin cells. Alpha particles exhibit low penetrating power, and even direct contact with an alpha source is typically safe. However, it's important to note that many alpha sources also emit beta radiation through radon daughters, and gamma-photon emission accompanies alpha emission. In cases where substances emitting alpha particles are ingested, inhaled, injected, or absorbed through the skin, a measurable dose of harmful radiation may occur.


Alpha particles were discovered by Ernest Rutherford, an English scientist, in 1899 while working with uranium. Rutherford's studies significantly contributed to our understanding of the atom and its nucleus, culminating in the Rutherford-Bohr planetary model of the atom.

Certain applications harness the positive charge of alpha particles. Radium-226, for instance, finds use in cancer treatment by introducing small amounts of radium into tumors. Polonium-210 acts as a static eliminator in paper mills and other industries, attracting loose electrons with its positive charge, thereby reducing static charge. Additionally, some smoke detectors utilize the alpha emissions from americium-241 to generate an electrical current. When alpha particles collide with air molecules within the detector, they dislodge electrons, creating positively and negatively charged ions that generate a current. When smoke particles enter the device, they disrupt the flow of charged particles, triggering the alarm.


Most alpha emitters occur naturally in the environment, such as uranium-238, radium-226, and other elements within the uranium decay series, which are found in rocks, soils, and even water.



Holmes and Watson understand alpha particles
The inspector studies alpha particles

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