Answer to Question #13412 Submitted to "Ask the Experts"

Does radiation have any affect on aluminum or mercury?

The answer depends greatly on the type of radiation you have in mind. I shall assume that you are referring to ionizing radiation—e.g., gamma radiation, x rays, neutrons, and charged particles such as alpha radiation and beta radiation.

Charged particles such as alpha particles and beta particles have quite limited ranges in metals and typically produce minimal effects on significant thickness metals. High intensity alpha radiation can produce some atom displacement within thin metallic foils of aluminum when the relatively heavy alpha particles occasionally collide with the metal nuclei and result in structural changes such as increased brittleness of the aluminum. Beta radiation has much less impact because the beta interactions do not involve such collisions but rather involve electrostatic interactions with the electronic structure of the metal atoms, resulting in ionization and excitation that yield very small amounts of heat. In general, mercury, being a liquid at room temperature, would not exhibit as noticeable effects from alpha radiation as would aluminum.

Gamma radiation has little permanent effect on either metal. The gamma energy results in ionization and excitation involving electrons in the metals, and very small amounts of internal heat are the common effect; the same is true for x rays.

Neutrons are much more likely to produce more dramatic effects in both metals. Neutrons, which are electrically neutral, can readily penetrate to the nuclei of metallic atoms. High energy neutrons may deliver appreciable kinetic energy to the nuclei, resulting in atom displacements within the metallic structures. Such displacements can lead to a chain of events in which multiple "knock-on" collisions occur that can lead to significant structural changes—strength, ductility, brittleness, etc. Because mercury is a liquid some of these displacement effects may not be as significant as they would be in aluminum at room temperature.

A second significant effect, especially important for low energy neutrons, is capture of neutrons by metallic nuclei, that yields atoms with one additional neutron compared to the usual stable configuration and with these species often being unstable (i.e., radioactive). For example, stable aluminum-27 (²⁷Al) will be transformed to radioactive ²⁸Al, which has a short half-life of about 2.3 minutes, and emits beta and gamma radiation. Mercury has several stable isotopes, and a few radionuclides are possible from neutron capture. One of the most significant of these is mercury-203 (²⁰³Hg), produced by neutron capture in ²⁰²Hg. The ²⁰³Hg has a half-life of about 46 days and emits beta and gamma radiation. A second radionuclide, ^199mHg, produced from neutron capture by ¹⁹⁸Hg, emits gamma radiation with a 43-minute half-life.

The processes of radiation-induced damage in metals, especially those exposed to high fluences of neutrons, can be a significant concern in some facilities. A common example is nuclear reactors, that operate for long periods, producing very high fluences of neutrons, some of which may irradiate metallic components and cause possible deleterious effects.

George Chabot, PhD, CHP